N° 26–2000: Largest environmental satellite takes shape at ESA's test centre

Mating of the payload module with the service module of Europe's largest ever environmental satellite is currently under way at ESA's test facilities in the Netherlands. Cranes in the clean-room, manoeuvred with extreme precision, will lower the 6 t, 7 m payload module vertically onto the service module. When the interface rings are bolted together, Envisat will stand over 10 m tall and the two elements combined will weigh over 8 t. The large, modular construction provides accessible accommodation and an unobstructed field of view for the various instruments.

During Envisat's operational phase, scheduled to last at least 5 years, the ten highly advanced instruments on board will help European scientists advance our understanding of global warming, climate change, ozone depletion, and changes in the oceans, ice sheets, vegetation and atmospheric composition. Thanks in particular to the advanced radar on board, Envisat will produce - day and night and in all weathers - high-quality images of the oceans, coastal zones, polar ice and land regions by bouncing microwaves off the Earth's surface and measuring the reflected radiation.

Once in orbit, the huge 15 m solar array powering the instruments will make the satellite's overall span an impressive 25 m. It is to be integrated in about three months, just before the complete spacecraft is submitted to mechanical testing, including deployment of the solar array.

Last August, the two spacecraft modules were submitted to thermal environment tests in ESTEC's Large Space Simulator. This unique chamber, 10 m in diameter and 15 m high (the size of a 5-storey building), one of the largest in the world, simulates the vacuum, cold, heat and solar radiation conditions of space. Temperatures in the chamber range from -190 to + 90 ºC, and a 6 m wide "sun", simulated by means of very powerful lamps, illuminates the satellite and its components.

Next August, Envisat will be submitted to acoustic tests in the Large European Acoustic Chamber (LEAF), also at ESTEC. Vibration tests, to check the satellite's ability to cope with the strong vibrations it will experience during the launch phase, will then be performed on the HYDRA hydraulic shaker in autumn. With its eight actuators delivering a force of 60 kN each, the HYDRA is one of the largest test facilities of its kind. ESTEC is thus one of the most complete tests centres in the world.

Over 100 highly skilled specialists from ESA and European companies, led by the prime contractors Matra-Marconi Space (UK) for the satellite platform and DaimlerChrysler-Dornier Satellitensysteme (D) for the payload, are currently involved in the testing of Envisat. In March next year the spacecraft will finally be prepared for shipment to Kourou by air.

Scheduled for launch on an Ariane 5 in June 2001, Envisat will orbit around the poles of the Earth with an inclination of 98 degrees at an altitude of 800 km. The orbital period (the time needed to complete each orbit) is one hour 40 minutes and the repeat cycle (the time needed to pass over exactly the same spot of our planet) is 35 days. ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany, will be responsible for command and control of Envisat, with payload data handling and distribution being coordinated by ESRIN, the Agency's data processing facility in Frascati, Italy.

Once in orbit, Envisat will provide international scientists with remote sensing data to chart, document and forecast changes in our environment and climate, helping Europe to meet the environment and economic challenges of the 21st Century.

A photo/film opportunity is being offered to the media on Monday 17 April. Media representatives wishing to film or take still pictures of the satellite on that day in the test facilities should contact the ESTEC Communication Office: telephone + 31 71 565 3006, fax: + 31 71 565 5728.

A selection of images is also available on the ESA web pages at

http://www.esa.int/gallery/pag0.html

For further information, please contact:

Heidi Graf,
Head of Communication Office, ESA/ESTEC
Tel. + 31 71 565 3006; Fax. + 31 71 565 5728

Peter Dubock
Envisat AIT Manager, ESA/ESTEC
Tel. + 31 71 565 4451; Fax. + 31 71 565 6652
e-mail: pdubock@estec.esa.nl

More information on ESA at http://www.esa.int