(ACRIMSAT) Active Cavity Radiometer Irradiance Monitor Satellite

ACRIMSAT is a satellite mission designed to measure the total solar irradiance, or the amount of energy received from the Sun at the Earth's surface. The satellite is equipped with an Active Cavity Radiometer, which is a highly precise instrument that can measure the total solar irradiance with great accuracy. The data collected by ACRIMSAT is used to study the Sun's variability and its impact on the Earth's climate and weather patterns. The mission was launched in 1999 and operated until 2014, providing valuable information about the Sun and its role in the Earth's climate system.

https://en.wikipedia.org/wiki/ACRIMSAT