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Deciphering the genesis and evolution of the Martian polar caps can provide crucial understanding of Mars' climate system. The growing scientific interest for the exploration of Mars at high latitudes, and the need of minimizing the resources onboard landers and rovers, motivates the need for adequate navigation support from orbit. We propose a novel concept based on a constellation that can support autonomous navigation of different kind of users devoted to scientific investigations of those regions. We study two constellations, that differ mainly for the semi-major axis, composed of 5 small satellites (based on the SmallSats design being developed in Argotec), offering dedicated coverage of the Mars polar regions. We focus on the architecture of the inter-satellite links (ISL), the key elements providing both ephemerides and time synchronization for the broadcasting of the navigation message. Our concept is based on suitably configured coherent links, able to suppress the adverse effects of on-board clock instabilities and to provide excellent range-rate accuracies between the constellation's nodes. The data quality allows attaining good positioning performance for both constellations with a largely autonomous system. Indeed, we show that ground support can be heavily reduced by employing an ISL communication architecture.

One of the main goals of the Mercury Orbiter Radio science Experiment (MORE), onboard the ESA-JAXA BepiColombo mission to Mercury, is to perform a test of gravitational theories by means of high precision radio-observables, constraining sev- eral Post-Newtonian (PN) parameters. This will be performed in two steps: (i) with a superior solar conjunction experiment during the cruise phase of the mission; (ii) by reconstructing the orbit of Mercury around the Sun once the spacecraft will be arrived at Mercury. In this work we present the results of numerical simulations of the MORE relativity experiment, carried out in a realistic scenario, showing how the experiment can improve over current estimates.

The Cassini spacecraft and its ground segment are currently testing a novel radio frequency multilink technology to perform radio science experiments. During solar conjunctions, this allows the complete removal of the solar plasma noise from the Doppler observables, with benefits for deep space navigation as well. This is obtained combining the carrier frequencies of three independent downlinks; two of them, at X and Ka band (Ka1), are coherent with an X-band uplink, whereas an additional Ka-band downlink (Ka2) is coherent with a Ka-band uplink. During the June–July 2002 Cassini solar conjunction, this procedure was fully tested for the first time. It is shown that, using the adopted multifrequency plasma calibration scheme, the standard deviation of the Doppler frequency residuals is reduced up to a factor of 200 over the uncalibrated X-band data. This large improvement in the data quality, revealed by values of the frequency stability previously achieved only during solar oppositions, makes the navigation accuracy of deep space probes nearly independent of the solar elongation angle.