A semi-analytic approach to spacecraft attitude guidance

Attitude slew motions for spacecraft are usually undertaken using feedback control where only the desired final attitude is stated. In this paper attitude guidance is considered which could be used, in addition to feedback control, to enhance the efficiency of slew motions by pre-planning time-dependent attitude motions. This is achieved using a three-step method in which the angular velocities are expressed as analytic functions in terms of free parameters (on the virtual time domain), and the boundary conditions on the rotation are matched using a shooting method based on a discretized form of Rodrigue's formula. Following this, the virtual time is reparametrized. This is applied to design a rest-to-rest two-impulse slew manoeuver and a slew motion using only two reaction wheels.