The CALIPSO minisatellite—a spacecraft in the 500-kg class—scans the skies daily to locate cloud layers and aerosols, measure their altitude and ascertain their optical properties in order to better understand how they affect Earth’s climate. Climatologists have long known that clouds and aerosols play a key role in climate mechanisms, but they are yet to work out exactly how. To accomplish its mission, CALIPSO is equipped with a lidar and telescope (a lidar is an instrument able to locate and analyse objects by bouncing a laser beam off them), a camera and an infrared imager. CALIPSO is also part of the A-Train, a constellation of Earth-orbiting satellites trailing one another by a few minutes.

CALIPSO is a joint CNES-NASA mission. CNES was responsible for the satellite and spacecraft bus (designed under contract with Alcatel) and the infrared imager (designed with Sodern), while NASA is leading the mission and supplied the payload and launch vehicle. Initially scheduled to end in 2011, the mission was extended to the end of 2023.