The core of the High Frequency Instrument (HFI) on-board the Planck satellite consists of 52 bolometric detectors
cooled at 0.1 Kelvin. In order to achieve such a low temperature, the HFI cryogenic architecture consists in
several stages cooled using different active coolers. These generate weak thermal fluctuations on the HFI thermal
stages. Without a dedicated thermal control system these fluctuations could produce unwanted systematic effects,
altering the scientific data. The HFI thermal architecture allows to minimise these systematic effects, thanks to
passive and active control systems described in this paper. The passive and active systems are used to damp
the high and low frequency fluctuations respectively. The results of the simulation of these active and passive
control systems are presented here. These simulations based on the use of thermal transfer functions for the
thermal modelling can then be used for finding the optimal working point of the HFI PID active thermal control
system.
KEYWORDS: Cryogenics, Control systems, Bolometers, Temperature metrology, Satellites, Space telescopes, Sensors, Thermography, Electronic filtering, Anisotropy
The core of the High Frequency Instrument (HFI) on-board the Planck satellite consists of 52 bolometric
detectors cooled at 0.1 Kelvin. In order to achieve such a low temperature, the HFI cryogenic architecture
consists in several stages cooled using different active coolers. These generate weak thermal fluctuations
on the HFI thermal stages. Without a dedicated thermal control system these fluctuations could produce
unwanted systematic effects, altering the scientific data. The HFI thermal architecture allows to minimise
these systematic effects, thanks to passive and active control systems described in this paper. The
passive and active systems are used to damp the high and low frequency fluctuations respectively. The
last results regarding the tests of the HFI passive and active thermal control systems are presented here.
The thermal transfer functions measurement between active coolers and HFI cryogenic stages will be
presented first. Then the stability of the temperatures obtained on the various cryogenic stages with PID
regulations systems will be checked through analysis of their power spectrum density.
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