ESA on mission to surf gravity's waves

Pathfinder craft to test Einstein prediction

A UK company has won the contract to build the heart of an ESA experiment designed to detect gravity waves, predicted by Einstein's general theory of relativity.

The Lisa (Laser Interferometer Space Antenna) Pathfinder mission, scheduled for launch in 2008, is a precursor to the main event. The Lisa mission itself could revolutionise astronomy, scientists say, but before that can happen, they need to know whether their experiments will work. This is where the pathfinder mission comes in.

Identifying the ripples in space-time is no easy task, and although there is indirect evidence for their existence, no-one has ever detected one directly. Experiments on Earth searching for gravity waves do so by bouncing laser beams down tunnels that are hundreds of metres long, and checking for tiny path deviations.The disturbances the astronomers are looking for are vanishingly small - approximately a thousandth of the size of a proton.

The idea behind the Lisa mission is that in space, a laser beam can be sent rather further, and so the disturbance in the photon's path will be larger and easier to detect. Easier, but not easy, and still only around a billionth of a millimetre over five million kilometres.

The Lisa mission will consist of three spacecraft flying in a triangular formation. The sides of this equilateral triangle will be five million kilometres long. Each craft will hold a free floating gold block held in place by electrostatic fields. The lasers will measure the distances between these blocks.

Part of the job of the pathfinder mission is to find out how well insulated the scientists have been able to make the craft from background noise that could overwhelm the instrumentation. They have also developed ways of allowing for the gravity of the individual components which also need to be tested.

Professor David Southwood, Esa's director of science told The BBC: "To find answers you have to search the unknown. Lisa takes us into totally new activities; a totally new kind of astronomy. Pathfinder is the necessary technological step that kicks us off into an unknown Universe." ®

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