Gravity Probe B GPS Orbit Determination with Verification by Satellite Laser Ranging

摘要

The Gravity Probe B (GP-B) satellite has recently completed its science mission. The payload is equipped with two redundant TANS Vector III GPS receivers, used to reconcile vehicle time with Coordinated Universal Time (UTC) and to provide coarse satellite position data. GPS position accuracy easily outperforms mission requirements of 100 m RMS per axis for onboard solutions. The GP-B precision orbit is determined in ground processing of 30-hour and 18-hour GPS data segments using MicroCosm software. Overlaps of consecutive 18-hour ephemeris segments are found to have maximum position errors whose RMS is 2.5 meters, and maximum velocity errors whose RMS is 2.2 mm/sec. Satellite Laser Ranging (SLR) measurements provide independent verification of the GPS-derived GP-B orbit. This paper begins with a brief background of the GP-B mission including a description of the GPS equipment and orbit determination operations. GP-B ephemeris errors estimated using ephemeris overlap comparisons and SLR residual computations are detailed. We conclude with a brief description of in-progress investigations that are anticipated to improve results.