Elastic Vehicle Research Articles

Design and Application of an Adaptive Tracking Filter Control System

The design of an adaptive tracking filter control system and its application to large flexible booster vehicles is described. The problem of elastic vehicle stability is considered along with its solution by conventional and adaptive techniques. The improvement in vehicle stability, which may be achieved with the adaptive tracking filter technique as compared to conventional techniques, is shown. The control system evolved uses two adaptive tracking filters to phase stabilize the first and second bending modes, in addition to conventional compensation techniques. The application of this adaptive technique to a vehicle in which the modal frequencies are in close proximity (<2.5 percent separation) is discussed. The mechanization of the adaptive control system involves the selection of design techniques and components that are electrically and physically compatible with the intended airborne application. The development of a suitable frequency tracking technique and tracking filter is described, in addition to the electronic and mechanical design of the adaptive control system prototype.

Aerodynamic load reduction techniques for large elastic launch vehicles

Parameters are determined for an autopilot that is required to stabilize an elastic launch vehicle and simultaneously provide aerodynamic load reduction in the presence of wind disturbances during the boost phase of flight. The vehicle model considered is aerodynamically unstable. Two methods of investigation were employed, 1) Digital frequency response studies at specific flight conditions and 2) Analog study of system response during the flight trajectory. The two independent approaches complement each other. Control gains and compensation dynamics that meet single-axis stability requirements are determined. Stability analyses take into account a flexible airframe at particular discrete locations on the trajectory. These gains are then incorporated in an analog simulation to determine vehicle response through the entire trajectory.