magnetic torque is produced by torque command signal generator 68 and applied over a data path illustrated by dash line 82 to the inverting input port of summing circuit 50 the signal representative of magnetic torque is subtracted in summer 50 from the pid signal produced by controller 46 on data path 48 in effect a command signal is thereby applied to the wheel just as though the spacecraft attitude had been shifted but without the actual shift taking place another way of looking at the magnetic torque signal applied over data path 82 is that it provides the pid loop with advance warning so that it expects the application of the magnetic torques with the arrangement of fig2 including data path 82 and summing circuit 50 a signal is applied over data path 82 to summing circuit 50 when magnetic torquer 20 is turned on which causes a change in the speed of wheel 54 which counteracts the torque provided by magnetic torquer 20 thus the wheel speed is brought closer to the nominal value without attitude error of course some residual attitude error may result if the estimated magnetic torque which is subtracted from the pid signal in summing circuit 50 does not correctly represent the actual magnetic torque but this residual error is corrected by the pid control channel fig3 is a simplified flow chart illustrating logic for performing the threshold comparison and for determining the bearing protection error signal bp err in fig3 the logic begins at a start block 310 and proceeds to a block 312 in which a wheel speed variable ws is set equal to the current wheel speed and the body speed variable wb is set equal to the current.