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LISA - Laser Interferometer Space Antenna

A Gravitational Wave Observatory

An artist's impression of the LISA spacecraft
An artist's impression of the LISA spacecraft

Gravitational waves are disturbances in space-time generated by accelerating masses; they are predicted by Einstein’s theory of general relativity but have yet to be observed. Because gravity is such a weak force in comparison to the other fundamental forces, the gravitational waves generated by everyday objects are impossible to detect, and the only significant sources are astrophysical ones such as binary neutron stars and supernovae.

LISA (the Laser Interferometer Space Antenna) (link opens in a new window) is a joint ESA/NASA mission which seeks to observe astrophysical and cosmological sources of low frequency gravitational waves. LISA consists of three spacecraft flying together in a triangle separated by 5 million kilometres. At the heart of each spacecraft is a free-falling 40mm metal cube, known as a test mass. A passing gravitational wave will change the separation between the test masses and this is detected by shining laser light between the test masses to form an interferometer. Such enormous separations are necessary to see a detectable change in distance, but even then the predicted test mass displacements are only at the picometre (10-12m) level. In order to avoid disturbing the measurement, the spacecraft position must be controlled to a similar picometre accuracy relative to the free-falling test masses, and this so-called drag-free formation flying technique cannot be tested on the ground. So in preparation for the mission, a technology demonstrator for LISA is being built to test the optical and mechanical methods that will be required for the final mission. This is LISA Pathfinder (link opens in a new window).

Closely orbiting compact stars, radiate large quantities of gravitational energy. Examples are the Binary Pulsar for which Hulse and Taylor were awarded the 1993 Nobel Physics Prize, and objects falling into Massive Black Holes which are now known to be at the centre of most galaxies.

ESA and NASA are planning to develop the technology for LISA ready for a launch around 2017, as a joint mission.

RAL has been studying the LISA mission and developing technology since it was first proposed to ESA in 1993. In 1999/2000 RAL managed for ESA an Industrial Study of the LISA Systems. The spacecraft configuration shown above is due to the contractor, Astrium.

Further information:

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