Dilution cooler – 0.1 K – 1.6 K  [ Return towards  Flight equipment for refrigeration  ]

The sensitivity of on-board detectors on scientific satellites critically depends on their operating temperature. For missions with a very high scientific return like the accurate thermal mapping of background radiation in the universe (Planck mission), these detectors have to operate at a stable temperature of 0.1 K. This may be achieved by using a cold chain that comprises at its coldest end a dilution cooler.
The dilution cooler operates by cryogenically mixing the 3He and 4He isotopes flowing in very small dimension tubes which make the system insensitive to gravity. Cooling power depends on isotope throughput. It is produced not only in the cold finger, but also continuously down to about 1.5 K, the temperature at which a 2nd cryogenic stage is found (obtained through Joule-Thomson expansion in relation to the mixture). This original principle of continuous cooling over more than ten degrees of temperature is particularly suited to the optimization of a high sensitivity cryogenic instrument. The gas stored is in sufficient quantity to run a mission over the operating lifetime required.