On-Board Calibration Monitor For Tracking Instrument Sensitivity

The On-board Calibration Monitor (OCM) is being developed as an integral component of the ACCESS instrument(1) and as a, pathfinder for other missions. It provides stable full-aperture illumination of the telescope for tracking the instrument sensitivity as a function of time. The light source is composed of an ensemble of LED pairs with central wavelengths that span the spectral range of the instrument and illuminate a diffuser that is observed by the full optical path. Feedback stabilization of the light source intensity is achieved by photodiode monitoring of each LED. This stable source will provide real time knowledge of the ACCESS sensitivity throughout the 5-year duration of the program. The present status of the design and laboratory evaluation of the OCM system will be presented.