Animation of the Planck spacecraft build-up, showing the different components from the inside out. Starting with the focal plane units (FPUs) of the Low Frequency Instrument (LFI) and High Frequency Instrument (HFI). The different stages of the cooling system are also indicated and animated, followed by all other parts, ending with the complete spacecraft.
A set of three V-grooves (coloured red through blue) thermally shield the focal plane from the warmer service module, providing passive cooling down to 50 K.
Three stages: a sorption cooler further lowers the temperature to 20 K for the LFI FPU and 18 K for the HFI FPU for pre-cooling. A Joule-Thomson cooler brings the HFI FPU down to 4 K. A 3He 4He dilution cooler reduces the temperature of the HFI bolometers to 0.1 K to allow these detectors to obtain the required sensitivity.
The gas tanks for the cooling system reside in the service module beneath the V-grooves. The focal plane sits beneath the large primary mirror and together with the secondary mirror they are encompassed by the telescope baffle.