Mars Rovers - Limits of Passive Thermal Design

Abstract

Rovers of successful missions to Mars made use of active and passive thermal control options. However, in order to survive the night, all of them relied on a heat source such as electrical energy stored in batteries or from radioactive decay. In this paper, we want to find an optimum point for a minimalistic rover design such as Mars Exploration Rovers that relies mainly on passive thermal control but might also include a small heat source, either RHU or electrical. A thermal model consisting of ten nodes allows varying the size of the rover in the range from Sojourner up to the size of MSL rover. We calculate the heat exchange of the internal components with the environment for each size of the rover and compare the influence of parameters such as body volume and insulation. Due to the different mechanisms of heat transfer, namely convection, conduction, and radiation, the ratio between heat loss and available solar energy on solar cells increases with the size of a rover necessitating usage of RTG (as in MSL rover) for heating or better insulation of the inner components. Investigated worst case cold environmental conditions include latitudes from 0°N to 40°S with wind speeds ranging from 0 m s-1 up to 15 m s-1