The 0.1 K cooler on the Planck spacecraft
Illustration of the active cooling system on board the Planck spacecraft, with the components of the 0.1 K cooler highlighted. Also the three V-grooves of the passive cooling system are coloured, representing their progressively lower temperature from bottom to top. To see where on the spacecraft these components are located, see the related video and image in the right-hand menu for context.
The 0.1 K cooler is the final, and coldest, stage of the active cryogenic cooling chain. It is a dilution cooler that cools the HFI detectors to 0.1 K. Three high pressure tanks filled with 4He and one high pressure tank filled with 3He are housed in the service module (four highlighted silver spheres in this view). From each tank a pipe runs to the flow regulation control unit (at lower left). From here the helium isotope gases flow separately towards the HFI focal plane unit (FPU) (in the middle of the blue highlighted focal plane).
Along the way the gases progressively cool down through heat exchangers with the spacecraft's three V-grooves and with the 18K and 4K stages of the active cooling system. Within the HFI FPU the 3He and 4He are mixed, after which a thermo-dynamical process causes the mixture to cool and the detectors at the heart of the FPU reach 0.1 K.