The A-train (from Afternoon Train) is a

satellite constellation A satellite constellation is a group of artificial satellites working together as a system. Unlike a single satellite, a constellation can provide permanent global or near-global pass (spaceflight), coverage, such that at any time everywhere on E ...

of four

Earth observation satellite An Earth observation satellite or Earth remote sensing satellite is a satellite used or designed for Earth observation (EO) from orbit, including spy satellites and similar ones intended for non-military uses such as environmental monitoring, me ...

s of varied nationality in

Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

at an

altitude Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...

that is slightly variable for each satellite. The orbit, at an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

of 98.14°, crosses the equator each day at around 1:30 pm

solar time Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Traditionally, there are three types of time reckoning based ...

, 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

minute A minute is a unit of time defined as equal to 60 seconds. It is not a unit in the International System of Units (SI), but is accepted for use with SI. The SI symbol for minutes is min (without a dot). The prime symbol is also sometimes used i ...

s apart from each other so their collective observations may be used to build high-definition

three-dimensional In geometry, a three-dimensional space (3D space, 3-space or, rarely, tri-dimensional space) is a mathematical space in which three values (''coordinates'') are required to determine the position (geometry), position of a point (geometry), poi ...

images of

Earth's atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...

and surface.

Satellites

Active

A-Train and C-Train constellations - 2019-09

The train, , consists of three active satellites: *

OCO-2 Orbiting Carbon Observatory-2 (OCO-2) is an American environmental science satellite which launched on 2 July 2014. A NASA mission, it is a replacement for the Orbiting Carbon Observatory which was lost in a launch failure in 2009. It is the seco ...

, lead spacecraft in formation, replaces the failed OCO and was launched for

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

on July 2, 2014. * GCOM-W1 "SHIZUKU", follows OCO-2 by 11 minutes, launched by

JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...

on May 18, 2012. * Aura, a multi-national satellite, lags OCO-2 by 19 minutes, launched for NASA on July 15, 2004.

Past

PARASOL An umbrella or parasol is a folding canopy (building), canopy supported by wooden or metal ribs that is mounted on a wooden, metal, or plastic pole. It is usually designed to protect a person against rain. The term ''umbrella'' is traditionall ...

, launched by CNES on December 18, 2004 and moved to another (lower) orbit on December 2, 2009. PARASOL was deactivated in 2013 *

CloudSat CloudSat is a Passivated NASA Earth observation satellite, which was launched on a Delta II rocket on April 28, 2006, and is awaiting disposal. It used radar to measure the altitude and properties of clouds, adding to the information on the relat ...

, launched with CALIPSO on April 28, 2006 and moved to another (lower) orbit on February 22, 2018. Now part of the C-train. *

CALIPSO CALIPSO was a joint NASA (US) and CNES (France) environmental satellite, built in the Cannes Mandelieu Space Center, which was launched atop a Delta II rocket on April 28, 2006. Its name stands for Cloud-Aerosol Lidar and Infrared Pathfinder Sa ...

, launched on April 28, 2006, is a joint effort of

CNES CNES () is the French national space agency. Headquartered in central Paris, the agency is overseen by the ministries of the Armed Forces, Economy and Finance and Higher Education, Research and Innovation. It operates from the Toulouse Spac ...

and NASA. It follows CloudSat by no more than 8.5 seconds. CALIPSO was moved to CloudSat's new orbit in September 2018. It was then part of the C-train with Cloudsat until it was officially decommissioned on August 1, 2023. *

Aqua Aqua is the Latin word for water. As such, it is often used in many words which relate to water, such as aquatic life. In English, it may also refer to: Arts * Aqua (color), a greenish-blue color Business * Aqua (Chicago), an 82-story resid ...

, used to run 4 minutes behind GCOM-W1, launched for

on May 4, 2002. In January 2022, it descended from the A-Train to save fuel and now is in a free-drift mode, wherein its equatorial crossing time is slowly drifting to later times.

Failed

OCO Oco, OCO or O.C.O may refer to: * OCO (video game), a 2D minimalistic platform indie game * Oco, a town in Navarre, Spain * Oco, Ávila, a town in Ávila province, Spain * O.co Coliseum in Oakland, California, United States * Old Cornish language ...

, destroyed by a launch vehicle failure on February 24, 2009, and was replaced by OCO-2. * Glory,Glory homepage
failed during launch on a Taurus XL rocket on March 4, 2011, and would have flown between CALIPSO and Aura.

References

External links

NASA A-Train Portal

NASA satellite program impacted

NASA Program Page

Orbital Sciences Program Page
* {{DEFAULTSORT:A-Train (Satellite Constellation) Earth observation satellites Satellite constellations