Thermal-Vacuum Test Data For Jem/Maxi Loop Heat Pipe System With Two Radiators 2008-01-1999
This paper presents thermal-vacuum test data obtained for the JEM MAXI loop heat pipe (LHP) with two separate radiators operating under transient regimes representative of those to be encountered during the flight.
The Monitor of All-sky X-ray Image (MAXI) in the Japanese Experiment Module (JEM), on the International Space Station (ISS), is an X-ray camera with wide fields of view to monitor the universe. The LHP collects about 32 Watts of heat dissipated by the detector and thermoelectrics and transports it to two separate radiators, with orthogonal views to space. Propylene is used as a working fluid due to a wide useful operating temperature range from -60°C to +60°C needed for this program. The LHP utilizes two fluid flow regulators to control fluid flow in the two parallel condensers and is equipped with two startup heaters, and three shutdown heaters controlled by six thermostats.
The LHP system was subjected to an exhaustive thermal-vacuum test program, which included multiple start-ups, shut downs, steady states, and transient regimes. The transient regimes were conducted with a 9-kg thermal mass attached to the evaporator and were intended to mimic the flight case orbit variations scenarios. Temperatures of the two separate heat sinks for the radiators varied independently in a cyclical manner from -180°C to +40°C.
Overall, the LHP demonstrated a reliable and predictable operation without a single failure or temperature instability on the evaporator. Even the most stressful transient test with both heat sinks above the evaporator temperature for some time did not interrupt the smooth evolution of the LHP evaporator temperature during the heat sink temperature cycling test.