A space vehicle is usually required to maintain a specific orientation with respect to Earth. If flexible appendages (such as panels of solar cells) are associated with the vehicle, the problem of controlling the attitude of the spacecraft becomes more complex. In this paper, attention will be directed towards the control of this class of vehicle when the control law suggested by Hughes is employed. This approach requires that the attitude and its rate of change with time are available in satisfactorily noise-free forms. The measurement of attitude is physically possible, but the measurement of rate is not. Consequently a Luenberger state observer was employed by the authors to reconstruct the rate information. A similar approach was adopted earlier where an analogue model of the observer was employed. It was found that in some situations the design procedure for the observer stipulated that very large amplifier gains should be incorporated into the model, and great care was needed to avoid this problem.