SUSIM NASA sponsors two Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) instruments in the SUSIM program at NRL. Each measures the absolute irradiance of the solar ultraviolet (UV) light in the 115- to 410-nm wavelength range. The SUSIM ATLAS instrument has flown repeatedly on the space shuttle. The SUSIM UARS instrument has taken data aboard the Upper Atmosphere Research Satellite (UARS) since October 1991.