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Description
APR Technologies, a Swedish SME, has developed an updated electrohydrodynamic (EHD) thermal switch for spacecraft thermal control and validated the design through a breadboard test campaign. The EHD thermal switch transfers up to 150 W of heat in the ON state while consuming less than 3 W of electrical power, and requires no power in the OFF state. Since the device contains no moving parts, it is free from mechanical wear and does not generate vibrations.
Although previous generations of the thermal switch demonstrated good performance, sporadic reductions in ON-state thermal conductance were observed during testing. Root-cause analysis identified the free-floating gas bubble used for volume compensation as the cause of the observed performance instability. To address this issue, a revised design incorporating an external accumulator for volume compensation has been developed.
Breadboard testing in thermal vacuum evaluated the thermal switch over operating temperatures ranging from −30 °C to +70 °C and heat loads between 30 W and 150 W. Repeated measurements at identical operating points were conducted to assess long-term performance stability. ON- and OFF-state thermal conductance were characterized for combinations of thermal switch and accumulator temperatures to establish the required accumulator temperature relative to the thermal switch cold-side temperature. Thermal vacuum cycling was also performed, with performance measurements repeated at all operating points following the test.
The test campaign demonstrated stable performance of the revised thermal switch, with no degradation observed over the 25-day thermal vacuum campaign. An ON-state thermal conductance of 330–700 W/(m^2K) and an OFF-state conductance of 41–51 W/(m^2K) was measured across the tested temperature and power range.