AAS 99-147

Precise Orbit Determination for the Mars Global Surveyor

F. Lemoine, D. Rowlands, D. Pavlis, D. Chinn, G. Neumann, D. Smith

NASA GSFC, Greenbelt, MD


Following an initial period of aerobraking, which ended in March, 1998, the Mars Global Surveyor (MGS) spacecraft was located in an interim orbit with a period of 11 hours and 38 minutes, and a periapse altitude of 170 km. From March to April 1998, and from June to July 1998, laser altimeter data from the Mars Orbiter laser altimeter (MOLA) was obtained. The proper interpretation of the altimeter data, including the derivation of the models of planetary topography depend on the calculation of reliable spacecraft orbits. In this paper we detail the orbit modeling to achieve this objective, including the use of improved models of the Mars gravity field derived from MGS data, the application of an MGS macro-model, and the introduction of altimeter crossovers into the MGS orbit determination.