3 November 1980 Baffle Design For Earth Radiation Rejection In The Cryogenic Limb-Scanning Interferometer/Radiometer
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The Cryogenic Limb-Scanning Interferometer/Radiometer (CLIR) is being developed to observe infrared emissions of the earth's upper atmosphere from space. The earth's surface is an extended source of intense background radiation with a small angular separation from the desired scene. The CLIR employs an off-axis Gregorian Telescope whose primary mirror and baffles are cooled by an open-cycle cryogen system. A system of specular annular baffles has been developed to minimize both stray light problems and cryogen consumption by retro-mapping the aperture into itself. Each off-axis ray which enters the aperture and strikes the specular baffle surface is reflected so that it passes out of the aperture and is not absorbed on a cryogenic surface. The specular baffle which lies closest to the aperture is an ellipsoid whose foci trace out the circular aperture on revolution about the axis. Its theoretical "ray trace" efficiency is 100 percent. A subsequent baffle has an elliptical cross section whose near focus traces out the central hole in the ellip-soidal baffle and whose far focus traces out the aperture. Its theoretical efficiency is about 90 percent. These baffles reduce the earth radiation heat load on the cryogenic cooler by an order of magnitude,changing it from the dominant cause of cryogen consumption to a relatively small effect. An aperture shield is also desirable to reduce cryogen consumption, stray light, and contamination.
© (1980) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
James C. Bremer, James C. Bremer, "Baffle Design For Earth Radiation Rejection In The Cryogenic Limb-Scanning Interferometer/Radiometer", Proc. SPIE 0245, Cryogenically Cooled Sensor Technology, (3 November 1980); doi: 10.1117/12.959333; https://doi.org/10.1117/12.959333


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