High resolution control torques may be applied to a space vehicle by means of angular momentum storage devices, such as the reaction wheel or sphere. The reaction sphere eliminates gyroscopic cross-coupling, bearing malfunctions, and friction effects inherent to reaction wheels, by suspending a spherical rotor within an electrostatic field and torquing by means of three orthgonal stators.
The present sphere design produces a peak torque of 0.02 ft-lb and is capable of storing 0.5 ft-lb-sec angular momentum. The rotor is 5 in. in diameter and is suspended by four series self-resonant, high-voltage circuits. Heat is rejected from the rotor by radiation to the electrodes and conduction from the electrodes to the structure. Dimensional tolerances are maintained by simplifying the housing assembly to two hemispheres within which the electrodes and stators are machined. The high vacuum required to maintain the suspension voltage gradient places severe restrictions on the selection of materials to minimize outgassing and sublimation.
Unique problems are encountered in designing inductive components with low winding capacitance for the suspension circuit and in stabilizing the suspension servo loop.
Some consideration is given to scaling up the present design for increased performance capability.