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Japanese X-ray astronomy satellite ASTRO-E2 named “SUZAKU“ was successfully launched on July 10, 2005. SUZAKU is the fifth Japanese X-ray astronomy satellite to observe X-ray coming from hot and active regions in the universe in collaboration with NASA GSFC, MIT and University of Wisconsin. “SUZAKU” has achieved the high sensitivity wide energy band X-ray spectroscopy than ever before. It is equipped with X -ray telescopes (XRT) and three kinds of focal plane instruments, X-Ray Imaging Spectrometer (XIS), X-Ray Spectrometer (XRS) and Hard X-Ray Detector (HXD). A radiation-cooling system, connected to XIS and HXD with heat pipes, is provided to cool them below −30 C and −20 C respectively. Furthermore, a side panel has a large cut out to expose XRS cryogenic Dewar for direct cooling. Flight temperatures indicate that the three sensors are kept below their cooling-requirement temperature.

Variable emittance radiator, called SRD, is a thin and light ceramic tile whose infrared emissivity is varied proportionally by its own temperature. Bonded only to the external surface of spacecrafts, it controls the heat radiated to deep space without electrical or mechanical parts such as the thermal louver. By applying this new device for thermal control of spacecrafts, considerable weight and cost reductions can be achieved easily. In this paper, the new design and the new manufacturing process of the SRD and its optical properties, such as the total hemispherical emittance and the solar absorptance, are described. By introducing this new design and manufacturing process, the weight of the SRD is easily decreased, keeping its strength and the optical properties.

The Smart Radiation Device (SRD) is a new thermal control material that decreases the temperature variation by changing the emissivity without using electrical instruments or mechanical parts. The emissivity of the SRD changes physically depending on its temperatures. Bonded only to the external surface of the spacecrafts, the SRD controls the temperature. The drawback of the SRD is the high solar absorptance. The multi-layer film for SRD was designed in order to decrease the solar absorptance from 0.81 to less than 0.2 by putting multi-layer film on it and the optical performance of the Smart Radiation Device with Multi-layer film (SRDM) was evaluated.