Abstract DGP2026-103

There are currently several missions in cruise phase and planned, operating a radar for sub-surface imaging to celestial bodies (e.g. RIME on JUICE or JURA on HERA/Juventas). With radars having a much wider field of view than e.g. Laser altimeters, reflections from the surface will be visible in recorded radargrams. Consequently, one objective is the separation of surface clutter from actual subsurface reflections. With the help of sufficiently good digital elevation models, it is possible to simulate clutter, which in turn can be subtracted from the recorded radargrams.

Due to the size of celestial bodies, commercially available full wave simulation tools are incapable of handling these scales. Furthermore, the detailed and broad capabilities of commercial simulation tools may also not be required to estimate the surface clutter. We therefore are developing in-house tools for the simulation of clutter or sub-surface reflections. Currently, two different tools are being developed: one that is based on physical optics (PO) and a raytracer (RT). The main differences are the possibility of the PO to calculate surface currents, which can help identify significant sources of surface clutter, and does conserve energy, which allows for link-budget estimation on the one hand and the ability of the RT to handle larger objects due to less information being calculated internally on the other hand.

Both tools are written in C++ and are highly optimized (AVX instructions, parallelization) to reduce simulation times. They are designed to handle triangulated surfaces to describe objects handle multiple frequencies to reproduce the behavior and performance of the employed radars. Furthermore, full-wave simulations of frequency-dependent antenna characteristics when combined with the spacecraft can be used as transmit and receive antennas. Additional system characteristics can be included in post-processing as they don‘t influence the wave propagation. Actual or planned trajectories including attitude can be manually extracted from SPICE kernels and used as input for the simulation to accurately match mission trajectories. Since the simulation results resemble S11 data, they can be processed with the same algorithms as are used for mission data.

We have successfully validated the tools by estimating the Phobos flybys of MarsExpress, or calculating the descent scenario of the Philae lander of ESA‘s Rosetta mission (CONSERT experiment) and we are able to handle scenarios for RIME or even clutter simulations for RIMFAX, the ground penetrating radar onboard NASA‘s Mars2020 Perseverance rover. Furthermore, we were also able to reproduce the data that was published by ESA for the JUICE lunar-earth gravity assist in August 2024. Simulations of the scenario of the JuRa (HERA Juventas Radar) can be used to develop tools for the reconstruction of the surface of Dimorphos and potentially its inner structure.