A NASA satellite launched into polar orbit in 2004 April which carried four precisely aligned gyroscopes to test two predictions about gravity made by the general theory of relativity. Slight changes in the rotation axes of the gyroscopes will reveal how space and time are warped by the mass of the Earth, and how the Earth's rotation drags spacetime around with it (an effect known as frame dragging). It ceased operation in 2005 September.
http://einstein.stanford.edu/ Official mission website.
Subjects: Astronomy and Astrophysics.