Terra (satellite)

For other uses, see Terra.

Terra (EOS AM-1) 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.^[1] It is the flagship of the Earth Observing System (EOS) and the first satellite of the system which was followed by Aqua (launched in 2002) and Aura (launched in 2004). Terra was launched in 1999.

Terra

Artistic rendering of the Terra satellite
Names	EOS AM-1
Mission type	Climate research
Operator	NASA
COSPAR ID	1999-068A
SATCAT no.	25994
Website	terra.nasa.gov
Mission duration	Elapsed: 24 years, 10 months, 25 days
Spacecraft properties
Manufacturer	NASA
Launch mass	4,864 kilograms (10,723 lb)
Start of mission
Launch date	December 18, 1999, 18:57:39 (1999-12-18UTC18:57:39Z) UTC
Rocket	Atlas IIAS AC-141
Launch site	Vandenberg SLC-3E
Contractor	ILS
End of mission
Disposal	Deorbited
Last contact	2025-2026 (planned)
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Semi-major axis	7,080.0 kilometers (4,399.3 mi)
Eccentricity	0.0001392
Perigee altitude	708.7 kilometers (440.4 mi)
Apogee altitude	710.6 kilometers (441.5 mi)
Inclination	98.2098°
Period	98.8 minutes
RAAN	251.3130 degrees
Argument of perigee	83.7699 degrees
Mean anomaly	276.3654 degrees
Mean motion	14.57110250
Epoch	25 June 2016, 02:58:27 UTC
Revolution no.	87867
Large Strategic Science Missions Earth Science Division Aqua → Earth Observing System ← QuikSCAT Earth Observing-1 →

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 705 km (438 mi), with a 10:30am descending node.

• 
  Terra's ascending orbital path in 2021
• 
  Terra's descending orbital path in 2021

Instruments

Fireball over the Bering Sea viewed from space by the Terra satellite
(December 18, 2018)

Terra carries a payload of five remote sensors designed to monitor the state of Earth's environment and ongoing changes in its climate system:^[2]

• ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer)^[3] ASTER creates high-resolution images of clouds, ice, water and the land surface using 3 different sensor subsystems. They are the Shortwave Infrared (SWIR); Thermal Infrared (TIR); and Visible and Near Infrared (VNIR). 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.^[4]
• CERES (Clouds and the Earth's Radiant Energy System)
• MISR (Multi-angle Imaging SpectroRadiometer)
• MODIS (Moderate-resolution Imaging Spectroradiometer)^[5]
• MOPITT (Measurements of Pollution in the Troposphere)^[6]

Data from the satellite helps scientists better understand the spread of pollution around the globe. Studies have used instruments on Terra to examine trends in global carbon monoxide and aerosol pollution.^[7] The data collected by Terra will ultimately become a new, 15-year global data set.

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 (MDA) Built-In Test Equipment (BITE) 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.^[8]

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.^[9]

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 (MMOD) strike.^[8]

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 (694 km). Decommissioning would occur around 2025-26 followed by an un-controlled reentry several years later.^[10]

Malicious cyber activities

In June and October 2008 the spacecraft was targeted by hackers who gained unauthorized access to its command and control systems, but did not issue any commands.^[11]

Gallery of images by Terra

• 
  The first image taken by Terra.
• 
  The Solar eclipse of August 1, 2008, over Russia, Norway, and the Arctic Ocean as seen from NASA's Terra satellite.
• 
  The effects of the European winter storms of 2009–2010 on Great Britain, seen from Terra.
• 
  The Deepwater Horizon oil spill oil slick as seen from space by NASA's Terra satellite on May 1, 2010.
• 
  The Deepwater Horizon oil slick just off the Louisiana coast on April 30, 2010, visible from space.
• 
  Hurricane Karl, the most destructive hurricane of the 2010 Atlantic Hurricane Season, approaches Mexico on September 16.
• 
  Satellite image of Sweden in March 2002.
• 
  Satellite image of the Ash distribution over Australia from the 2022 Hunga Tonga–Hunga Ha'apai eruption.
• 
  Animation of Terra's orbit around the Earth. Earth is not shown.

See also

• Aqua (satellite)
• Artificial structures visible from space
• Aura (satellite)

References

1. "NASA: TERRA (EOS AM-1)". nasa.gov. Retrieved 2011-01-07.
2. Maurer, John (November 2001). "Overview of NASA's Terra satellite". hawaii.edu (University of Hawai'i). Retrieved 2011-01-07.
3. Stevens, Nicki F.; Garbeil, Harold; Mouginis-Mark, Peter J. (2004-01-22). "NASA EOS Terra ASTER: Volcanic topographic mapping and capability" (PDF). Hawai'i Institute of Geophysics and Planetology. Retrieved 2011-01-07.
4. Wigglesworth, Alex (2019-11-06). "Satellite image shows Kincade fire burn scar". Los Angeles Times. Retrieved 2019-11-07.
5. "MODIS Terra Satellite Images". ucar.edu(National Center for Atmospheric Research: Earth Observatory Laboratory). Retrieved 2011-01-07.
6. "Measurements of Pollution in the Troposhere (MOPITT)". acd.ucar.edu (NESL's Atmospheric Chemistry Division). Archived from the original on 2011-01-28. Retrieved 2011-01-07.
7. "NASA's Terra Satellite Tracks Global Pollution". gsfc.nasa.gov (Goddard Space Flight Center). 2004-05-18. Archived from the original on 2010-11-24. Retrieved 2011-01-07.
8. Kelley, Angelita (17 August 2014). "Terra mission operations: Launch to the present (and beyond)" (PDF). Retrieved 5 April 2018.
9. "ASTER SWIR Alert". Retrieved 5 April 2018.
10. Owen, Tassia. "Terra Begins to Drift in Time". Retrieved 15 July 2021.
11. "2011 Report to Congress of the U.S.–China Economic and Security Review Commission" (PDF). uscc.gov. p. 216. Archived from the original (PDF) on 2013-02-15. Retrieved 2012-10-09.

External links

• NASA Terra site