Investigation of Multipath Effects on Mars Relay Network Overflights

The Mars Relay Network (MRN) is routinely used to increase data volume return from spacecraft on the Martian surface, including Mars 2020 (M2020) and the Mars Science Laboratory (MSL). The system performance, typically measured in daily returned data volume per vehicle, depends on several factors, including the time and geometry of the overflights, as well as the orientation and state of the vehicles at both ends of the proximity link. In this paper, we focus on understanding the effect of terrain occlusions and multipath fading on the performance of return proximity links. Using historical data, we first show that relay passes at low elevation angles experience a clear data volume degradation, and result in returned daily data volumes that are more difficult to predict ahead of time during the relay planning phase. Motivated by these findings, we study two methods to quantify the impact of multipath effects in returnable data volume, one based on simple terrain blockage, and another one using estimates of received signal level generated by an electromagnetic simulation engine. We also describe a proposed method to include multipath effects during planning of relay overflights, and introduce a new operational tool to aid in the selection of low elevation overflights.