Initial test performance of a closed-cycle continuous hydrogen sorption cooler, the Planck sorption breadboard cooler

The Jet Propulsion Laboratory (JPL) is developing a continuous hydrogen sorption cryocooler for the ESA Planck mission, which will measure the anisotropy in the cosmic microwave background. The sorption cooler is the only active cooling for one of the instruments and it is the first of a chain of three coolers for the other instrument on Planck. The cooler has been designed to provide a cooling capacity of 1.1 W at a temperature below 20 K with a temperature stability requirement of 100 mK over a compressor cycle (667 s). The performance of these coolers depends on many operating parameters (such as the temperatures of pre-cooling thermals shield and the warm radiator and their fluctuations) and compliance can only be assessed through a detailed testing of the whole cooler and its interfaces. A breadboard sorption cooler (EBB) is undergoing testing to verify the flight cooler design performance in terms of input power, cooling power, cold end temperature and cold end temperature fluctuations, heat load on the pre-cooling stages, and heat flow to the warm radiator. We present initial test data compared to predictions based on previously performed component tests.