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LISA Pathfinder liftoff
The LISA Pathfinder probe lifts off from the European Space Agency’s spaceport in Kourou. (ESA photo)

The LISA Pathfinder probe is heading for a vantage point a million miles from Earth to help look for gravitational waves and add a missing piece to the evidence for general relativity.

The European Space Agency said an Italian-built Vega rocket sent the spacecraft into low Earth orbit from ESA’s spaceport on the South American coast, at Kourou in French Guiana, at 04:04 GMT today (8:04 p.m. PT Wednesday).

Over the next two weeks, LISA Pathfinder will go through a series of maneuvers to set a course for L1, a gravitational balance point between Earth and the sun. The spacecraft is due to reach L1 in mid-February and begin its scientific mission in March.

The $630 million mission is all about gravitation: LISA Pathfinder is designed to release two identical 1.8-inch-wide cubes made of gold and platinum, floating in pure free-fall 15 inches apart. The spacecraft will then monitor their relative positions to an accuracy of a billionth of a millimeter, using a laser interferometer.

Such fine-scale measurements are required to detect gravitational waves – ripples in the fabric of spacetime that were predicted 100 years ago by Albert Einstein in his general theory of relativity.

Direct evidence for the existence of such waves has not yet been observed, largely because the effect is subtle: According to ESA, the ripples created by a pair of orbiting black holes would stretch a 620,000-mile-long (million-kilometer-long) ruler by less than the size of an atom.

LISA Pathfinder is designed to blaze a technological trail for an even more ambitious space mission in the 2030s, known as eLISA, or the Evolved Laser Interferometer Space Antenna. The eLISA mission calls for placing each of the gravitational test satellites a million kilometers away from the laser interferometer in an L-shaped pattern.

At the same time that LISA Pathfinder is gearing up for ts observations, the Advanced Laser Interferometer Gravitational-Wave Observatory is conducting similar experiments. The scientists behind Advanced LIGO are looking for the effect of gravitational waves on sensitive laser apparatus contained within 2.5-mile-long (4-kilometer-long) tubes at Hanford in Washington state and near Livingston in Louisiana.

The problem with Earth-based detectors is that our planet’s perturbations may be masking the subtle signature of cosmic gravitational waves. Depending on the nature of that signature, general relativity could get its strongest confirmation yet – or require additional tweaks.

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