TERRA

Terra carries ASTER, CERES, MISR, MODIS and MOPITT. Together they measure surface features and temperature, Earth's radiation budget, clouds and aerosols from multiple viewing angles, broad spectral imagery, and carbon monoxide in the lower atmosphere.

Terra carries ASTER, CERES, MISR, MODIS and MOPITT. Together they measure surface features and temperature, Earth's radiation budget, clouds and aerosols from multiple viewing angles, broad spectral imagery, and carbon monoxide in the lower atmosphere.

NASA's reference orbit for Terra was approximately 705 km (438 mi) above Earth with a 99-minute period, about 14 orbits per day and a 98.5-degree inclination. Terra's orbit has changed as the mission aged, so live catalog values can differ from those original reference numbers.

A Sun-synchronous orbit was designed to cross locations at nearly the same local solar time, helping scientists compare observations under similar lighting. Terra began drifting away from its original crossing time after maneuvers maintaining that geometry ended.

Repeated measurements are essential to Earth science. A single image records one moment, while a calibrated series collected across years can reveal seasonal cycles, unusual events and persistent change.

These spacecraft use cameras, radiometers, radar, spectrometers, or other instruments to measure features of Earth. Repeated observations make comparisons across seasons and years possible.

• Terra carries ASTER, CERES, MISR, MODIS and MOPITT. Together they measure surface features and temperature, Earth's radiation budget, clouds and aerosols from multiple viewing angles, broad spectral imagery, and carbon monoxide in the lower atmosphere.
• NASA's reference orbit for Terra was approximately 705 km (438 mi) above Earth with a 99-minute period, about 14 orbits per day and a 98.5-degree inclination. Terra's orbit has changed as the mission aged, so live catalog values can differ from those original reference numbers.
• A Sun-synchronous orbit was designed to cross locations at nearly the same local solar time, helping scientists compare observations under similar lighting. Terra began drifting away from its original crossing time after maneuvers maintaining that geometry ended.
• Repeated measurements are essential to Earth science. A single image records one moment, while a calibrated series collected across years can reveal seasonal cycles, unusual events and persistent change.

Terra carries ASTER, CERES, MISR, MODIS and MOPITT. Together they measure surface features and temperature, Earth's radiation budget, clouds and aerosols from multiple viewing angles, broad spectral imagery, and carbon monoxide in the lower atmosphere. NASA's reference orbit for Terra was approximately 705 km (438 mi) above Earth with a 99-minute period, about 14 orbits per day and a 98.5-degree inclination. Terra's orbit has changed as the mission aged, so live catalog values can differ from those original reference numbers. A Sun-synchronous orbit was designed to cross locations at nearly the same local solar time, helping scientists compare observations under similar lighting. Terra began drifting away from its original crossing time after maneuvers maintaining that geometry ended. Repeated measurements are essential to Earth science. A single image records one moment, while a calibrated series collected across years can reveal seasonal cycles, unusual events and persistent change.

The current two-line element set reports approximately 14.6116 revolutions per day. Dividing 1,440 minutes by that value gives an estimated orbital period of 98.6 minutes.

Terra, originally called EOS AM-1, launched on 18 December 1999 aboard an Atlas IIAS from Vandenberg Air Force Base in California. The spacecraft entered an initial orbit and was maneuvered toward its planned approximately 705-km (438-mi) Sun-synchronous polar orbit. Its five instruments were then activated and checked before routine science observations began.

Low Earth orbit is the region closest to Earth used by most crewed spacecraft, many science missions, Earth-observation satellites, and large constellations. Objects move quickly and commonly complete an orbit in roughly 90 to 130 minutes.

LEO can provide detailed Earth views, lower communications delay, and easier access than higher orbits, but it covers less area per spacecraft and is more affected by atmospheric drag.

• Why are repeated observations valuable?
• How can satellites observe through clouds or darkness?

Current identity and orbital elements come from CelesTrak’s public GP data. Calculated orbit values are derived from the current TLE and may change after catalog updates. Mission-history claims are added separately and require authoritative sources.

• CelesTrak NORAD GP Element Sets
• About Terra · NASA
• Terra Mission · NASA
• The Earth Observer, November/December 1999 · NASA Earth Science