Spacecraft-to-spacecraft radio occultations experiments are being conducted at Mars between Mars Express (MEX) and Trace Gas Orbiter (TGO), the first ever extensive inter-spacecraft occultations at a planet other than Earth. Here we present results from the first 83 such occultations, conducted between 2 Nov 2020 and 5th of July 2023. Of these, 44 observations have to-date resulted in the extraction of vertical electron density profiles. These observations are the successful results of a major feasibility study conducted by the European Space Agency to use pre-existing relay communication equipment for radio science purposes. Mutual radio occultations have numerous advantages over traditional spacecraft-to-ground station occultations. In this work, we demonstrate how raw data are transformed into electron density values and validated with models and other instruments.@en

Despite the growing importance of planetary Space Weather forecasting and radiation protection for science and robotic exploration and the need for accurate Space Weather monitoring and predictions, only a limited number of spacecraft have dedicated instrumentation for this purpose. However, every spacecraft (planetary or astronomical) has hundreds of housekeeping sensors distributed across the spacecraft, some of which can be useful to detect radiation hazards produced by solar particle events. In particular, energetic particles that impact detectors and subsystems on a spacecraft can be identified by certain housekeeping sensors, such as the Error Detection and Correction (EDAC) memory counters, and their effects can be assessed. These counters typically have a sudden large increase in a short time in their error counts that generally match the arrival of energetic particles to the spacecraft. We investigate these engineering datasets for scientific purposes and perform a feasibility study of solar energetic particle event detections using EDAC counters from seven European Space Agency Solar System missions: Venus Express, Mars Express, ExoMars-Trace Gas Orbiter, Rosetta, BepiColombo, Solar Orbiter, and Gaia. Six cases studies, in which the same event was observed by different missions at different locations in the inner Solar System are analyzed. The results of this study show how engineering sensors, for example, EDAC counters, can be used to infer information about the solar particle environment at each spacecraft location. Therefore, we demonstrate the potential of the various EDAC to provide a network of solar particle detections at locations where no scientific observations of this kind are available.

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Aerobraking is an effective technique to save significant amounts of fuel while lowering an orbit around a planet. It was first applied by NASA at Venus, with Magellan during its extended mission, in 1993. The first aerobraking at Mars was done, also by NASA, with Mars Global Surveyor, in 1999. ESA did its first experimental aerobraking with Venus Express, near the end of its mission, at Venus in 2014. ESA’s ExoMars Trace Gas Orbiter, TGO, was the first ESA spacecraft to do aerobraking as a part of its nominal mission. TGO reduced its apocentre attitude to near 400 km, to achieve a near circular orbit, during one full year of aerobraking, finishing in April 2018. Remote measurements of atmospheric parameters are difficult at high altitudes due to the tenuous medium. However, atmospheric drag experienced during aerobraking is directly proportional to the local atmospheric density and this drag can be measured accurately by on board accelerometers and so provide precise data on the local atmospheric density along the s/c trajectory. Additional, even more sensitive data, averaged along the trajectory, can be acquired by precise tracking of the s/c orbit. Large data sets have been collected from both the Venus Express and the TGO aerobraking campaigns. Both these data sets show larger than expected day to day variations of the atmospheric densities of the two planets throughout these campaigns. In spite of the large differences in the surface pressure/density at the two planets, the upper atmospheres are surprisingly similar, albeit highly variable. This talk will focus these atmospheric differences and similarities, and comparisons with existing models will be made. Potential improvements in the method and optimisation of measurements will be evaluated, and applications to ESA’s next Venus mission, ENVISION, will be discussed.@en