Lunar Prospector Orbit Determination and Gravity Filed Modeling Based on Weilheim 3-Way Doppler Measurements

Kurzfassung

In the summer of 1998, the Lunar Prospector (LP) spacecraft was tracked form DLR's Weilheim ground station. Over a period of six weeks passive 3-way Doppler data have been collected by the 30 m deep space antenna making use of the available uplink from stations of the Deep Space Network (DSN). The paper describes the tracking campaign and the subsequent data analysis using both Geodyn II and DLR's in house orbit determination software DEEPEST. The original measurements exhibit a noise level of 0.5 mm/s at count times of 30 s. Taking advantage of the LP75G gravity model, the data could be modeled to an accuracy of typically 6 mm/s rms in weekly orbit determinations. Attempts were also made to model the 0.2 rev/s rotation of the LP Spacecraft, which is evident as a periodic signal with a ~7 mm/s amplitude in tracking data sampled at a 1 s interval, but proved to be unsatifactory due to an apparent instability of the rotation rate. Finally all tracking data were processed using the GEODYN II & SOLVE program available at TU. Delft to generate partial derivatives for gravity field coefficients and demonstrate the basic capability of solving for a global 75x75 gravity model.