Abstract | The Mercury Orbiter Radio-science Experiment (MORE) will use BepiColombo’s MPO (Mercury Planetary Orbiter) as a test mass to carry out classical and novel tests of relativistic gravity. The relativity experiment will exploit the same microwave instrumentation used for a precise determination of gravity field and rotational state of Mercury. The use of a full multifrequency, coherent, radio link with the spacecraft at X and Ka band (7.2-8-4 GHz, 34-32.5 GHz) will effectively cancel charged particle noise nearly all solar elongation angles, both on Doppler and range observables. The data acquired during tests in cruise and during the first superior solar conjunction (SCE1) have shown range rate accuracies < 0.003 mm/s at 1000 s integration time. The ranging system, based on a novel 24 Mcps pseudo-noise code in the Ka/Ka link has provided measurement accuracies of about 4 cm after just 1 s integration.
However, the outstanding performances of the radio system are partly limited by stray accelerations acting on the spacecraft. In the hermean phase these accelerations will be compensated by means of a high accuracy accelerometer (ISA), whose sensitivities are about 10-9-10-8 m/s2 in the frequency band 10-4-10-1 Hz. However, in the cruise phase the dynamical disturbances are too small to be detected by ISA, forcing the adoption of a stochastic dynamical model to fit the data, that include the relativistic time delay on the ranging signal.
We will report on the first results from the MORE cruise relativity tests and on the expected results in the hermean phase for the precession of Mercury’s perihelion, in the estimation of PPN parameters, and for a direct, dynamical determination of the solar oblateness and mass loss. |
