Life Testing of an Irradiated Mars Flight Heritage Mechanically Pumped Fluid Loop for the Planned Europa Mission

The National Aeronautics and Space administration is planning to send a spacecraft to explore Jupiter’s icy moon, Europa. The baseline design for the Europa Mission spacecraft uses a mechanically pumped fluid loop as the primary thermal control system. The fluid loop design is based on the fluid loop system flown on NASA’s Mars Science Laboratory rover, Curiosity. This fluid loop system has been developed over the past two decades through the NASA Martian rover projects. However, unlike the previous Martian missions, the Europa Mission spacecraft will be exposed to high levels of ionizing radiation. The Mars heritage fluid loop has not operated in this type of environment before. In order to evaluate the effects of ionizing radiation on a Mars heritage mechanically pumped fluid loop, a test campaign was undertaken at the NASA Jet Propulsion Laboratory. A fluid loop similar to the anticipated Europa Mission fluid loop was designed and built. CFC-11 was used as the working fluid and the wetted materials were stainless steel and aluminum. The fluid in the system was exposed to between 5 and 6 Mrad of ionizing radiation during four irradiation sessions over the course of four months. Hydraulic performance of the system was monitored during and after each irradiation session. Flowrate, pressure drop and pump power consumption were continually measured. The degradation of the working fluid and containment tubing were evaluated via chemical and metallographic analyses carried out on testbed samples after each irradiation session. It was found that the hydraulic performance, fluid composition and mechanical integrity of the system were minimally affected by the radiation. This paper describes the experiment and its results.