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Envisat

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Envisat Credit: Manufacturer Image

Status: Operational 2002. First Launch: 2002-03-01. Last Launch: 2002-03-01. Number: 1 . Gross mass: 7,911 kg (17,440 lb). Unfuelled mass: 7,611 kg (16,779 lb).

It was later descoped to become something like the European equivalent of NASA's Earth Observing System. Envisat used a new modular satellite bus built at the defunct Matra Marconi Space/Bristol. Final integration was done at ESTEC in the Netherlands. The service module (SVM) was based on the SPOT 4 design. Prime contractor was Astrium (Dornier). Envisat carried 300 kg of hydrazine monopropellant for orbital adjustments. The active C-band phased array ASAR radar imaging antenna was 1.3 x 10 m in size. Envisat also carried atmospheric radiometers and spectrometers and a radar altimeter.

Envisat was an advanced polar-orbiting Earth observation satellite which provided measurements of the atmosphere, ocean, land, and ice over a five year period. The Envisat satellite had an ambitious and innovative payload that ensured the continuity of the data measurements of the ESA ERS satellites. The Envisat data supported Earth science research and allow monitoring of the evolution of environmental and climatic changes. The major driver for the Polar Platform/Envisat satellite configuration was the need to maximize the payload instrument mounting area and to meet the viewing requirements within the constraints of the Ariane 5 fairing and interfaces. Additionally, the configuration was driven by the reuse of the SPOT Mk II service module concept and the ERS payload accommodation concept (instrument electronics in an internal enclosure with externally mounted antennas).

In flight, the major spacecraft longitudinal axis (the Xs-axis) was normal to the orbit plane, the Ys-axis was closely aligned to the velocity vector and the Zs-axis was Earth pointing. This configuration concept provided a large, modular, Earth-facing mounting surface for payload instruments and an anti-sun face for radiative coolers, free of occultation by satellite subsystem equipment.

Specification

• Launch configuration: length 10.5 m, envelope diameter 4.57m
• In-Orbit configuration 26m * 10m * 5m
• Mass: Service Module 2673 kg; Payload Equipment Bay 1021 kg; Payload Carrier 2078 kg; Fuel 319 kg; Payload Instruments 2118 kg; Total 8211 kg.
• Average Power (W, sunlight/eclipse): Payload 1841/1886; Payload Module 860/ 527; Service Module 859/684; Total Load 3560/3097; System Capability 3847/ 3291

• Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) was a Fourier Transform spectrometer for the measurement of high resolution gaseous emission spectra at the Earth's limb. It operates in the near to mid-infrared where many of the atmospheric trace gases playing a major role in atmospheric chemistry had important emission features. It also measured temperature profiles.
• Global Ozone Monitoring by Occultation of Stars (GOMOS) provided altitude-resolved global ozone mapping between the tropopause and 100 km with a vertical resolution of 1.7 km. It also measured profiles of NO2, NO3, OClO, temperature and water vapor.
• Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) was an imaging spectrometer performing global measurements of trace gases in the troposphere and in the stratosphere. The solar radiation transmitted, back-scattered and reflected from the atmosphere was recorded at relatively high resolution over the range 240 - 1700 nm and in selected regions between 2.0 and 2.4 mm. This makes it possible to detect many different trace gases with low concentration.
• Medium Resolution Imaging Spectrometer (MERIS) was a push-broom instrument, measuring the solar reflected radiation from the Earth's surface and from clouds through the atmosphere in the visible and near infrared range during daytime. It measured ocean color with high spectral resolution and, with ASAR, RA-2 and AATSR, it provided a synergistic mission for bio/geophysical characterization of the oceans, land and coastal zones.
• Advanced Along Track Scanning Radiometer (AATSR) continues the ATSR-1 and ATSR-2 observations on ERS of precise sea surface temperature (SST) providing a 10 year near-continuous data set at the levels of accuracy required (0.3K or better) for climate research. It also provided information about vegetation biomass, moisture, health and growth stage. Its visible channels would be used to measure cloud parameters, such as water/ice discrimination and particle size distribution.
• Advanced Synthetic Aperture Radar (ASAR) was a high-resolution, wide-swath imaging radar instrument capable of taking images of the Earth's surface independent of weather conditions, cloud coverage and sun illumination. The ASAR could be used to monitor the Earth's environment to collect information on ocean wave characteristics, sea ice extent and motion, oil spills, snow and ice extent, glaciers, surface topography, land surface properties, soil moisture and wetland extent, deforestation, desertification and natural hazards.
• Radar Altimeter 2 (RA-2) measured the two-way delay of the radar echo from the Earth's surface to a very high precision: less than a nanosecond. It also measured the power and the shape of the reflected radar pulses, which then allowed the derivation of the parameters associated with ocean topography, bathymetry and the marine geoid . Furthermore, sea ice, polar ice sheets, and most land surfaces could be mapped. Measurement of the radar echo power and shape enables the determination of wind speed and significant wave height at sea.
• Microwave Radiometer (MWR) measured the integrated atmospheric water vapor column and cloud liquid water content as correction terms for the Radar Altimeter signal. In addition, MWR measurement data were useful for the determination of surface emissivity and soil moisture over land, surface energy budget investigations and ice characterization.
• Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) was a tracking system, which provided range-rate measurements of signals from a dense network of ground-based beacons. These make it possible to determine the satellite orbit with an accuracy of an order of centimeters. The data products were also used to help in understanding the dynamics of the solid Earth and to monitor glaciers, landslides and volcanoes. They also support the modeling of the Earth's gravity field and of the ionosphere.
• The Laser Retro-Reflector (LRR) was a passive device used to reflect pulses from ground-based laser stations, to support satellite ranging and RA-2 altitude measurement calibration.

• Envisat - . Mass: 7,991 kg (17,617 lb). Nation: Europe. Agency: Arianespace. Class: Earth. Type: Civilian Radarsat. Spacecraft Bus: SPOT-4. Spacecraft: Envisat. USAF Sat Cat: 27386 . COSPAR: 2002-009A. Apogee: 785 km (487 mi). Perigee: 783 km (486 mi). Inclination: 98.60 deg. Period: 100.50 min.

  This launch was the first Ariane 5 to use the 17-m Long Fairing and the first to launch north from Kourou. The booster placed the European Space Agency's Envisat polar platform in orbit. The flight profile was quite different from earlier Ariane 5 GTO launches where the EPC core stage usually reached a marginal orbit. In this case EPC separation at 350 km high 10 min after launch. The stage was on a -2610 x 651 km x 93.8 deg orbit, reaching apogee around 0125 UTC and reentering north of Ellesmere Island at about 0136 UTC. The EPS final stage with Envisat only achieved a positive perigee at 22 minutes after launch, with a circular 790 km sun-synchronous orbit reached at 25 min after launch. ESA reported the booster put the satellite to within 20 m of the desired orbital position.