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Measurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the formation and evolution of stars and planetary systems in galaxies over cosmic time. Previous infrared missions revealed a great deal about the obscured Universe, but were hampered by limited sensitivity.
SPICA takes the next step in infrared observational capability by combining a large 2.5-meter diameter telescope, cooled to below 8 K, with instruments employing ultra-sensitive detectors. A combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With mechanical coolers the mission lifetime is not limited by the supply of cryogen. With the combination of low telescope background and instruments with state-of-the-art detectors SPICA provides a huge advance on the capabilities of previous missions.
SPICA instruments offer spectral resolving power ranging from R ~50 through 11 000 in the 17–230 μm domain and R ~28.000 spectroscopy between 12 and 18 μm. SPICA will provide efficient 30–37 μm broad band mapping, and small field spectroscopic and polarimetric imaging at 100, 200 and 350 μm. SPICA will provide infrared spectroscopy with an unprecedented sensitivity of ~5 × 10−20 W m−2 (5σ/1 h)—over two orders of magnitude improvement over what earlier missions. This exceptional performance leap, will open entirely new domains in infrared astronomy; galaxy evolution and metal production over cosmic time, dust formation and evolution from very early epochs onwards, the formation history of planetary systems.
In many space sciences project cryogenic detectors are essential for the accomplishment of the scientific objectives, offering unique advantages and unmatched performance. In addition several other components such as the optics can benefit from a cryogenic cooling which reduces the radiative loading. The Service des Basses Températ- ures (SBT) of CEA Grenoble has been involved in space cryogenics for over 20 years now and features a dedicated laboratory, the Cryocoolers and Space Cryogenics group. Various cryocoolers have been developed in the past and our fields of activity focus now on four main technologies: sorption coolers, multistage pulse tubes, adiabatic demagnetization refrigerators (ADR), and cryogenic loop heat pipes. In addition work on two new concepts for ground based dilution refrigerators is also ongoing. Finally developments on various key technologies such as the heat switches, the suspension or structural systems are also carried out. These developments are mainly funded by the European Space Agency (ESA) or by the Centre National d'Études Spatiales (CNES).
In this paper we mostly give an overview of the developments carried out at SBT along with several examples of other relevant systems. We use space cryogenics as a thread. However these coolers or techniques can be used on ground, particularly on remote locations where liquid cryogen are unavailable and/or where maintenance must be limited to a strict minimum. In this case they can be simplified and take advantage of on ground resources, and their cost can be significantly reduced. For most of these systems the common feature is the absence of any moving parts or any friction, which guarantees a very good reliability and make them very good candidates for space borne instruments requiring cryogenic temperatures.
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