Terra (satellite)
Terra is a multi-national scientific research satellite operated by NASA in a Sun-synchronous orbit around the Earth. It takes simultaneous measurements of Earth's atmosphere, land, and water to understand how Earth is changing and to identify the consequences for life on Earth. It is the flagship of the Earth Observing System and the first satellite of the system which was followed by Aqua and Aura. Terra was launched in 1999.
The name "Terra" comes from the Latin word for Earth. A naming contest was held by NASA among U.S. high school students. The winning essay was submitted by Sasha Jones of Brentwood, Missouri. The identifier "AM-1" refers to its orbit, passing over the equator in the morning.
Launch
The satellite was launched from Vandenberg Air Force Base on December 18th, 1999, aboard an Atlas IIAS vehicle and began collecting data on February 24th, 2000. It was placed into a near-polar, sun-synchronous orbit at an altitude of, with a 10:30am descending node.Instruments
Terra carries a payload of five remote sensors designed to monitor the state of Earth's environment and ongoing changes in its climate system:- ASTER ASTER creates high-resolution images of clouds, ice, water and the land surface using 3 different sensor subsystems. They are the Shortwave Infrared ; Thermal Infrared ; and Visible and Near Infrared. They cover 14 multi-spectral bands from visible to the thermal infrared. The SWIR stopped working in 2008. ASTER was provided by Japan's Ministry of Economy, Trade, and Industry.
- CERES
- MISR
- MODIS
- MOPITT
Operations
After launch, operators observed that high energy protons like those found over the South Atlantic Anomaly or the poles could induce single-event upsets that would cause the Motor Drive Assembly Built-In Test Equipment to turn off the MDA. These false shut-downs occur 12–14 times a month and eventually the operations team automated the recovery to reduce the impact of these shut-downs.Starting in 2007, increased thermal resistance in the SWIR cryocooler of the ASTER instrument caused the temperature to gradually increase. By 2008, despite frequent attempts to recycle the cryocooler the data began to significantly degrade and on January 12, 2009, ASTER managers declared the SWIR no longer functional due to anomalously high SWIR detector temperatures. Data gathered after April 2008 was declared not usable.
On October 13, 2009, Terra suffered a single battery cell failure anomaly and a battery heater control anomaly likely the result of a Micrometeoroid or Orbital Debris strike.
On February 27, 2020, the Terra flight operations team conducted Terra's last inclination adjust maneuver due to the satellite's limited remaining fuel. With no more such maneuvers, Terra's mean local time has begun to drift starting in April 2021 and with it, its data quality. In October 2022, Terra is expected to reach and exceed a 10:15 AM MLT crossing which is expected to lead operators to initiate a constellation exit to a lower orbit altitude. Decommissioning began with the deactivation of the MOPITT instrument on April 2025. It will be eventually followed by an un-controlled reentry several years later.