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.