The SIM spectrometer that provides the first long-duration solar spectral irradiance measurements in the visible and near infrared (Vis/NIR).

The TSIS TIM is a heritage instrument of currently flying SORCE TIM. The TIM will measure the total solar irradiance (TSI), the spatially and spectrally integrated solar radiation incident at the top of the Earth’s atmosphere. Using electrical substitution radiometers (ESRs) and taking advantage of new materials and modern electronics, the TIM measures TSI to an estimated absolute accuracy of 100 ppm (0.01%).

NASA funded NRL to develop two Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) instruments. Each measures the absolute irradiance of the solar ultraviolet (UV) light in the 115- to 410-nm wavelength range. The ATLAS/SUSIM instrument flew repeatedly on the space shuttle. The UARS/SUSIM instrument was aboard the Upper Atmosphere Research Satellite (UARS) in October 1991 to August 2005.

The first SOLSTICE instrument flew aboard NASA's Upper Atmosphere Research Satellite (UARS) and was an ultraviolet spectrometer that measured the Sun’s ultraviolet (UV) energy in three channels. Scientists calibrated the instrument by looking at stars during the nighttime portion of the UARS orbit. During the daylight portion of the orbit, SOLSTICE measured the solar spectral irradiance of the total solar disk in UV wavelengths from 115 to 430 nanometers.

A series of Active Cavity Radiometers (ACRs) were developed for TSI measurement at the Jet Propulsion Laboratory (JPL) of the California Institute of Technology under the direction of ACRIM Principal Investigator, Dr. Richard C. Willson. Their use in a series of Active Cavity Radiometer Irradiance Monitor (ACRIM) space flight experiments has provided a TSI database during more than 90 % of its 34 year history, covering three solar cycles since 1978.