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The Cassini spacecraft, NASA's mission to investigate the Saturn system, has undergone an extensive thermal development test program to characterize subsystem thermal control designs. In the interest of cost and schedule, not every subsystem was subjected to thermal development testing. The majority of the testing demonstrated that the required system resources such as heater power were adequate. In the instances of the stowed magnetometer boom canister, the sun sensor head assembly, the Huygens Probe receiver front-end, the thruster cluster assembly, and radar science instrument, unexpected thermal design inadequacies were uncovered, but these problems were solved without a significant impact to system resources or thermal design robustness. Additionally, a self-regulating non-electrical heater, a radiant energy transport method, and a reverse louver were successfully demonstrated.

This paper describes the Radioisotope Thermoelectric Generator (RTG) waste heat system and its development, performance, and effectiveness at controlling the temperatures for the propulsion module for the Cassini spacecraft. To explore the Saturn system, the Cassini spacecraft relies on the electrical power from these RTGs, but the large power demand for science and engineering functions severely limits the electrical power available for temperature control. The waste heat system transfers heat radiatively and conductively from each RTG to the propulsion module to maintain temperatures and establish a stable temperature sink to which the rest of the orbiter is thermally anchored.

This paper describes the Variable Radioisotope Heater Unit; its development, performance, and effectiveness at controlling the temperatures for the Cassini spacecraft thruster clusters. To explore the Saturn system, the Cassini spacecraft relies on the electrical power from three Radioisotope Thermoelectric Generators, but the large power demand for science and engineering functions severely limits the electrical power available for temperature control purposes. The Variable Radioisotope Heater Unit combines the heating- and temperature-control functions into one nonelectrical self-controlled unit, thereby freeing up electrical heater power for other uses on the spacecraft.