Counterspin nutation damper analysis and design

A suitable counterspun nutation damping system was designed for IRIS, a combined spacecraft destined for geostationary orbit, and the perigee motor to put it into orbit after shuttle launch. A procedure is described for choosing a damper size, together with the number required, for any vehicle. For IRIS it is shown that two dampers, each with an angular momentum of 5 Nms, are sufficient, and that performance is adequate if one damper fails. Each damper would weigh just under 3 kg and require about 0.5 kg of batteries. The system can be operated immediately on ejection from the shuttle. Extensive computer simulations of damper performances show close agreement with predictions (for restricted cases) and reveal the effects of non-axisymmetry of the spacecraft, drive axle misalignment and Coulomb friction in the bearings.