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TECHNICAL PRESENTATION MINIATURIZED TOPSTAR
3000 SPACEBORNE GPS RECEIVER Jean-Luc
Issler ( CNES )
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Need for a GPS Sensor

• Present-day needs for GPS sensors natural
  sensor for LEO
• Absolute time reference for platform or payload
  ( AMS )
• Real-time navigation / positioning
• Ground operation simplification (orbit
  determination of the GPS antenna)
• GPS attitude determination (optional)

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First CNES GPS experiments in space (1)
TOPSTAR 100 on ARD ( ESA/CNES Ariane 503 1998
) ARD was guided by GPS ( more precise than
the IMU drift ) First space capsule re-entry
guided by GPS in the world Positioning
residuals close to 30 m ( 3D 1 sigma ) in the
presence of GPS selective availability Success
of the threshold reduction, providing continuity
and robustness of GPS service, even during rall
reversals CNES patent for threshold reduction in
orbit
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First CNES GPS experiments in space (2)
TOPSTAR 300 on
HETE2
. ( NASA/MIT/CNES
Pegasus october 2000 ) Goal spacecraft
navigation and timing ( platform and science
payload ) circular/equatorial orbit ( h600 km
) Good robustness of  PVT  and DIOGENE
Ionosphere tomography using C/A
code/carrier Succes criteria of NASA/MIT 18
months of nominal operations The receiver is
still operational in orbit. On ground tests of a
DIOGENE version provided with single frequency
IONO correction gt Accuracy lt 5 meters
OPERATIONAL USES OF GPS FOR NAVIGATION AND
TIMING
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GPS MEASUREMENTS OF HETE2DIOGENE 2 (code phase
single frequency ionospheric correction)
Cross-track difference mean 0,3 m RMS 1,4 m
Along-track difference mean 0,3 m RMS 3,9 m

Radial difference mean 0,5 m RMS 1,9 m
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TOPSTAR 3000 - Performances

• Enhanced performances in localisation are
  obtained
• thanks to the embedded orbital navigator
• Orbital navigator is a CNES development (DIOGENE)
  and benefits from CNES expertise in modelisation
  of orbital forces and orbit determination
• Orbital navigator is compliant with all types of
  orbit (LEO, MEO, GEO, ...)
• High sensitivity is obtained thanks to a fully
  parallel RF/IF architecture
• and state-of-the-art design
• Signal acquisition and tracking techniques
  benefit from 20-years experience in GPS receivers
  development (military and civil airbornes).
• Acquisition and tracking at very low
  signal-to-noise is a patented technique
• Cold start acquisition 40 dB.Hz
• Warm start acquisition 35 dB.Hz
• After 1st fix acquisition 19 dB.Hz
• Code-only tracking 17 dB.Hz

Time Transfer with TCXO better than 1 ms (3s)
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ALCATEL TOPSTAR 3000 - Present Day Product

• Product T3000/V1 - Available
• Modularity
• Multi-mission
• Product Complexity
• 50 000 lines of C code
• Computer power 6 MIPS
• Real Time 1 200 IRQ per second
• 2 digital ASICs (100k and 200k gates)
• 1 RF ASIC for frequency shifting
• Software quality meet higher level standards
  for space applications
• Experiments to come
• RPP Ranging Per Pseudolite ( STENTOR -GEO- )
  GPS GTO and GEO ( STENTOR )
• COA Autonomous Orbit Control (DEMETER -LEO-
  and STENTOR -GEO- )
• NB 13 flight models already contracted for
  diverse LEO missions

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• Miniaturized T3000 GPS Receiver
• Improved cost, mass, volume, power consuption
  
• New functionnalities
• Single or Dual Frequency L1-C/A L2C
• Compatibility with pseudolite signals
  (navigation GEO)

First flight model ( single frequency ) Q3
2004
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CONCLUSIONS
- The performances of the T3000 GPS receiver has
been already validated in orbit - A miniaturized
version, deliverable at Q3 2004, could be
compatible to the AMS needs - The T3000 receiver
has a modular architecture 1 to 4 GPS antennas,
for instance