Analytical Model for Transient Loop Heat Pipe Operation

Abstract

Loop Heat Pipes (LHPs) have proven themselves as reliable and robust heat transport devices for spacecraft thermal control systems (TCS). As they gained increasing acceptance, LHP-based TCS have become more and more complex; more than one LHP may be used to carry the waste heat from a common heat source to multiple radiator locations for rejection. In Low Earth Orbit (LEO), orbital variation of the thermal environment does not allow the LHPs to reach a “steady state” as it does in Geosynchronous Earth Orbit (GEO). Hence, their heat transport requirements are dependent not just on the applied heat load but also on the orbit beta angle, thermal mass and the TCS operation-specific conditions. LHP performance is characterized in 1-g for steady-state operation and is a good starting point for selecting an initial design. But in order to demonstrate that the TCS can meet its requirements during all phases of the mission, many or all of which are not steady-state, an integrated transient thermal model of the LHPs and the spacecraft environment becomes necessary. The thermal model must be flexible enough to handle different TCS configurations in trade studies and yet accurate enough to predict the TCS performance for both 1-g and 0-g operation. It must also be run-time efficient. To this end, an LHP transient fluid/thermal model has been developed.