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

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

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:


Earth Observation and Science

Mathias Pikelj

Tel.: +75458-9123

Fax: +7545 8-5589