Planck’s cooling system (at 20 degrees Kelvin)

To achieve the mission goals, the Planck instruments – the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI) - will operate at a few degrees above absolute zero. To achieve this, a series of cooling stages are required.

The picture shows the first cooling stage which brings the temperature of LFI and HFI down to around 20K.