Loop Heat Pipe (LHP) technology has advanced to the point that LHPs are baselined for thermal control systems in spacecraft applications. Many of the applications also require redundant systems to address reliability concerns. In the redundant design, two LHPs are plumbed in parallel to the same heat source and sink. The LHPs are totally separate, and each is designed to fully accommodate the total heat load at the source if the other LHP should fail. Due to the self-regulating nature of an LHP, questions have been raised regarding the expected behavior of two LHPs operating in parallel between the same source and sink, particularly their ability to self-start and equally share the heat load.
To demonstrate the application of LHPs in a redundant system, two totally independent LHPs, each with the same condenser plate and heat source, were fabricated and tested. The objective of the test program was to (1) investigate the start-up behavior of both loops and (2) verify the ability of two parallel LHPs to equally share the total heat load. Test results obtained to date indicate that both loops start normally, but they behave differently at low power. As the total heat load increases, the loops share the total load equally, and system conductance is maximized. Additional tests are planned to further characterize system behavior, particularly under conditions where the LHPs do not equally share the total heat load.