ENVISAT, ROSETTA, GRACE and SPOT 4
This month sees the anniversaries of three Earth observation satellites and one space exploration spacecraft for which Astrium was prime contractor.
1 March – ENVISAT – 9 years in orbit
Europe’s largest and most complex Earth observation satellite, the ENVIronmental SATellite, Envisat, was launched in 2002 by an Ariane 5 into an 800-km polar orbit. This European Space Agency satellite is helping scientists gain a better understanding of the effects of global warming, El Niño, climatic changes and the depletion of the ozone layer, as well as variations in ocean-levels, ice caps, vegetation and the composition of the atmosphere.
Development and construction of the 8,200kg spacecraft took more than 10 years, and involved almost 100 companies in 14 countries. Astrium sites in the UK, Germany, Spain and France all participated in the programme: Astrium UK was the prime contractor for the Polar Platform and two of the major instruments; Astrium Germany held overall responsibility for the instruments, the payload equipment bay and two instruments; Astrium Spain supplied the satellite structure and contributed to three of the instruments, and Astrium France supplied the service module and other instruments.
2 March – ROSETTA – 7 years in orbit
The international Rosetta mission is the third Cornerstone Mission in the European Space Agency’s long-term space science programme. Launched in March 2004, the mission’s objective is to rendezvous with the comet Churyumov-Gerasimenko in 2014. The spacecraft will orbit the comet at a distance of one kilometre for nearly two years, studying the comet’s nucleus and its environment, and a lander will carry out surface-science investigations and analyses on Churyumov-Gerasimenko.
Astrium Germany was prime contractor for the Rosetta mission, responsible for building the spacecraft. Other contributions were provided by Astrium UK which built the spacecraft platform, Astrium France which supplied the spacecraft avionics, and Astrium Spain which provided the medium-gain antenna.
17 March – GRACE – 9 years in orbit
The main task of geo-research and climate research today is to understand the Earth as an integral system. The two Grace (Gravity Recovery and Climate Experiment) satellites were developed to further advance research in this field. Grace, a system of two identical satellites, is a joint NASA–German Aerospace Centre (DLR) project, and the second mission under NASA’s Earth System Science Pathfinder programme.
The two Astrium-built satellites, each weighing just 480kg, were launched on 17 March 2002 by Eurockot (in which Astrium holds a 51% share) using a Rockot launcher for a five-year mission. They are orbiting in tandem, flying at about 220km apart, but the exact distance between them is altered by the influence of the Earth’s gravity. A microwave connection between the two satellites enables this fluctuating distance between them to be constantly determined to within a few thousandths of a millimetre, thereby ‘mapping’ the Earth’s gravitational field with unprecedented accuracy. It has been possible to detect minor gravitational changes, which result from revolving magma in the interior of the Earth or from melting glaciers or shifting ocean currents, for the first time.
24 March – SPOT 4 – 13 years in orbit
Astrium’s Spot multi-mission platform series, initially designed for the French space agency, CNES, is now used for many European Low Earth Orbit Earth observation satellites, including the Helios military reconnaissance satellites, the ERS radar satellites, the Envisat Polar Platform and the polar-orbiting MetOp spacecraft.
All five Spot satellites were built under the prime contractorship of Astrium, responsible for the platform and high-resolution imaging system on all Spot satellites.
In 1998, Spot 4 took the first picture of another satellite in space. ERS-1 was imaged whilst orbiting 41km below Spot 4, and travelling at a relative velocity of 250km/h. In the corrected image, ERS-1 can be seen with a 50cm resolution.