Attitude Propagation for a Slewing Angular Rate Vector

Attitude propagation typically involves only two coordinate frames one inertial and the other fixed with the vehicle body. If the angular rate vector maintains a fixed direction, attitude propagation is relatively easy. However, slewing or coning angular rate vectors cause difficulties in propagating attitude. As a result, coning algorithms have been developed to reduce coning error. In this work, a new method to propagate vehicle attitude is proposed. It employs an additional coordinate system that slews with the angular rate vector. In this intermediate slewing reference frame the angular rate vector is fixed, thereby eliminating coning error. The method improves attitude propagation accuracy. For pure coning motion, there is no propagation error using this new method.