UK researchers designing instruments for a joint ESA/NASA experiment to detect gravitational waves in space are facing some interesting problems.

The first part of the LISA (Laser Interferometric Space Antenna) experiment will see the electronics test-flown in 2008, with the full experiment eventually involving an array of three satellites.

Gravitational waves – ripples in the fabric of space-time caused by the acceleration of massive bodies – are very weak. The UK team is aiming at higher-amplitude low-frequency waves from bodies such as black hole binaries.

In simple terms, the gravitational wave measurement will be derived from a comparison of the phase of a laser shot between two satellites. The effect on the phase due to a gravitational wave will be tiny, needing a comparison accuracy of around 10-5 radian/vHz for detection.

"The type of phase measurements we have to make are really quite demanding, in a number of ways," said Professor Mike Cruise, head of the gravitation group in the University of Birmingham’s School of Physics and Astronomy. Birmingham is developing the phase-comparison electronics.

The low frequency of the waves – between 1-2Hz and 1-4Hz – presents its own challenges. Designing structures that do not succumb to thermal effects on a timescale of minutes-to-hours, and introduce spurious signals as a result, is tricky.

"I don’t think any of the engineers have ever worked in this frequency range before," said Cruise. "To design a filter to get the kind of phase stability we need, using components that have the normal kind of thermal tolerances, we have to work very hard indeed."

www.esa.int/science/lisa