The A-train (from Afternoon Train) is a satellite constellation of five Earth observation satellites of varied nationality in sun-synchronous orbit at an altitude of 705 km (438 mi) 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.
- OCO-2, lead spacecraft in formation, replaces the failed OCO and was launched for NASA on July 2, 2014.
- GCOM-W1 "SHIZUKU", follows OCO-2 by 11 minutes, launched by JAXA on May 18, 2012.
- Aqua, runs 4 minutes behind GCOM-W1, launched for NASA on May 4, 2002.
- 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 for NASA on July 15, 2004.
- PARASOL, launched by CNES on December 18, 2004 and moved to another (lower) orbit on December 2, 2009.
- CloudSat, launched with CALIPSO on April 28, 2006 and moved to another (lower) orbit on February 22, 2018.
- CALIPSO, launched on April 28, 2006, is a joint effort of CNES and NASA. It follows CloudSat by no more than 8.5 seconds. CALIPSO was moved to CloudSat's new orbit in September 2018.
- OCO, destroyed by a launch vehicle failure on February 24, 2009, and was replaced by OCO-2.
- Glory, failed during launch on a Taurus XL rocket on March 4, 2011, and would have flown between CALIPSO and Aura.
- «A-train Symposium October 2007: Constellation keeps its promises», CNESMAG, January 2008
- NASA, Introducing the A-Train, 10.26.10 (accessed April 30 2012)
- "Individual A-Train Missions". June 5, 2012. Retrieved 2013-11-15.
- Greicius, Tony (2018-02-23). "CloudSat Exits the "A-Train"". NASA. Retrieved 2018-04-01.
- CNES News on Calipso
- Sister Satellites, Briefly Separated, Working Together Again
- OCO homepage
- Media Briefing Scheduled To Discuss Orbiting Carbon Observatory Mission
- Glory homepage Archived 2008-09-16 at the Wayback Machine
- NASA A-Train Portal
- NASA satellite program impacted
- NASA Program Page
- Orbital Sciences Program Page
- L'Ecuyer, T.S.; Jiang, J.H. (2010). "Touring the atmosphere aboard the A-Train". Physics Today. 63 (7): 36–41. Bibcode:2010PhT....63g..36L. doi:10.1063/1.3463626. Archived from the original on 2013-02-24.