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Lisa (Astronomy) - For other uses for the acronym see LISA
The LISA is the Laser Interferometer Space Antenna. It will be launched in 2011 or later. LISA is supposed to measure gravitational waves by using laser interferometry over astronomical distances. It will use 3 spacecraft, each containing a freely floating mass, two optical setups and very precise thrusters to keep each piece in place. When a gravitational wave disturbes the space-time field between two of the spacecraft, a very small difference in the distance between the two masses should be measurable. The thrusters are supposed to be delicate enough to correct minor external disturbances like the pressure of sunlight. Also, the whole setup will form a triangle form consisting of 3 identical spacecraft, so that (if all is well) every measurement will be done with multiple redundancy. The distance between any two of the spacecraft will be about 5 million kilometers. Basically LISA will be a huge space-borne Michelson interferometer — or actually 3 spaceborne Michelson interferometers — calibrated by free-floating test masses measuring space itself. The big goal of the LISA mission is to test Einstein's theories about gravitational waves. Allthough most physicists believe they do exist — there are some indirect proofs — they have never been directly observed. The main reason for this is that their effect is extremely small. Observing them requires two things: a very large event generating the gravitational wave — such as a collapsing black hole — and extremely high detection sensitivity. The LISA instrument should be able to measure displacements with a resolution of 10 picometer over a distance of 5 million kilometer, yielding an astonishing strain sensitivy of better than 1 part in 10^20! A single satellite ("LISA Pathfinder") should be launched in 2008 to validate the design and configuration of the definitive mission in 2012-2013. The mission is sponsored jointly between NASA (which will provide the launcher) and the European Space Agency (providing the three spacecraft and science payloads from national research institutions) under the Beyond Einstein program. External links
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