Andrew Doyle/MUNICH
Dornier Satellitensysteme (DSS)has completed the fourth and final satellite for the European Space Agency's (ESA)c300 million ($309 million) Cluster II mission and handed the spacecraft over to Munich-based Industrieanlagen Betriebsgesellschaftfor testing.
The satellites are to be orbited in pairs by Russian Soyuz boosters next June and July. The original Clusters were destroyed in the failure of the maiden Ariane 5 launch in 1996. "We were down and out in 1996, but the Phoenix has risen and we will be ready to launch the four satellites in the middle of next year," says ESA Cluster II project manager Dr John Ellwood.
The satellites will fly in a tetrahedral formation to investigate the effects of solar wind on the Earth's magnetic field. Scientists believe that minor gusts in solar wind, which is made up of electrically charged particles ejected from the sun, can cause the failure of satellites and disrupt aircraft navigation and communications systems.
The distance between the spacecraft will gradually be varied between 1,000km and 18,000km over six-month cycles to gain accurate data on different parts of the Earth's magnetosphere. ESA director of science Professor Roger Bonnet says: "This will be the first mission to understand what is going on in the magnetosphere on a three-dimensional basis."
The satellites are to be launched by Franco-Russian venture Starsem from Baikonur in Kazakhstan, using a Soyuz booster mated with the uprated Fregat upper-stage under development. The Soyuz-Fregat will undergo two test flights, in January and March, with the latter carrying a Cluster II mock-up.
DSS says that if one of the test flights fails, all four Cluster spacecraft will be launched together on an Ariane 4 rocket, with insurance covering any resulting financial losses.
The Fregat upper stage is a development of the propulsion system that was used in two Russian Phobos craft that flew to Mars in 1988, and incorporates a digital guidance system.
It should deliver the satellites into an elliptical orbit of between 200km and 18,000km, after which their own engines will reposition them into a polar orbit of 25,500-125,000km.
Each Cluster II weighs 1.2t when fully fuelled, and is 2.9m (9ft 6in) in diameter. The mission is due to last two years.
Source: Flight International
