Model feedback applied to flexible booster control

The problem of the filtering of elastic phenomena (bending and sloshing) from space booster-control feedbacks has become increasingly difficult as bending frequencies approach control frequencies in large vehicles. The design problem is compounded by the loop-gain requirements for control of an aerodynamically unstable airframe in a dynamic wind environment. This paper presents a "model feedback" approach to this design problem in which the system does not attempt to "adapt" to body bending, but instead is contrived to ignore it. The vehicle-body feedbacks, required for stability and control, are synthesized by a combination of actual body motion and information from a model of the rigid body acted upon by the control force. Following an investigation of stability and response for this system, attention is focused on the problem of response to disturbances such as wind, gusts and shear.