A-train (satellite constellation)

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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.[1]

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;"[2] 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, as of June 2012,[3] 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'),[4] launched by CNES on December 18, 2004; moved to other (lower) orbit on 2 December 2009[5]


  • OCO,[6] destroyed by a launch vehicle failure on February 24, 2009,[7] and would have preceded Aqua by 15 minutes
  • Glory,[8] failed during launch on a Taurus XL rocket on March 4, 2011, and would have flown between CALIPSO and Aura


  1. ^ «A-train Symposium October 2007: Constellation keeps its promises», CNESMAG, January 2008
  2. ^ NASA, Introducing the A-Train, 10.26.10 (accessed April 30 2012)
  3. ^ "Individual A-Train Missions". June 5, 2012. Retrieved 2013-11-15. 
  4. ^ PARASOL page (accessed 30 April 2012)
  5. ^ CNES News on Calipso
  6. ^ OCO homepage
  7. ^ Media Briefing Scheduled To Discuss Orbiting Carbon Observatory Mission
  8. ^ Glory homepage

External links[edit]