Gyroscope rotor and housing from Gravity Probe B experiment with case
The Gravity Probe B experiment was designed to test two predictions of general relativity: that a massive body such as the Earth should warp and twist the space-time around it. Four spheres like this one - among the most perfect ever made - were set spinning on a spacecraft precisely pointed towards a guide star. Scientists spent seven years analysing the mission data to see if the angles of the spheres' spins were altered by the warp and twist. The final experimental results were annouced in 2011 and confirmed Einstein's predictions.