improved ssa through orbit determination of two-line element sets
DESCRIPTION
Improved SSA through Orbit Determination of Two-Line Element Sets. David A. Vallado, Benjamin Bastida Virgili , and Tim Flohrer. Paper 6ECSD 13-4a.0-7 presented at the 6 th European Conference on Space Debris in Darmstadt, Germany, 2013 April 22-25. Outline. Introduction - PowerPoint PPT PresentationTRANSCRIPT
Improved SSA through Orbit Determination of Two-Line Element Sets
David A. Vallado, Benjamin Bastida Virgili, and Tim Flohrer
Paper 6ECSD 13-4a.0-7 presented at the 6th European Conference on Space Debris in Darmstadt, Germany, 2013 April 22-25
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Outline
• Introduction– Two-Line Element Sets (TLEs)
• Problem Definition– TLEs have no covariance– Operations increasingly require covariance
• Previous Studies• Process• Results• Conclusions
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Introduction
• Development– SGP
• Drag through mean motion rates– SGP4
• Drag through Bstar and analytical development• Developed in late 1960’s and early 1970’s
– Brouwer and Kozai theories (1959)• Documentation
– 1980 – Consolidated code– 2006 – update from various versions (code and description)– 2008 – initial effort to assemble an OD version
• Widespread Use– Large data bases exist for a majority of the space catalog
• www.Celestrak.com • www.space-track.org
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Introduction
• Force models– Simplified J2 - J5 zonals– Bstar for Atmospheric Drag– Simplified terms for 3rd body, SRP
• Much investigation– Hartman 2003, Boyce 2004, Muldoon et al. 2009,
Flohrer et al. 2008, 2009, etc.• Comparisons
– To Reference orbits (high quality)– To TLEs over time (lower quality)
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Whole Catalog processing
• Flohrer et al. 2008, 2009
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TLE Formation and Prediction
• Fit Spans– Uncertainty increases with prediction
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OD Processing and Prediction
• Comparison to future TLEs – KF processing, initial uncertainty 1 km
• Vallado and Cefola (2012)
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OD Processing and Prediction (II)
• Comparison to future TLEs– KF processing, initial uncertainty 5 km
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Process
• Develop Orbital Classes to study• Sub-categories
– Active (maneuvering)– Calibration– Debris – fragments, PL, RB, Mission Related Objects (MRO)
• Examine options– How to form the reference orbit
• Backwards, midpoint, etc– OD Force Models– OD Fit Span– Number of TLEs used– Object Size
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Orbital Categories
• Satellite Catalog Feb 2013– ~17000 objects– Satellites tested
• ~74%Category Name
Eccentiricity / Inclination
Mean Altitude km (perigee/apogee)
Number in Catalog
% of catalog
LEOLow Near Earth
Circular 0.00 < e < 0.05 0 < alt < 575 400 2.35
LEOMedium Near Earth
Circular 0.00 < e < 0.05 575 < alt < 1000 6564 38.61
LEOHigh Near Earth
Circulr 0.00 < e < 0.05 1000 < alt < 2500 2147 12.63
LEONear Earth Eccentric 0.05 < e < 1.00 0 < alt < 2500 623 3.66
NSONavigation Satellites 50 < i < 70 18100-24300 / 18100-24300 253 1.49
GTO GEO Transfer 0 < i < 55 100-2000 / 34786-36786 232 1.36MEO Mid Earth 0 < i < 180 2000-34786 / 2000-34786 200 1.18HEO Highly Elliptical 0 < i < 180 100-34586 / 38586-90000000 895 5.26GEO Geosynchronous 0 < i < 70 32986-38586 / 32986-38586 1176 6.92
HAOHigh Altitude Above GEO 0.0 < i < 180 38586-90000000 / 38586-90000000 54 0.32
Orbital Categories
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Force Models
• Gravity– JGM3 30 × 30– JGM3 8 × 8 GEO
• Atmosphere– NRLMSIS-00
• Third Body• Solar Radiation pressure
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Results – UVW components
• Eccentricity vs Inclination– Uncertainty during OD of TLE ephemeris– LEO, MEO, HEO, GEO
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Results – smaller uncertainty
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Results – smaller uncertainty
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Results – larger uncertainty
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Results – larger uncertainty
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Object Size Results
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Conclusions
• Confirmed earlier results:– Number of TLEs did not seem to matter– Force models added only a small effect
• New results:– Reference orbit formed backwards appears to perform better– Force models do not seem to make much difference
• Gravity and atmospheric in particular
– Object size• Unable to find correlation between category and size
– Object type seemed to be a factor in some cases…• Category, maneuverable, calibration, etc.
– Fit span• Observed larger uncertainty with longer fit spans
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Conclusions
• Largest uncertainty in almost all cases was in the along-track direction – GEO radial
• HEO and GTO orbits consistently experienced largest uncertainty– Then GEO and MEO– Then the NSO – Then all the LEO orbits
• TLE Epoch “uncertainty”– LEO ~ 0.5 km– NSO ~ 0.5 km – MEO ~ 1-2 km– GEO ~ 2-4 km– HEO and GTO ~ 6-8 km
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Questions?