Design of lifted dual-rate digital controllers for X-38 vehicle

A new state-matching digital redesign method to find the lifted dual-rate p ulse-amplitude-modulated (PAM) and pulse-width modulated (PWM) digital cont rollers from a predesigned, state-feedback, continuous-time controller is p resented. The proposed method provides close matching of the states of the continuous-time controlled analog system with those of the digitally redesi gned system (including intersample behavior). The redesigned lifted dual-ra te controller enables the digitally controlled X-38 vehicle to track the de sired trajectory while remaining insensitive to modeling parameters, initia l conditions, and exogenous disturbances for larger sample times than exist ing methods. The X-38 will require a PAM controller for commanding the elec tromechanical actuators that operate its aerodynamic surfaces far Eight in the atmosphere, PWM control will be used to command the reaction control je ts during orbital operations. The proposed method provides a new alternativ e for indirect digital design of state-feedback multivariable continuous-ti me systems.