The "A-Train" is a NASA satellite formation consisting of seven satellites flying in close proximity: Aqua, Aura, CloudSAT, CALIPSO, PARASOL, OCO, and Glory.

Aqua carries six state-of-the-art instruments in a near-polar low-Earth orbit. The six instruments are the Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU-A), the Humidity Sounder for Brazil (HSB), the Advanced Microwave Scanning Radiometer for EOS (AMSR-E), the Moderate Resolution Imaging Spectroradiometer (MODIS), and Clouds and the Earth's Radiant Energy System (CERES). Each has unique characteristics and capabilities, and all six serve together to form a powerful package for Earth observations.

Aura (Latin for breeze) was launched July 15, 2004. The design life is five years with an operational goal of six years. Aura flies in formation about 15 minutes behind Aqua. Aura is part of the Earth Observing System (EOS), a program dedicated to monitoring the complex interactions that affect the globe using NASA satellites and data systems.

CALIPSO is a joint U.S. (NASA)/French (Centre National d’Etudes Spatiales/CNES) mission. Observations from spaceborne lidar, combined with passive imagery, will lead to improved understanding of the role aerosols and clouds play in regulating the Earth’s climate, in particular, how aerosols and clouds interact with one another.

CloudSAT, a cooperative mission with Canada, uses advanced radar to "slice" through clouds to see their vertical structure, providing a completely new observational capability from space. CloudSAT will look at the structure, composition, and effects of clouds and is one of the first satellites to study clouds on a global basis.

Glory’s remote sensing mission is designed to collect data on the optical, microphysical, and chemical properties, and spatial and temporal distributions of aerosols and clouds and to continue the long-term total solar irradiance climate record.

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The Orbiting Carbon Observatory (OCO) provides space-based observations of atmospheric carbon dioxide (CO2), the principal anthropogenic driver of climate change. This mission uses mature technologies to address NASA's carbon cycle measurement requirement. OCO generates the knowledge needed to improve projections of future atmospheric CO2.

The Orbview-2 (aka SeaStar) spacecraft, developed by Orbital Sciences Corporation, carries the SeaWiFS instrument and was launched to low Earth orbit on board an extended Pegasus launch vehicle on August 1, 1997. The purpose of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project is to provide useful data on ocean color to the Earth science community. Subtle changes in ocean color indicate various types and numbers of marine phytoplankton (microscopic marine plants), knowing this information can have both scientific and practical uses.

PARASOL (Polarization and Anisotropy of Réflectances for Atmospheric Sciences coupled with Observations from a Lidar) is a French's CNES microsatellite project. Its main purpose is to improve the characterization of the clouds and aerosols microphysical and radiative properties, needed to understand and model the radiative impact of clouds and aerosols.

QuickBird was manufactured by Ball Aerospace and launched in October 2001. It collects high resolution imagery - panchromatic (black & white) imagery at 60-70 centimeter resolution and multispectral imagery at 2.4- and 2.8-meter resolutions.

The Solar Radiation and Climate Experiment (SORCE) is a NASA-sponsored satellite mission that is providing state-of-the-art measurements of incoming x-ray, ultraviolet, visible, near-infrared, and total solar radiation.

The Terra (formerly called EOS AM-1) satellite is the flagship of NASA’s Earth Science Missions. Terra is the first EOS (Earth Observing System) platform and provides global data on the state of the atmosphere, land, and oceans, as well as their interactions with solar radiation and with one another.

The Tropical Rainfall Measuring Mission (TRMM), is the first mission dedicated to measuring tropical and subtropical rainfall through microwave and visible infrared sensors, and includes the first spaceborne rain radar.