ALBERT

Description: Shuttle mission STS-69 was launched on September 7, 1995, 10:09 CDT, carrying the Wake Shield Facility (WSF-02). The WSF-02 spacecraft included a set of payloads provided by the Texas Space Grant Consortium, known as TexasSat. One of the TexasSat payloads was a GPS TurboRogue receiver loaned by the University Corporation for Atmospheric Research. On September 11, the WSF-02 was unberthed from the Endeavour payload bay using the remote manipulator system. The GPS receiver was powered on prior to release and the WSF-02 remained in free-flight for three days before being retrieved on September 14. All WSF-02 GPS data, which includes dual frequency pseudorange and carrier phase, were stored in an on-board recorder for post-flight analysis, but "snap- shots" of data were transmitted for 2-3 minutes at intervals of several hours, when permitted by the telemetry band- widdl The GPS experiment goals were: (1) an evaluation of precision orbit determination in a low altitude environment (400 km) where perturbations due to atmospheric drag and the Earth's gravity field are more pronounced than for higher altitude satellites with high precision orbit requirements, such as TOPEX/POSEIDON; (2) an assessment of relative positioning using the WSF GPS receiver and the Endeavour Collins receiver; and (3) determination of atmospheric temperature profiles using GPS signals passing through the atmosphere. Analysis of snap-shot telemetry data indicate that 24 hours of continuous data were stored on board, which includes high rate (50 Hz) data for atmosphere temperature profiles. Examination of the limited number of real-time navigation solutions show that at least 7 GPS satellites were tracked simultaneously and the on-board clock corrections were at the microsec level, as expected. Furthermore, a dynamical consistency test provided a further validation of the on-board navigation solutions. Complete analysis will be conducted in post-flight using the data recorded on-board.

Description: The results of geodynamic research from the analysis of satellite laser ranging data to Starlette are summarized. The time period of the investigation was from 15 Mar. 1986 to 31 Dec. 1991. As a result of the Starlette research, a comprehensive 16-year Starlette data set spanning the time period from 17 Mar. 1975 through 31 Dec. 1990, was produced. This data set represents the longest geophysical time series from any geodetic satellite and is invaluable for research in long-term geodynamics. A low degree and order ocean tide solution determined from Starlette has good overall agreement with other satellite and oceanographic tide solutions. The observed lunar deceleration is -24.7 +/- 0.6 arcsecond/century(exp 2), which agrees well with other studies. The estimated value of J2 is (-2.5 +/- 0.3) x 10(exp -11) yr(exp -1), assuming there are no variations in higher degree zonals and that the 18.6-year tide is fixed at an equilibrium value. The yearly fluctuations in the values for S(sub a) and S(sub sa) tides determined by the 16-year Starlette data are found to be associated with changes in the Earth's second degree zonal harmonic caused primarily by meteorological excitation. The mean values for the amplitude of S(sub a) and S(sub sa) variations in J2 are 32.3 x 10(exp -11) and 19.5 x 10(exp -11), respectively; while the rms about the mean values are 4.1 x 10(exp -11) and 6.3(10)(exp -11), respectively. The annual delta(J2) is in good agreement with the value obtained from the combined effects of air mass redistribution without the oceanic inverted-barometer effects and hydrological change. The annual delta(J3) values have much larger disagreements. Approximately 90 percent of the observed annual variation from Starlette is attributed to the meteorological mass redistribution occurring near the Earth's surface.