European satellite to test Einstein’s gravitational theory

National Geographic : On Monday the European Space Agency launched a low-cost space probe into Earth orbit. LARES (Laser Relativity Satellite) is designed to measure frame dragging , or the distortion of spacetime caused by the rotation of a massive object, such as Earth. The probe, a solid metal sphere 35.5 cm wide and weighing 362 kg, is covered with reflectors. As the craft orbits the planet, an international network of laser-ranging stations will track its position. According to Einstein’s general theory of relativity, LARES‘s orbital plane should slowly precess over time. Although the shift will be small, measuring only about a few tens of millionths of a degree, the displacement should be about 4 m, enough for the laser-ranging system to record. At a cost of just $10 million, LARES may achieve greater accuracy measuring Earth’s frame dragging than did NASA’s Gravity Probe B , which cost $800 million.