Sister Satellites, Briefly Separated, Working Together Again

Sept. 28, 2018, 8 a.m.

Project: CALIPSO

In February 2018, facing a mechanical challenge, CloudSat had to exit the A-Train, or afternoon constellation, of Earth-orbiting satellites, and move to a lower orbit. Following an exit maneuver of its own in September, CALIPSO has joined CloudSat, forming what NASA scientists are calling the C-Train � C being the first letter of each satellite.

CALIPSO began its exit from the A-Train Sept. 13 and entered its new orbit Sept. 20. The C-Train orbit is approximately 428 miles (688 kilometers) above the Earth's surface. It'll take some time to get the satellites in phase with one another and they'll be a little farther apart than they once were � about 60 seconds. But once they're completely settled in � likely in late October � they'll continue to provide indispensable, complementary views of clouds and aerosols for what scientists hope will be another two years or more.

CloudSat and CALIPSO are known as "active" sensors because they direct beams of energy at the Earth (Radio wave signals in the case of CloudSat and laser light in the case of CALIPSO) and measure how these beams reflect from the clouds and aerosols in the atmosphere. Other orbiting science instruments use "passive" sensors that rely on collecting reflected sunlight or radiation emitted from the Earth or clouds to make measurements.

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