THE DEVELOPMENT OF AN INERTIAL REFERENCE UNIT (IRU) APPLICABLE TO LASER WEAPON POINTING SYSTEMS

摘要

Airborne laser systems are directed energy weapons designed to defend against enemy missile attacks. These systems must be able to accurately and steadily track a target from several hundred miles away. Errors in the pointing of the laser beam at the target reduce the accuracy and lethality of the weapon system. There are two types of pointing errors: bias errors and jitter errors. Bias errors are pointing errors that do not change over time and cause the beam to partially or completely miss the target. Jitter errors are oscillations of the beam around the target that spread the beam over a larger area, thereby reducing the energy density of the beam impinging on the target and decreasing the probability of a kill. Jitter errors are usually the result of vibrations of the optical platform and vibrations between the different optical components mounted to the platform. The purpose of the IRU is to reduce the jitter errors of the system by providing an inertially stable reference beam that can be used as part of a feedback control system to measure and eliminate the jitter in the laser pointing system. The IRU works in conjunction with a fast-steering mirror and a detector to measure and correct jitter errors occurring within the optics of the laser pointing system. A single-axis IRU prototype with an outer-axis large angle positioner was designed and modeled. The outer-axis assembly is driven by a DC motor and its purpose is to extend the IRU's range and also provide a source for input disturbances that the IRU will attempt to cancel. An analog feedback control system was developed to close loops around the IRU and outer-axis assembly that will provide two modes of control; large angle positioning and IRU rate-stabilized mode. After the prototype has been fabricated and assembled, the IRU will be tested by driving the outer-axis assembly in an oscillatory fashion to create a base disturbance that the IRU will attempt to cancel. The finished mechanism will be primarily used as a laboratory instructional tool to demonstrate the principles of classical control theory.