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The CHANDRA X-ray Observatory (formerly AXAF), one of NASA's “Great Observatories” was launched aboard the Shuttle in July 1999. CHANDRA comprises a grazing-incidence X-ray telescope of unprecedented focal length, collecting area and angular resolution - better than two orders of magnitude improvement in imaging performance over any previous soft X-ray (0.1-10 keV) mission. Two focal-plane instruments, one with a 150°K passively-cooled detector, provide celestial X-ray images and spectra. Thermal control of CHANDRA includes active systems for the telescope mirror and environment and the optical bench, and largely passive systems for the focal plane instruments. Performance testing of these thermal control systems required 1-1/2 years at increasing levels of integration, culminating in thermal-balance testing of the fully-configured observatory during the summer of 1998.

This paper presents the Compound Parabolic Lightshade geometry as a candidate for shading of cold passive radiators in space. Use of solid-state detectors is increasing for space-based scientific observation of the earth and in astronomy. Many detectors require cooling to reduce background noise and damage from the radiation environment in space, with target temperatures anywhere from 270°K down to 100°K or lower. A passive radiator system is a desirable choice for detector cooling, but parasitic thermal loads from the earth, sun and nearby surfaces are a design challenge, especially at lower detector system temperatures. Conical or trapezoidal geometries are often used for shades against direct solar and earth thermal radiation. The Compound Parabolic (CP) geometry, originally developed for non-imaging concentrators of low-level electromagnetic radiation, may also be used as a near-optimal shade for a cold radiator.

A large telescope aperture, stringent thermal stability and temperature range requirements, and a passively-cooled 150°K module presented major challenges in thermal design and hardware fabrication of this Small Explorer satellite. This paper reviews briefly the thermal design of the SWAS science instrument, and examines the first three months of on-orbit thermal history. Measured temperatures for both the science payload and the spacecraft module and solar arrays are compared with those predicted by the correlated analytical model. Similarities and differences are interpreted in terms of the major uncertainties remaining after thermal-balance testing, especially those of MLI performance and telescope aperture properties. Review of the thermal model adequacy and thermal design verification are included to suggest improvements in the thermal design process for future missions.