Design aspects of attitude control systems

Figures of merit, besides those of performance, are discussed relative to the attitude control system of a vehicle capable of leaving and returning to the atmosphere. In addition to extreme changes in flight condition, these applications are subject to variations in configuration and performance requirements. Traditionally, control optimization has been concerned with minimizing or maximizing a variable system function such as error. Quite often these error criteria are replaced by other criteria such as invariance and the capacity for adaptability. In fact, during a complete mission including exit to re-entry it is desirable to utilize variable figures of merit. Examination of the control requirements of a modern returnable space vehicle illustrates how the various figures of merit dictate the design configuration. In those phases of the mission where self-adaptive control is employed, the figure of merit is usually determined by the particular technique selected. It is further demonstrated how the figure of merit varies with the mission phase as the control actuation configuration changes.