Stray-light issues for background-limited far-infrared telescope operation

The detector in a background-limited infrared telescope receives less power due to the thermal emission from telescope components than from the background. The Arizona Program for the Analysis of Radiation Transfer has been used to set the temperature of the telescope components so that each component contributes less than 10-13 W of thermal power to the detector in the Space Infrared Telescope Facility long-wavelength configuration. The secondary mirror assembly, seen from the detector, is the most critical emitter even at 3 K.