Two gold-platinum cubes inside the Lisa Pathfinder spacecraft are being put into the state of perfect free fall

Spacecraft to start gravitational waves experiment

The European scientific spacecraft Lisa Pathfinder is preparing to start an experiment designed to detect gravitational waves in space.

Operated by the European Space Agency (ESA), Lisa Pathfinder has released two gold-platinum cubes, which will be put into the most perfect state of free fall ever obtained, to enable scientists to measure the effects of gravity on them.

ESA controllers confirmed on Monday the two 46mm cubes were floating completely freely at the distance of 38cm from each other, linked only by a laser beam, each inside its own housing.

For the whole duration of the six-week flight to Lisa Pathfinder’s destination in the Lagrangian Point 1 – a spot between the Earth and the Sun where the gravitational forces of both bodies are equal - the two cubes were firmly held in place by eight locking fingers pressing on their corners.

After the spacecraft reached its destination on 22 January, the spacecraft controllers began releasing the cubes from the grip. First the fingers were removed and a valve was opened to allow any residual gas molecules around the cubes to vent to space.

Each cube remained in the centre of its housing held by a pair of rods softly pushing on two opposite sides.

The rods were finally released from the objects earlier this week, allowing them to float completely freely with zero contact with the spacecraft’s walls.

“This is why we sent the test cubes into space: to recreate conditions that are impossible to achieve in the gravitational field of our planet,” said Paul McNamara, ESA’s project scientist.

“Only under these conditions is it possible to test free fall in the purest achievable form. We can’t wait to start running experiments with this amazing gravity laboratory.”

The cubes are still controlled by minute electrostatic forces adjusting their positions but in about a week’s time, the engineers will switch of these forces too, leaving the cubes only under the influence of gravity.

On 23 February, the team will switch LISA Pathfinder to science mode. The spacecraft’s instruments will then start detecting motions of the cubes – a result of the effects of gravity.

The existence of gravitational waves was predicted by Albert Einstein a hundred years ago but they had never been detected before this year, when the LIGO scientific collaboration announced on 11 February that faint signals had been picked up by land-based detectors in the United States.

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