Nonlinear resonance scanning

A new scanning concept is suggested for causing a flat mirror (or telescope) to execute a symmetric sawtooth scan pattern. The concept is based on the use of a pair of control moment gyros whose spin axes are synchronously counterrotated. If these gyros are mounted on the back of the mirror, then through the nonlinear interactions associated with the counterrotation of the spin axes of the pair of gyros, the mirror will be caused to scan back and forth through a symmetric sawtooth pattern without external drive being required. By careful choice of the parameters of the control moment gyros, scan efficiencies of the order of 90% can be achieved. This scanner concept has the virtues not only of high scan efficiency but also of requiring very little power and not reaching back on the scanner mount. It therefore seems particularly well suited for use in space applications. In this paper, the concept is described in detail and an explanation of the principles of operation is presented. An approximate analysis is worked out to provide an insight into the significance of the various design parameters. Finally, an exact analysis is presented and detailed computer calculations of the expected scan performance for a particular case are carried out.