NASA Logo, National Aeronautics and Space Administration

The Afternoon Constellation

The Afternoon Constellation - A-Train

What is the A-Train?


Afternoon Constellation The Afternoon Constellation
web view | hi-resolution

The changing Earth environment is increasingly a focus of many societal concerns. Sound policy decisions are needed to address these issues. From their vantage point high above the Earth’s surface, NASA’s Earth observing satellite missions are uniquely positioned to obtain comprehensive global observations of our home planet. NASA’s Earth Science Division shares these Earth Science data with various federal, state, local, and tribal partners, who incorporate the data into various models, databases, and other tools linked to a variety of practical applications for society.  Policy makers use these decision tools to help them craft sound and equitable environmental policy.

Satellite constellations are groups of satellites that fly in close proximity to each other in a carefully planned formation that allows for synergy between the missions—synergy means that more information about the condition of the Earth is obtained from the combined observations than would be possible from the sum of the observations taken independently.

The Afternoon1 Constellation, or A-Train2, is one such satellite constellation whose members all have equator crossings in the early afternoon at about 1:30 p.m. (and also in the middle of the night, at about 1:30 a.m.). At the present time, the A-Train consists of five NASA missions and a Japan Aerospace Exploration Agency (JAXA) mission flying in close proximity to one another. PARASOL — a French Centre National d’Etudes Spatiales (CNES) mission — fully exited the A-Train and ceased operation on December 18, 2013. See Table 1 for a complete list of current and past missions.

Take the A-Train to Scientific Discovery

At present five NASA missions are part of the A-Train. This includes Aqua (launched in 2002), Aura (launched in 2004), the second Orbiting Carbon Observatory (OCO-2, launched in July 2014), and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat (both launched together in 2006). In addition, there is a Japanese mission (launched in 2012) named the Global Change Observation Mission-Water (GCOM-W1). The French mission named the Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar (PARASOL) fully exited the A-Train and ceased observation on December 18, 2013.

Each one of these missions has its own objectives and makes its own unique contribution to improving our understanding of aspects of the Earth’s climate. The real advantage of constellation flying, however, is that the data from the various satellites are synergistic and can be combined together to allow for even more comprehensive studies of climate.

> Take a tour of the A-Train

Satellite Summary of Instruments Launch Date Responsible Organization
Aqua A synergistic instrument package measuring at visible, infrared, and microwave frequencies allows comprehensive studies of water in the Earth/atmosphere system, including its solid, liquid and gaseous forms, plus studies of vegetation, both on the land and in the ocean. AMSR-E, AIRS, AMSU-A, HSB, CERES, MODIS May 4, 2002 NASA/GSFC
Aura Observations from limb sounding and nadir imaging allow studies of the horizontal and vertical distribution of key atmospheric pollutants and greenhouse gases and how these distributions evolve and change with time. HDRLS, MLS, TES, OMI July 15, 2004 NASA/GSFC
CALIPSO Observations from space-borne lidar, combined with passive imagery, will lead to improved understanding of the role aerosols and clouds play in regulating the Earth’s climate. CALLIOP, IIR, WFC April 28, 2006> NASA/GSFC, NASA/LaRC, CNES
CloudSat Cloud Profiling Radar will allow for the most detailed study of clouds to date and should better characterize the role clouds play in regulating the Earth’s climate. CPR April 28, 2006 NASA/GSFC, NASA/JPL
GCOM-W1 Observations of water circulation changes. Specifically it will observe precipitation, vapor amounts, wind velocity above the ocean, sea water temperature, water levels on land areas, and snow depths. AMSR2 May 18, 2012 JAXA
OCO-2 Three grating spectrometers will make global, space-based observations of the column-integrated concentration of CO2, a critical greenhouse gas. Three grating spectrometers July 2, 2014 NASA/GSFC NASA/JPL
PARASOL Polarized light measurements will allow better characterization of clouds and aerosols in the Earth’s atmosphere. PARASOL fully exited the A-Train and ceased operation on December 18, 2013. POLDER December 18, 2004 CNES

1 This is in contrast to the Morning Constellation, whose members all have equator crossings in the late morning around 10:30 a.m. (and late evening, at about 10:30 p.m.)  The morning constellation presently consists of Terra, Landsat-7, SAC-C and the New Millennium Program’s Earth Observing-1 (EO-1).

2 The term “A-Train” comes from an old jazz tune, Take the A-Train, composed by Billy Strayhorn and made popular by Duke Ellington’s band, and has become a popular nickname for the Afternoon Constellation, particularly since EOS Aqua and Aura are both part of the formation.

A-Train Fact