Simulations of Mars rotation radioscience observation and retrieval for a rover/lander on Mars

The variation of Mars’ rotation rate (or length-of-day variations), the orientation of Mars’ rotation axis in space (precession and nutation), and the orientation of Mars around its rotation axis (polar motion), can be determined by monitoring the Doppler shift due to the motion of a probe landed on Mars relative to tracking stations on Earth (DTE: Direct To Earth) and/or relative to spacecraft orbiting Mars. Our work is in the perspective of future missions to Mars, foreseeing to land a rover (ex: ExoMars), or one or more landers (ex: MarsNet) at the surface of Mars before 2020. We have performed numerical simulations for assessing the determination of Mars’ Orientation Parameters (MOP) and their improvement with respect to present day knowledge of Mars interior. We have evaluated the precisions that can be achieved with different Doppler measurements: (1) from a DTE in X-band radio link, (2) from an X-band radiolink through an orbiter, (3) from an UHF radiolink through an orbiter, and (4) with both, a DTE radio link and radio links using an orbiter. In order to perform our simulations we have used the GINS (Géodésie par Intégrations Numériques Simultanées) software developed by CNES and further adapted at Royal Observatory of Belgium for planetary geodesy applications. As the MOP are related to the interior of the planet as well as to its seasonal angular momentum changes induced by the CO2 sublimation/condensation process, we further discuss the expected improvement in our knowledge of the density (total and core moment of inertia) and physical state (solid/liquid) of the Martian core, and in our knowledge of the CO2 mass budget in the Martian atmosphere and ice caps.