The A-Train consists of four satellites, with another two failed (Glory and OCO), and one no longer in the constellation (PARASOL).
The A-train (from Afternoon Train) is a satellite constellation of four French and American Earth observation satellites in sun-synchronous orbit at an altitude of 690 kilometers above the Earth.
The orbit, at an inclination of 98.14°, crosses the equator each day at around 1:30 pm solar time, giving the constellation its name; the "A" stands for "afternoon;" and crosses the equator again on the night side of the Earth, at around 1:30 am.
They are spaced a few minutes apart from each other so their collective observations may be used to build high-definition three-dimensional images of the Earth's atmosphere and surface.
The train currently consists of five active satellites:
- GCOM-W1 (SHIZUKU), lead spacecraft in formation, launched by JAXA on May 18, 2012
- Aqua, runs 4 minutes behind GCOM-W1, launched by NASA on May 4, 2002
- CloudSat, a cooperative effort between NASA and the Canadian Space Agency, runs 2 minutes and 30 seconds behind Aqua, launched with CALIPSO on April 28, 2006
- CALIPSO, a joint effort of CNES and NASA, follows CloudSat by no more than 15 seconds, launched on April 28, 2006
- Aura, a multi-national satellite, lags Aqua by 15 minutes, crossing the equator 8 minutes behind due to different orbital track to allow for synergy with Aqua, launched by NASA on July 15, 2004
- PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar'), launched by CNES on December 18, 2004; moved to other (lower) orbit on 2 December 2009
- OCO, destroyed by a launch vehicle failure on February 24, 2009, and would have preceded Aqua by 15 minutes
- Glory, failed during launch on a Taurus XL rocket on March 4, 2011, and would have flown between CALIPSO and Aura
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