Electromagnetic suspension for the tip-II satellite

Inside a chamber in the TIP-II satellite a "proof mass" consisting of a small aluminum cylinder is suspended electromagnetically, and is free to move in the flight path direction (X), but constrained in the transverse motion. The X position of the proof mass is detected optically, and a plasma jet thruster is fired to make the satellite follow the proof mass. Since the proof mass is shielded from aerodynamic drag and solar radiation pressure it responds to gravity forces only, therefore it should be in a "drag-free" trajectory, and so also, the satellite. Thus drag is automatically compensated and more accurate prediction of satellite location is possible. The proof mass is a hollow cylinder of aluminum, and is suspended by eddy-current repulsion. A current at 2.08 kHz square wave is applied to a center rod which threads the proof mass, to provide the suspension. The theory of this type of suspension has been developed and measurements have confirmed the theory quite well. For TIP-II the maximum suspension force is on the order of 10
^-7
g's, a very small force relative to the proof mass weight on earth, but sufficient to suspend it in orbit. This system is being manufactured and will be put in orbit in late 1975.