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Programme

European Space Surveillance Conference 7-9 June 2011, INTA HQ, Madrid, Spain

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LIST OF CONTENTS

1) Scientific Programme …………………………………………………….3 2) Abstracts (oral presentations) …………………………………… 10

3) Abstracts (poster presentations) …………………………………45


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PROGRAMME Tuesday 7 June 2011

08:30 Registration 09:00 Welcome

- Carmen Rodríguez Augustin, Sub-Director General, Commercial Policy and Institutional Relations, Instituto Nacional de Técnica Aeroespacial (INTA) (SPAIN) - Juan Carlos Cortés Pulido, Director of Global Innovation Markets Centro para el Desarollo Tecnológico Industrial (CDTI) (SPAIN) - Nicolas Bobrinsky, Manager, SSA Preparatory Programme European Space Agency (ESA) (SPAIN) - Commander Philippe Rosius Commandemant Interarmées de l'Espace (CIE) (France)

SSA and SST

09:40 SSA - A Global Perspective Weeden, B. Secure World Foundation, (UNITED STATES) 10:00 Insurance Underwriting Perspective on Space Debris Stevens, N. Atrium Space Insurance (UK) 10:20 ESA SSA Space Weather Services Supporting Space Surveillance and Tracking Luntama, J-P ; Glover, A. ......................................................................................10 ESA, (SPAIN) 10:40 An Overview of ESA's "CO-VI: Space Surveillance Precursor Services" Frouvelle, N. 1; Garmier, R. 1; Fletcher, E. 2 1CS SI, (FRANCE); 2ESAC, (SPAIN).........................................................................10

11:00 Coffee Break

Operational Experience

11:20 Adaptations to Changes in Collision Avoidance Operations at CNES for In- Orbit Satellites Laporte, F. ; Moury, M. CNES, (FRANCE)..................................................................................................11 11:40 Operational Collision Avoidance Assessment of DEIMOS-1 satellite Máure, M.A. 1; Sánchez-Ortiz, N. 2; Belló-Mora, M. 2; González, E. 1 1DEIMOS Imaging, (SPAIN); 2DEIMOS Space S.L.U., (SPAIN) .....................................12 12:00 The Impact of Collision Avoidance Maneuvers on Satellite Constellation Management Stoll, E. ; Schulze, R. ; Oxfort, M. RapidEye AG, (GERMANY) .....................................................................................12 12:20 GEO Satellite Collision Avoidance Maneuver due to the Close Approach of an Inclined GSO Satellite Lee, B.-S. 1; Hwang, Y. 1; Kim, H.-Y. 2; Kim, B.-Y. 2 1ETRI, (KOREA, REPUBLIC OF); 2KARI, (KOREA, REPUBLIC OF)...................................14 12:40 Use of Optical Directional Observations for Routine Meteosat Orbit Determination Klinc, M. ; Lázaro, D. ; Siemer, A. EUMETSAT, (GERMANY) ........................................................................................15

13:00 Lunch Break

System Design

14:00 Collision Risks Management in Astrium Satellites Bonaventure, F. ; Gicquel, A.H. Astrium Satellites, (FRANCE) .................................................................................15


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14:20 Optical System Requirements for a Leak-Proof, Non-tasked Cataloging Mission at GEO Murphy, L ; Gow, C. ; Lefever, J. ; Haeberle, D. ; Breslin, J. TASC, Inc., (UNITED STATES)................................................................................16 14:40 Space-Based Space Surveillance as Complementary Element in an SSA Architecture Utzmann, J. ; Wagner, A. Astrium GmbH - Satellites, (GERMANY)...................................................................16 15:00 Using Space-Based Sensors to Catlogue LEO Objects Liu, Zhonggui ; Hao, Shifeng Beijing Institute of Tracking and Telecommunications Technology, (CHINA)..................17 15:20 Required Accuracy for a Reliable Space Objects Collision Avoidance Assessment within the European Space Situational Awareness System. Sánchez-Ortiz, N. 1; Krag, H. 2 1DEIMOS Space S.L.U., (SPAIN); 2ESA/ESOC, (GERMANY) .........................................17 15:40 Requirements for a LEO Surveillance Radar in Response to Collision Avoidance User Needs Krag, H. ; Flohrer, T. ; Merz, K. ESA, (GERMANY) .................................................................................................18

16:00 Coffee Break Radar Observations

16:20 Satellite Observations using the Chilbolton Radar during the Initial ESA 'CO-VI' Tracking Campaign Eastment, J. 1; Ladd, D. 2; Walden, C. 1 1STFC Rutherford Appleton Laboratory, (UNITED KINGDOM); 2STFC Chilbolton Observatory, (UNITED KINGDOM).............................................................19 16:40 Implementation of a Low Power Mini-Radar Demonstrator Sessler, G. 1; Martinez de Mendijur Iriarte, M. 2; Montagna, M. 3; Martin Recuenco, A. 1; Winterstein, F. 1; Dauron, G. 1; Besso, PM. 1 1ESA, (GERMANY); 2Callisto, (GERMANY); 3Makalumedia, (GERMANY) .........................19 17:00 A Concept for an Advanced Reflector-Based Space Surveillance Radar Patyuchenko, A. ; Younis, M. ; Krieger, G. ; Weigel, M. German Aerospace Center (DLR), (GERMANY)..........................................................20 17:20 Cataloguing Capacity and Achievable Accuracy for the Low-altitude Orbital Regimes by Means of Radar Sensor within the Future European Space Situational Awareness System Olmedo-Casal, E. 1; Sánchez-Ortiz, N. 1; Guijarro-López, N. 1; Sessler, G. 2; Krag, H. 2 1DEIMOS Space S.L.U., (SPAIN); 2ESA/ESOC, (GERMANY) .........................................21 17:40 Results of ESA CO-VI Radar Tracking Campaigns Fontdecaba Baig, J. 1; Martinerie, F. 1; Martinot, V. 1; Fletcher, E. 2 1Thales Alenia Space, (FRANCE); 2ESA - European Space Astronomy Centre, (SPAIN) ...................................................................................................21 18:00 European Space Situational Awareness - Radar Simulation Halté, Stéphane ; Sciotti, Massimo ; Quintanilla, Jorge ESA/ESOC, (GERMANY) ........................................................................................22

18:00 Welcome Cocktail at INTA HQ


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Wednesday 8 June 2011

Data Exchange and Governance

09:00 Sharing SSA Data Bird, D. US Strategic Command, (UNITED STATES) ..............................................................23 09:20 Supporting a Space Surveillance Data Model with Standards Martinez, F. ; Agueda, A. ; Arregui, J.P. ; Martín, L. GMV, (SPAIN)......................................................................................................23 09:40 Space Situational Awareness in Europe - Analysis of Potential Sensor Network Topologies in Front of Existing Governance Challenges Ernst, H. Astrium Space Transportation, (GERMANY)..............................................................24 10:00 SSA-DPM: A Model-based Methodology for the Definition and Verification of European Space Situational Awareness Data Policy Gianni, D 1; Lindman, N 1; Moulin, S 2; Fuchs, J 1 1European Space Agency, (NETHERLANDS); 2European Space Agency, (SPAIN) ..............................................................................................................24 10:20 A Technical Contribution Supporting the Definition of the European Space Situational Awareness Governance and Data Policy: the SPA project Valero, J.L.; Albani, S. ; Gallardo, B. ; Matute, J. ; O’Dwyer, A. European Union Satellite Centre, (SPAIN)................................................................25

10:40 Coffee Break

Collision Avoidance

11:00 Collision Risk Assessment For Multiple Encounters Garmier, R 1; Dolado, J.-C. 2; Pena, X. 2; Legendre, P. 3; Revelin , B. 1 1CS SI, (FRANCE); 2CNES, French National Space Agency,(FRANCE); 3CEMAES,(FRANCE) ..............................................................................................25 11:20 Screening the Collision Risk of the Iridium 33 - Cosmos 2251 Clouds Rossi, A. 1; Valsecchi, G.B. 2 1IFAC-CNR & ISTI-CNR, (ANDORRA); 2INAF-IASF, Rome, (ITALY) ...............................27 11:40 Optimal Collision Avoidance Maneuvers using Pseudospectral Methods Martin, E. ; Pineiro, J.J. ; Fuentes, J. E&Q Engineering, (SPAIN).....................................................................................27 12:00 The Applicability Research of Nonlinear Collision Probability Xiong, Yongqing ; XU, Xiaoli Purple Mountain Observatory, (CHINA) ...................................................................28 12:20 The Transfer Orbit Threat to Geostationary Satellites Finkleman, D Analytical Graphics, Inc., (UNITED STATES).............................................................28 12:40 Collision Risk Assessment for Spacecraft with CASS Ma, Chaowei ; Huang, Jianyu Beijing Institute of Tranking and Telecommunications Technology, (CHINA); ............................................................................................................29

13:00 Lunch Break


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Observation Techniques and Processing

14:00 Anomaly Resolution using Optical Signatures Kervin, P 1; Hall, D 2; Hamada, K 3; Lambert, J 2 1US Air Force Research Laboratory, (UNITED STATES); 2Boeing, (UNITED STATES);3Pacific Defense Solutions, (UNITED STATES)..............................................29 14:20 A Dynamic Observation Concept as a Key Point for an Enhanced SSA Optical Network Cibin, L 1; Chiarini, M 1; Milani, A 2; Bernardi, F 2; Dimare, L 2; Pinna, G 3; Zayer, I 4; Besso, P 4; Ragazzoni, R 5; Rossi, A 6 1Carlo Gavazzi Space Spa, (ITALY); 2Dipartimento di Matematica Università di Pisa,(ITALY); 3ESAC, (SPAIN); 4ESOC, (GERMANY); 5INAF, (ITALY); 6IFAC, (ITALY)..........................................................................................29 14:40 Optical Observation Campaign in the Framework of the ESA Space Surveillance System Precursor Services Früh, 1; Schildknecht, T. 1; Hinze, A. 1; Reber, M. 2 1Astronomical Institute University of Bern, (SWITZERLAND); 2EARLY- SPACE, (SWITZERLAND) .......................................................................................30 15:00 Innovative Orbit Determination Algorithms for a complete Debris catalog in the upper LEO region Dimare, L. 1; Milani, A. 1; Bernardi, F. 1; Farnocchia, D. 1; Rossi, A. 2 1Department of Mathematics, University of Pisa, (ITALY); 2IFAC-CNR & ISTI-CNR, (ITALY)................................................................................................30 15:20 Results from First Space Debris Survey Observations in MEO Hinze, A. 1; Vananti, A. 1; Schildknecht, T. 1; Krag, H. 2 1University Bern, (SWITZERLAND); 2ESA/ESOC, (GERMANY) ......................................31

16:00 Coffee Break

Optical Systems

16:20 SSA Products from Wide Field of View Optical Sensors Herridge, P. ; Dick, J. Space Insight Limited, (UNITED KINGDOM) .............................................................33 16:40 Dedicated Telescopes with Large Field of View for Space Surveillance Molotov, I. 1; Agapov, V. 1; Yudin, A. 1; Kardashenko, M. 2 1Keldysh Institute of Applied Mathematics, RAS, (RUSSIAN FEDERATION); 2JSC Sientific-industrial enterprise "Project-Technics", (RUSSIAN FEDERATION) ......................................................................................................34 17:00 Space Debris Observations with ZimSMART Herzog, J. ; Ploner, M. ; Schildknecht, T. University of Berne, (SWITZERLAND)......................................................................35 17:20 Ground-based Optical Sensor Network for Space Surveillance Blanchet, G. 1; Fau, N. 1; Pyanet, M. 1; Vial, S. 1; Legoff, R. 2 1ASTRIUM SAS, (FRANCE); 2EADS SODERN, (FRANCE) ..............................................35 17:40 Upgraded Camera for ESA Optical Space Surveillance System Abreu Rodríguez, D. ; Kuusela, J. Ataman Science, (SPAIN)......................................................................................36 18:00 Laser Tracking of Space Debris Gao, Y ; Smith, C ; Greene, B EOS Space Systems Pty Ltd, (AUSTRALIA)...............................................................36

20:00 Evening Cocktail at Hotel The Silken Puerto de America


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Thursday 9 June 2011

Software Architecture

09:00 Cloud Computing and Service Orientation in the SSA programme - Space Surveillance services and data in the Cloud Michelbach, T. 1; Tueffers, C. 1; Águeda Maté, A. 2; Amstutz, B. E. 3; Frith, G. 3; Stogdill, J.3; Ziegler, M. 1; Usrey, T. T. 3 1Accenture, (GERMANY); 2GMV Aerospace and Defence, S.A., (SPAIN); 3Accenture,(UNITED STATES)................................................................................36 09:20 Applying Cloud Computing to Space Situational Awareness Johnston, S ; White, A ; Lewis, H ; Cox, S ; Hart, E University of Southampton, (UNITED KINGDOM) ......................................................37 09:40 Reuse of Operational Flight Dynamics Software for Space Surveillance Martínez, F. ; Agueda, A. ; Fernández, J. ; Escobar, D. GMV, (SPAIN)......................................................................................................38 10:00 Open Source Space Situational Awareness Analyses - Requirements, Design, and Examples Cefola, P 1; Weeden, B. 2; San-Juan, J. 3; Lara, M. 4 1University at Buffalo, (UNITED STATES); 2Secure World Foundation, (CANADA);3Universidad de La Rioja, (SPAIN); 4Real Observatorio de la Armada, (SPAIN) .................................................................................................38 10:20 Predicting Collision Risk for European SSA System Escobar, D. ; Agueda, A. ; Martín, L. ; Martínez, F. GMV, (SPAIN)......................................................................................................39

10:40 Coffee Break

Propagation and Correlation

11:00 Efficient Tracking Correlation Techniques for Space Surveillance Agueda, A. ; Martínez, F. ; Fernández, J. GMV, (SPAIN)......................................................................................................41 11:20 Mathematical and Algorithmic Description of Software Correlator for Space Debris Data Processing in VIRAC Jekabsons, N. ; Kotlere, D. ; Smelds, I. ; Nechaeva, M. Ventspils University College, (LATVIA) ....................................................................41 11:40 High Fidelity Models for Orbit Propagation: DROMO vs. Stoermer-Cowell Peláez, J. 1; Urrtutxua, H. 1; Bombardelli, C. 1; Huhn, A. 2 1Universidad Politécnica de Madrid (UPM), (SPAIN); 2Technical University of Munich,(GERMANY)...........................................................................................42 12:00 Long Term Propagation of GEO and GTO Orbits, in the Frame of the French Space Act: Methodological Concepts, Simulations. Deleflie, F. 1; Morand, V. 2; Le Fevre, C. 3; Wnuk, E. 4; Wailliez, S. 5; Portmann, C. 6; Lamy, A. 3; Vienne, A. 7; Emilion, L. 7; Fraysse, H. 3; Hautesserres, D. 3 1IMCCE/GRGS, (FRANCE); 2Thales Group, (FRANCE); 3CNES, (FRANCE); 4Poznan University, (POLAND); 5IMCCE/FUNDP, (FRANCE); 6OCA/GEMINI, (FRANCE); 7IMCCE, (FRANCE).................................................................................43 12:20 Covariance Determination,Propagation and Interpolation Techniques for Space Surveillance García, P. ; Escobar, D. ; Agueda, A. ; Martínez, F. GMV, (SPAIN)......................................................................................................43 12:40 Short-term Orbit Propagator of Space Debris Moving on LEO and MEO Wnuk, E. ; Golembiewska, J. Adam Mickiewicz University, Astronomical Observatory, (POLAND)..............................44

13:00 Closing

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Posters

Posters will be on display during the entire Conference. Poster presenters will be available next to their poster during the lunch breaks to answer questions from the audience. P1

Development of a Web Front End for ESA’s CRASS collision avoidance system Madero, FJA ; Del Pino , JR ; Uruñuela, S ; Villanueva, J Indra Espacio, (SPAIN) ...................................................................................................45 P2

Motion Compensation for ISAR Imaging of Spinning Targets Li, Hailin Beijing institute of tracking and telecommunication technology, (CHINA) ...............................45 P3

The FABRA-ROA Telescope at Montsec (TFRM): A Fully Robotic Wide-field Telescope for Space Surveillance and Tracking Montojo, F.J. 1; Fors, 0. 2; Muiños, J.L. 1; Nuñez, J. 2; López Morcillo, R. 1; Baena, R. 3; Boloix, J. 1; López Moratalla, T. 1; Merino, M. 2 1Real Instituto y Observatorio de la Armada (ROA), (SPAIN); 2Observatori Fabra, Reial Acadèmia de Ciències i Arts de Barcelona (RACAB), (SPAIN); 3Dep. d’Astronomia i Meteorologia i Institut de Ciències del Cosmos (ICC), Universitat de Barcelona, (SPAIN)..............................................45 P4

A Satellite Orbit Design Method for Space-based Space Surveillance Hou Yuzhuo, H ; Huang Xuexiang, H ; Su Zengli, S Beijing Institute of Tracking and Telecommunications Technology, (CHINA)............................46 P5

Space Surveillance Educational Outreach - Video Monitoring Ocaña, F. 1; Zamorano, J. 2 1Universidad Complutense de Madrid, (SPAIN); 2Dpto. de Astrofísica y CC de la Atmósfera - Universidad Complutense de Madrid, (SPAIN) ....................................................................47 P6

Orbit Determination Error Analysis for a Space Debris Tracking Radar Weigel, M. 1; Patyuchenko, A. 2 1German Space Operations Centre (GSOC) of DLR, (GERMANY); 2DLR Microwaves and Radar Institute, (GERMANY) .....................................................................................................47 P7

Orbit Determination of the Extended Kalman Filter for GEO Optical Observation ZHANG, W. ; Zhao, C.Y. ; Wang, X. ; Wang, H.B. Purple Mountain Observatory, Chinese Academy of Sciences, (CHINA)...................................48 P8

Optical Space Surveillance and Active Space Debris Mitigation at Kayser-Threde Hofmann, P.; Bellido, E. Kayser-Threde GmbH, (GERMANY) ...................................................................................48 P9

AS4, a Simulator Supporting the Definition of the European Space Surveillance Segment of SSA Sánchez-Ortiz, N. ; Olmedo-Casal, E. ; Guijarro-López, N. ; Belló-Mora, M. DEIMOS Space S.L.U., (SPAIN)........................................................................................49 P10

Operational Optical Observation Campaign based on Survey-only Strategies: Preparatory Phase and Expected Performances


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Olmedo-Casal, E. 1; Nómen, J. 2; Sánchez-Ortiz, N. 1; Guijarro-López, N. 1 1DEIMOS Space S.L.U., (SPAIN); 2OAM, (SPAIN) ................................................................49 P11

Cataloguing Capacity and Achievable Accuracy for the High-altitude Orbital Regimes by Means of Ground-based Optical Sensors within the Future European Space Situational Awareness System Sánchez-Ortiz, N. 1; Olmedo-Casal, E. 1; Guijarro-López, N. 1; Keinänen, P. 2; Krag, H. 3 1DEIMOS Space S.L.U., (SPAIN); 2ASRO, (FINLAND); 3ESA/ESOC, (GERMANY) .......................50 P12

ATV-1 Re-entry Fragments Trajectory Reconstruction and Footprint Optimal Estimation Gil-Fernandez, J. 1; Blasco, A. 1; van der Linden, B. 2; Janssen, B. 2; Hatton, J. 3 1GMV, (SPAIN); 2LIME, (NETHERLANDS); 3ESA, (NETHERLANDS)..........................................50 P13

Monitoring and Control for Space Surveillance Sensors Gil, J.C.; Fraga, E. GMV, (SPAIN) ...............................................................................................................51 P14

Operational Survey and Catalogue Maintenance in MEO Fernández, J. 1; Aivar, L. 1; Agueda, A. 1; Dick, J. 2; Herridge, P. 2; Krag, H. 3; Flohrer, T. 3 1GMV, (SPAIN); 2Space Insight Ltd., (UNITED KINGDOM); 3ESA/ESOC, (GERMANY) ................52 P15

Study of an Innovative System for Debris Surveillance in LEO Regime Fernández, J. 1; Agueda, A. 1; Dick, J. 2; Jamar, C. 3; Jorden, P. 4; Besso, P.M. 5; Pinna, G.M. 6 1GMV, (SPAIN); 2Space Insight Ltd., (UNITED KINGDOM); 3AMOS, (BELGIUM); 4e2v, (UNITED KINGDOM); 5ESA/ESOC, (GERMANY); 6ESA/ESAC, (SPAIN)..................................................52 P16 EUMETSAT Operational Software for Debris Conjunction Analysis Lázaro, D.; Aguilar, D.; Righetti, P.L. EUMETSAT, GERMANY ....................................................................................................53 P17 A New Astronomical Orientation Method for Space Debris Zhang , Xiaoxiang ; Xu, ZhanWei ; Ping, YiDing Purple Mountain Observatory, (CHINA) .............................................................................31 P18 A dedicated Space Surveillance Optical Network cooperates with Radar to assure LEO debris catalogue build up and Maintenance Cibin, L. CGS Spa (ITALY) ...........................................................................................................56


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ABSTRACTS

ESA SSA Space Weather Services Supporting Space Surveillance and Tracking Luntama, J-P; Glover, Alexi

ESA

In 2009 European Space Agency (ESA) started a new programme called Space Situational Awareness (SSA) Preparatory Programme. The objective of the programme is to support the European independent utilisation of and access to space research or services. This will be performed through providing timely and quality data, information, services and knowledge regarding the environment, the threats and the sustainable exploitation of the outer space surrounding the planet Earth. SSA serves the implementation of the strategic missions of the European Space Policy based on the peaceful uses of the outer space by all states, by supporting the autonomous capacity to securely and safely operate the critical European space infrastructures.

The SWE Segment of the SSA will provide user services related to the monitoring of the Sun, the solar wind, the radiation belts, the magnetosphere and the ionosphere. These services will include near real time information and forecasts about the characteristics of the space environment and predictions of space weather impacts on sensitive spaceborne and ground based infrastructure. The SSA SWE system will also include establishment of a permanent database for analysis, model development and scientific research. These services are will support a wide variety of user domains including spacecraft designers, spacecraft operators, human space flights, users and operators of transionospheric radio links, and space weather research community. The precursor SWE services to be established starting in 2010.

This presentation will provide an overview of the ESA SSA SWE services focused on supporting the Space Surveillance and Tracking users. This services include atmosheric estimates, archive of geomagnetic and solar indices and forecasts of geomagnetic and solar indices. These services will support estimations of the atmoshperic drag. In addition, the SSA SWE system will provide nowcasts of the ionospheric group delay to support mitigation of the ionospheric impact on rada signals.

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An Overview of ESA's "CO-VI: Space Surveillance Precursor Services" Frouvelle, N.1; Garmier, R.1; Fletcher, E.2

1CS SI, parc de la plaine, 5 rue bindejonc des moulinais, BP15872, 31506 Toulouse; 2ESAC - P.O. Box 78, E-28691 Villanueva de la Canada, Madrid

ESA is developing a Space Situational Awareness preparatory program. The SSA program covers the Space Surveillance and Tracking (SST), the Space Weather monitoring (SWE) and Near Earth Object (NEO) risk. The phase 2009 - 2012 of the Preparatory program is itself composed of 4 areas: 1. SSA Core Element (CO): Comprising activities related to system architecture, governance, data policy, security and the SST segment 2. Space Weather Element: Including development of both the SWE Segment and the NEO Segment 3. Radar Element: Focusing on the specifications and design for a future radar system and creation of a prototype radar 4. Pilot Data Element: All activities related to common data storage and system-wide management for all segments

In 2010, ESA issued the ITT " CO-VI: Space Surveillance Precursor Services". A European consortium (AIUB (Switzerland), ATAMAN Spain, CS SI (France), Early Space (Switzerland), TAS France) lead by CS SI was selected to realize the CO-VI project.


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The CO-VI project is part of the SSA Core Element and its main goal consists in initiating the installation of precursor SST services. The aim of SST services are to catalogue space objects such as debris or satellites, to monitor the collision risk between satellites and other objects as well as the risk caused by re-entry of objects to population and infrastructure. Within the SSA Preparatory Programme, the implementation of these initial precursor services plays an important and visible role. Based on already existing assets and competencies in ESA and participating States, it offers an excellent opportunity for an early validation of the federative approach outlined in the whole SSA Programme.

The Precursor SST services are located at ESA / ESAC (Villafranca, Spain).

The CO-VI activities are separated into 5 topics:

- Compile all documentation related to the legacy collision risk assessment tool CRASS. - Deployment and maintenance of a SST web-based interface to allow users access to the conjunction prediction services. The interface can handle different services as analysis request, displaying results and generation of reports, providing authenticated and user based access to specific data. - The development, coordination and execution of tracking campaigns for LEO, GEO and MEO satellites. - Specification of the SST Common Data Model (CDM) to ensure a consistency of the data among all involved services as well as the federation and exchange of data generated by the sensors. - Creation of specification documents to propose future enhancements in-line with the whole SSA programme.

The whole ESA SST precursor Services will be presented with a specific focus on SST common Data Model and on future enhancements within the SSA programme.

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Adaptations to Changes in Collision Avoidance Operations at CNES for In-Orbit Satellites

Laporte, F.; Moury, M. CNES

Because of the ever-increasing number of orbital debris, the possibility of a satellite collision with space debris or another satellite is becoming more and more likely. This phenomenon particularly concerns the LEO altitude regime. Therefore CNES settled in July 2007 an operational collision risk monitoring. Most of the operational collision avoidance activities are gathered at OCC (Orbit Computation Center) in CNES Operations Sub-directorate.

In France, CDAOA (Air Defense and Air Operation Command) is responsible for French space surveillance. CDAOA operates the French surveillance radar GRAVES and is in charge of coordinating French means which contribute to SSA (tracking radars and OCC). CNES, as the French space agency, represents France at the ESA SSA control board and has the responsibility to authorize launching satellites from French Guiana. CNES, as the French technical space center, performs the in-orbit control of governmental satellites, monitors collision risks and performs collision avoidance maneuvers. CNES and CDAOA have established direct and close operational links and signed a dedicated agreement to collision detection and avoidance in January 2010.

After the first collision with an operational satellite in February 2009, major changes began in USA : JSpOC started to monitor collision risk for all the operational satellites and to send alerts to operators worldwide. In July 2010, Conjunction Summary Messages (CSM) which are complete information to assess a collision alert, are made available for all by USSTRATCOM with a secured access on Space Track website. CNES operational Collision Avoidance process evolved to take into account access to CSM data.


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This paper presents the evolution of the CNES Collision Avoidance Process which includes OCC contingency operational procedure for collision risks management, procedure which is divided in five stages, each successive stage representing an escalation in the contingency from collision risks screening to dangerous conjunctions fine analysis and risk mitigation.

- At its beginning, the process was based on Space Track TLE analysis using maximum probability to detect conjunctions : for instance, the Iridium-Cosmos collision is detected with that method, but the case cannot be analysed and therefore it is impossible to identify really risky conjunctions. - The process was greatly improved in 2009 using GRAVES data : first GRAVES TLE (since they were directly available) to detect conjunctions and matching GRAVES measurements to analyse and identify risky conjunctions. GRAVES data confirmed that Space Track TLE were not suitable for Conjunction Assessment. - CSM available since July 2010 again confirmed the conclusion about Space Track TLE and required new adaptations of the process.

This paper mentions in conclusion the tools with their on-going evolutions to adapt to the different changes and the perspective for near-future.

***** Operational Collision Avoidance Assessment of DEIMOS-1 satellite

Máure, M.A.1; Sánchez-Ortiz, N.2; Belló-Mora, M.2; González, E.1 1DEIMOS Imaging; 2DEIMOS Space S.L.U.

During its lifetime the satellite DEIMOS-1 satellite devoted to Earth Observation, has experienced several high risk encounters with other satellites, one of them, leading to a collision avoidance maneuver. DEIMOS Space S.L.U. and DEIMOS Imaging have developed and operate a Collision Risk Computation Software (CORC). This paper briefly describes the main algorithms and assumptions for the development of that tool, and it provides detailed information on the operational experience from the launch of the satellite. In particular, a review of the alarm events raised by the CORC tool, together with the comparison with alarms reported by the Conjunction Service Message (JSpOC) is provided. Additionally, a comparison of the operational experience with the results from pre-launch analysis performed during the mission design phases is also addressed. This pre-launch analysis was done with statistical information of the expected population by means of the ESA DRAMA tool. A review of the aspects impacting the decision of manoeuvring under this type of events is presented (miss-distance, geometry, collision risk, orbits uncertainties), together with the operational concept for DEIMOS-1.

Keywords: collision risk, avoidance maneuver, CORC, DRAMA

***** The Impact of Collision Avoidance Maneuvers on Satellite Constellation Management

Stoll, E.; Schulze, R.; Oxfort, M. RapidEye AG

RapidEye AG is a geospatial information provider focused on developing customized solutions for agriculture, forestry, infrastructure, security, and emergency monitoring applications. As the backbone of these information services, RapidEye own and operate a satellite constellation consisting of five satellites in a sun-synchronous Low Earth Orbit that are capable of downloading over 4 million km2 of high resolution, multi-spectral imagery per day. A dedicated Spacecraft Control Center (SCC) and a full ground segment plan, acquire, and process several millions of square kilometers every day. While telemetry and telecommands are directly transceived by the SCC located in Brandenburg a.d. Havel / Germany, image data is downlinked via an X-band ground station in Svalbard/ Norway and forwarded to RapidEye. RapidEye currently evaluate the operational potentials and impacts of performing collision avoidance maneuvers with their


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constellation. The initial - by the satellite manufacturer recommended - operational concept didn't foresee such a mode of operations. However, RapidEye regularly perform orbit raise maneuvers to maintain their constellation with respect to baseline orbit elements and phasing. This assures a consistency of the ground tracks and the capability of a daily revisit of any point on Earth. A maneuver, similar to an orbit maintenance burn, could obviously also be used for collision avoidance purposes. However, such a maneuver on short notice would disturb the well planned constellation properties. It would not only have an impact on the ground tracks of the five satellites but also influence the optimized transmission windows over Svalbard. This paper describes the impact of collision avoidance maneuvers on RapidEye's satellite constellation management and the subsequent actions that have to be undertaken with the remaining satellites of the constellation. It further outlines the efforts that have to be undertaken to incorporate appropriate methods into daily mission operations.

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GEO Satellite Collision Avoidance Maneuver due to the Close Approach of an Inclined

GSO Satellite Lee, B.-S.1; Hwang, Y.1; Kim, H.-Y.2; Kim, B.-Y.2

1ETRI; 2KARI

A series of close approach between GEO COMS satellite and GSO Raduga satellite occurred every month when Raduga satellite passed by COMS station-keeping box. The Korean COMS satellite is in GEO at 128.2°±0.05° East longitude and the Russian Raduga satellite is in inclined GSO at 128.0°±0.5° East longitude. When the Raduga satellite is pass through the longitude of 128.2 deg East, close approaches of the two satellite happens two times a day for a few days. There is no orbital information exchange between the two satellite operators. Only the JSpOC warning message is delevered when there is a close approach between the two satellite. A collision avoidance maneuver of the COMS satellite was performed on Feb. 8, 2011. At that time, the closest distance between the two satellite was estimated as about 1.4 km. The maneuver was performed to move COMS satellite away from Raduga satellite about 8.6 km. The ΔV of the maneuver was three times bigger than the normal East-West station-keeping maneuver. A compensation maneuver was also performed after four days. In this paper, a surveillance of the close approach between the two satellites is reported and possible collision avoidance maneuver strategy is investigated.


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***** Use of Optical Directional Observations for Routine Meteosat Orbit Determination

Klinc, M.; Lázaro, D.; Siemer, A. EUMETSAT

An initial pilot system for orbit determination, combining standard ranging data with optical directional observations from a Starbrook space surveillance sensor, has been repeatedly used in EUMETSAT since 2010. The enhanced orbit determination method proved to be immediately of practical use for Meteosat operations, by improving orbit determination accuracy for the cases with limited availability of ranging data and by providing independent means for ground station calibrations. Assessments during conjunctions with uncontrolled objects in GEO, to improve the space situational awareness, have also been carried out successfully. This paper illustrates how the operational flight dynamics software for the Meteosat Second Generation satellites has been upgraded to be able to routinely process optical directional observations made available by a space surveillance sensor.

***** Collision Risks Management in Astrium Satellites

Bonaventure, F.; Gicquel, A.H. Astrium Satellites

Introduction Astrium Satellites is developing satellite systems, payloads and ground infrastructures for Telecom, Earth Observation and Science missions. For most customers, Astrium is in charge of the satellite in-orbit delivery including LEOP operations. In addition, Astrium provides an in-orbit follow-on support during the entire operational life including Flight Dynamics activities. Risks of collision in space being increasing, a collision risk alert and avoidance system shall be developed and implemented as part of satellite routine operations. Operational experience feedback Over the past few months, several conjunction alerts have been raised by JSpOC concerning Astrium build satellites. Therefore, Astrium has developed collision risk management procedures to support operators in deciding whether an avoidance manoeuvre is necessary or not, and computing the manoeuvre. In parallel, a dialog with JSpOC has been initiated in order to clarify their alert level and the different formats of their messages depending on the type of the orbit. A review of the Astrium operational experiences is presented for a LEO observation satellite, a GEO telecommunication satellite and a GTO micro-satellite. Collision risk and avoidance system TLEs are definitively not accurate enough to be used for collision risk assessment. JSpOC CSMs (Conjunction Summary Message) are prefered as they provide accurate orbit parameters and covariance. These informations are processed in QUARTZ, Astrium Flight Dynamics Software, to support the response to the alert. QUARTZ first compares the accuracy of the CSM orbits and determines the probability level of the collision. If necessary, it computes the avoidance manoeuvre(s), taking into account station keeping constraints in order to minimize the operational impacts (mission interruption, propergol overcost). As CSMs are sent only three days before the conjunction, a quick reactivity is required and a Flight Dynamics on-call service is being set up in the frame of the standard In-Orbit Service activities. Examples of current and future operations: - Computation of conjunction risks with ISS and operational GEO satellites in the frame of the French Space Act for GTO orbits. - Astrium Services will operate the SPOT 6 & SPOT 7 satellites and is in charge of the collision avoidance management.


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***** Optical System Requirements for a Leak-Proof, Non-tasked Cataloging Mission at GEO

Murphy, L; Gow, C.; Lefever, J.; Haeberle, D.; Breslin, J. TASC, Inc.

An effective cataloging strategy at GEO should maintain previously cataloged objects as well as detect and catalog newly discovered objects. These two missions require a different amount of track data, as newly discovered objects require multiple tracks to produce a reliable orbit, whereas maintaining an orbit often requires only a single observation. Most current optical networks that perform GEO space surveillance use tasking to provide the necessary observations to maintain their catalog. This strategy is appropriate for maintaining a current GEO catalog, but not as effective at cataloging everything in the GEO region, especially highly-inclined objects. We present a number of sensor design and search strategy combinations that would allow a system to acquire sufficient metric data for catalog maintenace AND catalog entry on every GEO object visible to the site on every night, even during short summer nights. The study parameterizes on field of view, scan pattern, and sensor latitude. We present a theoretical model to identify the solutions. These strategies were also tested for their ability to track a variety of GEO objects using real data.

***** Space-Based Space Surveillance as Complementary Element in an SSA Architecture

Utzmann, J.; Wagner, A. Astrium GmbH - Satellites

Up to the present day, a variety of studies regarding the development of a European SSA system architecture have been performed under the supervision of ESA. Two of the most recent of them, the GSP "Study on the Capability Gaps Concerning European Space Situational Awareness" (GSP, 2007) and the "Proof of Concept for Enabling Technologies for Space Surveillance" (GSTP, 2010) were successfully performed by a team under the lead of Astrium. In the framework of these studies, the SSA user needs were translated into functional and performance requirements. An overall architecture to meet these requirements was specified and a phased implementation approach with increasing capabilities was proposed. The basic SSA system building blocks and technology options for space surveillance, tracking and imaging can be grouped into three segments: Ground-based optical sensors, space-based telescopes and ground-based radars. One solution proposed to relax requirements on the radar systems (e.g. power, number of sites) by introducing novel ground-based optical solutions for additional LEO-and-beyond surveillance. However in both studies, space-based surveillance sensors were identified as an important complementing element to the ground-based architecture. Space-based telescopes can provide a valuable contribution to both the surveillance and the imaging component of an SSA system. This capability was already demonstrated in the past, when the Space-Based Visible (SBV, 1996-2008) instrument on MSX (Midcourse Space Experiment) improved greatly the build-up and maintenance of the US SSN object catalogue. SBV's success resulted in several current follow-on missions: SBSS Block 10 (USA, launched in 2010), Sapphire and NEOSSat (both Canada, launch planned for 2011). Plans for an SBSS constellation exist. Self-standing or in combination with ground-based sensor resources, space-based surveillance sensors can provide flexibility, timeliness, 24/7 availability, high accuracy tracking, fast revisits, reduced sky background noise and do not have geographical/political site limitations. For an SSA system, this results in a greater coverage of the orbital population, timely follow-up observations and the improvement of not only detection, but also cataloguing capabilities. One very crucial element in a space-based surveillance concept is the development of efficient observation strategies. This paper will provide a review and discussion of different survey approaches. Besides strategies for LEO telescopes for beyond-LEO observation, the analysis comprises also other orbit regimes for both telescopes and the targets to be observed, e.g. LEO-LEO observations. Furthermore, constellation concepts are addressed. Last but not least, the unique capabilities in comparison with ground-based sensors and where both concepts can complement each other are examined.

*****


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Using Space-Based Sensors to Catalogue LEO Objects

Liu, Zhonggui; Hao, Shifeng Beijing Institute of Tracking and Telecommunications Technology

With the development of its capability and reliability, space-based visible (SBV) sensors on sun-synchronous orbit have been used to detect and track Deep Space Objects. But till now, they are not used, as primary mission, to detect Low Earth Orbit (LEO) objects. This paper intends to present a space-based surveillance draft which can: - Detect and collect observations of LEO objects to support its catalogue and maintenance - Using fixed sensors to fulfill the above mission without special pointing operation and mission planning - Be installed on normal-commercial small satellite platform less than 300kg The result shows that a equatorial orbit with inclination of zero degree can be a competent candidate. The given example of a MEO at altitude of about 9000km can acquire a good enough opportunity in detecting LEO objects with observations well-proportioned. If it is equipped with 4 fixed telescopes with FOV of about 7oiA7o, a single satellite can provide enough observations to support the catalogue and its maintenance of LEO objects with inclination greater than 50 degrees. The disadvantages of the draft are the launch cost and the on-board data processing.

***** Required Accuracy for a Reliable Space Objects Collision Avoidance Assessment within

the European Space Situational Awareness System. Sánchez-Ortiz, N.1; Krag, H.2

1DEIMOS Space S.L.U.; 2ESA/ESOC

The future Space Surveillance and Tracking segment of the European Space Situational Awareness System aims to support collision avoidance assessment which allows reducing the catastrophic collision risk of space objects by one order of magnitude whilst keeping a low number of false alarm events. In order to translate this aim into system requirements, an evaluation of the current risk for different orbital regimes, the required accuracy of the catalogued objects and the population coverage of the system (limiting size of observed objects) have to be addressed. Those issues have been analyzed before. This paper focuses on the analysis of the two first aspects by means of the ESA DRAMA tool. For allowing such reliable collision avoidance support, a large part of the objects that pose a risk of catastrophic collision have to be observed in a manner that allows an accurate computation of the orbits. The assessment of possible conjunctions is normally done by computing the estimated miss-distances between objects and comparing that with a defined distance threshold or by computing the associated collision risk and comparing with the corresponding accepted collision probability level. This second method is normally recommended since it takes into account the reliability of the orbits to reduce false alarm events. The collision risk depends on the estimated miss-distance, the object sizes and the accuracy of the two orbits at the time of event. This accuracy depends on the error of the orbits at the orbit determination epoch and the error derived from the propagation from that epoch up to the time of event. This paper addresses the required accuracy for the different orbit regimes to be imposed to the system in order to fulfill with this mission requirements. Additionally, a discussion on the capability of achieving the requested accuracy is presented to analyze the impact of those requirements in the future system.

Keywords: collision risk assessment, orbit determination accuracy, false alarm rate, DRAMA

*****


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Requirements for a LEO Surveillance Radar in Response to Collision Avoidance User

Needs Krag, H.; Flohrer, T.; Merz, K.

ESA

Europe has initialised the development of an autonomous system for space situational awareness. One important task of this new system is to establish a service that provides timely and reliable collision warnings to spacecraft operators. This service is considered to be the main design driver for the whole surveillance and tracking segment. The minimum size of objects to be covered, the accuracy of the orbit information to be maintained and the system's response time are the major performance issues connected with this service. The exact performance parameters and scope of the service are currently under definition.

A system design has to meet those requirements. Studies on a first architectural concept and related capability analyses have led to a draft proposal for the system architecture. This foresees, in a first deployment step, a ground-based system consisting of radar sensors and a network of optical telescopes. While existing radar facilities might be suitable for re-use, in particular as tracking sensors, it will be necessary to newly develop radar-based surveillance capacities. The covered object population will increase and the its distribution will evolve throughout the system's lifetime. This will have an impact on the system design and needs to be considered beforehand, using suitable models for the future object population.

This paper will outline the fundamentals for a design definition process based on the collision avoidance service. It will outline the core user requirements on collision avoidance from a user perspective: accuracy of the orbit information and the associated alarm/false alarm rate, remaining collision risk and the timeliness of alerts. The influence of these drivers on the system design under the aspect of an evolving object population will be analysed. As a result, a first compilation of settled performance parameters for the surveillance and tracking segment will be presented and discussed. It will be further analysed, whether a survey-only strategy using a single radar-based surveillance source can cope with these requirements for LEO operators. The performance w.r.t. the detection of fragmentation clouds and the accuracy of re-entry predictions of such a system will be presented

*****


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Satellite Observations using the Chilbolton Radar during the Initial ESA 'CO-VI'

Tracking Campaign Eastment, J.1; Ladd, D.2; Walden, C.1

1STFC Rutherford Appleton Laboratory; 2STFC Chilbolton Observatory

The Chilbolton radar, a high-power S-band system equipped with a fully-steerable 25 m diameter dish antenna, has hitherto been used almost exclusively for meteorological and atmospheric science-based research. This radar was recently modified for use as a tracking asset in support of ESA's Space Situational Awareness Preparatory Programme (SSA PP). In late November and early December of 2010, the radar participated in a set of satellite tracking measurements comprising the first campaign of the SSA PP's 'CO-VI' activity.

This campaign involved observations of the satellites ENVISAT, METOP-A, CRYOSAT-2, GRACE-1, JASON-2, PROBA-1 and STARLETTE. In addition to these ESA-mandated objects, we also tracked the ISS, AQUA, COSMOS_1346, COSMOS_1782 and many IRIDIUM satellites.

In this paper, we report the details of the modifications to the Chilbolton radar which were necessary in order to adapt it for SSA work. We present examples of the satellite tracks obtained, and comment on interesting features noted in the data. We compare the calculated sensitivity of the radar in its current configuration with the results obtained in practice. We discuss our plans for upgrading the radar's hardware and software, so as to improve detection performance against small-RCS targets. Finally, we explore the use of the upgraded radar for Space Object Identification and characterisation by exploiting both its wideband waveform and polarimetric capabilities.

***** Implementation of a Low Power Mini-Radar Demonstrator

Sessler, G.1; Martinez de Mendijur Iriarte, M.2; Montagna, M.3; Martin Recuenco, A.1; Winterstein, F.1; Dauron, G.1; Besso, PM.1 1ESA; 2Callisto; 3Makalumedia

The European Space Agency (ESA) has implemented a low power (10 mW to 10 W) mini-radar demonstrator at the European Space Operations Centre (ESOC) in Darmstadt (Germany). The purpose of this mini-radar demonstrator is to have a reference system for ESA’s involvement in the SSA (Space Situational Awareness) preparatory program, which includes building up a larger scale radar breadboard (5-15 kWatt mean power) for space surveillance. Yet, this larger scale radar breadboard is again just a small version of the anticipated final radar system, which would include several thousands of transmitter and receiver phased array antenna elements and would operate with a transmit power in the range of one MWatt. The final radar would perform space surveillance for low earth orbit (LEO) objects, and shall be able to systematically survey and track all objects above an altitude dependant size threshold. Based on these data, the radar will maintain a catalogue with physical and orbital information.

The mini-radar demonstrator is intended – among others - to be an internal cross verification for the on-going radar breadboard developments, which are contracted to industry. The system design of the mini-radar includes one transmitter and one receiver rack, such that a bi-static as well as a close mono-static (i.e. distinct transmitter and receiver antennas, but geographically collocated) radar system setup can be achieved. Both racks are mobile so that measurements at different locations can easily be performed. The transmitter system consists of an arbitrary waveform generator which can generate almost any radar waveform. Yet it is foreseen to focus on the two waveforms which were identified in earlier studies, which are Continuous Wave (CW) and pulsed Linear Frequency Modulation (LFM).

The mini-radar transmitter sends out the radar signal (CW or LFM) using a horn antenna (in Phase B of the mini-radar project the horn antenna will be replaced by a 16 element phased array antenna). The transmitted radar signal is centred around 1307 MHz and has a transmit power of 100 mW (Phase A) and 10 W (Phase B).


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The receiver rack consists of a 16 element array antenna, which is followed by 16 fully parallel receiver chains. In each chain the signal is amplified, filtered, down-converted, A/D converted and then processed by an FPGA and PC. The full signal processing and digital beam-forming is implemented in the FPGA. The un-processed digitized signal can also be fed directly to a PC and post-processed.

The current design allows detection of objects up to a few hundred meters for Phase A and around a km for Phase B. Currently, the implementation of Phase A is completed and the implementation of Phase B is foreseen for the second half of 2011.

In the full paper we will present the detailed design of the mini-radar system and show measurements of the Phase A mini-radar, which demonstrate its performance and detection limits.

***** A Concept for an Advanced Reflector-Based Space Surveillance Radar

Patyuchenko, A.; Younis, M.; Krieger, G.; Weigel, M. German Aerospace Center (DLR)

This paper presents an innovative concept of the ground based radar system for space debris detection and tracking using a reflector antenna with multiple feed elements and utilizing digital beam-forming (DBF) techniques. The concept originates from the novel idea of a spaceborne Synthetic Aperture Radar (SAR) system combining a reflector antenna with a digital feed. The paper starts with a description of the classical ground based radar, its basic performance aspects and parameters. The discussion is followed by the introduction of a concept of the novel reflector based DBF radar and its main operational principles. Afterwards the main advantages of the novel system compared to the conventional radar are described. With the new system a target can be tracked within a large angular range relaxing the requirements on the mechanical steering of an antenna. Multi-beam capability of the novel system and availability of multiple digital channels with independent data make possible the realization of an advanced Track While Scan mode characterized by a large search volume. Comparing basic performance parameters of the conventional reflector-based space debris radar it is shown that the novel DBF system operated at the same frequency band achieves higher probability of target capture while still can have an unchanged detection probability. Overall results show that a combination of the reflector antenna with a digital feed array to be used for the detection and tracking of space debris is a promising concept allowing to obtain higher operational flexibility and an improved performance compared to the conventional reflector based radars.

*****


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Cataloguing Capacity and Achievable Accuracy for the Low-altitude Orbital Regimes by

Means of Radar Sensor within the Future European Space Situational Awareness System

Olmedo-Casal, E.1; Sánchez-Ortiz, N.1; Guijarro-López, N.1; Sessler, G.2; Krag, H.2

1DEIMOS Space S.L.U.; 2ESA/ESOC

In the frame of the future European Space Situational Awareness System, detailed analysis of the capacities required for radar observation of lower orbits (altitudes between altitude 200 and 2000 km) are executed. In this analysis, different radar configurations are proposed. This paper addresses the capabilities of constructing a catalogue of low orbiting objects for different radar sensors. Different radar sensors types and locations are studied. In particular, the performances for a sensor located in south of Spain is compared with one in Germany, the capabilities provided with different sensors types providing longer revisit time and split Field of Regard are also shown. Simulation of radar observation of each object is based on the detection probability depending on the computed signal to noise ratio. The analysis is based on the study of different parameters that provide an assessment of the feasibility of constructing a catalogue: timeliness, re-observation periods, duration of tracks, number of measurement within the tracks. Additionally, the correlation capacities and the orbit determination achieved is provided as a function of the type of orbits. Grids in orbit pericenter, inclination and eccentricity are used to characterize the cataloguing features. All the results are obtained with the AS4 simulator, developed by DEIMOS Space S.L.U, in the frame of the ESA study "Definition of Ground Segment Requirements for a UHF Radar for the ESSAS", and in particular, within the work-package devoted for the "Cataloguing Capacities of the Radar" (ESA Contract n° 22062/08/D/HK). Keywords: radar observation of space debris, orbit determination, correlation and cataloguing activities AS4

***** Results of ESA CO-VI Radar Tracking Campaigns

Fontdecaba Baig, J.1; Martinerie, F.1; Martinot, V.1; Fletcher, E.2 1Thales Alenia Space; 2ESA - European Space Astronomy Centre

Following the decision at the Ministerial Council 2009 to initiate a Preparatory Programme on Space Situational Awareness, the European Space Agency has started a series of activities with the industry, implementing both classical design approaches: bottom-up and top-down. For Space Surveillance and Tracking, it translates in particular into an activity in CO-VI consisting of an assessment of the existing European assets that can be used in tracking campaigns, both in low and high altitude regions. It addresses non only the technical performances of the assets but also the identification of their current operational constraints that could be in fine parts of a Service Level Agreement for their contribution in the future European SSA System.

In that context, this paper presents both aspects, concentrating on the radar tracking campaigns only i.e. the LEO region (a similar article is written on the high altitude region). During the campaigns, the following existing European radars - EISCAT and Chilbolton - were used to track several satellites selected to cover a wide range of altitude and inclination in the LEO region. Two different campaigns were done to track the satellites. Orbit restitution was performed in order to characterize the role of the different observation parameters and to point out the best way to improve the orbit estimation performance with a single assets or with a combination of the different assets.

This paper describes the preparation of the campaigns as well as the results obtained. The campaigns were mainly driven by the availability of radar assets and the visibilities of the satellites. The precise orbit determination enabled the comparison of the performance of the different assets.

*****


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European Space Situational Awareness - Radar Simulation

Halté, Stéphane; Sciotti, Massimo; Quintanilla, Jorge ESA/ESOC

The ESA (European Space Agency) Space Situational Awareness Preparatory Programme (SSA-PP) was authorized at the November 2008 Ministerial Council and formally launched 1 January 2009 for an initial period to 2011-2012. SSA is defined as a comprehensive knowledge, understanding, and maintained awareness of the (i) population of space objects, of the (ii) space environment, and of the existing (iii) threats/risks. In the frame of the SSA-PP, an L-band close-monostatic phased array radar (named RR-I) is being developed by a European consortium. Its deployment is expected in early 2012 and it is intended for demonstrating radar technologies and techniques for LEO surveillance, hence paving the way for future radar systems that will contribute to the overall SSA surveillance strategy.

In the SSA-PP frame, ESA also placed a Contract in 2010, named CO-IV, for the development of an end-to-end phased array simulator, covering potential SSA radar architectures, radar techniques and radar data processing algorithms. The role of the CO-IV simulator is (i) to support end-to-end architecture analysis using realistic mathematical models, (ii) to test and verify data processing algorithms over real/synthetic data of LEO objects, and (iii) to support RR-I breadboard verification and validation testing. The CO-IV simulator will be fully capable of synthesizing raw radar data for multi-day LEO object orbits.

Modeling of potential SSA radars is highly demanding. SSA programme requirements for LEO target detection and volume scanning led to the selection of phased array antennas in both close-monostatic and bistatic radar configurations. Digitalization of all the antenna elements needs to be investigated - and simulated by CO-IV- as well as sub-arraying and antenna thinning strategies. The SSA radar is asked for high target location accuracy over both range (range rate) and angular domains. This implies the use of digital processing techniques for target location (monopulse, range interpolation, range migration compensation, acceleration compensation, etc), which need to be fully simulated. It is well known that their performance is largely degraded by several effects such as antenna beam mis-pointing, SNR losses, timing errors, target fluctuation, etc. These effects need to be reproduced by the CO-IV simulator in order to derive sub-systems and component low-level requirements for final radar design.

This paper describes the activities carried out by ESA in the design of the CO-IV end-to-end phased array simulator for Space Surveillance. The requirements posed on the simulator are herein discussed and prioritized; preliminary SW/HW design tradeoffs are then presented. Interfacing with real HW breadboards is also discussed.


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***** Sharing SSA Data

Bird, D. US Strategic Command

My presentation will summarize the brief history, current status and way ahead for US Strategic Command's sharing of SSA data. Specifically I will go discuss the Conjunction Summary Message (CSM) and give examples of how it is used by satellite operators today. I will also provide an update on the status of the proposed international standard, Conjunction Data Message (CDM). Finally, I will briefly mention some initiatives we are considering for expanding/improving the data we share and how we share it.

***** Supporting a Space Surveillance Data Model with Standards

Martinez, F.; Agueda, A.; Arregui, J.P.; Martín, L. GMV

The European Space Situational Awareness program is aiming at deploying a fully European system that supports the scenarios for Space Surveillance and Tracking, Space Weather and Near Earth Objects. This also covers the definition of the operational and data processes and the identification and definition of interfaces. Common to all scenarios and activities are the data objects required for the operation that contain the information stored in service and application data centres and used to interface internally and with external entities. Standardisation organisations like CCSDS have already performed and analysis on data entities that are partially or fully applicable to the SSA domain, in particular to the Space Surveillance and Tracking (SST), and that can be reused in the implementation of the SST data models and also to facilitate the exchange of data via standardised mechanisms. This paper focuses on the application of navigation standards to describe elements of the SST data model from a point of view different from the mere internal data architecture for data storage, addressing benefits of and drawbacks of the approach with respect to other traditional data modelling approaches. The motivation for this approach comes from the way in which these standards are created, based on the knowledge of several agencies and organisations with different points of view that contribute robust and well established solutions. The objective is to define the data model such that the contents of the standard (not quite the format) are mapped into the data model. Of course this does not prevent from other data elements being included in the model, but the approach guarantees that the internal representation and the usage of the information by all other entities (internal and external to SSA) is done consistently. The data domains inside the SST that are covered by CCSDS standards are the following: - Trajectories and ephemerides, to be represented by Orbit Parameter Message (OPM) and Orbit Mean-elements Message (OMM) and Orbit Ephemeris Message (OEM) - Covariance, to be also included in the OPM as the result of an orbit determination process and in the OEM for covariance evolution representation o Tracking, covered by the Tracking Data Message - Collision avoidance, not yet supported by a CCSDS standard but a dedicated Collision Data Message is being prepared to support this domain - In orbit tracking sensors that can be supported by the Attitude Data Messages (APM, AEM) - Sensor planning for survey or tasking that can be supported by the future Pointing Request Message (still in the early stages of standardisation at CCSDS) In addition to the previous, the need to cover other future SST service products by standards will be studied, in particular fragmentation and re-entry events. The usage of CCSDS standards in other SSA fields like NEO (also object trajectories can be supported with ODM) and Space Weather can be analysed.

*****


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Space Situational Awareness in Europe - Analysis of Potential Sensor Network Topologies in Front of Existing Governance Challenges

Ernst, H. Astrium Space Transportation

In order to ensure a secure utilization of space in the future, Space Situational Awareness (SSA) is one of the major issues to be addressed. The growing population of controlled and uncontrolled space objects raises the necessity for a better knowledge of the exact orbit parameters and behaviour of all objects, especially those which might lead to critical damages on space born assets.

Several organizations are concerned about the growing risk on valuable space assets and several initiatives take place to address the challenge. Listening carefully to the different actors, it becomes obvious that none of the involved organizations such as agencies or nations will/can take the full responsibility for the challenge and full ownership of the required capability in Europe.

Cost is an obvious driver for this. Furthermore, the federated nature of Europe and the existence of national interests will also influence the overall architecture and will - most certainly - lead to a federated architecture. The presentation will elaborate on the impact of above described background on a potential SSA sensor network architecture in Europe.

It can be expected that sensors will be owned and operated by different organizations or nations. At the same time, such sensor capabilities shall contribute to improve the overall knowledge and assessment of the current and future situation in space. By utilizing synergies, data distribution and information fusion, a network of sensors per se is supposed to create benefits for all participants of the network.

On the other hand, organizations and nations have a strong interest to maintain operationally self-standing systems, not being "too" dependent on the availability of others.

Thoughts on governance aspects for such a European sensor network will be discussed. Properly defined data policies and service level agreements will be presented as key aspects for the implementation of SSA in Europe. It will be crucial that the different communication partners agree on "what to expect" from the network and to commit to a well defined quality of service vice versa. Also, certain rules which information shall be shared and which information shall be suppressed need to be defined and accepted by all parties. This is specifically important for any information with military relevance.

The presentation will not only reflect on theoretical concepts, but will concretely report on achievements being made in the context of self-funded R&D studies. Based on service oriented architecture, the company has established a test-bed for SSA, bringing together different data sources, algorithmic functions etc. Information about lessons learned, best practices and architectural patterns are expected to deliver value to the audience.

As a concrete SSA network integration scenario, the presentation will also showcase a hardware-in-the-loop scenario, namely the integration of an SSA optical sensor.

***** SSA-DPM: A Model-based Methodology for the Definition and Verification of European

Space Situational Awareness Data Policy Gianni, D; Lindman, N; Moulin, S; Fuchs, J

European Space Agency

The European Space Situational Awareness (SSA) System of Systems (SoS) will provide services concerning space weather, near-Earth objects and surveillance and tracking. The successful provisioning of these services relies also on the availability of observation data from the systems participating in the European SSA SoS. Critical to ensure the reuse of the largest set of existing


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assets is that observation data are guaranteed to be used and disseminated only according to the data policy requirements of the individual European institutions owing or operating the assets. To gain the trust of these institutions and to ensure that their requirements are actually satisfied, a methodical approach must be introduced to support a systematic definition of the SSA data policy and allow the subsequent verification of SSA SoS architectural designs according to these policies. In this paper, we introduce SSA-DPM, a model-based methodology that can be used to guide data policy makers and programme managers in the formulation of the SSA data policies. SSA-DPM can also support the verification of completeness and consistency of a data policy specification, thus further contributing to the accurate definition of SSA data policy. Furthermore, SSA-DPM lays the foundations for the verification of SSA SoS architectural design by leveraging on the European Space Agency Architectural Framework (ESAAF). We present an example definition of a SSA data policy and we show examples verifications of SSA SoS architectural design.

***** A Technical Contribution Supporting the Definition of the European Space Situational

Awareness Governance and Data Policy: the SPA project Valero, J.L.; Albani, S.; Gallardo, B.; Matute, J.; O’Dwyer, A.

European Union Satellite Centre

The Support to Precursor space situational Awareness services (SPA) project is an FP7 Support Action managed by the European Union Satellite Centre (EUSC) and started on the 1st of March 2011 with duration of 18 months.

EUSC will provide its expertise in handling, analysing and disseminating sensitive data and derived products within the highest security standards to contribute, through the SPA action, to the technical definition of the European Space Situational Awareness Governance and Data Policy testing possible models in the EUSC operational and secure environment by experimenting with three preliminary services: Satellite Conjunction Warning, Satellite Over-flight Alert and Space Debris Re-entry Prediction.

Space Situational Awareness refers to the knowledge of location and function of space objects and space environment, including operational satellites, space debris, near earth objects and space weather. The development of a European Space Situational Awareness system will underpin the exploitation of European space assets, a key capability contributing to the autonomous access to (and utilization of) space for Europe (as requested by the European Space Policy, drawing on existing capabilities and infrastructures at national and European level).

The final output of the SPA supporting action will be a report summarising knowledge gained on Space Situational Awareness, including lessons learned, during the execution of the SPA study and recommendations for further development of Space Situational Awareness in Europe, particularly on the technical aspects of its Governance and Data Policy.

***** Collision Risk Assessment For Multiple encounters

Garmier, R1; Dolado, J.-C.2; Pena, X.2; Legendre, P.3; Revelin, B.1 1CS SI, Parc de la Plaine, 5 rue Brindejonc des Moulinais BP 15872, 31506 Toulouse; 2CNES,

French National Space Agency, 18 Avenue Edouard Belin, 31401 Toulouse; 3CEMAES, 9 route de Damiatte, 81500, Fiac

CNES realizes a daily monitoring of its satellites and computes individual collision probability in case of a dangerous conjunction. Sometimes, the encounter between the target and the chaser will occur several times per orbit, for several consecutive orbits. For such multiple encounters, assessing the risk for each individual risk separately as if they where independents events, is not sufficient to characterize the real risk of such a conjunction. So this study will focus on efficient ways to asses the collision probability of such a recurrent encounter.


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As the collision probability for N encounters is not necessarily equal to the summation of the N individual probabilities, we first propose to compute a collision probability over N orbits through a Monte Carlo shooting. For each trial, we randomly disperse the initial position vectors of the chaser and the target according to their respective covariance matrices. We then propagate the two trajectories over the N orbits and search the dangerous conjunctions (i.e. conjunctions with a close approach distance lower than a security threshold). The collision probability is then equal to the number of trials with at least one dangerous conjunction divided by the total number of trials. Unfortunately, to reach a probability in 10-M with a 10-M-1 accuracy, one needs to realize 10M+2 shootings, which is dramatically expensive in term of computation.

To bypass this problem, we develop two criteria to avoid, when possible, the use of Monte Carlo simulation. For the first criterion, the multiple encounters probability is bound by lower and upper limits. Theses boundaries are computed with no extra cost by using the individual collision probabilities obtained during the daily assessment. This way, we can probe the magnitude of the collision probability. If the two boundaries are close enough, we have a good estimation of the collision probability without computing it. The collision probability is indeed equal to the upper bound probability when no trajectory of the Monte Carlo simulation presents more than one unique dangerous conjunction. This configuration is very common.

In addition to this probabilistic method, we introduce a geometric criterion to complete the analysis. The geometric criterion allows us to analyze if for the given security threshold, we are able to compute the collision probability through the summation of the individual probabilities. This criterion is based on the modeling of the evolution of the close approach distances. We estimate the parameters of this model by covariance propagation and finally derive the distance criteria as the smallest distance between any dangerous and any another close approach distance. We test the two proposed criteria on real or simulated geometries of multiple encounters and compare their predictions to collision probabilities computed through the Monte Carlo simulation. The results show the efficiency of the method.


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***** Screening the Collision Risk of the Iridium 33 - Cosmos 2251 Clouds

Rossi, A.1; Valsecchi, G.B.2 1IFAC-CNR & ISTI-CNR; 2INAF-IASF, Rome

As was first shown more than 10 years ago in Rossi, Valsecchi and Farinella (Nature 399, p. 743-744, 1999), a near polar multi-plane constellation such as Iridium is particularly at risk of a collisional cascade if one of its satellites is first accidentally fragmented. At that time, the risk of such a catastrophic impact was estimated to be about 10 % per decade. Unfortunately, what was a "gedankenexperiment" in 1999 became a reality on 10 February 2009, with the Iridium 33 - Cosmos 2251 collision. Two large clouds of fragments, currently including about 2000 cataloged objects, are now jeopardizing the operational constellation spacecraft.

Correctly understanding and modeling the clouds dynamics is essential to the collision risk monitoring within the two clouds. As a matter of fact, the Iridium-Cosmos collision took place on the third plane of the Iridium constellation that, as was shown in Rossi et al. (1999), is one of the most protected planes, in dynamical terms. In fact the resulting cloud does not encounter the nearby constellation planes in an unfavorable head-on geometry in the aftermath of the fragmentation (e.g., as would have been the case for a fragmentation happening on plane number six).

In the present work the long term collision risk on the Iridium satellites, due to the relative motion of the orbital planes of the constellation and of the clouds, is analyzed. Screening methods are used to estimate the frequency of close approaches and collisions within the clouds and an analysis of the overall collision probability is performed using an evolution of the analytical method used in Rossi et al. (1999).

***** Optimal Collision Avoidance Maneuvers using Pseudospectral Methods

Martin, E.; Pineiro, J.J.; Fuentes, J. E&Q Engineering

The increasing concentration of space debris represents a rising threat to space security. This fact, along with the growing number of satellites in orbit, entails a higher probability of collision that leads as well to a higher number of Collision Avoidance Maneuvers (CAM). In this scenario new methods both to improve and optimize CAM are needed.

Along past decades, two general types of methods have been developed for solving optimal control problems: direct and indirect methods. While indirect methods derive the first-order optimality conditions using the Pontryagin's minimum principle and the calculus of variations, direct methods discretize the states and controls at points in time along the trajectory called nodes.

Over the last two decades, a particular class of direct collocation methods -based on a set of orthogonal collocation points- called PseudoSpectral (PS) methods have raised to prominence in the numerical solution of optimal control problems such as missile guidance, trajectory optimization, re-entry and nonlinear optimal control design.

PS methods have two main procedures to minimize the computational time and the error. The first one is the approximation of integral calculation by Gaussian quadratures, and the second is based on the selection of the collocation points. The nodes are non-uniformly spaced in time, the number of nodes selected depends on the accuracy desired and this number determines the spacing. One of the main advantages of these methods is their extremely fast convergence rate called spectral rate (faster than any given polynomial rate).

In this paper, Legendre and Chebyshev PS Methods will be used to find optimal solutions to the control problem stated in a CAM scenario.


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Taking into account satellite dynamics and different types of constraints (physical, path-related), it will be shown how to find optimal maneuvers minimizing cost functions such as time, fuel consumption, risk or service downtime among others.

The planning and implementation of the CAM calculated using PS Methods is integrated into a global operational framework. This framework includes the decision making process of a maneuver taking into account uncertainty, calculation of collision probability, risk analysis and risk acceptance criteria.

***** The Applicability Research of Nonlinear Collision Probability

Xiong, Yongqing; XU, Xiaoli Purple Mountain Observatory

When encounters occur at extremely low velocities, it is necessary to compute collision probability with nonlinear method. For nonlinear motion, the direction associated with relative velocity must be reintroduced, so special attention should be paid to the integration limits for the time-dependent dimension. When different limits are adopted, probabilities and integration time will change significantly. We also analyze the application scope of nonlinear method, the results show that the nonlinear effect becomes important only in some extreme situations, and also varies with encounter condition. When two objects in circular orbits encounter with a tiny inclined angle, the linearity assumption is not suitable anymore. For LEO, when the inclined angle between two orbit planes is less than 0.02°, collision probabilities derived from linear and nonlinear methods begin to diverge. The same case also occurs for MEO and GEO whose inclined angles are 0.01° and 0.005° respectively. Although the deviation between linear and nonlinear results depend on the miss distance and the combined covariance, the similar conclusion will be also found in very small eccentric orbits.

***** The Transfer Orbit Threat to Geostationary Satellites

Finkleman, D Analytical Graphics, Inc.

The objective of this paper is to characterize the threat of spent boosters locked in geostationary transfer orbits. These objects have very consequential and frequent intersections with the geostationary protected region. We present analysis of the current catalog that demonstrates persistence of GTO debris. We have characterized the nature of this threat and the consequences of such collisions. Geometries vary from direct side impact with significant relative vector velocity to relative slow approaches of meters per second. . We used fragment mass as the discriminating parameter since mass is directly related to fragment energy whereas fragment size is not. We used the Debbie debris model, which is well documented. We chose a minimum fragment mass of either 0.1 or 0.5 kg. Thousands of fragments can be generated and propagated over whatever interval is reasonable. However, this is not necessary for estimating the consequences of a collision. Debbie has a number of free parameters and user selectable physical hypotheses. Our debris research revealed that a non-equilibrium, non-Newtonian hypothesis is most realistic. The degree of contact between the colliding satellites is very important. Our experience is that 10% involvement was appropriate and that fragments more massive than 500 grams were sufficient. There are three distinct debris clusters: one each along the original orbits of the satellites involved and another Newtonian like along the resultant velocity vector otherwise specified by conservation of momentum. Much more will be accomplished before the conference. Observations to date are as follow. 1. There is no coherent "debris cloud." The fragments disperse rapidly in many directions. The volume that bounds the fragments is quickly so large that the density of fragments taken over the whole volume is effectively zero. The statistical distributions of fragment properties are not Gaussian. Even if they were Gaussian, the Gaussian would not be preserved during propagation with several nonlinear perturbations. 2. We executed the analysis to determine size distributions for the largest number of fragments our tools currently allow, 10,000 down to masses of one gram. More than 8500 of 10,000 fragments were smaller than ten centimeters. 3. There are no specifically contaminated regions of the geostationary region. The regions of risk in near Earth orbit are not static. The susceptibilities are


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best described in terms of orbital parameters for satellites at risk. This investigation is pursued to provide information for developing safe disposal procedures for boosters locked in geostationary orbit. A much more broad sample of probable encounters must be executed. Since debris from collisions of GTO objects will permeate all orbital regimes, it is wise to consider mitigating this threat in the near term.

***** Collision Risk Assessment for Spacecraft with CASS

Ma, Chaowei1; Huang, Jianyu2 1Beijing Institute of Tranking and Telecommunications Technology; 2Beijing Institute of Tracking

and Telecommunications Technology

Along with the rapid growth of the Earth orbital objects in recent years, especially the collision of the American Iridium-33 satellite and the Russian Cosmos-2251 satellite in February 2009, the amount of the space debris is increasing faster than ever due to the human growing space activities, which causing an increase in the risk of collision with operational satellites. In order to provide technical supports for spacecrafts flight-safety assessment, BITTT has developed CASS, a software for conjunction assessment,orbit covarience analysis,collision probability calculation and collision avoidance maneuver simulation. By which, BITTT continual performs operational satellites high-risk collision analysis based on Two-Line Element (TLE) data from space-track website and satellites ephemeris. This paper presents the composition, structure, functions of CASS, and introduces BITTT's process for the identification and assessment of operational spacecraft high-risk conjunction events.This paper consists of five parts, including the introduction,basic information of CASS, process overviews of collision assessment, examples of high risk analysis and conclusions.

***** Anomaly Resolution using Optical Signatures

Kervin, P1; Hall, D2; Hamada, K3; Lambert, J2 1US Air Force Research Laboratory; 2Boeing; 3Pacific Defense Solutions

When an Earth-orbiting satellite experiences anomalous behaviour, it is often useful to attempt to understand the nature and possibly the cause of the anomaly by analyzing optical signatures of the satellite. One optical signature that is very useful is temporal photometry, brightness as a function of time. A benefit to this type of signature is that it does not require sophisticated instrumentation or large apertures. We will discuss some of the techniques that can be used to understand anomalous behavior, as well as the importance of a historical baseline for comparison. As an example of these techniques, we will examine and interpret data from the Galaxy 15 satellite as well as other similar satellites.

***** A Dynamic Observation Concept as a Key Point for an Enhanced SSA Optical Network

Cibin, L1; Chiarini, M1; Milani, A2; Bernardi, F2; Dimare, L2; Pinna, G3; Zayer, I4; Besso, P4; Ragazzoni, R5; Rossi, A6

1Carlo Gavazzi Space Spa; 2Dipartimento di Matematica Università di Pisa; 3ESAC; 4ESOC; 5INAF; 6IFAC

Carlo Gavazzi Space SpA, INAF (Istituto Nazionale di Astrofisica), DM Dipartimento di Matematica Pisa) and IFAC-CNR (Istituto di Fisica Applicata), constitute an ItalianGroup focussed on Space Surveillance thematic. The group is now studying, in the frame of the ESA TELAD CO-V Telescope Analysis and Design Programme, an enhanced optical instrument based on an innovative Fly-Eye architecture and a core of key technologies, with advanced performances. This technology is developed to make available a common optical instrument for survey and follow-up of the GEO, MEO and HEO orbital belts, as well as for the observation of NEO objects. The TELAD innovative telescope is designed with a one meter equivalent aperture and covers a 45square degrees field of view with a pixel scale of 1.5 arcsec, for a total 256 Mpix image size. Further, the application of the Fly-Eye concept lead to the design of a compact instrument, suitable for fast dynamics and very precise positioning.


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The Group, through the development of the previous ESA SARA SSA programme, has evidenced and analyzed the fundamental key elements necessary for the design and development of a successful optical observatory network. It was taken in consideration the most demanding case of high LEO observations, by developing a very detailed and realistic simulation. This way it was possible to demonstrate that the designed optical network, based on the enhanced Fly-Eye telescope, satisfies completely the SSA Requirements. It was also demonstrated the capability to tightly cooperate with a Radar based complementary network. In this work it is discussed how the enhanced dynamic capabilities, which are offered by the TELAD debris telescope, allow to implement novel observation strategies which greatly improve the overall optical network performances. The paper describes in particular the observation strategies to be implemented for different orbital belts which can be developed on the basis of a dynamic fence of optical sensors concept. The main advantages offered by this approach are analyzed and compared with more traditional configurations, based on a static fence observation strategy.

***** Optical Observation Campaign in the Framework of the ESA Space Surveillance System

Precursor Services Früh, 1; Schildknecht, T.1; Hinze, A.1; Reber, M.2

1Astronomical Institute University of Bern; 2EARLY-SPACE

The ESA SSA CO-VI study Space Surveillance Precursor Services is evaluating the conditions to implement an operational European Space Surveillance network and is proving first precursor services. In the framework of this study seven European optical sensors were tasked to provide quasi simultaneous observations of operational GEO and MEO spacecraft. GPS and GLONASS navigation satellites served as calibration targets. The observations were organized in three one-week campaigns from December 2010 to February 2011.

The paper presents the overall campaign planning including the target selection, the detailed sensor coordination activities during the campaigns, the data reduction and processing, as well as the results. The astrometric accuracy and possible epoch biases of the observations provided by the sensors were estimated by comparing the measurements of the calibration objects with precise ephemrides. Orbits were determined for all target objects using the acquired optical measurements and compared to operator orbits where available. The lessons learned are discussed and suggestions concerning the further development of an operational European optical space surveillance sensor network are made.

***** Innovative Orbit Determination Algorithms for a complete Debris catalog in the upper

LEO region. Dimare, L.1; Milani, A.1; Bernardi, F.1; Farnocchia, D.1; Rossi, A.2

1Department of Mathematics, University of Pisa; 2IFAC-CNR & ISTI-CNR

We present the results of a large scale simulation, reproducing the behavior of a data center for the build-up and maintenance of a complete catalog of space debris in the upper part of the low Earth orbits region (LEO). The purpose is to determine the achievable possibilities of an advanced optical network, through the use of the newest orbit determination algorithms developed by the Department of Mathematics of Pisa (DM). Such a network has been proposed to ESA in the Space Situational Awareness (SSA) framework by Carlo Gavazzi Space SpA, Istituto Nazionale di Astrofisica (INAF), DM and Istituto di Scienza e Tecnologie dell'Informazione (ISTI-CNR).

A new orbit determination algorithm, based on the first integrals of the Kepler problem and on rigorous tools of Computational Algebra, was developed by DM to solve the critical issue of LEOs orbit determination. Standard methods require at least three observations per pass in order to compute a preliminary orbit, while the proposed algorithm needs only two tracklets, observed at different passes. This results in a significant reduction of the number of telescopes and then of the cost of the entire system. In addition, the proposed method takes into account the Earth oblateness effect, which in this case is not negligible. This is essentially due to the low altitude of the orbits considered and to the availability of only one tracklet per pass.


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The population sample used in the simulation was selected from a MASTER2005 Population Model, updated with recently occurred fragmentation events. The sample contained Debris objects down to 5 cm with perigee altitude ranging between 1000 and 2000 km.

The simulation was divided in three parts: catalog build up, orbit improvement and fragmentation analysis.

The developed orbit determination algorithm allowed us to achieve in just two months of survey observations a very high percentage of catalogued objects relative to the sample selected. In particular, the attained results are comparable to the possible performances of a next generation radar.

The accuracy of the obtained orbits was good enough to perform follow-up observations, to be used for the orbit improvement. In this phase, a very high accuracy in the prediction of position and angular velocity was achieved in just 3 weeks of tasking observations.

Finally, we simulated the fragmentation of a satellite at the altitude of 1400 km, due to both an explosion and a catastrophic collision. The ISTI implementation of the NASA-JSC model was used. The catalog build-up of the fragments through survey observations was completed in two weeks. Anyway, the information obtained in 6 days was more than enough to assess the fragmentation event.

From these results we conclude that the problem of Debris surveillance in the LEO region can be faced in a very effective way by joining together the existing technology, the use of advanced optical sensors and the most innovative computational approaches.

***** Results from First Space Debris Survey Observations in MEO

Hinze, A.1; Vananti, A.1; Schildknecht, T.1; Krag, H.2 1University Bern; 2ESA/ESOC

The Medium Earth Orbit (MEO) region becomes increasingly populated as new navigation satellite constellations are deployed or existing constellations are replenished with new satellites. As a consequence a growing number of space debris including small-size objects can be expected. Based on the findings for the GEO region one could expect small-size operational debris, delamination debris from aging objects, and debris from fragmentation events. The Astronomical Institute of the University Bern (AIUB) performed several survey campaigns between January 2010 and November 2010 to search for debris objects in the MEO region. The optical observations were conducted in the framework of an ESA study using ESA’s Zeiss 1-m telescope located at the Teide Observatory at Tenerife, Spain. To estimate the population and the density of debris objects in MEO orbits, first surveys covering particular orbital planes of the GLONASS and GPS constellations have been performed. These orbital planes include a high number of operational and defunct satellites, as well as spent upper stages. The results from the different observation campaigns will be presented. Based on the measured data a statistical analysis was performed to estimate upper limits for the debris density in the investigated orbital planes.

***** A New Astronomical Orientation Method for Space Debris

Zhang, Xiaoxiang; Xu, ZhanWei; Ping, YiDing Purple Mountain Observatory

The traditional astronomical orientation is to build a map between measuring coordinates and ideal coordinates by using plate constant model, whose essential is to calculate the least squares solutions of linear equations. Because the accuracy of measuring coordinates varies with the different magnitude of stars, the weight of stars should not be same when the plate constant is calculated. In this paper, a new expression, based on the traditional plate constant model, is given, which coefficient is six or twelve. Because the measuring coordinates is the function of ideal coordinates in the new expression, the weighted least squares parameter estimation


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method can be used in astronomical orientation, which is similar with the weighted least squares parameter estimation method used in precise orbit determination of space debris. In order to prove the correctness of new expression, the simulated data is used firstly. Assume that the pointing of telescope varies according to the increment of azimuth is 30 degrees and the increment of elevation is 10 degrees, we make 72 groups random numbers of normal distribution whose mean is zero and variance is 0.5 pixel(the scale of pixel is 24.6 arc-second). By using the six or twelve coefficient expression, the first calculated result is as priori value, iterated calculation is in turn. The mean of right ascension and declination residuals are almost zero, and the variance are close to 12.3 arc-second. From the calculated result, it is show that the new expression with six or twelve coefficient is feasible. In this paper, we only do first situation that the accuracy of stars¡¯ centroid are with the same weight, some research must be carried forward, such as weighted values of different magnitude stars, priori weight and observation data.


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***** SSA Products from Wide Field of View Optical Sensors

Herridge, P.; Dick, J. Space Insight Limited

Small field of view optical sensors which track objects one at a time have historically been the norm for observation of the higher Earth orbits. The large number of high-orbit objects and the diversity of their orbits are better covered by a new generation of wide field of view surveying sensors. For the commercially and strategically important GEO regime in particular, wide field sensors can provide frequent scans of the population.

Creating SSA from sensor observations is not trivial. Given the large volume of observations from a network of surveillance sensors, dealing with information quality issues (such as correlation accuracy) is critical to ensure the SSA database purity. In generating SSA knowledge, exploiting non-metric data is extremely important to add value to the pool of SSA products, as well as helping with the maintenance of information quality.

In this paper we discuss the use of surveying sensors in the provision of enhanced-value data to an SSA system and provide examples of its utility with particular reference to the maintenance and verification of SSA on GEO clusters, cluster member discrimination, and optimal sensor scheduling.


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***** Dedicated Telescopes with Large Field of View for Space Surveillance

Molotov, I.1; Agapov, V.1; Yudin, A.1; Kardashenko, M.2 1Keldysh Institute of Applied Mathematics, RAS; 2JSC Sientific-industrial enterprise "Project-

Technics"

ISON optical network represents one of largest ground systems specialized in observation of space debris and other objects on high geocentric orbits. A few types of dedicated telescopes with large field of view (FOV) - 22 cm (FOV 4x4 degree), 40 cm (FOV 2.3x2.3 degree) and 50 cm (FOV 1.8x1.8 degree) telescopes are designed, produced and installed at the ISON observatories during 2007-2009.

Moreover, new telescopes are elaborated in 2010 as parts of two types of dedicated observation facilities. First type includes 40-cm, 25 cm (FOV 3.5x3.5 degree) and double 19.2 cm (FOV 7.5x7.5 degree) telescopes, second type includes 65 cm (FOV 2.5x2.5 degree), 40-cm and quad 19.2 cm telescopes. The concept of modernization of the old 1-m class telescopes is also proposed. The KIAM expeditions visited Argentina, Armenia, Brazil, Bulgaria, Italy, Kazakhstan, Mexico, Mongolia, Venezuela, North Caucasus and Far East of Russia to find the acceptable places for observatory installation. New sites are selected to improve current ISON structure.

The paper will describe aforementioned instruments and results we already obtained after initial operational phase for some of them.

Fig. 1. Double 19.2 cm telescope.


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***** Space Debris Observations with ZimSMART

Herzog, J.; Ploner, M.; Schildknecht, T. University of Berne

The Zimmerwald observatory, located about 10 km South of Berne (Switzerland), consists of several optical telescopes. One of them, the Zimmerwald SMall Aperture Robotic Telescope (ZimSMART) is best suited for surveying the sky searching for space debris. ZimSMART is used to develop an orbital elements catalogue, i. e. without any a priori information. Two different orbital regions are surveyed: the geostationary ring (GEO) and the Medium Earth Orbit region (MEO). The aim of the surveys of the geostationary ring is a coverage of as much as possible around the celestial equator we can observe from Zimmerwald. Surveys of the MEO region will give a first hint about the population of large-sized, uncatalogued space debris there. In this paper we will present observation strategies of ZimSMART for building up such a catalogue. The observation strategy for the MEO region differs significantly from that of the GEO region. We will discuss survey results we could obtain, including the catalogue itself, the limiting magnitude of ZimSMART, the fraction of catalogued objects we can observe and their composition concerning different object types. The same analysis was performed for new objects, which were not found in any external catalogue. With the latter we build up our internal AIUB catalogue. We took in consideration the period between June 9th, 2008 and February 25th, 2011 with 233 nights of observations in total. During this period we used three different set-ups of the telescope alternatively. We could identify 1281 objects of the USTRATCOM catalogue. Furthermore we detected in total 1136 uncatalogued objects, but those are most likely not all unique objects due to difficulties to connect short orbit arcs with long gaps in between.

***** Ground-based Optical Sensor Network for Space Surveillance

Blanchet, G.1; Fau, N.1; Pyanet, M.1; Vial, S.1; Legoff, R.2 1ASTRIUM SAS; 2EADS SODERN

Space surveillance is a major stake for the future of space transportation. Indeed, studies show that the number of debris in orbit is exponentially growing and the already existing population of small and medium debris is a concrete threat to operational satellites. Space surveillance necessitates that a catalogue of Earth orbiting objects is built and maintained. Such a catalogue shall contain physical and orbital information of all the Earth orbiting objects that have to be known and taken into account in SSA services.

Traditionally the surveillance of the LEO is achieved by using ground-based radars, while the Surveillance of MEO and GEO is obtained via ground-based telescopes. Astrium-ST is investigating feasibility and performance of an optical ground based system to efficiently complement radar systems even for LEO orbits. The overall system concept is composed of various type of optical stations dedicated to specific functions (survey, passive tracking, active tracking), distributed around the globe.

To support these investigations, two in-house operational breadboards are implemented and operated for survey and tracking purposes.

This paper presents synthesis of Astrium-ST activities regarding the end-to-end optical-based survey concept. For the detection of new debris, a network of wide field of view survey stations is considered: those stations are able to detect small objects and adequate image processing algorithms allow extraction of the relevant information for orbit determination. The survey concept relies on relevant observation strategy to efficiently scan the local sky.

*****


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Upgraded Camera for ESA Optical Space Surveillance System

Abreu Rodríguez, D.; Kuusela, J. Ataman Science

ESA has carried out space surveillance of man-made objects already over 10 years with the OGS telescope at the Observatorio del Teide. The telescope is equipped with a CCD camera for this purpose. The camera electronics is approaching the end of life and a new camera has been developed to replace it. In this paper we explain the motives behind the architecture of the new camera, the final specifications and the design of the camera. We also have look to the first test results and compare the performance to the old camera. We explain also the advantages of this cameras for other applications in space surveillance.

***** Laser Tracking of Space Debris

Gao, Y; Smith, C; Greene, B EOS Space Systems Pty Ltd

EOS has been investigating tracking space debris using E-O and laser based technologies since 1998. EOS has successfully tracked space debris using laser since 2003 in both cued and un-cued modes through several projects in collaborations with several defence agencies. EOS was the first organization in the world successfully tracked space debris using laser in 2003. EOS has tracked space debris less than 10 cm using laser. A range accuracy of 1.5 m has been achieved through laser tracking. In this paper a quick overview about EOS space technologies, research and development activities in relation to space surveillance will be given first. The advantages of tracking space debris using laser in comparison with conventional radar technologies will be discussed. Some results and milestones EOS has achieved with tracking space debris using laser since 2003 will be described. In addition to the space debris tracking EOS has also been investigating space debris de-orbiting or removal using laser technologies since 2001, and achieved some encouraging results. Some preliminary results can be presented if there is a sufficient interest in this. Finally some activities proposed for the Australian government funded Australian Space Research Program - Automated Laser Tracking of Space Debris which EOS has won recently will be presented.

***** Cloud Computing and Service Orientation in the SSA programme - Space Surveillance

services and data in the Cloud Michelbach, T.1; Tueffers, C.1; Águeda Maté, A.2; Amstutz, B. E.1; Frith, G.1; Stogdill, J.1; Ziegler,

M.1; Usrey, T. T.1 1Accenture; 2GMV Aerospace and Defence, S.A.

This paper articulates how service oriented computing and cloud computing together can facilitate technology enablement in the SSA programme - closely aligning a highly scalable IT landscape to business needs. Moreover, this paper illustrates how cloud computing service and deployment models enable software and hardware decoupling, making flexible computing structures possible. The European Space Agency (ESA) has launched the Space Situational Awareness (SSA) programme, an initiative combining three different segments focusing on near earth objects (NEO), space surveillance & tracking of manmade objects (SST) and space weather (SWE). SSA faces a challenging computational and data management landscape, given the volume of data and processing power required to fulfil its missions. Cloud computing is a disruptive technology changing the way organizations approach IT assets and business models. Through cloud computing, processing power and storage become commodity goods - utilities similar to electricity. Furthermore, the large amount of resources available facilitates a shift in approaches to software development, deployment and operations. Service oriented computing provides patterns to better structure systems, supply IT services, enable interoperability, and facilitate the business and IT alignment. We will sketch how the


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flexibility of both concepts can support the SSA programme. Using service oriented computing and cloud computing hardware/software abstraction techniques, the Agency can focus its resources on investments and initiatives related to its missions. The substantial scalability and elasticity of cloud architectures can and should influence technical and financial aspects of SSA's hardware/software landscape. We focus on the space surveillance area, currently coping with immense amounts of observations to draw conclusions in the areas of cataloguing, collision avoidance, among others. The flexibility to leverage highly scalable and distributable algorithms and the agility aspect to provision and de-provision resources on-demand will be discussed. We frame how the SSA programme could benefit from using such cloud characteristics. In addition to computational flexibility, cloud and service oriented technologies release the opportunity for collaboration and innovation in data utilization. We explore the emerging patterns of markets for data and applications, where academia, space industry and space agencies in Europe can develop, consume and provide services or data. Moreover, through such IT ecosystem, the SSA programme can foster innovation to accelerate, streamline, and further enhance the SSA programme accomplishments. We are confident that service oriented computing and cloud computing can drastically improve the approach, the SSA programme designs, implements and operates its solutions, from a technical, a financial and a mission agility standpoint.

***** Applying Cloud Computing to Space Situational Awareness

Johnston, S; White, A; Lewis, H; Cox, S; Hart, E University of Southampton

Within the last two decades, space-based technology has become a ubiquitous component of everyday life, from satellite television, to in-car GPS and weather forecasting. Space debris is, however, now feared as a significant risk to satellite operations, particularly in the low Earth orbit (LEO) region. Approximately 19,000 objects larger than 10 cm are known to exist, with around 500,000 at 1 to 10 cm, and the number of smaller particles is likely to exceed tens of millions (NASA, 2009). Conjunctions (encounters within 5 km) between satellite payloads and other catalogued objects occur at a rate of 2,400 per day, with operators having to perform avoidance manoeuvres in extreme cases. It is estimated that the number of detectable conjunctions will increase by 100 times by 2020 as the debris population continues to grow and surveillance capability improves. In this paper we demonstrate the applicability of Cloud computing and data handling for the important international problems of Space Situational Awareness (SSA), space debris removal and mitigation. Cloud computing is internet based computing that allows resources, software, data and services to be provided on demand. It provides the ability to trade computation time against costs and inherently favours an architecture which scales, providing burst capability. Many individuals and businesses use Cloud-based services for email, web searching, photo sharing and social networking. Scientists and Engineers are using a similar paradigm to make use of massive amounts of compute and data handling resources provided by companies such as Amazon, Microsoft and Google. With the use of a Microsoft Azure based architecture, we demonstrate a cloud based framework to tackle space debris tracking and analysis. The paper demonstrates a pluggable framework which harnesses super-scalable compute power for propagation and conjunction analysis, and how this can be used to assist with algorithm development and comparison. As an example of the latter case, we show how a Cloud solution to optimising a debris removal mission can be achieved. The Cloud based framework demonstrates an architecture which can scale to cope with an unlimited number of objects, providing there are sufficient Cloud resources and funding. The burst capability ensures that costs are kept to a minimum, i.e. when routinely processing the complete space-track catalogue but can quickly expand in the event of a collision, or as more objects are located.

*****


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Reuse of Operational Flight Dynamics Software for Space Surveillance

Martínez, F.; Agueda, A.; Fernández, J.; Escobar, D. GMV

The deployment of the Space Surveillance and Tracking (SST) precursor service in the frame of the European SSA preparatory programme is demanding a lot of infrastructure software for a wide variety of applications. Many of these applications are closely related to flight dynamics and are optimal in the reuse scenario intended by the precursor services of SST. GMV has been traditionally contributing to the development of flight dynamics related software for ESA and also a consumer of those developments to provide ad-hoc solutions in other related areas. From this prospective, this paper provides a view on the potential reuse of ESA and other parties’ software packages for different activities associated to the development of the SST precursor services and potential extension to the final SST system. Three main approaches for the reuse of software are identified, which are complementary and not mutually exclusive:

- Direct reuse, for cases where the existing package readily provides the required functionality with very minor adaptations (e.g. interfaces) - Adaptation and enhancement when the package provides a core functionality but requires additional enhancements or even needs to be reengineered to adhere to adequate software and algorithm standards - Validation when the package is not adequate for reengineering (e.g. too expensive or there is another better suited package) but the implementation provides reliable results that can be used as reference for other implementations. An initial collection of software packages fulfilling some of the needs of the initial developments of the space surveillance services has been identified. This paper addresses among others: - NAPEOS, the Navigation Package for Earth Orbiting Satellites developed by ESA that provides a comprehensive suite of tools for flight dynamics operations and data analysis. NAPEOS falls in the category of direct reuse and also permits the development of additional functionality on its structured core library. - CRASS (Collision Risk Assessment) and ODIN (Orbit Determination with Improved Normal Equations) are two packages providing conjunction analysis and ad-hoc orbit determination for SST. Their software approach is to some extent obsolete but the algorithms and core functions can be easily reengineered to be more efficient and maintainable. Both elements are operational at ESA and represent an excellent reference for the validation of new implementations. - Closeap is GMV’s evolution of CRASS to object orientation with an optimised implementation that allows parallelisation. It inherits the algorithms from CRASS being therefore compatible with ESA’s approach for collision risk assessment. - SSASIM is the result of a GSTP study for space debris cataloguing. This package belong to the second category since it cannot be directly reused but implement modules that adequately adapted can be reused for tracking correlation and objects cataloguing.

***** Open Source Space Situational Awareness Analyses - Requirements, Design, and

Examples Cefola, P1; Weeden, B.2; San-Juan, J.3; Lara, M.4

1University at Buffalo; 2Secure World Foundation; 3Universidad de La Rioja; 4Real Observatorio de la Armada

The accuracy of the Space Surveillance System orbital data products is affected by the sensors feeding the network, by the errors in the sensor network, by the space environment, by the available computing resources, and by the number of space objects to be monitored. However, the quality and quantity of the orbital data products has evolved slowly over time. Further, error analysis of key issues is still in flux. The Iridium/Cosmos collision event in 2009 demonstrated that the technical factors contributing to the erroneous prediction of the close approach distances were still uncertain.


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In 2010, the first two authors presented a plan for an "Open Source Software Suite for Space Situational Awareness and Space Object Catalog Work". This paper included:

- Adapting current SSA tools to modern distributed computing environment - Migration to language platform employing object-oriented and component technologies - Non-invasive encapsulation of legacy binaries creating a Web 2.0 architecture

For an orbit analysis tool to be useful, it should

- correctly predict the Orbit Determination performance of future tracking and orbit determination systems, - correctly predict the performance of existing SSA systems, - generate high accuracy reference orbits, - include conventional weighted least squares, Kalman Filters, and modern Nonlinear Filters, - be flexible with respect to the choice of orbit propagators/solve-for variables, - be flexible with respect to the available observation models including ground-based and space-based observation types, and - be flexible with respect to the total number of allowable sensors.

The design effort supports the application of modern hardware and software technology to the SSA problem:

- Modern platforms: Linux, Unix, Windows, Mac, Commodity computing (Amazon EC2) amenable to object-oriented software - Well structured C++ code Parallelization via multi-core CPU’s and GPUs - High Performance via OpenMP and CUDA - Non-invasive encapsulation for legacy programs - Web services-based architecture

The analyses employ the Linux version of the R&D GTDS orbit determination program. A Silicon Graphics workstation version of this program was developed at the Draper Laboratory, and subsequently used by the staff at Kaman Sciences Corporation to compare the accuracies of some General Perturbations and Semi-Analytical Satellite Theories under a high level of tasking. The Linux version of R&D has multiple capabilities that are relevant to SSA and is a candidate for non-invasive encapsulation. However, in this paper we employ the GTDS implementation of several orbit propagators: special perturbations, PPT2, PPT2 with the tesseral m-dailies, Russian AP, and the DSST. The intent is to process real observations and compare the results. Use of two sets of real obs data (one for a group of satellites and the other for a single satellite) is anticipated.

***** Predicting Collision Risk for European SSA System

Escobar, D.; Agueda, A.; Martín, L.; Martínez, F. GMV, SPAIN

In recent years, the space debris has gained a lot of attention due to the increasing amount of uncontrolled man-made objects orbiting the Earth. This population poses a significant and constantly growing thread to operational satellites. In order to face this thread in an independent manner, ESA has launched an initiative for the development of a European SSA System where GMV is participating via several activities. Apart from those activities financed by ESA, GMV has developed closeap, a tool for efficient conjunction assessment and collision probability prediction. ESA´s NAPEOS has been selected as computational engine and numerical propagator to be used in the tool, which can be considered as an add-on to the standard NAPEOS package. closeap makes use of the same orbit computation, conjunction assessment and collision risk algorithms implemented in CRASS, but at the same time both systems are completely independent. Moreover, the implementation in closeap has been validated against CRASS with excellent results. This paper describes the performance improvements implemented in closeap at algorithm level to


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ensure that the most time demanding scenarios (e.g., all catalogued objects are analysed against each other - all vs. all scenarios -) can be analysed in a reasonable amount of time with commercial-off-the-shelf hardware. However, the amount of space debris increases steadily due to the human activities. Thus, the number of objects involved in a full collision assessment is expected to increase notably and, consequently, the computational cost, which scales as the square of the number of objects, will increase as well. Additionally, orbit propagation algorithms that are computationally expensive might be needed to predict more accurately the trajectories of the space debris. In order to cope with such computational needs, the next natural step in the development of collision assessment tools is the use of parallelization techniques. In this paper we investigate the implementation of these techniques in the Smart Sieve filter. The computational memory requirements in an all vs. all scenario are low and thus, the OpenMP parallelization standard, which is specifically designed for shared memory architectures, seems to be an adequate choice. Apart from the computation of the orbits, the covariances of the different objects have to be computed at the time of closest approach of the detected conjunctions. So far, closeap implemented a numerical integrator to propagate the covariance of the objects. However, this approach has two important disadvantages. Firstly, it introduces an inconsistency as the SGP theory is used for the orbit computation while the covariance is numerically integrated. And secondly, the time needed for the numerical integration is also very significant. We analyse in this paper the use of SGP theory for the propagation of the covariance by means of numerical differentiation to overcome the previous issues.


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*****

Efficient Tracking Correlation Techniques for Space Surveillance Agueda, A.; Martínez, F.; Fernández, J.

GMV

Correlation is one of the key elements of the cataloguing process for space surveillance operations. The maintenance of the catalogue relies on a proper correlation process assigning to each object in the catalogue the tracklets coming from the tracking network to the data processing chain for the update of the catalogued information for the object. The correlation process looks simple at first glance but it represents a complex task and, as a result, many methodologies have been proposed in the literature to perform it in a reliable and efficient manner. These methodologies are normally performed either on the tracklet level or on the orbit level. This means that either pseudo-tracklets are obtained from the orbital information of all the catalogued objects and compared against the input tracklet or a certain orbital information is derived from the tracklet in order to compare it to the one stored in the catalogue for each object. Both methodologies can be implemented in a quite large variety of spaces of "attributables", the variables on which the comparison for the correlation process is performed. Additionally, this comparison process is based on the evaluation of a certain distance between the different data sets considered. Several distances between distributions can be considered and will be analysed (not only Euclidean but also Mahalanobis and Bhattacharyya distances). The computation of these distances between data distributions (either measurements or orbital parameters/attributables) requires counting on data synchronized at the same epochs. In the case of the orbits, this is quite simple as the synchronization of the orbital elements to compare is achieved by means of orbit interpolation at known epochs. For the correlation at tracking level, pseudo-measurements need to be generated from the catalogued orbital information at the epochs when the actual tracking is available. However, this process can be very time consuming as it would represent re-generating the pseudo-tracklets for all catalogued objects for each tracklet to be correlated. A solution to this is generating the pseudo-tracklets at known epochs for all catalogued objects (only once) and interpolating within the measurements in the input tracklet to get new pseudo-measurements at the same known epochs. Other information contained in the space surveillance tracklets (magnitude for optical sensors and RCS for radar sensors) can also be used while correlating. Normally this information is not very accurate but it can be used when the selection based in the distance is not trivial and there are significant differences in the sizes (obviously related to the magnitude and the RCS in the tracklets) between the candidate objects. The purpose of this paper is to review, describe and present these correlation techniques paying special attention to their suitability to the space surveillance problem in terms of performance, robustness and efficiency.

***** Mathematical and Algorithmic Description of Software Correlator for Space Debris Data

Processing in VIRAC Jekabsons, N.; Kotlere, D.; Smelds, I.; Nechaeva, M.

Ventspils University College

With its RT-32 radio telescope VIRAC already have been attended in the several VLBI space debris observation sessions. Notable trait of VIRAC during these sessions was somehow limited data processing capabilities. Further intensification of space debris session schedule sets high priority on development of fast, reliable and accurate quasi real-time data processing software and hardware.

Recently VIRAC team is testing in-home built auto-correlation and cross-correlation software. The standard FX approach is find to be applicable for evaluation of auto-correlation integrals, while time-domain based spectral methods and related algorithms seems to be favorable for processing both transmitted and received signals simultaneously. Processed data are used for accurate measurements of radial velocity of the objects, which further can serve for determination of more exact orbit elements of space debris.


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Both algorithms are engineered to be scalable, thus single correlation may run on a several HPC cluster nodes. Our further plans includes cross-correlation of signals, received by two or more VLBI-stations.

***** High Fidelity Models for Orbit Propagation: DROMO vs. Stoermer-Cowell

Peláez, J.1; Urrtutxua, H.1; Bombardelli, C.1; Huhn, A.2 1Universidad Politécnica de Madrid (UPM); 2Technical University of Munich

There is a large number of perturbations which can be acting on satellites. Would it be possible to obtain an analytical solution for each particular case? Similar to the numerical solutions, the answer depends on the forces we model, since due to the complex nature of the equationsrepresenting the physical models exactly integrable expressions are difficult to obtain. The simplest analytical model to be used in thepropagation of an orbit is the theory of the Keplerian motion of a celestial body. This theory, which is essential fromseveral points of view, becomes hardly useful when perturbations are involved in the dynamics. A classical approach to the many-body problem is that of using special perturbations. Nowadays and due to theavailability of high-speed computers is an essential tool in Space Dynamics which exhibits a great advantage: it isapplicable to any orbit involving any number of bodies and all sorts of astrodynamical problems, especially whenthese problems fall into regions in which general perturbation theories are absent. One classical special perturbation methods is the Cowell's method in which the equations are formulated in rectangular coordinates and integrated them numerically. There is some confusion in the terminology regularly used when describing the numerical propagation of orbits. Some authors talk about the Cowell's method as a special perturbation method; other authors talk about the Cowell's method as a set of multistep algorithms especially designed for the direct integration of second-order differential equations. This situation is probably due to a particular integration scheme called the St¨ormer-Cowell method which, at present, is widely used to the propagation of orbits in many astrodynamical problems. In the Stoermer-Cowell method the Cowell's method (as special perturbation method) is used, by integrating the equations of motion with the Stoermer-Cowell formulas. Many people prefer these methods for improved round-off error and ease of programming. But this is an open question and there is no a general agreement about the supremacy of any particular method relative to others. The Group of Tether Dynamics of UPM (GDT) has developed a new regularization scheme that we call DROMO which is characterized by only 8 ODE. The method was presented for the first time in the winter meeting of the AAS: Paper AAS 05-167 of the 15th AAS/AIAA Space Flight Mechanics Meeting, Copper Mountain, Colorado, USA, 23-27 January 2005. The novel Special Perturbation Method we called DROMO is especially appropriated to carry out the propagation of complex orbits. The goal of this communication is to compare the characteristics of DROMO as orbit propagator with the propagation scheme based in the Cowell method by using the Stoermer-Cowell algorithms to integrate the equations.

*****


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Long Term Propagation of GEO and GTO Orbits, in the Frame of the French Space Act:

Methodological Concepts, Simulations. Deleflie, F.1; Morand, V.2; Le Fevre, C.3; Wnuk, E.4; Wailliez, S.5; Portmann, C.6; Lamy, A.3;

Vienne, A.7; Emilion, L.7; Fraysse, H.3; Hautesserres, D.3 1IMCCE/GRGS; 2Thales Group; 3CNES; 4Poznan University; 5IMCCE/FUNDP; 6OCA/GEMINI;

7IMCCE

Space debris mitigation is one objective of the French Space Act, in line with IADC (Inter-Agency Space Debris Coordination Committee) recommendations, through removal of non-operational objects from populated regions. At the end of their operational life, space objects are to be placed on orbits that will minimize future hazard to space objects orbiting in the same region. In that framework, this paper stresses on the long term propagation of geostationary ("GEO") and geostationary transfert orbits. The equations of motion are written in a set of orbital elements suitable for orbits with small eccentricities and inclinations. They are averaged over the short periodic terms so as to be propagated thanks to very large integration step sizes (of the orders of a couple of days). This will ensure short computation times, even over periods of decades or centuries: this approcah is hence semi-analytical. The orbital modelling accounts for the very first terms of the geopotential (including the tesseral resonant part), the perturbations induced by the luni-solar attraction, the solar radiation pressure, and the atmospheric drag (using classical models). We will show some comparisons with classical numerical integration seen as a reference, in various dynamical configurations. In particular, we will show some examples where the effects induced by the solar radiation pressure have a strong impact of the stability of the trajectory (in case of a resonance). We will show the concepts of the analytical transformation to make averaged orbital elements be compatible and comparable with osculating elements coming from the numerical integration. At last, we will show the main functionalities of the STELA s/w, provided by CNES, and based on the dynamical modelling shown in that paper.

*****

Covariance Determination,Propagation and Interpolation Techniques for Space Surveillance

García, P.; Escobar, D.; Agueda, A.; Martínez, F. GMV, SPAIN

The uncertainty of the state vector and the orbit parameters must be known in order to monitor the orbit with respect a certain accuracy threshold or envelope imposed by the necessary performances of the services to be provided with these computed orbits. As long as the mean error in the orbit is close to zero, the orbital error follows a normal Gaussian distribution and therefore the covariance matrix is representative of these uncertainties. This matrix can be obtained at a given time as a part of the statistical orbit determination process. The evolution of the covariance matrix can be computed together with the predicted ephemeris to consider the increasing uncertainty of the orbital states during the orbit propagation. The state transition and sensitivity matrices contain the variational partials of the state vector with respect to the initial state vector and the dynamical parameters respectively. These matrices can be propagated together with the state vector to compute the relative change of the state components with respect to the initial state. Thus, these matrices allow the computation of the state covariance at any time. The covariance matrix can also be propagated by analytical methods. A fast computation of the transition matrix based on the Clohessy-Wiltshire equations can be used to propagate the covariance with a reduced gravity force model. Deriving the analytical or semi-analytical expressions of an orbital theory, like the Simplified General Perturbations (SGP) theory, it is also possible to obtain the transition and sensitivity matrices used for the covariance propagation. Another aspect in the handling of covariance is its interpolation, linked to the interpolation of the corresponding orbital states, but with several additional numerical problems. Using Lagrange polynomials to interpolate every element in the matrix can introduce artificial correlations between the parameters, changing the determinant of the covariance matrix and, in some limit cases, not guaranteeing that the resultant matrix is positive definite. Some alternative interpolation methods have been analysed. The first one is based on the


44

Lagrange interpolation of the eigenvalues and eigenvectors obtained from the covariance matrix, but the computational performances of this method are quite poor as the decomposition of the matrix is a computationally expensive task. Besides, there is another issue in this computation, since resultant matrix may shift its principal axes. Instead of directly interpolating the covariance, it is possible to interpolate the correlation matrix. However, this method presents dependencies on the reference frame used to obtain this correlation. The direct interpolation of the propagated transition matrix solves the frame dependency, but has the additional cost of interpolating all the elements in the matrix. Unfortunately, this matrix is not always available, so the usage of analytical interpolation methods has been considered.

*****

Short-term Orbit Propagator of Space Debris Moving on LEO and MEO Wnuk, E.; Golembiewska, J.

Adam Mickiewicz University, Astronomical Observatory

There are two aspects of the orbital evolution of space debris: the long-term evolution and the short-term prediction of individual object orbits. In the case of the long-term evolution (years or tens of years time span) general characteristics of a future space environment are predicted. In the short-term orbital evolution of space debris objects, as considered in this paper, future positions and velocities of individual objects are calculated for a few days or a few weeks time span. The paper presents the orbital prediction tool that uses an analytical and semi-analytical theories of satellite motion. The propagator is based on the second order analytical theory in the sense of the Hori-Lie canonical transformations. The direct transformation from osculating to mean orbital elements and the inverse transformation from mean to osculating elements are realized with the use of the Mersman version of a canonical transformation and are calculated with same high level accuracy. The applied theory is non-singular for the small eccentricity. The force model includes all important perturbing factors: geopotential effects with arbitrary degree and order spherical harmonic coefficients taken into account, luni-solar attractions, solar radiation pressure and atmospheric drag. An arbitrary degree and order contemporary geopotential model may be applied (in max. 360x360, typically 70x70 or 90x90). Orbital resonance terms are identified and separated. In the case of a deep resonance predicted orbits are calculated with the use of numerical integration. Luni-solar perturbations up to the second order are calculated with the use of the Giacaglia-Lane formulas. JPL ephemeris for the years 2000-2020 are used for calculations of the Moon and the Sun positions. Atmospheric drag perturbations are calculated with the use of numerical integration of equations of motion. The NRLMSIS-00 atmospheric model based on the MSISE90 model is applied. Solar radiation pressure perturbations are calculated with the use of the Harwood and Swinerd formulas. The shadow function is included in calculations, and the Sun positions are calculated from JPL ephemeris.

The paper will present the model of the prediction tool and several examples of future space debris trajectories determination for different classes of LEO and MEO orbits.


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POSTERS

***** Development of a Web Front End for ESA’s CRASS collision avoidance system

Del Pino, JR; Uruñuela, S; Villanueva, J Indra Espacio, SPAIN

The objective of the activity presented in this paper is develop a Web Front End for CRASS to enable the provision of collision avoidance services over the web.

CRASS is an ESA system providing conjunction prediction services to evaluate the collision risks between satellites, rocket bodies and space debris. Originally, CRASS services could be only accessed locally at ESA premises. The new Web Front Ent for CRASS brings all the advantages of Web enabling services. In this way CRASS can be accessed by other users out of ESA premises.

In addition, the Web Front End has introduced new capabilities not provided by the underlying CRASS system: 1) New administration options, such as creation of user profiles, satellite objects and actions a particular user can do over a particular object. 2) New exploitation options, with a broad range of reports and visualization graphics, providing a much more user friendly interface. 3) New planning and scheduled options, so that it is possible to plan when to evaluate collision risks – under request or on a systematic basis – and over what objects to evaluate the collision risks.

This paper will present the development process of the Web Front End web application for CRASS, summarizing the technical aspects of the application and focusing on the functionalities that it provides to the users. Specifically, the availability of mechanisms for scheduling the conjunction prediction analyses, launching specific on-demand analyses and also the powerful representation of the conjunction prediction analysis results for helping the collision avoidance tasks.

***** Motion Compensation for ISAR Imaging of Spinning Targets

Li, Hailin Beijing institute of tracking and telecommunication technology, CHINA

As to the ISAR imaging of spinning targets, such as space debris,due to the existence of the motion errors (ME) including the arbitrary translational motion and random radar systemic error, the sinusoidal envelope corresponding to scatterers on the spinning target gets in disorder in the range-slow time image which makes ISAR imaging of the targets impossible without motion compensation. Focusing on invalidation of the conventional methods for this issue, this letter proposes a robust algorithm for motion compensation for spinning targets, which utilizes the generalized Radon transform (GRT) to detect the curves in the range-slow time domain and align each range profile based on entropy of the reconstructed image minimization. Hence, the motion errors (ME) can be almost eliminated by this proposed method, and then a final two-dimensional (2D) ISAR image is to be achieved by the GRT. In this letter, both the theoretical analysis and simulation results confirm the effectiveness of this proposed algorithm.

***** The FABRA-ROA Telescope at Montsec (TFRM): A Fully Robotic Wide-field Telescope for

Space Surveillance and Tracking Montojo, F.J.1; Fors, 0.2; Muiños, J.L.1; Nuñez, J.2; López Morcillo, R.1; Baena, R.3; Boloix, J.1;

López Moratalla, T.1; Merino, M.2 1Real Instituto y Observatorio de la Armada (ROA), SPAIN; 2Observatori Fabra, Reial Acadèmia de Ciències i Arts de Barcelona (RACAB), SPAIN; 3Dep. d’Astronomia i Meteorologia i Institut de

Ciències del Cosmos (ICC), Universitat de Barcelona, SPAIN


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Since the beginning of the Space Age optical sensors have been one of the main instruments for positioning and tracking of known space objects. Nowadays, the unrelenting growth of man-made object together with of the useful satellite orbits overcrowded and the real space debris and NEO hazards has made necessary to carry out surveys of the space looking for uncatalogued objects. Optical telescopes play a key role in the Space Surveillance and Tracking (SST) as a primary Space Situational Awareness element and it is known that the best instrument for this task is a fully robotic wide-field telescope with a minimum aperture of 40 cm.

The Baker-Nunn Cameras (BNCs) were produced by the Smithsonian Institution during the late 50s as an optical tracking system for artificial satellites. These wide-field telescopes of 50 cm of aperture were manufactured by Perkin-Elmer (optics) and Boller & Chivens (mechanics) with the highest quality specifications. The TFRM is a fully robotic refurbished BNC that exploits the excellent mechanical and optical original design to obtain an equatorial telescope with a useful 4.4deg x 4.4deg FoV. TFRM is therefore an European asset very well suited for SST (satellites and space debris) and NEO observations. Moreover, its control system allows tracking all kinds of orbits, including LEOs.

For the time being the TFRM is in a commissioning period and our team is developing the data processing pipeline and testing the observing strategies and schedulers for Surveillance, Tracking and NEO observation tasks.

This paper explains in detail the refurbishment project together with its very reliable dome design and all the autonomous system based on commercially available off-the-shelf products.

***** A Satellite Orbit Design Method for Space-based Space Surveillance

Hou Yuzhuo, H; Huang Xuexiang, H; Su Zengli, S Beijing Institute of Tracking and Telecommunications Technology, CHINA

Space-Based Space Surveillance (SBSS) is one of the important development trends in the area of space surveillance system. Space-based sensors provide a great mount of opportunity of acquiring orbit data on a wider array of targets without atmospheric effects. Furthermore, the effectiveness of ground-based optical sensors is further curtailed by atmospheric effects such as weather conditions and local light pollution.

Although SBSS have considerable advantages over their ground counterparts, an important question needs to be considered, i.e. how to maximally utilize its efficiency and effectiveness. Generally, the factors of affecting the efficiency of SBSS include satellite orbit, pixel number of CCD, optical system, etc. Among them, satellite orbit is one of important effects. Thus, a discussion on optimization of orbit design method for space-based space surveillance is given.

Firstly, this paper analyzes the main requirements for SBSS. It points out that the main purpose of SBSS aims at acquiring orbit-data of GEO, and at the same time, acquiring orbit-data of LEO/MEO in passing. Based on that, this paper gives a in-depth discussion on an orbit of 0o inclination and a sun-synchronous orbit. It concludes that sun-synchronous orbit could fulfill three kinds of requirements.

Secondly, the function of detection period of GEO, orbital altitude, regressive cycles, regressive period, and orbital inclination is given by analyzing detecting GEO procedure. According to the function thus provided, if the field of view (FOV) and regressive cycles N are fixed, semi-major axis of the orbit of surveillance satellite can be deduced. And then, in term of the rule of sun-synchronous orbit (a,i), orbital inclination is presented. Thus, the basis of three general orbital elements (a,e,i) are provided.

Thirdly, SBSS will be able to detect objects of interest within its sensor's footprints. LEO or MEO is not always in sensor's footprints, and the detection is an incident one. There isn't a determinate function to describe the relationship between efficiency and orbital elements. Simulation might be the best way to ascertain surveillance orbit. By adjusting the FOV of a GEO-


47

detection optical system, several teams including the semi-major axis and inclination are deduced. Considering the lighting phase angle among the sensor-target-sun, several parameters of longitude of ascending node are designed. Then by simulation, a more efficient orbit is determined. Thus, the basis of general orbital elements (a, e, i) is designed.

Finally, an example of surveillance satellite orbit design for detecting GEO and LEO is given. The detection efficiency, data validity and orbit determination are analyzed and compared.

In conclusion, the design method presented in this paper for SBSS is feasible, by which the optimization of orbit design and optical system can be achieved. Not only could it be used in GEO detection but also in MEO or LEO detection.

***** Space Surveillance Educational Outreach - Video Monitoring

Ocaña, F.1; Zamorano, J.2 1Universidad Complutense de Madrid, SPAIN; 2Dpto. de Astrofísica y CC de la Atmósfera -

Universidad Complutense de Madrid, SPAIN

There is no need of sophisticated instrumentation to observe satellites illuminated by the Sun during twilight and dawn since they could be easily seen with the naked eye. In the framework of the Space Situational Awareness, satellite observing programs are promising activities to be carried out by students at High School and University.

Video cameras at the Universidad Complutense de Madrid are being used to detect meteors. Our cheap CCTV cameras are currently detecting several satellite passes each day, showing the feasibility of carrying out such monitoring programs. Their highlights of the observations are tumbling flaring satellites, a huge recent reentry and monitoring satellites with undisclosed orbits.

Being a low cost scientific and attractive project it is possible to build an observing network with cameras operated by students as now it exists for other fields, like meteors observing (another important SSA topic). Such a network could also participate actively in tracking recently-launched satellites or maneuvering satellites from several locations around the world. Their webpages would be a great help in public educational outreach of space surveillance.

***** Orbit Determination Error Analysis for a Space Debris Tracking Radar

Weigel, M.1; Patyuchenko, A.2 1German Space Operations Centre (GSOC) of DLR, GERMANY; 2DLR Microwaves and Radar

Institute, GERMANY

A recently proposed radar system concept for space debris detection combines a reflector antenna and digital beam-forming techniques. The utilization of multiple digital feed elements allows illumination of a larger survey zone, compared to the relative narrow pencil beam of conventional tracking radars. Signal processing from independent digital channels preserves a high antenna gain on the reception path and is a prerequisite for the implementation of an advanced Track While Scan operational mode. During the design phase an optimal combination of surveillance and tracking functionality will have to be found. As the number of observable space debris is directly linked to the extension of the survey zone and the amount of received power, it is straightforward to define system requirements to meet an envisaged survey performance. Moreover, it is less obvious to characterize tracking data that lead to reliable and accurate orbit determination results. Variables of influence are the type of involved measurement data, their temporal and geometrical distribution as well as systematic measurement errors, e.g. measurement bias and noise, or erroneous measurement correction and force modelling. The amount of error introduced by each variable can be quantized in a so called Consider Covariance Analysis. The paper presents the outcomes of this kind of error analysis performed by the Modular Orbit Determination Error Analysis Program MODEAS. A short outline on GSOC procedure for collision risk assessment reveals timely constraints under which tracking requests arise in praxis. In case


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of a conjunction warning measurement data for refined orbit determination are assumed to be provided by a future radar system located at Weilheim ground station complex. A set of tracking requests, representative for satellite missions operated at GSOC, serves for investigations of the influence of the different tracking variables mentioned above. Based on analysis findings a standard tracking strategy and a consolidated list of system requirements are established. Finally an analytical formula is given for the optimization of the number of station passes space debris can be tracked on.

***** Orbit Determination of the Extended Kalman Filter for GEO Optical Observation

ZHANG, W.; Zhao, C.Y.; Wang, X.; Wang, H.B. Purple Mountain Observatory, Chinese Academy of Sciences, CHINA

The extended Kalman filter (EKF) is used to process GEO optical observation by the space debris telescope to improve the satellite orbit. The optical observation type is right ascension and declination. The orbit accuracy of EKF is equal to the least-squares estimation. The extended Kalman filter subroutine takes less computational time and has good convergence. The dynamic models for orbit propagation applied perturbations due to the 20*20 geo-potential, the gravity of the Sun and Moon, solar radiation pressure. The 7(8)th-order Runge"CKutta numerical integration was applied for orbit propagation.

*****

Optical Space Surveillance and Active Space Debris Mitigation at Kayser-Threde Hofmann, P.; Bellido, E.

Kayser-Threde GmbH, GERMANY

Kayser-Threde GmbH, Germany, is very active as systems and prime contractor in projects and programmes dedicated to optical surveillance of the Earth (ESA earth observation programmes, e.g. Sentinel 4 and 5), the Earth atmosphere (e.g. for weather satellites such as MTG) and in space observation (such as for the German space-borne AsteroidFinder mission).

Furthermore, Kayser-Threde has taken a leading role in observation, identification and active space debris mitigation both in GEO and LEO (e.g. the On Orbit Servicing projects OLEV and DEOS). In line with this Kayser-Threde has organised the first European industrial workshop in our premises in September 2010 to discuss active SDM (space debris mitigation) and SSA. Technology, programmes, market and financial aspects were debated by approximately 20 delegates from the German Space Agency, the DLR Research Institutions DLR-RM and GSOC, CNES, ESA-SSA, ESTEC and Kayser-Threde.

This presentation will describe some flagship projects of Kayser-Threde relevant for the SSA programme:

These include a description of the AsteroidFinder mission, which is aimed to search for NEO asteroids within the Earth orbit. The satellite will fly on a dusk/dawn sun-synchronous orbit with an altitude of approx. 600 km, and will observe the sky between 30° and 60° in solar elongation. Kayser-Threde is responsible for the development of the AsteroidFinder instrument in cooperation with DLR-Optical Systems in Berlin. The AsteroidFinder project is presently in a phase B. The launch of the mission is foreseen for the year 2014 with a subsequent mission of at least 1 year.

A number of optical instruments for the SSA programme are well suited for accommodation on a small satellite bus. A good example is TET (TechnologieErprobungsTraeger). TET is a technology satellite programme in Germany. TET-1 is aimed to demonstrate and validate 11 technology experiments and subsystems in space (On-Orbit-Verification, OOV), including e. g. an optical camera, novel solar cells, on-board computers and novel GPS receivers. Flight Acceptance Review took place in December 2010. The launch from Baikonur in Russia is presently planned for May 2011.


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Finally, the active space debris removal projects of Kayser-Threde will be shortly described including examples for the observation approach and docking strategies developed.

***** AS4, a Simulator Supporting the Definition of the European Space Surveillance

Segment of SSA Sánchez-Ortiz, N.; Olmedo-Casal, E.; Guijarro-López, N.; Belló-Mora, M.

DEIMOS Space S.L.U., SPAIN

In order to study the capabilities of a Space Surveillance and Tracking segment, an end-to-end simulator of the system is required. This simulator shall include at least population environment, propagation capacities, measurements generation (ground based radar and telescopes and space-based telescopes), initial and routine orbit determination tasks, correlation and cataloguing activities and delivery of products, among them, collision risk computation, re-entry events reporting, fragmentation analysis, launch detection, and ephemeris generation. DEIMOS Space S.L.U. has co-funded the development of the Advanced Space Surveillance System simulator (AS4), under several ESA and Spanish R& D programs. This paper summarizes the main capabilities and algorithms implemented in the tool. This tool has been used from 2004 to support the definition of requirements to be imposed to the SST segment and to analyze the possible architectures, observation strategies, required sensors,... A summary of former activities based on AS4 and main lessons-learnt from the use of the tool are reported in this paper. This work has allowed identifying the most challenging aspects of the cataloguing process which are detailed here. In particular, this paper addresses: the most promising observation strategies for the different sensor types and orbit regimes, the observational aspects driving the capabilities of constructing a catalogue, the most suitable initial orbit determination algorithms, orbit determination methods, the correlation process at measurement or orbit level, the computation of covariance matrix for the initial orbit determination and the propagation of such uncertainty. Additionally, the AS4 was evolved into a prototype for the processing of real observations done during an experimental observation campaign with sensors in La Sagra Observatory. A brief explanation of the evolution from AS4 to this prototype and an introduction to the results of the campaign are also provided. Keywords: AS4, observation strategies, initial orbit determination, routine orbit determination, correlation techniques, covariance matrix.

***** Operational Optical Observation Campaign based on Survey-only Strategies:

Preparatory Phase and Expected Performances Olmedo-Casal, E.1; Nómen, J.2; Sánchez-Ortiz, N.1; Guijarro-López, N.1

1DEIMOS Space S.L.U., SPAIN; 2OAM, SPAIN

DEIMOS Space S.L.U. and Observatorio Astronómico de Mallorca (owner and operator of the La Sagra Observatory) are currently involved in a project devoted to testing the operational feasibility of enhanced survey-only observation strategies that minimize the tracking needs to create and maintain a catalogue of high altitude objects. This project is co-funded by these two organisms and the Spanish CDTI (Centro de Desarrollo Tecnológico Industrial). These enhanced strategies are based on observation approaches that provide a frequent re-observation capability of the observed objects, which allow computing the first orbit without the need of dedicated follow-up of the observations. A brief summary of the proposed strategies and the expected performances with the La Sagra Observatory sensors is provided in this paper. During the first stages of this activity, DEIMOS is improving the existing prototype for processing the observations and creating the catalogue of observed objects. At the same time, OAM is characterizing their sensors and processing software for the work to be done. OAM work was mainly devoted to asteroid observations, and it is currently transferring the developed technologies from that field into the space debris observation. A summary of the capabilities of their sensors and processing software is provided, together with the developed tools so far. The observation campaigns will last for at least two periods between Full Moon interval. The objective is to create a catalogue during the first period, and after a time without observations (due to the illumination conditions), to check that the appropriate correlation between the new observations and the catalogued object is ensured. These campaigns are scheduled by early 2012.


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***** Cataloguing Capacity and Achievable Accuracy for the High-altitude Orbital Regimes by Means of Ground-based Optical Sensors within the Future European Space Situational

Awareness System Sánchez-Ortiz, N.1; Olmedo-Casal, E.1; Guijarro-López, N.1; Keinänen, P.2; Krag, H.3

1DEIMOS Space S.L.U., SPAIN; 2ASRO, FINLAND; 3ESA/ESOC, GERMANY

In the frame of the future European Space Situational Awareness System, several strategies have been analyzed for the ground-based optical observation and cataloging of space objects in high altitude orbital regimes (from upper-MEO up to beyond GEO ring). Apart from the transient objects crossing through the different space regions, four main groups of objects appear in both real observed (TLE) and synthetic populations (like MASTER): GEO, sub-GEO, upper-GEO and MEO high inclined orbits. The three first mentioned sub-populations behave, from an observation point of view, in a similar way, whereas the MEO high-inclined orbits (GNSS-like orbits) have different observational patterns. Discussions on the required number of sensors for cataloguing this kind of orbits are presented. Information on the telescope features required for the tasks are provided. In particular analysis of the relations between required aperture, Field of View and cost are addressed. For the creation and maintenance of a catalogue of objects, the capability of correlation observations of objects and the achievable accuracy depend, apart from the technical features of the telescope, on the observation strategy capacities in terms of re-observation time, duration of observation arc and number of measurements per arc. Enhanced leak-proof strategies for the ‘survey-only’ observation of GEO ring are demonstrated as the most promising ones for the observation of this region, but also for sub- and upper-GEO sub-populations. Architectures based on reduced number of telescopes provide achievable accuracies for those objects which are good enough for constructing the catalogue of space objects and perform reliable collision avoidance assessment. The accuracy obtained for different observation scenarios is presented and compared with possible accuracy constraints to be imposed to the Space Surveillance and Tracking System catalogue. On the contrary, for MEO high-inclined orbits, the formerly mentioned accuracy observation parameters are poor, leading in a reduced accuracy which does not fulfill the imposed accuracy requirements. This work presents the achievable accuracy for these objects in the basis of survey-only scenarios, how this accuracy can be improved by supporting the observations through dedicated tracking of those objects, and the derived number of tracking sensors. The work presented was done in the frame of the study 'Preliminary Design and Analysis of the Optical Space Surveillance Subsystem' (PDAOSSS), ESA contract number 22738/09/D/HK. All the results are obtained with the AS4 simulator, developed by DEIMOS Space S.L.U.

Keywords: survey and tracking optical observation of space debris, orbit determination, observation strategies, AS4

***** ATV-1 Re-entry Fragments Trajectory Reconstruction and Footprint Optimal Estimation

Gil-Fernandez, J.1; Blasco, A.1; van der Linden, B.2; Janssen, B.2; Hatton, J.3 1GMV, SPAIN; 2LIME, NETHERLANDS; 3ESA, NETHERLANDS

At the end of its mission to the ISS, the first Automated Transfer Vehicle (ATV) performed a controlled ballistic re-entry over the Pacific Ocean on 29th September 2008. To observe the events occurring during the re-entry, a joint ESA/NASA multi-instrument aircraft campaign was performed. Two aircraft were equipped with a suite of optical instruments including video systems and spectrographs covering the near-UV, visible and near-IR wavelengths.

This paper presents the methodology and results to complete the reentry trajectory reconstruction and footprint analyses of the ATV-1 fragments. The steps of these analyses are, fragments and stars tracking, image calibration, fragment triangulation, optimal state estimation, and footprint estimation.


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Tracking involves the automated processing of movies to extract fragments and stars from each of the frames. The tracking procedure assures that within the same movie a certain fragment gets the same identification label.

In the camera calibration process, the stars are used to estimate the camera orientation and the parameters of the camera mathematical model. Because of aircraft noise and other disturbances, the camera motion can have a high frequency component, meaning that interpolation between frames is often not possible.

In the triangulation, the image coordinates of the fragments in the movie are translated to WGS84 coordinates. The algorithm uses simultaneous observations from two different locations (the DC8 and GV aircraft), or a model for the orbit and two different observations in time.

The short data arcs from the triangulation were filtered to estimate the initial conditions at epoch of the identified ATV fragments. The augmented state vector permits to estimate the footprint of the identified ATV fragments considering the uncertainties on the initial conditions. The mathematical procedure consists of the following steps,

- Filter initialization, computes the initial guess of fragment conditions at the epoch. - Estimation of fragment conditions at the epoch, optimal fit of triangulation position measurements. - Smoothed trajectory, backward propagation for verification of the trajectory fit and to allow explosion delta-V estimation. - Unscented covariance analysis, computes the non-linear estimate of the footprint based on the unscented transformation. Conventional methods are covariance analysis and Monte Carlo. Linear covariance propagation is not valid because of the high non-linear propagation. The Monte Carlo analysis requires a huge number of propagation to achieve statistical significance.

The footprint analysis is carried out with the novel (so-called) unscented covariance analysis in order to efficiently approximate non-linear distributions (only few tens of propagations per fragment). The obtained downrange dispersion is ~1000 km (3-sigma) while the crossrange dispersion is ~30 km (3-sigma).

***** Monitoring and Control for Space Surveillance Sensors

Gil, J.C.; Fraga, E. GMV, SPAIN

A dense network of geographically well distributed sensors is necessary for all space surveillance applications, not only encompassing radar and optical ground sensors but, potentially, also space-based assets. But, as for any other distributed system, the real challenge is ensuring interoperability among them, timely gathering of data as well as efficient planning and control. There is very limited operational experience in Europe for the monitoring and control of this type of sensor, however vast existing experience on the fields of monitoring and control (M&C) of spacecrafts, payloads and satellite ground segment is largely relevant to the problem at hand. While spacecraft and payload M&C is directly applicable to the space elements of the space surveillance network (provided they exist), the M&C of the satellite ground segment (encompassing antennas, radiofrequency equipment and baseband equipment) can be related to that of the ground sensors network, albeit with a number of important differences that will be identified and discussed. This paper describes this approach from the point of view of GMV considerable experience in spacecraft, payload and ground segment M&C and explores the possibility of reusing GMV products in those fields: hifly, smart rings and magNet, respectively for the space surveillance domain.

*****


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Operational Survey and Catalogue Maintenance in MEO

Fernández, J.1; Aivar, L.1; Agueda, A.1; Dick, J.2; Herridge, P.2; Krag, H.3; Flohrer, T.3 1GMV, SPAIN; 2Space Insight Ltd., UNITED KINGDOM; 3ESA/ESOC, GERMANY

The future European Space Surveillance System will incorporate a set of sensors to catalogue debris in LEO, MEO and GEO. These different regions require different sensor capabilities and observation strategies. Traditionally LEO has been tracked using radar systems that, although expensive, are quite reliable and accurate. GEO has been typically tracked using telescopes. Finally MEO brings its own difficulties and until now, few campaigns have focussed here due to the sparseness of the known population (contrary to the GEO population) and the big volume it represents. Under an ESA contract carried out by GMV and Space Insight, a first MEO observational campaign has been carried out with two different telescopes, Starbrook and ESA's OGS. The former has a large field of view that was used mainly for surveying while the latter has a large aperture but a relatively small field of view most suitable for follow-up. This configuration was perfectly suited to split the job between surveying and follow-up (catalogue maintenance) and to simulate a future system where some sensors are devoted to find new objects (surveying) while others obtain accurate measurements of known objects to maintain a catalogue by the means of tasking activities. Due to the characteristics of the MEO region (wide inclination and semi-major axis ranges), surveying is a difficult task. A leak-proof strategy has been analyzed and tested and will be presented in this paper. Due to the difficulties and sparseness of the known population, the final implemented trial strategy relied also on the knowledge of the population (GNSS population, including several constellations) to maximize detections. Apart from routine operations with each sensor, a hand-off mechanism was also tested to use the observations gathered by Starbrook in survey mode, to schedule a follow-up with the OGS the following night. This procedure has been tested several times successfully and, for ESA, it is the first proof of this concept with MEOs. The authors also studied the characteristics of the sensors and image processing algorithms and their suitability for MEO objects, assessing the impact of the sensitivity of the CCDs, the field of view, object identification, accuracy of the measurements, etc. Finally the real observations have been used to simulate the maintenance of a catalogue of MEO objects without relying on any external orbital information. As each of the observation campaigns was carried out around new Moon, the accuracy of the estimated orbit has to be sufficient to re-acquire the object with a small field of view one month later. An additional problem of orbit visibility affects GNSS satellites as their orbits are nearly semi-synchronous so usually objects are observed every night approximatelly in the same part of their orbit. This study shows that catalogue maintenance of MEO objects can be done with the OGS telescope and survey can also be done with the Starbrook sensor.

***** Study of an Innovative System for Debris Surveillance in LEO Regime

Fernández, J.1; Agueda, A.1; Dick, J.2; Jamar, C.3; Jorden, P.4; Besso, P.M.5; Pinna, G.M.6 1GMV, SPAIN; 2Space Insight Ltd., UNITED KINGDOM; 3AMOS, BELGIUM; 4e2v, UNITED

KINGDOM; 5ESA/ESOC, GERMANY; 6ESA/ESAC, SPAIN

LEO debris has been surveyed typically using radars, owing to the range to the object, the high number of objects in LEO, and the high accuracy of radars; the only inconvenience of radars is cost. ESA is preparing a Space Surveillance system that contains a wide range of systems, from telescopes to survey GEO or MEO regimes, to radars to survey LEO. The definition of LEO used here reaches up to 2000 km altitude, putting a big constraint on a radar system that has to track small objects up to this distance. For the GEO orbit, optical sensors are typically used because the distance is large, being a constraint for radars. Also for MEOs, from 2000 km to GEO altitudes, the reasonable approach is also to use optical sensors in a way that can share time between GEO and MEO regimes. It is also clear that for very low LEOs, up to 800 km altitude, radar is almost the only approach as the relative velocity of the objects and the visibility constraints limit seriously the usefulness of optical telescopes.


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The range of LEO altitudes from 800 to 2000 km is where the question of using telescopes arises. The height of these orbits imposes a cost penalty for a radar system which justifies the idea of studying the use of telescopes instead, where both construction and operational cost are much lower. Initial difficulties of using telescopes in this regime are clear: visibility constraints (compared to radars that can work 24h and through clouds), high relative velocity of objects, short passes, and dense coverage of the orbit-parameter space (from low to high inclination and from small to large semi-major axis) all complicate the surveying strategies. This paper presents an innovative system to survey LEOs by optical means, developed by GMV / Space Insight / AMOS / e2v, under contract of ESA. It addresses firstly the visibility constraints for LEOs, the weather conditions in the site locations and the time characteristics of passes. It then presents a survey strategy suitable for this task and analyzes the cataloguing capacity of this system, taking into account revisit times, visibility constraints (including the effect of the seasons) and weather conditions. Expected orbit determination accuracies are also presented. Finally a preliminary design of the telescopes is presented, that includes optics and detectors. The type of telescopes needed for surveying this region face enormous challenges driven by the dual requirement of large field of view (of the order to 20°-30°) and high accuracy needed by the cataloguing process.

***** EUMETSAT Operational Software for Debris Conjunction Analysis

Lázaro, D.; Aguilar, D.; Righetti, P.L. EUMETSAT, GERMANY

Metop is the space segment of the EUMETSAT Polar System (EPS), Europe’s first polar or-biting operational meteorological satellite system. Since end of 2008, EUMETSAT has been re-ceiving conjunction warning messages from JSpOC (Joint Space Operations Centre of the US Air-Force) for Metop-A based on the high accuracy orbits estimated by the US space surveillance network. The EUMETSAT Flight Dynamics team (FDF) has since then developed a set of soft-ware prototypes and operational procedures to properly handle the conjunction warning messages to first identify conjunctions with unacceptable level of collision risk and, if deemed necessary, compute the optimal maneuver that permits to reduce the collision risk to negligible values. The paper will present the Debris Conjunction Analysis software being developed at EUMETSAT and that will replace the prototypes to become an operational tool. The Debris Con-junction Analysis tools consist of two separated modules: the Collision Warning Ingestion mod-ule (CWINGEST) and the Conjunction Analysis module (CONANA). The new software maps most of the functionalities currently implemented in the (off-line) prototype and is integrated into the (on-line) EPS FDF QA software. As a consequence it can make direct use of other EPS FDF features like TLE orbit generation, orbit file interpolation and processes sequencing. In addition the software will be able to access the operational context (e.g. on-orbit position telecommand), to operate autonomously (currently the prototype requires manual intervention), making use of the same Flight Dynamics monitoring protocol (i.e. info, warning and alarms messages) and au-tomatically (daily screening of the received Conjunction Warning Messages). The new software will have furthermore enhanced functionalities as for example: - High flexibility of input data and automatic selection of best available input (regarding cova-riance, position, velocity or size). - Detailed conjunction analysis of multiple events. Enhanced events filtering by: Time of Clos-est Approach (TCA), issue date, miss distance, latest entry per event. - Enhanced handling of covariance information. - Enhanced analysis of maneuver effect. CWINGEST is in charge of ingesting either Conjunction Warning Messages (CWM) and Conjunction Summary Message (CSM), provided by JSpOC or manually input equivalent information. TLE catalogues and Satellite Situation Report Files (SATCAT), from NORAD, can additionally be parsed for the NORAD IDs of the debris objects involved in the conjunctions present in the so-called Miss Distance File, that contains the conjunction records from CWM and CSM. CWINGEST manages automatic input file deletion and enhanced event filter based on TCA epoch.

CWINGEST converts the ingested input data (manually or via file) into standardized internal input files for the second module CONANA. CWINGEST design is such that only a few changes in the


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code are required to ingest conjunction information from other agencies or formats. The output generated and the functioning of CONANA, that relies on internal interface, remain unaltered. CWINGEST flow process is shown in Figure 1.


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CONANA processes the detailed conjunctions information generated by CWINGEST and is in charge of performing the collision risk analysis of the identified conjunction events (records) in different configuration modes: - Multiple Events: analyzes all future conjunction events, performing an educated guess of the debris covariance and computing the so-called Depth of Intrusion (DoI) parameter which describes the scale factor to be applied to the debris covariance ellipsoid in order to have the spacecraft trajectory tangent to it. - Single Event with Covariance Scattering: analyzes a single conjunction event with potential high risk performing a systematic scattering in covariance in order to identify worst case conditions in terms of risk. Resulting Probability of Collision Values (PoC) lead to a recommendation on whether to execute a mitigation action (collision avoidance maneuver) or not. - Single Event with Maneuver Scattering: analyzes the effect of a set of in-plane maneuvers (scattered in execution time prior to TCA and size) in terms of risk reduction, assuming worst case covariance conditions. - Multiple Events with Metop single Maneuver: assesses the new DoI and PoC with the other known close-in-time conjunctions for updated post-maneuver Metop state vector and covariance to ensure that the selected collision avoidance maneuver does not cause an unacceptable increase of collision risk with the other objects. CONANA flow process is shown in Figure 2.

CONANA includes the following main functions: - Analysis of the conjunction geometry with optimum graphical representation. - Estimation of the conjunction risk via computation of the DoI. - Ingestion of Metop's solar panel and on-orbit-position telecommand to accurately model the collision area. - Computation of the probability of collision (PoC) applying Alfriend formula, and correction to consider probability variation within the impact area. - Conjunction events can raise warning and alarm events in the Mission Control System upon violation of user-defined DoI or PoC thresholds. This mechanism triggers FDF engineer intervention. - Scatter in covariance matrix. Worst case PoC. Graphical representation of resulting PoC.

- In-plane maneuver application on Metop with associated execution uncertainty. Application of Clohessy-Whiltshire equations. Geometry, DoI and PoC recomputation for all assessed conjunction events.


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- Scatter in in-plane maneuver. Graphical representation of resulting PoC. The current prototype software is operationally used as part of a System Operations Procedure (MIAMI) with which CWINGEST and CONANA tools shall be compatible.

The paper shall address architectural and design aspects of the software as well as its current implementation status and its approach to operational use.

***** A dedicated Space Surveillance Optical Network cooperates with Radar to assure LEO

debris catalogue build up and Maintenance Cibin, L.; CGS Spa (ITALY)

CGS SpA, INAF (Istituto Nazionale di Astrofisica), DM (Dipartimento di Matematica Pisa) and IFAC-CNR (Istituto di Fisica Applicata), all members of an Italian Team studying Space Surveillance topics, have been awarded the ESA SSA Feasibility study of an innovative system for debris surveillance. The aim of this paper is to present the architecture of the optical network used for the monitoring of the upper part of the LEO region and to build up and maintain an object catalogue to support the collision avoidance. The proposed Optical Network can in principle increase performances with a relatively small impact on the overall system costs, compared to the radar system so far considered to be the baseline LEO observation methodology. The feasibility of the proposed approach results from an innovative optical telescope architecture with performances tailored for the detection of objects in any Earth orbit (and also of Near Earth objects). The innovative approach allowed to demonstrate the â€˜observabilityâ€™ of an object passing above a given station horizon despite the combination of demanding interplaying factors such as light, Earth shadow and clouds. The proposed network is able to cooperate with radar allowing the RF technology to limit its application range to the lower part of the LEO. The study also evidenced that there is an orbital belt where both optical and radar observations can overlap, collect data working in a cooperative way.

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