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Probe aims to detect gravitational waves


BERLIN—The European Space Agency today launched a rocket carrying two cubes of gold and platinum almost a million miles from Earth so scientists can see how they’ll behave in free fall at a cost of more than $450 million.

What may sound like a frivolous enterprise actually is the prelude to a far more ambitious mission that it’s hoped will measure ripples in space-time caused by black holes and other massive objects lurking unseen in dark corners of the galaxy.

Also known as gravitational waves, these ripples were predicted by Albert Einstein a century ago but never have been directly detected.

In order for that mission—tentatively scheduled for launch in 2034—to succeed, the European Space Agency first has to test whether it can shield objects from external influences well enough to measure the minute effects of gravitational waves.

“We want to see whether we can create an environment in orbit that’s free of interference, and where we can conduct these high-precision measurements,” said Michael Menking, senior vice-president for Earth observation, navigation, and science at Airbus Defence and Space.

The company is the main technology contractor on the LISA Pathfinder mission.

The probe separated from the Vega rocket two hours after its launch from ESA’s space port in French Guiana early this morning (local time).

“We have a mission,” project scientist Paul McNamara said to cheers and hugs at the control rooms in Kourou and Darmstadt, Germany after receiving the first signal from the spacecraft.

By mid-January, the probe will have reached an orbit about 1.5 million km from Earth, where the pull from the planet’s gravity is balanced by that of the sun.

The cubes—made from gold and platinum to reduce their susceptibility to magnetic fields—then are carefully released inside a box that shields them from cosmic particles and other interference which might affect the measurements performed by a sensitive laser.

The laser is capable of detecting movements of less than 10 millionths of a millionth of a metre.

“Our biggest enemy is the light from the sun that hits the satellite and pushes it around,” said Oliver Jennrich, a scientist working on the LISA Pathfinder mission.

To counter this, the satellite uses NASA-supplied thrusters capable of making tiny corrections to the probe’s position to keep it in the right orbit and prevent the free-falling cubes from crashing into the inside of the box.

This should provide a near-perfect cosmic isolation chamber to measure the effect of gravitational waves, said Jennrich.

The LISA Pathfinder mission itself won’t detect any gravitational waves, though.

Because the pair of two-kg cubes only are 38 cm apart, any object big enough to affect their relative position would have to be so huge that it would be visible with the naked eye, noted Jennrich.

Instead, the real measurements likely will have to wait almost two decades for the follow-up mission, provisionally called LISA.

It will involve three satellites positioned in a triangle five million km apart from each other.

Together they should be able to detect gravitational waves caused by enormous objects such as supermassive black holes—like the one that’s thought to sit at the centre of the Milky Way.

Jennrich said measuring gravitational waves also would allow scientists to peer through the dust and debris that obscures much of what’s going on at the centre of the galaxy.

By the time LISA is launched, ground-based experiments already may have succeeded in detecting gravitational waves for the first time, said Toby Wiseman, a physicist at Imperial College, London, who isn’t involved with the space project.

But because of the interference they suffer from on Earth, ground-based experiments likely will be limited to measuring the extreme bursts of gravitational waves that occur during rare, dramatic events.

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