Sorption cryocooler development for the Planck Surveyor mission

We are developing metal-hydride based sorption cryocoolers for the Planet S urveyor mission. The sorption coolers work by thermally cycling a metal-hyd ride to absorb and desorb hydrogen gas, which is used as the working fluid in a Joule-Thomson refrigerator. Pressure ratios of 100:1 or more can be ac hieved by varying the temperature of the compressor by a factor of 2-3. The major advantages of sorption coolers are that they are truly vibration-fre e and can be readily scaled to perform over a wide range of cooling powers. We present here a review of sorption cooler operation, important factors i n the design of coolers, and the details of the design of a 20 K cooler sys tem for the Planet mission.