SIM meaning in Space Science ?

The Solar Radiation and Climate Experiment (SORCE) was a NASA-sponsored satellite mission that measured incoming X-ray, ultraviolet, visible, near-infrared, and total solar radiation. These measurements specifically addressed long-term climate change, natural variability, atmospheric ozone, and UV-B radiation, enhancing climate prediction. These measurements are critical to studies of the Sun, its effect on our Earth system, and its influence on humankind. SORCE was launched on 25 January 2003 on a Pegasus XL launch vehicle to provide NASA's Earth Science Enterprise (ESE) with precise measurements of solar radiation.

SORCE measured the Sun's output using radiometers, spectrometers, photodiodes, detectors, and bolometers mounted on a satellite observatory orbiting the Earth. Spectral measurements identify the irradiance of the Sun by characterizing the Sun's energy and emissions in the form of color that can then be translated into quantities and elements of matter. Data obtained by SORCE can be used to model the Sun's output and to explain and predict the effect of the Sun's radiation on the Earth's atmosphere and climate.

Flying in a 645 km (401 mi) orbit at a 40.0° inclination, SORCE was operated by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, Colorado. It continued the precise measurements of total solar irradiance that began with the ERB instrument in 1979 and extended to the 21st century with the ACRIM series of measurements. SORCE provided measurements of the solar spectral irradiance from 1 to 2000 nm, accounting for 95% of the spectral contribution to the total solar irradiance.