The Variable Effective Surface Radiator, Novel Heat Switch Technology Based on the Oscillating Heat Pipe Principle

This paper describes a novel mechanism for heat switch applications in space. The VARiable Effective Surface Radiator (VARES) is a heat switch based on the Oscillating Heat Pipe (OHP) principle. In general all power consuming space objects need radiator surface to radiate surplus of heat. However when switched off the power dissipating objects (electronics) will decrease to unacceptable low temperatures present in space. To overcome this design challenge, several solutions are available such as paraffin heat switches, thermal louvers, and loop heat pipes. Objective of all is to isolate the electronics from the radiator (low temperatures) when switched off. The work described in this paper is performed at NLR on the development of the VARES-radiator for application in spacecraft thermal control systems. The VARES makes use of the property of oscillating heat pipes whereby at low temperatures the oscillation process stops. Therefore it is in principle possible to vary the effective radiator area and thus the power dissipation to the environment. The work presented contains an explanation of the principle of operation in hot and cold conditions, descriptions of performed tests, and VARES breadboards test results. Further it describes design improvements to start the VARES after long cold periods. It is demonstrated that with the right choice of variables (Working fluid and fill charge) an OHP can be used as a heat switch in space applications.