Further consideration of an electromechanical thrust vector control actuator experiencing large magnitude collinear transient forces

Thrust vector control (TVC) for the Space Shuttle Main Engines (SSMEs) is accomplished by hydraulic servo actuators. Marshall Space Flight Center (MSFC) is developing electromechanical actuator technology to be physically and functionally interchangeable with the existing hydraulic actuator. One of the major concerns for this design task is the large transient loads experienced by the TVC during start-up and shut-down. A non-linear model is developed to overcome the problem of integrator wind-up. A need is shown for some mechanism such that the system characteristics are different during transient force disturbances and during nominal servo conditions. It has been proposed that increased system damping during the transient force loading offers the best disturbance rejection.