Boffins are set to discover if the Earth distorts space-time as it spins, as the Gravity-B probe is scheduled to launch today at 18:01 GMT.
The satellite will provide precise measurements of how a massive object, such as the Earth, bends space. It will also test the theory that the Earth drags space along with it as it spins
The probe will carry four of the most perfect spheres ever made. By watching how these near-perfect spheres spin, the US Space Agency hopes to test two predictions of Einstein's General Theory of Relativity.
The experiment is very simple, on paper, and was first proposed in the 1930s by Sir Arthurs Eddington. The spacecraft will be aimed constantly at a distant star. The spin axes of the on-board gyroscopes should drift minutely if the dragging effect occurs.
Actually carrying out the experiment depended on being able to build spheres perfect enough to detect the tiny changes predicted by Einstein's equations. The balls must also be kept close to absolute zero, and are held inside the biggest vacuum chamber ever sent into space, according to the BBC.
Gravity-B is due to take off on a Boeing Delta 2 rocket from Vandenberg Air Base in California. If successful, the van-sized spacecraft will orbit the planet 640km over our heads. ®