How does the mass centering work?
Two objects not at the same position are generally in slightly different gravity fields; the difference in their gravitational acceleration will be A =gDX, where DX is the difference in position and g is the gravity gradient. The accelerometer measures A, and we work backwards to find an estimate for DX. Then we move the masses to reduce DX. This adjustment is made repetetively under computer control until DX is as small as possible. The limitation is the drag free residual acceleration in the differential mode. When the remaining acceleration from gravity gradient is smaller than the residual, no further adjustment is possible. The magnetic bearings are made in quadrants so we can adjust the masses’ positions easily by changing the current trapped in them. After adjustment these supercurrents will be permanently trapped and never change. The stability of the adjustment depends on the stable supercurrents rather than a possibly variable current supply. The centering error signal A occu
