A group of Earth-observing satellites operated by NASA and its international partners that closely follow one after another along the same orbital ‘track’. The satellites are in a polar orbit, crossing the equator northbound at 1:30 pm local time, within seconds to minutes of each other, allowing near-simultaneous observations of the Earth for the benefit of society. Popularly known as the A-Train, five satellites currently fly in the constellation: Orbiting Carbon Observatory-2 (OCO-2), Global Change Observation Mission–Water (GCOM-W1), Aqua, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and Aura. Its CloudSat, Glory, and PARASOL satellites have either exited the constellation or ceased operations.

Artist’s concept of the Afternoon Constellation (A-Train) of satellites.

Credit: NASA