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