Variable Conductance Thermal Control by Passive or Active Control of Fluid Manipulation

A concise survey is given of international research done in the last decades for developing spacecraft-oriented (variable conductance) two-phase thermal control systems, based on passive or active control of fluid manipulation. The various methods of variable conductance heat pipe control are discussed, focusing on control using non-condensable gas. The historical development is given, including the arguments why these relatively simple two-phase thermal control systems often have been and will be the preferred solution to meet the large variety of different restrictions, induced by the typical requirement specifications of many, relatively low power (up to 5 kW) applications in space. The paper briefly mentions alternative control approaches considered in the past, while focusing on those that are regaining attention, i.e. systems, based on electro-hydrodynamics and electro-osmosis. It touches also a novel switching/pumping control alternative based on electric wetting. More detailed discussions on the current status of these alternative control issues are given in the follow-up paper SAE-2006-01-2230.