Surface Gravity Modelling and Space Gravimeter Development in the Context of Solar System Small Bodies by Matthias Noeker

Small bodies in the Solar System hold an exciting position in the family of celestial bodies, as they might play a key role in understanding the formation of our heliocentric system, and, ultimately, life. Unlike (terrestrial) planets and larger natural satellites (moons), small bodies have experienced far less transformation, comparing today's state with theirs state in the early Solar System. Next to the scientific avail, those bodies might pose a future risk of impacting on Earth. The two planetary defense ESA Hera and NASA DART missions aim at demonstrating asteroid deflection capabilities. The former will follow the latter to the binary asteroid system Didymos. After the kinetic impact of the DART spacecraft into the secondary asteroid Dimorphos, altering its orbital period, the European mission will embark for detailed characterisation of the binary system. One payload of this mission is the GRAvimeter for small Solar System bodies (GRASS) to land on Dimorphos, for in-situ surface gravimetry. This will be the first-ever extraterrestrial surface gravimeter experiment on a small body. The presented PhD thesis contributed to this novel instrument development, from early prototyping to the final instrument flight model (FM), scheduled for launch in 2024.

The preparation of gravimeters to any celestial target, but moreso the interpretation of the finally returned data to Earth, demand excellent (surface) gravity simulations. Especially on small, generally non-spherical, bodies, this is non-trivial and addressed in the second part of this thesis. Firstly, the different contributions to gravity and the different existing gravitation modelling methods are introduced. This is followed by a comparison of three of these methods and the subsequent computation of surface gravity for different cases, including Hera's target. Finally, zooming in from the global to the local scale, the novel Wedge-Pentahedra Method (WPM) is presented, allowing to take into account local topography surrounding a gravimeter measurement location and influencing the measurement.