Feedback Servo-Stabilization of a Rocket During Take-Off

Author: Saxon, John Solon

Year: 1953

Degree: Engineer's thesis

Advisor: Marble, Frank E.

Committee Member: Unknown, Unknown

Option: Aeronautics

DOI: 10.7907/BV8Y-QT45

Abstract

When a rocket is launched, there is a short initial period of acceleration during which the rocket is unstable. As the flight velocity increases, the aerodynamic forces acting on the fins and stabilizers become large enough to give stability. Various methods have been employed to stabilize the rocket during this launching period. Guide rails, "zero length" launchers, booster rockets which produce high initial acceleration, and auto-pilot controlled nozzles are typical devices that have been used.

This is an investigation of the requirements of a nozzle control which would stabilize the rocket during the launching period. The configuration investigated is unique in that the nozzle of the rocket is mounted as a compound pendulum, and the movement of the pendulum is utilized to furnish the signal for the nozzle control servo-mechanism, thereby eliminating the need for gyroscopic elements in the control system. The pendulum motion of the nozzle caused by a change in flight attitude of the rocket is introduced into a computer which produces an output signal proportional to the attitude of the rocket. This attitude signal is fed back to the nozzle control, which positions the nozzle.

The results of the analysis showed that the rocket was unstable during the take-off period when the nozzle control acted on the rocket attitude signal alone. Stability over a narrow range of feedback gains was indicated for the system using a simple lead circuit as a nozzle control, or in other words, when the nozzle control acted on both the attitude signal and the rate of change of attitude of the rocket. The damping characteristics of this system were poor. By changing the nozzle control function to include a response to the acceleration of the rocket attitude, the damping characteristics were improved and the range of feedback gains was widened.

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