Acra Astronautica Vol. 46, Nos. 2-6, pp. 389-395,200O 0 2000 Published by Elsevier Science Ltd. All rights reserved

Printed in Great Britain PII: SOO94-5765(99)00235-O 0094-576YOO % - see front matter

CONAE’s SATELLITE MISSIONS

Daniel Caruso

Comisidn National de Acfividades Espaciales

Av. Pnseo Colh 751 - 1063 -Buenos Aires, Argentina

.Ianuary IYYY

ABSTRACT - This paper reports on the Satellite Missions developed or under development at CONAE, the Argentine National Commission on Space Activities, the Argentine space agency.

The planning of satellite missions is a part of .the Argentine Space Program, which is the frame for all of CONAE related activities.

To accomplish the Program requirements, CONAE has channeled the Activities and Projects in 5 Courses of Actions, Satellite Systems being one of them. A short description of all satellite missions, whether developed or under development, is presented; as it will be seen, most missions have been planned with intemafional partners in joint efforts providing different assemblies for each one, based on a non-funding interchange cooperation philosophy. Q 2000 Published by Elsevier Science Ltd. All rights reserved

INTRODUCTION

This paper presents a short description of the satellite missions developed or under development at CONAE, Comisi6n National de Actividades Espaciales ( the Argentine National Commission on Space Activities - Argentine Space Agency ).

The planning of satellite missions is a part of the Argentine Space Program, which is the frame for all of CONAE related activities.

The National Space Program was approved bv the Argentine government in 1994; contdining all planning activities to be carried out in the 11 years following each revision. The program is revised and submitted to the authorities for its approval every two years. To accomplish the Program requirements, CONAE has channeled the Activities and Projects in 5 Courses of Actions, Satellite Systems being one of them. The aim of this course of action is defining the strategy to complement CONAE’s satellite missions

with other space missions following the demands of the domestic community, mainly as regards the Earth Observation field, optimizing the available resources with Internalional Cboperation as a priority policy.

Table 1 shows satellite missions developed or under development. Nearly all missions have international partners in a joint effort providing different assemblies to each mission, within a non-funding interchange cooperation philosophy.

SAC-B, the first mission, was a scientific one in cooperation with NASA from the U.S.. INPE from Brazil and ASI from Italy. The satellite was launched in November 1997 by a Pegasus XL launcher which failed to separate its third stage from the satellite.

SAC-A, a technological mission based on a microsatellite, is a CONAE-NASA joint effort. The satellite was launched on December 4’h, 1998 as a secondary payload aboard the STS-88.

389

390 Smull Satellites ftir Earth Obser-vation

Table I - CONAE’s Satellite Missions ___. ~~

Primary Mission Range Partners

SAC-B Scientific / --- USA - BRAZIL ITALY

SAC-A Technological j --- USA ____

SAC-C Earth Observation Visible USA - DENMARK BRAZIL - ITALY

CESAR 1 I

SABIA3 Earth Observation

-~ bzh Observation

1

SAOCOM - 1 [

u Visible

Visible

SAR

FRANCE

SPAIN

BRAZIL

TBD

SAC-C. CESAR. SABIA3 and SAOCOM arc mninl!~ cart11 obsemation satellite missions: the first three arc planned to scan in the optical range. while the SAOCOM will hn1.e a Synthetic Aperture Radar as main instrument.

This paper Lvill \\ ill now give an outline of these missions and a sun’e!. of their present status

SAC-B

The Scientific SAC-B Mission. with solar and non-solar ob.joctives. was carried out as an International cooperative prqject \kith N.4S.4. CONAE \vas responsible for the design. construction and test of the SAC-B Satellite ( SW Figure I ) and one of its payload instruments [solar observation Hard &-gay Spcctromcter J. NASA provided two other instruments [Goddard X-&,, Experiment for solar and non solar gamma ra! detection. and Cosmic Unresolved X-Ra!. Background !nstnunent using CCDs to study the X ra) background of certain regions of the skyJ and launch serj ICCS on a dual launch aboard a Pegasus XL vehicle. CONAE also established separate agreements with the Italian Space Agency (ASI) for the provision of ;I scientific instrument @iiag i ng Particle Spectrometer for Energetic Neutral Atoms to study neutral particles at satellite orbit altitudes] plus the satellite GaAs solar arrays and the Brazilian National Institute on Space Research ( MPE ) for the provision of the facilities and support for system level environmental qualification tests of the SAC-B spacecraft

The SAC-B satellite, with a weight of some 19 1 Kg (50 Kg corresponding to its payload). was launched by Pegasus XL in a dual configuration with the HETE satellite. but Pegasus failed to separate both satellites and to achieve the required attitude once the orbit altitude had been reached.

Because of the Pegasus failure, the overall assembly was inserted into the nominal planned orbit, but tumbling. This assembly, composed of the launcher 3rd. stage plus the avionics system plus HETE plus SAC-B. shadowed the SAC-B solar panels bringing about the continuous discharge of the spacecraft batteries. which lasted 12 hours before they became completely discharged.

Durmg the 5 contacts (two from Wallops Island. USA: and three from San Miguel Ground Station. Argentina) with the satellite during these 12 hours. all commands sent and telemetry received exhibited the nominal expected response of the power equipment on board. The SAC-B.

Small Satellites for Earth Observation 391

SAC-A

To sum up the SAC-A Mission: the satellite was launched by STS-8X earl? December 1998. into a 390 Km height orbit with - 5 1 degrees of inclination. The satellite planned lifetime is 6 months.

$*.,.; I‘--+ iliLTLON *E’.iioNI\*

Figure 2 - SAC-A inside the Canister

During launching the spacecraft was held in a CAN mounted on the wall of the shuttle bay. At some point in the launch timeline. a command provided by the shuttle crew opened the canister lid and the satellite separation was then achieved, once the required orbit for SAC-A had been reached.

After the initial RF contacts the satellite exhibited a nominal performance of all powered equipment The Early Orbit and the Engineering Phases of the mission have started on December 1 4’h: 1998.

The spacecraft. \vith a weight of 64 Kg. (6X Kg. is the maximum allowed by this type of launching configuration) is three- axis stabilized using a momentum wheel and magnetic coils. a Magnetometer, a Differential GPS Receiver and an assembly of Si cells as a coarse Sun sensor, for attitude determination.

Tracking. Telemetry and Command can be achieved through S-band (telecommand, real time and stored telemetry). with redundancy through VHF (TC) and UHF

(TM).

The technological mission is performed b\’ the use of :

- The Si cells assembly to be tested in orbit

Figure 3 - SAC-A Satellite

md also used as coarse Sun sensor. consisting of cells built in Argentina.

- The in-house developed deployment mechanism for the solar panels.

- The momentum wheel itself, which has also been built in-house.

- Special DGPS algorithms for non-nadir pointing satellites.

- A whale tracker receiver for Franca whales monitoring (the on-board transceiver to carry out this mission is also used for TUTM purposes as a redundancy chain).

- Three axes magnetometer with a 20 bit resolution.

- A specially updated commercial Panchromatic Camera (not an imager).

SAC-C

SAC-C is a cooperative mission, having NASA and CONAE as the main partners. CONAE provides the spacecraft bus plus payload instrumentation (two CCD cameras, Multispectral and Panchromatic; the Whale Tracker Experiment; an UHF Receiver for on ground generated Data Collection Platforms; a Radio-Amateur Transponder). NASA is going to provide scientific instrumentation (GPS from JPL) and launch services for the SAC-C satellite.

The other partners of the mission are :

392 Small Satellires for Earth Observation

J Denmark. pro\,lding the Magnetic Mapping Pa! load Magnctometcrs (one Scalar Hclinm and one Triasial from JPL) mounted on ;I deplo!able X meters boom. supplying measurements of the Earth Magnetic Field with I IIT resolution.

J Ital!. pro\ IdIng the solar panel

mechanisms. a GPS rccciver which can opcrntc \\~th both GPS and GLONASS satellites. and a Star Tracker

J Brazil. pro\ Idtng the s\stem level cm ironmental testing facilities and its test support capabilities

J Fmncc. pro\ rding OIIC Radiation Monitor instrument ( 1CARE ).

The SAC-C satellite IS due to be launched

in December 1999 b\, a Delta IT rocket. in a dual launch configuration with the NASA EO I Spncccrafi.

A 4 !.ears lifetlmc has been planned for the SAC-C. The sclcctcd orbit \vill be a Sun s\,nchronous one at an approximate 700 km height. I\-ith 10, 15 AM local tmc for Its descending node

The satellite. about 1 .X s I .7 s 2 meters in size. \vill \vcigh 352 kg. with almost 100 kg devoted to Its payload. A drawing of the satellite \iith its solar panels deployed is depicted in Figure 4. \vhere boom is not she\\-II.

the 8 111 long

Figure 4 - SAC-C Satellite

The spncecrnti has fised. two-\\ mg-solar panels I\-hich \\ill provide a total of 456 \vatts EOL power Lund t\vo redundant 12 Ah NiH battcms to s~ppl>, 100 watts for

continuous pa! lond opmtion.

The satellite will be three axis Nadir pointing stabilized, with 0.3 degrees of real time pointing error and 0.05 degrees post-facto attitude knowledge. This attitude will be maintained by means of two momentum wheels and torque rods while two partially redundant star trackers. two redundant DGPS receivers. two redundant horizon sensors ( in fact. two scan wheels are used ) and a coarse sun sensor will be used for attitude determination purposes.

As a summary of the Earth observing part of the SAC-C mission. three push broom cameras will provide real and storage Images with the following characteristics :

J A Multispectral Medium Resolution Scanner -MMRS- will image with 5 spectral bands. with a 175 meter geometric resolution 011

approximately 360 km swath. T: satellite orbit and the swath of this MMRS provided by CONAE will bring about 9 days of Nadir revisit time. with 2 or 7 days subcycles by moving the camera pointing axis across track.

J A Panchromatic Camera will image with 40 meters geometric resolution on a swath of about 90 km.

J A High Sensitivity Tech. Camera

The SAC-C satellite will make it possible to obtain multispectral terrain data in the following ways :

7 Real time with two resolutions :

J Images with 175 meter geometric resolution dumped only at

J Images with 350 meter geometric resolution which could be dumped on smaller ground stations distributed throughout the country. Users with these capabilities need not ask for these type of images.

I Stored images with I75 meter geometric resolution dumped only at Cordoba ground station.

In conjmiction with the image data. other terrain data (acquired b>, on-ground- distributed Data Collection Platforms and subsequently transmitted to the satellite) \vill be downlinked by the SAC-C satellite

Small Satellites for Earth Observation 393

once within visibility from a ground station. in both transmission modes: high or low resolution.

CESAR

The CESAR mission. in cooperation with INTA from Spain. will have Cartography and Thematic/Geophysics studies as primaIy objectives.

A j-year lifetime has been planued for the CESAR satellite. orbiting at a 613 km height in a Sun synchronous circular type orbit, with a proposed 23:30 hr of local time ascending node. The 47 days repeat cycle orbit and the swath of the Multispectral Camera will provide between 6 and 7 days of repeat cycle for a 60 km scene.

The satellite will allow across and along track movement of the cameras pointing axes. providing better revisit times.

Figure 5 - CESAR Satellite

J P,4NcHRoMAUc CAMER.4~ with a 5 meter geometric resolution for cartography and topography purposes.

J MLLTISPECTRAL CAMERA, with 6 bands and 34 meter geometric resolution (VNIR) for thematic studies.

4 PANCHROMATIC HIGH SENSIBILITY CAMERA, with 1 km geometric resolution for geophysics and environment studies.

J SPECTROMETER, studies

for geophysics

A Data Acquisition System will also be part of the Payload, in order to add certain terrain data to the image data (data provided by on-ground-distributed Data Collection Platforms ).

As a way to sum up the main characteristics of the CESAR cameras, the panchromatic images will have 5 meter spatial and 10 bit radiometric resolution (camera PAN here in Table 2 ).

On the other hand, thematic studies will have 5 spectral bands with 34 spatial and 10 bits radiometric resolutions, plus another band in the short wave infrared having around 80 meter and 10 bit resolutions (Multispectral camera in Table

2 ).

The High Sensibility Panchromatic Camera ( PAS camera in Table 2 ) with 1 km geometric and 8 bit radiometric resolution and the Spectrometer ( ESP in Table 2 ) are the instruments to be used for the geophysics applications.

A modular concept will be used on the CESAR satellite: Payload and Bus Modules. The estimated weight of the satellite is around 400 kg, with some 160 kg taken up by the Payload Module.

The satellite will be three axis stabilized, with 0.05 degrees attitude pointing accuracy and 0.04 degrees of post-facto knowledge.

The CESAR Mission Ground Segment will use the facilities already installed in Cordoba (Argentina) and Maspalomas (Spain).

394 Small Satellites@ Earth Observation

Table 2 - Payload Characteristics - CESAR Mission Camera

PAN PAS

Spectral Band / 1 2 / 80 Bl I32 I33 84 65 El E2

Spectral Range P 945 04. 0 4% 04% 054. 062- 07% 16~ 033. 047. 08 O? 645 ( 050 056 066 082 17 046 060

Geometric Resolution m 5 ‘000 34 I 34 34 34 34 60 10 10

Radiometric Resolution bits 10 8 1C 10 IO IO 10 10 8 8

Swath km 60 2100 420 420 420 420 420 420

v Repeat Cycle - days / 47 / ? / 6/Y / ii,i / 6,7 / 6,7 / 6,7 / 6,7 / I

I ---c----+-----c----c-4 ! I I ! ! I ( Sensibility mW/cmzsrv ( 003 ( 10' ( Oil1 j 001 ( 003 ( 002 ( 002 ( 0003 I 0002 (0002 (

SA131A3

Cooperatlvc IIIISSIOII with the Brazllinn Space Agent!,. SABIA-’ mcnns 3atcllite of Argentina and Brazil for InformatIon 011

Food (agriculture). Water and Environment” l@tllitc Argentino Brasileiio pnrn !nforniacZn cn

&imentaci&~. Agun !’ Ambiente I.

The main goal of the SABIA IIIISSIOI~ IS J

providing a complete coverage of nearl!~ all South America every 3 da!s. which can be reached through a 780 Km. SW

J s!,nchronous orbit. I 1 :OO hrs local time descending nodz A 4 !‘cnr lifetime satellite mission has been planned.

The Satellite I\-ill use a Modular Concept J allowing the reuse of its bus for fiuther satellite missions

The Satellite Pa!+oad will consist of two multispectral pushbroom CCD cameras. J with 6 bands. one being panchromatic: plus a data reccixr for the environment data generated b! the ground distributed Data Collection Platforms.

The terrain data received (acquired b! ground-distributed DCPs ) will be added to the image data to be do\vnlinked b>, the

( ‘crmerns C’hatwc~ert.stics

B 1 - Blue - Green ------40 m B2 _ Green ________________ X() n,

B? _ Red ___________________ X() n1

BJ _ N[R ___________________ X() n1

B5 - SWIR -------------- Ih() 111

BP - Panchromatic ------ 40 nl

Mission Control Centers and TT&C Stations under responsibility of the corresponding agencies.

Main Receiving Stations. using the available facilities of both agencies [Cuiaba in Brazil and Cordoba in Argentina 1.

Low Cost Remote Receiving Stations lvith the capability to receive real time compressed data, directly operated b? the users.

Low Maintenance Environmental Data Collection Platforms, to acquire terrain data to be uplinked to the satellite for the post facto correlation with the image data.

SAOCOM

satellite once it is \I ithin visibilit! from a The main instrument of the SAOCOM ground station Mission satellites is a low power

The planned 350 kg satellite \v111 image conxmiption Synthetic Aperture Radar

ivith an X0 meter geometric resolution and (SAR). To accomplish the interferometry

a total s\vath of 900 km. having storage requirements imposed to the mission, two

cauabilitics on board satellites with some overlapping in their

The Ground Segment of the SABIA’ Mission \vill consist of:

corresponding operational phase have been contemplated.

Small Satellites for Earth Observation 395

The maximum technology and architecture developed for the SAC-C satellite shall be applied in both the SAOCOM-1 A and SAOCOM-IB satellite spacecraft buses.

A 5 years lifetime is planned for both satellites having an overlap between them during the last 213 years of the SAOCOM- 1 A operational phase.

The orbit of both satellites has not been completely defined yet but it will be a Sun synchronous circular one with height in the range 600-700 km; and local time of the ascending node between 6:00 hr and 7:00 hr PM. A revisit time lower than 10 days is required for some of the functional modes of the on-board SAR.

The preliminan, concept studies of the SAOCOM-1A SAR pres~lted the following results :

l L Band - Vertical and Horizontal simultaneous polarization.

. Three operational modes:

p Narrow swath - 100 Km - 10 meter spatial resolution.

b Wide swath - 250 Km - 25 meter spatial resolution.

>- Scan SAR mode - 3501450 Km - 100 meter spatial resolution

1 INSAR capabilities using SAOCOM- IA and SAOCOM-1B during satellites overlap.

DEVELOPMENT STATUS

SAC-B was a model example of profitability at low national cost by means of international cooperation demonstrating the in-house ( within the country ) capabilities for managing, designing, constructing and testing of space level hardware and software. The process afforded a positive synergism between scientists and engineers from the participating countries which has been capitalized by CONAE in the follow-on Satellite Missions.

Unfortunately the Pegasus XL launcher did not perform as was expected and the spacecraft demonstrated its nominal good behavior during the 12 hours after launch, before its batteries were completely discharged due to the shadow produced on the SAC-B solar panels by the attached launcher 3’d stage and its avionic system.

SAC-A is orbiting since December 14’h, 1998, starting with Early Orbit and Engineering Phases of the mission. The spacecraft powered electronics has exhibited nominal behavior. The attitude is ahnost perfect ( less than 1 degree off the Sun ) and the Sun acquisition control algorithms were successfully verified ( 20 seconds to achieve the Sun after eclipse ). Up to now VHF/UHF have been used for commanding and real time telemetry reception. Also S-band telecommanding has been performed.

SAC-C Satellite is being integrated. The Structural and Thermal model have been tested. The Ground Segment is ready and the spacecraft is due to be launched in December 1999.

The Phase A ( Feasibility Studies, Mission Concept Design and Mission Compatibility Requirements ) for CESAR Mission was completed in July 1998, and Phase B ( Preliminary Design ) is in progress. The CESAR Satellite is foreseen to be launched circa 2002/2003,

The SABIA3 Mission is planned as a 5 years development project. Phase 0: where the requirements of both countries have been compatibilized, is completed and Phase A/B 1 starts early 1999.

For SAOCOM Mission, the Phase A started for the design and construction of the Synthetic Aperture Radar, together with the spacecraft bus of SAOCOM-1 A Satellite.