Mars Exploration Rover Heat Rejection System Performance – Comparison of Ground and Flight Data

Mars Exploration Rover (MER) mission launched two spacecraft to Mars in June and July of 2003 and landed two rovers on Mars in January 2004. A Heat Rejection System (HRS) based on a mechanically pumped single-phase liquid cooling system was used to reject heat from electronics to space during the seven months cruise from Earth to Mars. Even though most of this HRS design was similar to the system used on Mars Pathfinder in 1996, several key modifications were made in the MER HRS design. These included the heat exchanger used in removing the heat from electronics, design of venting system used to vent the liquid prior to Mars entry, inclusion of pressure transducer in the HRS, and the spacecraft radiator design.

Extensive thermal/fluids modeling and analysis were performed on the MER HRS design to verify the performance and reliability of the system. The HRS design and performance was verified during the spacecraft system thermal vacuum tests. Based on the analysis and the testing of the HRS system, operations of the HRS during launch, cruise and prior to the Martian entry were developed and implemented. The electronics and radiator temperatures were within the range of the predicted values. The HRS system pressure was maintained at the predicted levels indicating any liquid or gas leakages were within the predicted values. The venting system on both spacecraft performed flawlessly in January 2004 when the pyro-valves in the HRS were actuated before the spacecraft entered the Martian environment.

The paper describes the various design modifications made on the MER HRS from that of Mars Pathfinder spacecraft. A description of the flight performance during the seven-month cruise of the spacecraft and a comparison of the performance on the ground and the flight is presented. Any significant deviation in the flight performance will be described.