On-orbit performance of deuterium calibration lamps during four years of SUSIM operations on the UARS

The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) on the Upper Atmospheric Research Satellite (UARS) carries four deuterium discharge lamps to assist in tracking inflight degradation of the instrument in the spectral range between 115 nm and 410 nm. The lamps have been in orbit since the launch of UARS on 12 September 1991. In this paper we discuss the performance of the two most-used lamps during the first four years of the UARS mission, and offer recommendations for improving the ability of the lamps to track inflight degradation in future space instruments.