David E. Smith

Improved force modeling on Mars-Orbiting spacecraft

We present improvements to the modeling of non-conservative forces affecting Marsorbiting spacecraft. Recent high-resolution gravity fields enable the recovery of smaller signals in the radio tracking data, previously obscured by mismodeled gravitational anomalies. In particular, we show that the estimation of the atmospheric drag experienced by the spacecraft benefits from the new force models. More precise calculations of the spacecraft cross-sectional areas entering the equations for the atmospheric drag and direct solar radiation pressure are possible after accounting for the inter-plate self-shadowing of the spacecraft physical model. The relevant surface areas can vary by as much as 20% on average, and the effects can be very variable within one orbit (±10%). We assess the benefits of these updated models by studying two spacecraft, Mars Odyssey and Mars Reconnaissance Orbiter. We study the effects of modeling on the magnitude and characteristics of the accelerations, on the reconstructed spacecraft trajectory and on the estimated atmospheric density. We plan to use these model improvements with the upcoming Lunar Reconnaissance Orbiter.