Modeling the Lunar Gravity Using Passive 3-Way Doppler Data from Lunar Prospector

Abstract

During the month of July and August 1998 a six wees tracking campaig of Lunar Prospector was conducted at DLR/GSOC`s 30 m ground station at Weilheim. Throughout this period, entirely Passive 3-way Doppler data was collected with uplinks being provided by the Deep Space Nework stations at Madrid, Canberra and Goldstone. In total about 1,030,000 data points have been collected, providing for the first time a European tracking data set unseful for low lunar orbit and gravity field determination. The original count interval of 1 sec was reduced to 30 sec prior to the actual processing, thus reducing the data noise level, and, moreover, effectively removing the effect of periodic Doppler variations due to the 12 rpm spacecraft rotation. Several gravity field models have been derived, supporting investigations of the effect of various processing algorithms on the solution. Quality assessment is done using both the conventional methods of measurement fit and orbit consistency as wellas modern geodetic tools. While the gravity models may be inferior to one derived from a full-year cycle of continuous data, they mark an important step in European lunar gravity modeling and moreover demonstrate the readiness for more detailed investigations in the framework of the upcoming missions.