Aqua (satellite)

Aqua (EOS PM-1) is a multi-national NASA scientific research satellite in orbit around the Earth, studying the precipitation, evaporation, and cycling of water. It is the second major component of the Earth Observing System (EOS) preceded by Terra (launched 1999) and followed by Aura (launched 2004).

The name "Aqua" comes from the Latin word for water. The satellite was launched from Vandenberg Air Force Base on May 4, 2002, aboard a Delta II rocket. Aqua is on a Sun-synchronous orbit. It flies as the second in the satellite formation called the "A Train" with several other satellites (Aura, CALIPSO, CloudSat, OCO-2, the French PARASOL, and the Japanese GCOM W1).

Instruments
Aqua carries six instruments for studies of water on the Earth's surface and in the atmosphere:
 * AMSR-E — Advanced Microwave Scanning Radiometer-EOS — measures cloud properties, sea surface temperature, near-surface wind speed, radiative energy flux, surface water, ice and snow. Furnished by the National Space Development Agency of Japan.
 * MODIS — Moderate Resolution Imaging Spectroradiometer, also measures cloud properties and radiative energy flux, also aerosol properties; land cover and land use change, fires and volcanoes.  This instrument is also aboard Terra.
 * AMSU-A — Advanced Microwave Sounding Unit — measures atmospheric temperature and humidity.
 * AIRS — Atmospheric Infrared Sounder — measures atmospheric temperature and humidity, land and sea surface temperatures.
 * HSB — Humidity Sounder for Brazil — VHF band equipment measuring atmospheric humidity. Furnished by Instituto Nacional de Pesquisas Espaciais of Brazil. The HSB instrument has been in survival mode since 2/5/2003.
 * CERES — Clouds and the Earth's Radiant Energy System, Flying Models 3 and 4, measure broadband radiative energy flux.

The Aqua spacecraft has a mass of about 2850 kg, plus propellant of about 230 kg (at launch). Stowed, the satellite is 2.68 m x 2.49 m x 6.49 m. Deployed, Aqua is 4.81 m x 16.70 m x 8.04 m.