Operation of an Eight-Loop Heat Pipe Architecture for High Dissipative Applications

Architectures with several Loop Heat Pipes (LHPs) connected to a network of Heat Pipes (HPs) can be considered as an attractive solution for space missions with highly dissipative equipment onboard. This kind of architecture allows transferring significant heat loads efficiently on long distances towards different cold thermal sinks, while ensuring stable and uniform temperature of the dissipating units. Operation of several LHPs in parallel has been historically considered unstable due to the intrinsic features of the LHP performance during transients and in particular for start-up. A system based on eight LHPs connected to a network of 12 HPs has been defined for the thermal control of all Dual State Solid Power Amplifiers (DSSPAs) in a highly dissipative Active Antenna. The system design has been challenged to cope with stringent operational requirements such as high heat transport capability in the range of 5kW and temperature homogeneity among the DSSPAs, with temperature gradients < 5K. To prove the concept, a dedicated Thermal Model (TM) has been built and tested at different operational scenarios and boundary conditions. The TM consists of eight LHPs distributed on a network of 12 HPs in parallel, each LHP being mounted on six HPs, so that each HP remains in contact with at least three, and up to five, LHP evaporators. The TM has been tested both in vacuum and in climatic chamber. The test sequence included start-up in cold and hot environment and from different initial conditions including dry-out and preconditioning, shut-down tests and performance with several power and sink levels, with and without heat leaks to the reservoir. Start-up and shut down ability of the LHPs, plus reliability of the system operating during steady conditions and transients has been proven.