Clean sweep

A spacecraft designed to act as a giant road-sweeper, clearing space of potentially damaging debris such as old satellites, could soon be orbiting the earth.

As part of a project for the European Space Agency, Qinetiq is investigating the possibility of building a vehicle to protect satellites from the increasing danger posed by space junk, by moving the objects out of harm’s way.

While the risk of satellites being damaged in this way is still quite small, the amount of space junk in orbit is increasing, said Walter Flury, who is co-ordinating Esa’s space debris programme. ‘Only six to seven per cent of catalogued large objects are actually operating spacecraft. the rest present a danger. One French satellite, Cerise, was seriously damaged in 1995 when it was hit by an old piece of Ariane rocket.’

Qinetiq is leading a European team looking at the possibility of developing a spacecraft, called the Robotic Geostationary Orbit Restorer, or Roger, to re-orbit ‘dead’ satellites.

The team is studying a variety of possible designs for the vehicle, said Dr Clare Martin, a space scientist at Qinetiq. ‘In the past we have been looking at the use of a robotic arm, but given that the satellites are at the end of their lives, it is not necessary to handle them gently, so we are looking at non-robotic options.’

Debris is a particular problem in the geosynchronous (GEO) orbit, the region of space inhabited by large geostationary communications and weather satellites. When a satellite in the GEO dies there is no natural decline in the orbit, so it just stays there. These dead satellites can also break up into smaller pieces, and it takes only a fragment, travelling up to 17km/s, to do immense damage to a satellite. Operators are encouraged to re-orbit their satellites at the end of their lives, into an area about 250km above the GEO, but only about a third of companies do this, said Martin.

Once launched into its position either just above or below geosynchronous orbit, Roger will remain in space, and when needed will travel to the out-of-use satellite and dock with it, before dragging it into a graveyard orbit. Dragging the object rather than pushing it will reduce the risk of small fragments breaking off, said Martin.Roger will be powered by the massive solar arrays used by most satellites, but researchers are looking into the use of ion propulsion systems, as well as more traditional chemical propulsion.

The team, which also includes Guildford-based Esys, OHB Systems of Germany and Dutch Space, is compiling a report detailing the requirements for building a demonstrator vehicle, and will submit its results to Esa in February.

On the web