NIRCam cryo filter wheel assembly design and performance

The filter wheel assembly (FWA) is an integral and important sub-system of the Near Infrared Camera (NIRCam) instrument on the James Webb Space Telescope (JWST). The optic elements in each of the four FWA mechanisms on NIRCam are used to conduct science operations as well as calibration of the NIRCam instrument and the JWST observatory. The FWA mechanism can position one of 12 different filters in the optical path of the camera and position one of 12 different pupil optics in the same path. The filters and pupil optics are mounted in two separate wheel assemblies in the FWA that can be positioned independently to provide the desired optical configuration for imaging. Along with the rest of the instrument, the FWA operates at cryogenic temperatures and is used for both short and long wavelength imaging. This paper reviews significant elements of the FWA mechanism design.