Planck cooling system
To achieve its scientific objective of measuring the cosmological parameters, the Planck mission must make measurements of the temperature variation in the Cosmic Microwave Background with an unprecedented sensitivity down to ΔT/T ~ 2×10-6 and an angular resolution of 5 arcminutes.
In order to reach these sensitivity levels, the detectors of Plancks two instruments (the low frequency instrument (LFI), and the high frequency instrument (HFI)) need to be cooled to cryogenic temperatures. The LFI detectors require an operational temperature of 20 K while the HFI detectors need to be cooled down to a mere 0.1 K.
These operational temperatures are achieved with a cooling chain using several temperature steps, through a combination of passive cooling and a sophisticated active cooling system, which are detailed in the two related articles in the right-hand menu.