Abstract | The Mercury Orbiter Radioscience Experiment (MORE) includes advanced radio-science instrumentation both onboard and on ground to provide accurate range and range-rate observables. Thanks to a 5-way link configuration the noise induced from the solar plasma can be compensated allowing for plasma-free radiometric measurements at nearly all solar elongation angles. This is allowed by the presence onboard of a Deep Space Transponder (DST) used for Telemetry, Tracking and Command (TT&C) functions, and a Ka-band transponder (KaT) which is the key onboard instrument for scientific investigations. The DST supports an X-band uplink (7.167 GHz) coherently retransmitted back to the ground in X- (8.420 GHz) and Ka-band (31.997 GHz), while the KaT can receive a Ka- uplink (34.384 GHz) and retransmit it coherently to ground (at 32.101 GHz). The MORE KaT is endowed with a novel wide-band ranging system, based upon a high rate (24 Mcps) pseudo-noise (PN) ranging code. Recent in-flight tests of BepiColombo have proven an extreme accuracy of less than 1 cm (at a few seconds of integration time) for MORE’s PN regenerative range at 24 Mcps at 0.3 AU and confirmed range-rate accuracy at 0.003 mm/s at 1000 s integration time (Cappuccio et al. 2020b).
Thanks to the unprecedented performance of the radiotracking system, MORE will be able to probe the validity of general relativity and competing theories of gravity in the Solar System, by estimating several parametrized post-Newtonian (PPN) parameters. These parameters will be determined through an accurate estimate of the heliocentric motion of Mercury and propagation time of radio waves, which are obtained as an output of a precise orbit determination process.
We performed a comprehensive numerical simulation of the MORE fundamental physics test which will be held during the hermean phase of the mission. We report the results of the simulation describing the improvement which can be obtained on the estimated PPN parameters, and providing also an assessment of the benefits of an extended mission.
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