Atmospheric Modeling Using Accelerometer Data DuringMars Reconnaissance Orbiter Aerobraking Operations

Abstract

Aerobraking as an enabling technology for the Mars Reconnaissance Orbiter mission was used in numerous analyses based on various data types to maintain the aerobraking time line. Among these data types were measurements from spacecraft accelerometers. This paper reports on the use of accelerometer data for determining atmospheric density during Mars Reconnaissance Orbiter aerobraking operations. Acceleration was measured alongthreeorthogonalaxes,althoughonlydatafromthecomponentalongtheaxisnominallyintothe flowwereused during operations. For a 1-s count time, the root-mean-square noise level was 0:004 mm=s 2 , permitting density recovery to 0:008 kg=km 3 , or about 0.023% of the mean density at periapsis, during aerobraking. Accelerometer data were analyzed in near real time to provide estimates of density, density scale height, orbit-to-orbit variability, latitudinal-seasonalvariations,longitudinalwaves,andotherphenomenainthethermosphere.Summariesaregiven of the aerobraking phase of the mission, the accelerometer data analysis methods and operational procedures, some applications to determining thermospheric properties, correlation with the Mars Global Surveyor and Odyssey missions, and some remaining issues on interpretation of the data.