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LISA Pathfinder
Image: picture alliance/dpa/S. Hoppe

Europe's LISA Pathfinder 'exceeds expectations'

Zulfikar Abbany
June 7, 2016

After three months of operation, LISA Pathfinder scientists are confident their technology "exceeds expectations." Europe may now become the first collective to investigate gravitational waves in space.


Ever heard of gravitational waves? No? Don't know what they are? Well, even if you have heard of them and know what they are, you may still be wondering, "What have they got to do with me?"

Alas, the answer is "nothing."

But when a top physicist like Professor Karsten Danzmann says we may soon be able to hear the big bang itself - as he did in an interview with DW on Monday (6.6.2016) - your wonder should turn to awe. Danzmann is a co-principle investigator on the space detector LISA pathfinder.

"The space detectors are at the beginning of space and time," says Danzmann, who also heads institutes for gravitational physics at the Leibniz Universität Hannover and the Max Planck Institute.

Testing LISA Pathfinder

In March LISA Pathfinder began testing its technology at an operational orbit of about 1.5 million kilometers from Earth. Now, the scientists behind the satellite say tests show it is beyond good.

"LISA Pathfinder is an absolutely remarkable mission," says project manager, Dr Jens Reiche. "It not only met the requirements, but actually surpassed them by far."

LISA Pathfinder is a space-borne laboratory designed to detect and investigate low frequency gravitational waves.

LISA Pathfinder
LISA Pathfinder was launched December 3, 2015 from Europe's spaceport in Kourou, French GuianaImage: picture-alliance/dpa/Guillon/Cnes/Handout

Gravitational waves were predicted by Albert Einstein in his general theory of relativity in 1915. Since then, scientists have been trying to prove they exist, because it's thought gravitational waves will expand our understanding of the universe and life itself.

A month before the LISA Pathfinder tests began, scientists working on a ground-based setup, the Advanced LIGO Detector in the US, said they had detected gravitational waves emitted by two colliding black holes. They were the first.

But Danzmann says LISA Pathfinder will take space science into a whole new era, because it will focus on low frequencies. LIGO only detects gravitational waves at high frequencies.

"The frequency at which we are observing is almost a factor of a million lower and that is the challenge in space," says Danzmann. "At high frequencies everything is easy to isolate, particularly from vibrations but also from other noise sources. But at low frequencies everything is noise."

And noise is a problem. All the truly big events in the universe radiate at low frequencies.

"If you are a black hole of millions of solar masses, then just because of your mass you can't move fast. And so all the signals that come from the big things in the universe are in this low frequency range. It is utterly impossible to [observe] this on the ground," says Danzmann.

Better than expected results

The objective of the test mission was to demonstrate its key technology. That involved putting two test masses in a near-perfect gravitational free-fall to control and measure their motion - to detect gravitational waves you need to measure the distance between two free bodies.

LISA Pathfinder
LISA Pathfinder is unique as a space laboratory for detecting gravitational wavesImage: Getty Images/ESA

The test is a bit like a space game. There is a pair of identical 2 kilogram, 46 millimeter gold cubes, separated by 38 centimeters on the spacecraft, and the spacecraft's job is shield the cubes from "external forces," such as solar winds and pressure from sunlight. It does this by constantly adjusting its position.

In between the two cubes there is a laser interferometer, measuring the test masses positions and orientations.

Danzmann's team says the results show "the two test masses at the heart of the spacecraft are falling freely through space under the influence of gravity alone." This indicates a "precision more than five times better than originally required."

"The requirements of a 'technology precursor mission' are rather relaxed, because it's just a stepping stone to the main mission," says Danzmann, "but in our case, everything worked so well that we have the requirements for the main mission in hand [...], and in principle we could fly tomorrow."

A paper detailing the results is published in Physical Review Letters on Tuesday.

Heading for a Nobel Prize

It's been said before and it will be said again. Gravitational waves are big for physics, they are big for science and humanity as a whole - even if you don't understand them. The physics community knows this and there's an international race to take the lead in this field. Not least for the knowledge we may win, but also for the prestige.

LISA Pathfinder
An inside look at the technology behind LISA PathfinderImage: ESA/ATG Medialab

It is widely expected the team behind the LIGO project, which includes scientists at Danzmann's Albert Einstein Institute in Hannover, will be awarded the Nobel Prize in Physics.

"We don't do this for Nobel Prizes," says Danzmann. But he says he's sure the ground-based discovery team behind LIGO will get one in 2017.

"It's not a hundred percent clear, but I don't see an alternative to that," he says. "Not in 2016, because it was too late. The deadline to be in the running for Nobel Prizes is February 1 and the publication was February 11, but I don't see anything else that could get it."

All we need is the political will

Nobel Prizes aside, this is a major step forward for Europe as a hub for space science. LISA Pathfinder includes a payload from the American space agency NASA, but essentially, it's a European mission. It includes research institutions from France, Germany, Italy, the Netherlands, Spain, Switzerland and Britain - although you would know it from listening to the current Brexit debate.

As for Germany, 2016-2017 could turn out to be some of its big years in space science.

"Germany has been a pioneer in gravitational waves research from day one, and the one to propose a space-based observatory," says Danzmann. "And what we've shown now with LISA Pathfinder is that we have done our homework. All it takes now is money and the political will and we can start tomorrow!"

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