LARES, a disco ball in space, measures relativity

By James Maynard , Jun 02, 2013 07:35 PM EDT

A "disco ball" orbiting Earth could help researchers test one important aspect of general relativity called rotational frame-dragging. The Itaian Space Agency (ASI) is trying to measure this phenomenon using the Laser Relativity Satellite (LARES). This effect, also called the Lense-Thirring effect, was missed by its much more expensive NASA predecessor nine years ago.

The Italian-made satellite, operated by the European Space Agency (ESA) is designed to measure this odd effect, predicted by Albert Einstein. This pulling on space-time is created by large rotating bodies such as the Earth. The effect is predicted to affect smaller bodies rotating next to a planet or star. The frame-dragging will cause the rotating object to begin to precess. This behavior is like a child's top as it winds down. At first, the top stands straight up, but as it loses energy, the vertical axis of the top begins to travel in an ever-widening circle before falling over.

Rotational frame-dragging is an effect that is extremely hard to measure. The difference in precession between an object exhibiting frame-dragging and one free of the effect is only one part in a few trillion. But, by bouncing lasers off the reflectors on the satellite, and carefully measuring how the spacecraft moves,researchers at the ASI believe they will see evidence of frame-dragging. However, these effects could be swamped out by other subtle effects, which researchers have to eliminate from their calculations. To do this, Measurements from the spacecraft are combined with those from the LAGEO and LAGEO 2 satellites, two other reflective satellites launched earlier by Italy.

Antonio Paolozzi from the University of Rome La Sapienza and Ignazio Ciufolini of the University of Salento are two of the researchers who have been studying data from the LARES experiments.

"By adding the LARES orbital data, it will be possible to eliminate... the effects of [these perturbations], thus allowing the achievement of about 1% accuracy," Paolozzi and Ciufolini said.

Launched in early 2012, LARES is made of tungsten, and is covered in 92 reflectors, but has no moving parts. It weighs about 880 pounds, but is only about the size of a soccer ball. The small size and significant weight make it the densest known object in orbit anywhere in the solar system, and it is the first object made of tungsten placed into orbit.

In order to measure rotational frame-dragging, NASA launched the Gravity Probe B, a $750 million dollar test facility into space in 2004. The spacecraft included four gyroscopes covered in superconducting materials. Procession of the gyroscopes was measured through the movement of electrons through the system. Faults in the equipment lowered the accuracy of the measurements from 99 percent to just 80 percent. LARES is predicted to produce readings at least ten times more accurate than the actual results achieved with Gravity Probe B nine years ago.

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