Gravity and Einstein

The gyroscope case of the Gravity-B spacecraft, before launch / Stanford University

NASA's Gravity Probe B (GP-B) mission confirmed two key predictions derived from Albert Einstein's general theory of relativity, which the spacecraft was designed to test. The experiment, launched in 2004, used four ultra-precise gyroscopes to measure the hypothesized geodetic effect, the warping of space and time around a gravitational body, and frame-dragging, the amount a spinning object pulls space and time with it as it rotates. GP-B determined both effects with unprecedented precision by pointing at a single star, IM Pegasi, while in a polar orbit around Earth.
Popular outreach article on Gravity B in Greek.