The 20 K cooler on the Planck spacecraft
Illustration of the active cooling system on board the Planck spacecraft, with the components of the 20 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 20 K cooler is the first cooler in the active cryogenic cooling chain. It is a closed-cycle sorption cooler, with hydrogen as the working medium. It cools the detectors of the Low Frequency Instrument (LFI) to 20 K. It also pre-cools the focal plane unit of the High Frequency Instrument (HFI) to 18 K.
The cooler consists of a sorption compressor unit (orange), piping, and a cold end. The hydrogen leaves the sorption compressor and flows through piping to the cold end, located inside the focal plane (blue). The piping runs past the three V-grooves that efficiently pre-cool the gas through heat exchange down to about 45 K.
To provide full redundancy to the mission, two identical 20K coolers are installed on the Planck spacecraft. The sorption compressor unit of the second cooler can be seen at lower right in this view (grey, not highlighted).