ACRIMSAT is a small satellite mission to monitor the amount of total solar energy input to Earth. Its objective is to monitor the solar constant, or TSI (Total Solar Irradiation), with maximum precision and provide a long-term TSI data record. ACRIMSAT is part of a multi-decade effort to understand variations in the sun's output and resulting effects on Earth.

The Active Cavity Radiometer Irradiance Monitor instrument-3 (ACRIM-3) was built by Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, under contract with NASA.