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LISA Pathfinder en route to seek gravitational waves

05 December 2015

The UK-led spacecraft has been successfully launched into a low orbit from where it will travel to its final destination, 1.5 million kilometres above the earth.

Artist's impression of the LISA Pathfinder, courtesy of ESA

The LISA Pathfinder will help open up a completely new observational window into the gravitational Universe, by testing new technologies needed to measure gravitational waves in space. Predicted by Albert Einstein, these waves are ripples in the curvature of space-time produced by massive celestial events, such as the merging of black holes.

The UK’s involvement in LISA Pathfinder’s technology demonstration payload and the operational phase of the mission is funded by the UK Space Agency and was formerly funded by the Science and Technology Facilities Council (STFC). Airbus Defence and Space is the prime contractor for the mission, having built the spacecraft, as well as being the LISA Test Package (LTP) architect, on behalf of ESA and the participating Member States.

SciSys UK developed the satellite’s on-board software and UK scientists from the University of Birmingham, the University of Glasgow and Imperial College London designed and built elements of the innovative and complex LTP. STFC RAL Space was involved in several technology development projects in the early stages of the mission in 2001.

At the core of LISA Pathfinder is a pair of identical 46mm gold–platinum cubes separated by 38cm, which will be isolated from all external and internal forces acting on them except one: gravity.

The mission will put these cubes in the purest free-fall ever produced in space and monitor their relative positions with astonishing precision, laying the foundations for gravitational wave observatories in space.

LISA Pathfinder is currently in a low orbit. Over the next two weeks, the spacecraft itself will raise the orbit’s highest point in six critical burns. The final burn will propel the spacecraft towards its operational location, orbiting around a stable virtual point in space called L1, some 1.5 million kilometres from Earth towards the Sun.

LISA Pathfinder is expected to reach its operational orbit about ten weeks after launch, in mid-February. After final checks, it will begin its six-month scientific mission on 1 March.

En route to the final orbit, the two cubes will be released from the locking mechanisms that hold them during launch and cruise. Once in orbit around L1, the final mechanisms will be unlocked and the cubes will no longer be in mechanical contact with the spacecraft.

A complex system of laser beams bouncing between the two cubes will measure how close to true free-fall they are to within a billionth of a millimetre – never previously achieved in space.

Among the anticipated sources of gravitational waves are supernova explosions and double black holes.

These objects are thought to be associated with overwhelmingly powerful events. For example, the energy released in gravitational waves during the last few minutes of the merging of just one pair of super-massive black holes is comparable to the total energy emitted as light by all stars and galaxies across the cosmos over the same time.

Detecting gravitational waves would also be an additional confirmation of General Relativity.

Scientists are also looking forward to discovering even more, unexpected cosmic sources once they are able to ‘listen’ to the Universe on this new channel.

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