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 coverage, such that at any time everywhere on Earth at least one s ...

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, ...

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 or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

of 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 Ea ...

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. Two types of solar time are apparent solar time (sundial ti ...

, 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 The minute is a unit of time usually equal to (the first sexagesimal fraction) of an hour, or 60 seconds. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds (there is a provision to insert a neg ...

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

three-dimensional Three-dimensional space (also: 3D space, 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called '' parameters'') are required to determine the position of an element (i.e., point). This is the inform ...

images of

Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...

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 agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

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 Aura most commonly refers to: * Aura (paranormal), a field of luminous multicolored radiation around a person or object * Aura (symptom), a symptom experienced before a migraine or seizure Aura may also refer to: Places Extraterrestrial * 1488 ...

, 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 usually mounted on a wooden, metal, or plastic pole. It is designed to protect a person against rain or sunburn, sunlight. The term ''umbr ...

, launched by CNES on December 18, 2004 and moved to another (lower) orbit on December 2, 2009. PARASOL was deactivated in 2013 * CloudSat, 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 is a joint NASA (USA) 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 Sat ...

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

CNES The (CNES; French: ''Centre national d'études spatiales'') is the French government space agency (administratively, a "public administration with industrial and commercial purpose"). Its headquarters are located in central Paris and it is und ...

and NASA. It follows CloudSat by no more than 8.5 seconds. CALIPSO was moved to CloudSat's new orbit in September 2018. Now part of the C-train. * Aqua, 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, 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