Stray Light field dependence for the James Webb Space Telescope

The James Webb Space Telescope (JWST) is a large space based astronomical telescope that will operate at cryogenic temperatures. The architecture has the telescope exposed to space, with a large sun shield providing thermal isolation and protection from direct illumination from the sun. The instruments will have the capability to observe over a spectral range from 0.6 m to 29 m wavelengths. Stray light analysis has been performed to characterize the stray light getting to the instrument focal planes from the celestial sky. A Radiance Transfer Function (RTF) is defined for the susceptibility of the stray light to sky radiance at locations relative to the observatory frame of reference. The stray light is calculated by overlaying the radiance maps of the celestial sky background (both galactic and zodiacal background) onto the RTF map. The product of the two is summed to obtain the total stray light background at the instrument detectors. The orientation of the observatory for observing a given field location in the sky depends on the direction of the sun, hence the day of the year. The variability of stray light with time of year for observing a given sky locations is determined.