Bounds on Achievable Closed-Loop Bandwidth for Satellite Launchers

Atmospheric flight of a satellite launcher is the most challenging phase of a launch vehicle mission. Aerodynamic disturbances play a major role in the design of an attitude control system. This paper addresses the issue of selecting suitable closed-loop bandwidth to ensure stability and performance of an attitude control system. Explicit expressions are derived in this paper, for lower bounds of achievable bandwidth. Link between actuator slew rate and upper bounds of the achievable bandwidth is also established. It is shown that on the lower side it is bounded by the aerodynamic characteristics of the launcher. On the higher side, bandwidth of the attitude control loop is bound by the actuator nonlinearity. Using describing function analysis it is found that as the design bandwidth increases, closed-loop system becomes unstable for lower amplitude of the input command.