Environmental Satellite Envisat Readied for Launch
Paris / Le Bourget, le 15 juin 2001
Europe's largest and most complex Earth observation satellite, the environmental satellite Envisat - with a mass of approximately eight tons and a stowed height of ten meters - is being prepared for its launch from the European launch site in Kourou (French Guyana). In late summer, the space-borne environmental Earth monitoring spacecraft, developed and built under the industrial lead of the Astrium space company, will be boosted into space by an Ariane 5 rocket.
The industrial contract is worth about 1.5 billion EURO in total. The development and construction of Envisat has taken about ten years, with the involvement of almost 10 companies in 14 countries. Astrium sites in Germany, the U.K. and France have participated in the programme with Astrium (U.K.) as prime contractor to ESA for the Polar Platform and two of the major instruments, Astrium (Germany), as Mission Prime to ESA with overall responsibility for the instruments; the Payload Equipment Bay (PEB) and two instruments, Astrium (France) as supplier of the Service Module and other instruments.
During the mission of at least five years, Envisat will orbit the Earth every 100 minutes by revisiting every part of the Earth's surface every 35 days. Ten advanced instruments on board Envisat will help scientists gain a better understanding of global warming, climatic changes and ozone depletion, as well as changes in the oceans, the ice caps, vegetation and the composition of the atmosphere. Envisat's radar system - which operates independently of the time of day and weather conditions - will send microwave pulses to the Earth's surface and, by measuring the reflected pulses, will deliver valuable images of the seas and the land masses. This understanding is becoming more important given the scale of the recent climatic events seen over recent years.
The technical backbone of the satellite is the Polar Platform which consists of two main assemblies: the Service Module (SM) and the Payload Module (PLM). The SM, for example, accommodates the components for power supply, attitude and orbit control as well as data transfer, whilst the PLM carries the instruments and associated systems including instrument data transmission for Earth observation and atmospheric research. The Polar Platform is a further development of the SPOT satellite platform of Astrium. ESA's 'successful ERS satellites were also based on developments of the SPOT family of satellites.
Completely new developments are the S-band transponder and the solar array. The 70 square meter collector area is equipped with 14 rigid individual elements of one by 5 meters each, which generate a total of 6.6 kilowatts of electrical power. During the launch, the individual panels are folded together at the deployment arm like a concertina and fixed to the spacecraft. After satellite separation from Ariane 5, the arm will be extended and the panels will be unfolded. In this condition Envisat will have a total length of 25 meters.
From a scientific and application point of view, the Envisat instruments form an ideal payload combination to monitor and explore our Earth and its atmosphere. The complete payload comprises seven ESA instruments and three to be provided by the national space agencies of Germany/the Netherlands, France and Great Britain. Five of these instruments were developed and built by Astrium. These are:
ASAR, the Advanced Synthetic Aperture Radar, is a high-resolution radar delivering valuable ocean and land images independent of time of day and weather conditions. It is the largest instrument on board Envisat and a product of Astrium UK.
AATSR, the Advanced Along Track Scanning Radiometer, also a product of U.K., measures the sea surface temperatures and monitors the land vegetation.
GOMOS, the Global Ozone Monitoring by the Occultation of Stars, was built in Toulouse and is to be used for exploring the processes causing ozone depletion in the stratosphere.
MIPAS, the Michelson Interferometer for Passive Atmospheric Sounding, was developed in Ottobrunn, near Munich. It is to be used for simultaneous measurement of more than twenty trace gases in the atmosphere.
Sciamachy, the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography, is a German-Dutch joint development built by Astrium in Friedrichshafen. It allows high-precision determination of trace gases, aerosols, cloud height and coverage.
The other five instruments are:
The Medium Resolution Imaging Spectrometer (Meris), for which Alcatel, France, is the prime contractor, will primarily serve oceanographic and secondarily atmospheric and land-oriented applications. Meris measures the solar radiation reflected by the Earth in the optical and near-infrared spectrums.
The Radar Altimeter 2 (RA-2), for which Alenia Spazio, Italy, is the prime contractor, is derived from the ERS-1 and ERS-2 altimeters providing markedly improved measurement performance. The main objectives of this instrument are high-precision measurements of the ocean surface, the polar ice regions, and their short and long-term variations.
The Microwave Radiometer (MWR), for which Alenia Spazio, Italy, is the prime contractor, will measure the water content (clouds, vapour and rain) of the atmosphere. These data are required to calculate correction values for the evaluation of the RA-2 measurements by means of which RA-2 altitude values can be improved with an accuracy of a few centimeters.
The Laser Retro-Reflector (LRR), originating from Alcatel, France, is to be used to support satellite ranging and RA-2 altitude measurement calibration. Using the data delivered by LRR and Doris, the spacecraft orbit can be determined to a precision of a few centimeters.
The range finder Doris (Doppler Orbitography and Radiopositioning Integrated by Satellite), developed under contract to CNES, will be employed on Envisat to exactly determine the satellite's position.
Paris / Le Bourget, June 2001 /01007
For further information:
Astrium
Earth Observation and Science
Mathias Pikelj
Tel.: +75458-9123
Fax: +7545 8-5589
