A proposed milestone mission in the study of gravitational waves — LISA, the Laser Interferometer Space Antenna project — received a boost, as the first, encouraging results from the LISA Pathfinder , a smaller, “walk before you run” project were released in a paper in Physical Review Letters on June 7.
One experiment that the LPF has carried out involves two cubical test masses placed at the heart of the spacecraft. The experiment has demonstrated that these two masses are almost motionless with respect to each other and show a relative acceleration which is less than one part in ten millionths of a billionth of Earth’s gravity. This is an accuracy about five times better than expected. This extraordinary degree of precision is needed by this experiment as the measured strain caused by gravitational waves on their detectors is comparably minute.
The LISA spacecraft will need to use the technology tested by LISA Pathfinder. LISA itself plans to use a combination of three spacecraft, trailing the earth at a distance of about 50 million kilometres, these will orbit the sun. The three spacecraft will lie at the corners of a giant huge equilateral triangle, and will be about 5 million kilometres from each other. Using special laser beams and telescopes, the trio will measure gravitational waves.
The three spacecraft are expected to act as an interferometer which can detect gravitational waves, ripples in the fabric of space-time, caused by mergers of supermassive black holes. Since there are three points from which the observation is carried out, this space antenna will be able to pinpoint the location of the source of the detected gravitational waves to a high accuracy. This mission is to be carried out jointly by NASA and ESA.
As a prelude to this massive mission, the smaller LISA Pathfinder was launched by ESA in 2015. This is stationed around the L1 point between the Earth and the Sun which is nearly 1.5 million km away from the Earth. The aim of the mission is to demonstrate the technology needed to establish a space-based observatory to study gravitational waves.
LISA Pathfinder was launched on December 3, 2015. It reached its operational orbit this January and started operations on March 1.
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