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ENVISAT IS READY FOR ACTION

The European Space Agency (ESA)'s involvement in the area of environmental monitoring dates back to the early 1970s when the Meteosat series of weather satellites entered service. Then in 1992 the first European Remote Sensing Satellite ERS-1, specially equipped for monitoring our sensitive and vulnerable environment, was launched. This was followed in 1995 by ERS-2. Operating in tandem mode, the two satellites have been encircling the earth for some years and supply important data every day not just to scientists but also to politicians, town planners and environmental organisations.

Again, in 1984 the then US President Ronald Reagan invited western Europe to collaborate on the construction and operation of the US "Freedom" space station. ESA's contribution, designated "Columbus", was to comprise three parts: a laboratory module for the station, a free flying manned module and an unmanned polar platform. The laboratory is soon to be implemented in the form of the Columbus Orbital Facility (COF) as part of the International Space Station. The Man-Tended Free Flyer (MTFF) was cancelled for financial and technical reasons, but the Polar Platform survived, and will be launched in the form of the large earth observation satellite Envisat in June 2001. This will be followed soon afterwards by a companion weather satellite, the Meteorological Polar Platform (METOP).

After that, there are plans to launch additional satellites which will also follow a polar orbit. These will alternate between the Envisat and METOP types. Larger and more capable than all their predecessors, the two satellites will provide us with a new view of our world and help scientists to detect environmental changes in good time so that possible climatic catastrophes can be averted.

The Polar Platform has undergone many years of definition and design. Its payload capacity is up to 2500kg and it has three to five kilowatts of electrical power. Other elements of the programme included launching with the European heavy-duty launcher Ariane 5 and the development of a standard and flexible data management system capable of being used for every possible scientific payload. The financial resources needed for this programme were made available at various meetings of ESA's Council at Ministerial Level, while the funds for the scientific equipment had to be approved separately on a case by case basis.

Envisat now comprises not just a satellite, but it also includes a ground segment which accounts for around one-third of the development effort that has gone into the whole system. This ground facility in turn breaks down into the Payload Data Segment and the Flight Operation Segment and is intended to ensure that independent users too can receive data directly via a relay satellite.

The prime contractor for the Polar Platform was Matra Marconi Space, while Dornier Satellitensysteme GmbH was responsible for building the Payload Equipment Bay and also for running the mission. Today, shortly before the launch of the satellite, all these companies have merged into a single organisation, Astrium, so that future missions too will benefit from this European collaboration.

This not only facilitates development and building of the system, but of course it will also make regular observation of our environment in ongoing operations a lot easier, also the management of renewable and non-renewable earth resources and research on improving our understanding of the structure and dynamics of the earth's crust and interior. In addition, the data service which was established in connection with the ERS-1 and ERS-2 missions is undergoing further development.

Altogether ten scientific instruments will supply this data, two of which were developed by Astrium in Friedrichshafen. MIPAS and SCIAMACHY will both observe the photochemical interaction of 20 trace gases in the middle terrestrial atmosphere and the stratosphere up to an altitude of 90km. Environmental data on our planet will be collected during 14 daily orbits around the earth. Approximately every 35 days the same point on the earth's surface will be overflown again, so that all the changes which have taken place in the intervening period can be captured in their entirety.

After almost eight years of preparation time, it will not be long now before the environmental look-out is finally launched. In April 2000 assembly of the satellite commenced in the European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands. The payload and service modules have been mated, and even the engineers involved on the programme have been impressed by the size and complexity of the space vehicle they have created.

Prior to that, the subassemblies had been tested one at a time in ESTEC's large space simulator under the environmental temperatures to be expected. This 15m high chamber has a diameter of 10m, equivalent to a five-storey house, and is one of the biggest test facilities in the world, in which solar radiation and the prevalent vacuum and temperature conditions in space can be simulated. There have also been acoustic trials in an acoustic chamber and vibration tests which demonstrated that the satellite can withstand the stresses to which it will be exposed during the launch phase.

Shortly before launch, ESA has once again taken steps to promote public awareness of the project by initiating a competition for young people to design a "flag for the earth". Children aged between eight and twelve are to design a single flag for our planet, as the satellite will be observing the entire earth. The prize-winning design will then be incorporated on the satellite body and will fly with Envisat into space.

For many years satellite data was the preserve of academia and the military, but the Envisat programme will enable large-scale commercial use of the data. It is not just a matter of using the earth observation data, which can be sold for good money so that an annual growth of 20% is nothing unusual here. The market segment of the participating companies in the aerospace industry is also constantly changing. However, the transition from academic to financial exploitation is expensive and protracted, too long drawn out by European standards compared with the market in the USA. Support is needed from the politicians, as the industry alone cannot provide all the start-up capital needed.

From page 44 of FLUG REVUE 1/2001