Improvement of BepiColombo’s Radio Science Experiment Through an Innovative Doppler Noise Reduction Technique

Abstract

The Mercury Orbiter Radio science Experiment (MORE), onboard the ESA/JAXA BepiColombo mission to Mercury, is designed to estimate Mercury’s gravity field, its rotational state, and to perform tests of relativistic gravity. The state-of-the-art onboard and ground instrumentations involved in the MORE experiment will enable to establish simultaneous X/X, X/Ka and Ka/Ka-band links, providing a range rate accuracy of 3 μm/s (at 1 000 s integration time) and a range accuracy of 20 cm. The purpose of this work is to show the improvement achieved on MORE’s performance by means of the Time-Delay Mechanical Noise Cancellation (TDMC) technique. The TDMC consists in a combination of Doppler measurements collected (at different times) at the two-way antenna and at an additional, smaller and stiffer, receive-only antenna located in a site with favorable tropospheric conditions. This configuration could reduce the leading noises in a Ka-band two-way link, such as those caused by troposphere and ground antenna mechanical vibrations. The results of end-to-end simulations and estimation of Mercury’s gravity field and rotational state considering the TDMC technique are presented. The results for a two-way link from NASA’s DSS-25 (in Goldstone, CA) or from ESA’s DSA-3 (in Malargue, Argentina) are compared, while the APEX is assumed as the receive-only antenna. It shows that in best-case noise conditions, the TDMC technique allows to obtain a factor-of-two accuracy gain on both global and local parameters, considering DSA-3 as a two-way antenna. Such improvement in the scientific objectives of MORE is of geophysical interest as it could provide a constraint on the interior structure of Mercury.