Frame dragging is the influence of mass-energy currents, especially rotation, on local inertial directions in general relativity. In a stationary axisymmetric metric tensor, an observer with zero angular momentum has coordinate angular velocity when the other spatial coordinates are held fixed. Around a rotating source this can be nonzero even without an applied azimuthal torque.
Gravity Probe B tested the effect with four cryogenic gyroscopes in Earth orbit, comparing their spin directions with a guide-star reference. Its analysis separated the much larger geodetic precession from the smaller rotation-dependent drift. This tests a change of inertial orientation, rather than ordinary frictional dragging of the spacecraft.[ref]
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Frame-dragging is a phenomenon predicted by Einstein's General Theory of Relativity, which describes how the rotation of a massive body influences the spacetime around it. When an object with a significant mass, such as a planet, star, or black hole, rotates, it "drags" the fabric of spacetime around with it. This effect is particularly pronounced near very massive and fast-rotating objects.