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The Mars Exploration Rover (MER) flight system uses mechanical, paraffin-actuated heat switches as part of its secondary battery thermal control system. This paper describes the design, flight qualification, and performance of the heat switch. Although based on previous designs by Starsys Research Corporation1,2, the MER mission requirements have necessitated new design features and an extensive qualification program. The design utilizes the work created by the expansion of a paraffin wax by bringing into contact two aluminum surfaces, thereby forming a heat conduction path. As the paraffin freezes and contracts, compression springs separate the surfaces to remove the conduction path. The flight qualification program involved extensive thermal performance, structural, and life testing.

A paraffin-actuated heat switch has been developed for thermal control of the batteries used on the 2003 Mars Exploration Rovers. The heat switch is used to reject heat from the rover battery to a radiator. This paper describes the development test program designed, in part, to measure the thermal conductance of the heat switch in an 8 Torr CO2 environment over the expected operating temperature range of the battery. The switch has a closed conductance of about 0.6 W/°C and an open conductance of 0.019 W/°C. The test program also included measuring the battery temperature profile over a hot case and a cold case Mars diurnal cycle. The test results confirm that the battery will remain well within the upper and lower allowable flight temperatures in both cases.