The 2.4 meter aperture Large Space Telescope to be flown by the National Aeronautics and Space Administration in 1982 will include a far IR spectrophotometer which will operate from 2 to 1000 microns. The sensitivity of the instrument will be limited by the statistical fluctuations of the photons readiated by the primary, secondary, and asso-ciated relay optics over a large portion of the spectrum. To maintain the required sensitivity the detectors within the instrument must be cooled to 2 deg K as are the optical filters and some of the relay optics. At the long wavelengths diffraction effects within the relay optics must be included in the analysis because the optics dimensions are comparable to the Airy disc dimensions. The radiometer has been designed to minimize modulation noise resulting from a symmetrical imaging and non uniform background flux distribution.
J. G. Thunen,
W. H. Alff,
"Optical Design Considerations For A Far Infrared Spectrophotometer", Proc. SPIE 0067, Long-Wavelength Infrared, (10 November 1975); doi: 10.1117/12.954535; https://doi.org/10.1117/12.954535