Measurements of Martian Rotational Variations by Space Geodetic Techniques

Abstract

Variations of Mars' rotation provide us information concerning both the interior structure and the surface mass redistribution of Mars. Precession and nutation of Mars mainly reveal the core-mantle subsystem, besides length-of-day variation and polar motion of Mars are generally referred to the atmosphere-cryosphere sub-system. As one of the missions of MELOS (Mars Exploration with Lander-Orbiter Synergy), we are proposing areodetic observations using space geodetic techniques including four-way Doppler measurement (FWDP) and inverse VLBI (IVLBI). FWDP is ranging rate measurement of target spacecraft via a relay spacecraft. Utilizing the heritage of four-way Doppler measurements by SELENE, we plan to track the MELOS Landers relayed by the MELOS Orbiter. We also introduce the new technology of IVLBI. In the framework of this technology, one ground radio telescope observes the phase-shift between mutually coherent signals on the orbiter and the landers. The estimated accuracy for the rotation obtained by IVLBI is better than 1 mas (milli-arc second) including the systematic phase noise. The measurements will provide the core radius estimation with the errors of less than 200 km by 50 weeks observations with two landers.