SPACE-SHUTTLE PRECISION ORBIT DETERMINATION IN SUPPORT OF SLA-1 USINGTDRSS AND GPS TRACKING DATA

On January 11, 1996, the Space Shuttle Endeavor, mission STS-72, was l aunched, carrying aboard the first of four Shuttle Laser Altimeter (SL A) experiments. In support of SLA-1, precise orbits have been computed from Tracking and Data Relay Satellite System (TDRSS) Doppler observa tions. In some cases, these data were combined with Global Positioning System (GPS) pseudorange observations. Traditionally, the Tracking an d Data Relay Satellite (TDRS) orbits themselves have been the dominant source of error in Shuttle orbit determination during quiescent attit ude periods. However, a new technique utilizing TOPEX/Poseidon's (T/P) precise orbit knowledge plus the TDRSS-T/P Doppler tracking is used t o significantly reduce the TDRS orbit errors. That approach, along wit h improved modeling and parameterization have allowed us to compute pr ecise Shuttle orbits from TDRSS-Shuttle Doppler tracking data. Orbit o verlap comparisons indicate these Doppler-derived orbits have a meter level (1 sigma) radial precision, and they agree radially with the com bined Doppler and GPS derived orbits at the 1.5 m level (1 sigma).