Cryogenic Shutter
Electrically actuated shutter designed to operate many thousands of time at cryogenic temperatures. Open shutter allows light at wavelenghts between 1 and 300 micrometers to enter instrument measures background cosmic radiation. Closed shutter blocks outside radiation from instrument and positions mirror to reflect light from internal source to instrument calibrated. Designed, if power failure occurs, shutter remains in or assumes open position so measurements continue without calibration.
Tyler, Allen↗