A dilution cooler for PLANCK [ Return towards  Space programs  ]

Air Liquide has been a long-standing participant in preparations for this mission, and has been responsible, on behalf of the French National Centre for Space Studies (CNES) and the Institute for Space Astrophysics (IAS), and in close collaboration with researchers at the CNRS-CRTBT, for designing and making a dilution cooler for the HFI instrument which has attained unprecedented levels of performance. It is fitted with 94 bolometers and in fact requires a temperature stabilized at 0.1 K above absolute zero to guarantee the quality of the measurements collected. The technology developed for this cooler is particularly well suited to such temperatures since it is able to operate continuously between 0.085 K and 0.300 K, with very great stability (fluctuations in temperature not exceeding a millionth of K) without emitting vibrations or magnetic interference fields which might disturb the observations.
It is the first time this technology has been qualified for use in the space industry.
Developing a cooler of this kind involves not only the cryogenic part (which remains the real technological core of the unit), but also the gas storage and distribution part, as well as the development of the related ground resources (filling, purification, etc.).

Achieving perfect leak tightness and guaranteeing that no capillaries (with a diameter of 20 µm) will get blocked over a period of several years has been a real challenge. Another real challenge lay in preparing a device that was able to withstand being sent into orbit and operate for 2 years in space just because 2 valves were opened.
To operate at 0.1 K, the cooler needs wafer thin supports to minimize any heat input by conduction. On the other hand, to withstand take-off, with accelerations at 30 G, it has to have supports that are extremely strong. To handle this contradiction, it is clamped at take-off, when the cooler is at ambient temperature, between sturdy clamps made of shape-memory alloy. Once in orbit, the cold in space causes these clamps to open, thereby releasing the cooler and its ultra-light support structure.

• Dilution cooler