Development of a Mechanically Pumped Fluid Loop for 3 to 6 kW Payload Cooling

With the fast growing demand for space based telecommunication capabilities in combination with application of high density electronics, the cooling requirements for future telecommunication satellites is steadily increasing, up to a point that conventional cooling technologies using (loop) heat pipes are no longer ennough to cope with in-orbit load and heat rejection variations, large number of thermal interfaces and testing constraints. To prepare for future high performance cooling requirements, the European Space Agency, ESA initiated the development of a Single-Phase Mechanically Pumped Fluid Loop (MPFL) which was one of the two heat transfer element options for the large Alphabus deployable radiator (see Figure 2). The purpose of the project was to design, develop and qualify an European manufactured single-phase cooling loop components such as pumps, valves, an accumulator and coolant fluid that can be used as high performance heat transfer device for extended payload power ranges between 3 and 6kW. The main requirements for MPFL were: operational temperature range of −20°C to +90°C, non operational −100°C to +100°C, 3 KW heat transportation, <30°C increase of fluid temperature in the PHX, piping length PHX 70m and RHX 90m, Lifetime >15 years. As the temperature, reliability and lifetime requirements are severe, this put highly challenging requirements to the coolant (temperature range), pump (bearings, motor) and accumulator design. The selected and (space) qualified fluid was Galden Zt85 (manufactured by Solvay Solexis) which gives the best overall performance. The baseline selected MPFL pump is a design with a demonstrated accelerated life test for 10 years. The pump provides for an almost constant fluid flow through the Payload Heat Exchanger (PHX) branch whereas the By-pass Valve regulates the flow through the Radiator Heat Exchanger (RHX) branch. The accumulator compensates for fluid expansion over the operation and non-operational temperature range. A modular design which can be used for applications within a 3 to 6 kW payload range and compatibility with a variety of coolants was the result of this approach. Hence the qualified equipment for MPFL is suitable for multiple applications.