Playing Telephone Through Martian Rock: Assessing Terrain Occlusions to Enhance Telecom Predictions

As the Curiosity Mars rover has traversed through Gale Crater, a wide variety of terrain and rock formations have been observed. Earlier in the mission, the rover experienced relatively flat local terrain, with few hills or buttes in its immediate vicinity. As the rover traversed into the "clay-sulfate transition region," the terrain changed dramatically to include higher elevation features. Despite the intrigue and beauty of these formations, their proximity to the rover can impact performance of both Ultra-High Frequency (UHF) and X-Band communications by physically occluding some or all of the link. This paper will describe and demonstrate a tool developed to assess the risk of terrain occlusions, enabling more accurate telecom predictions in addition to providing advanced knowledge of hardware visibility, both from Earth and from the orbiters at Mars. By utilizing Digital Elevation Models (DEMs) derived from images taken by the High Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO), in addition to images from the High Resolution Stereo Camera (HRSC) onboard the Mars Express (MEX) orbiter, a horizon map of the surrounding terrain elevation can be produced at a localized rover position on the surface. The horizon map can then be compared to predicted Earth positions and predicted orbiter geometry during scheduled communication windows to assess the impact of terrain occlusions on those upcoming windows. During nominal operations, the rover utilizes its UHF radio to transmit telemetry to Mars-orbiting relay assets, which then return that data back to Earth. In addition, the rover utilizes its X-Band radio to receive commands directly from Earth via the Deep Space Network (DSN). However, occlusions of either antenna directly impact the planning timeline by delaying the return of critical data required for planning and/or forcing the team to relay commands to the rover via the orbiters. These deviations from the standard procedure almost always result in loss of one or more planning days and present uncommonly encountered risks. By providing invaluable situational awareness of the telecom subsystem in advance of daily planning, this terrain occlusion checking tool reduces the number of lost planning cycles, directly increasing science return.