In search of Gravity Waves

LISA Pathfinder about to enter the space environment vacuum test. Credit: Astrium, United Kingdom

By ESA, Noordwijk, Netherlands

Published: November 15, 2011

Sensors destined for the European Space Agency’s (ESA) LISA Pathfinder mission in 2014 have far exceeded expectations, paving the way for a mission to detect one of the most elusive forces permeating through space — gravity waves.

The Optical Metrology Subsystem underwent its first full tests under space-like temperature and vacuum conditions using an almost complete version of the spacecraft.

The results exceeded the precision required to detect the enigmatic ripples in the fabric of space and time predicted by Albert Einstein — and did it by two to three times.

In space, the LISA Pathfinder will measure the distance between two free-floating gold-platinum cubes using lasers. In the ground tests currently being performed by the team in Ottobrunn, Germany, separate mirrors replace these cubes.

In addition to measuring the distance between the cubes, it also measures their angles with respect to the laser beams — and the tests show an accuracy of 10 trillionths of a degree.

“This is equivalent to the angle subtended by an astronaut’s footprint on the Moon!” said Paul McNamara from ESA.

Under perfect conditions in space, the free-floating cubes would be expected to exactly copy each other’s motions.

However, according to Einstein’s general theory of relativity, if a gravitational wave were to pass through space, possibly caused by an event as catastrophic as the collision of two black holes, then a minuscule distortion in the fabric of space itself would be detectable.

The accuracy required to detect such a subtle change is phenomenal — around a hundredth the size of an atom — a picometer.

The requirement set for the instrument was around 6 picometers, measured over 1,000 seconds, which the team initially bettered in 2010.

During the latest testing, a staggering 2-picometer accuracy was obtained, far exceeding the best performance for an instrument of this type.

“The whole team has worked extremely hard to make this measurement possible,” said McNamara. “When LISA Pathfinder is launched, and we’re in the quiet environment of space some 1.5 billion kilometers [930 million miles] from Earth, we expect that performance will be even better.”

The instrument team from Astrium GmbH, the Albert Einstein Institute, and ESA are testing the Optical Metrology Subsystem during LISA Pathfinder’s thermal vacuum tests in Ottobrunn by spacecraft prime contractor Astrium in the United Kingdom.

LISA Pathfinder is expected to be launched in mid-2014 to demonstrate the technologies and endurance in space for a New Gravitational wave Observatory mission, one of the candidates for ESA’s next flagship mission planned for a launch early in the next decade, aiming to find this final piece in Einstein’s cosmic puzzle.