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Boffins tentatively fire up grav wave sniffer

ESA LISA Pathfinder spacecraft gradually comes to life

By Lester Haines, 13 Jan 2016

European Space Agency (ESA) scientists have begun to fire up systems aboard the LISA Pathfinder spacecraft - designed to "test the technology needed to develop future space-borne gravitational wave detectors".

The LISA (Laser Interferometer Space Antenna) Pathfinder is now on its way to its final destination orbiting Lagrange point L1, some 1.5 million km from Earth. Following its launch on 3 December last year, the spacecraft's propulsion module pushed it into six progressively higher elliptical orbits before dispatching it into the wide black yonder.

The LISA Pathfinder trajectory from launch to final destination

Next stop, Lagrange point L1. Click for embiggenment

Having done its job, the propulsion unit will be released on 22 January. In the meantime, boffins will continue to test onboard systems and hardware. Once fully operational on 1 March, LISA will attempt to "put two test masses in a near-perfect gravitational free fall, and control and measure their motion with unprecedented accuracy".

The LISA Pathfinder LTP core assembly

LISA's floating cubes and interferometer

This involves precisely measuring the free-falling test masses' (identical 46mm gold/platinum alloy cubes) positions relative to each other and the spacecraft using a laser interferometer. The idea is that gravitational waves will cause minute, but measurable, test mass displacements. LISA itself can't do this, because "since the impact of gravitational waves is so tiny, the test masses would need to be millions of kilometres apart rather than the 38cm available on board".

The agency elaborates: "A low-frequency gravitational wave would cause a 1m bar to move 10-21 m to 10-24 m – orders of magnitude smaller than an atomic nucleus at 10-15 m. Using a space-based interferometer, one arm could act as a bar 5 x 106 km long, making the effect of a low-frequency gravitational wave measurable."

Ultimately, ESA hopes to have three spacecraft, each with its own cube, forming a triangle whose "arms" measure 5,000,000km.

That all depends on whether LISA can prove the tech actually works. Scientists have already activated the cold gas micro-newton thrusters, "which will be used to accurately adjust the spacecraft position by tiny shifts during the operations phase".

This week, they'll boot up the onboard computer and other electronics, as well as firing up the interferometer laser. In February, the test masses will gradually be released from the locking mechanisms which protected them during launch.

So far, everything appears to be going according to plan. Paul McNamara, ESA's LISA Pathfinder project scientist, said: "We are very happy with how the spacecraft commissioning has gone so far, and by switching on the first subsystem of the payload we are now one step closer to science operations." ®

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