Gravity Probe B

Gravity Probe B carried four of the most precisely machined gyroscopes ever built to test two predictions of general relativity: the geodetic effect, the warping of spacetime by Earth's mass, and frame-dragging, the much smaller twisting of spacetime by Earth's rotation. Science data was collected through 2005, but separating the tiny frame-dragging signal from instrument noise took years; final results confirming both effects were published in 2011.