CONSERT Link Budget Simulator for the Direct Path

Abstract:

The Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) will determine the dielectric properties of comet 67P/Chuyurmov-Gerasimenko’s nucleus. This is achieved by performing a sounding of the comet’s core between the lander "Philae" located on the comet’s surface and the orbiter "Rosetta".
For these measurements a stable synchronization between lander and orbiter has to be ensured. This has to be done with the direct propagation path between orbiter and lander as close as possible to the point of occultation.

The point of occultation can be estimated with the Rosetta link budget simulator. The simulator uses the radiation pattern for orbiter and lander calculated with an integral-equation based numerical solver. The orbiter pattern is calculated in free-space and the lander pattern considers the bulk material of the comet represented by an infinite half-space, which enables the investigation of mutual coupling effects. The underground can be modeled with arbitrary values for the relative permittivity and the conductivity in order to investigate the influence on the received signal at the orbiter.

For the synchronization scenario the losses due to free-space path-loss, different complex permittivity values and the polarization mismatch are considered, especially the latter has a major influence on the received power. Thereby the latest possible point for synchronization can be estimated dependent on the antenna alignment between orbiter and lander.

Moreover a statistical analysis of the received power can be performed in order to investigate the impact of the antenna misalignment for a normal distributed and arbitrarily chosen angular deviation between orbiter and lander.