Suppression of noise in the airborne laser system

The problem of suppressing acoustically induced Vibration in precision equipment is addressed. The study specifically addresses acoustically induced vibration in an airborne optical train. Two approaches were studied. (1) The first approach is to inertially instrument each optical element, sensing the motion causing optical jitter. The array of vibration measurements is used with a robust feedback control Law and with an adaptive feed forward algorithm to precisely cancel the optical jitter. (2) The second approach is to adapt an SVS active sound barrier concept to the airborne problem. The active sound barrier uses a combination of feed back and adaptive feed forward control to attenuate the sound passing through the barrier. Both approaches were demonstrated in a laboratory experiment to have excellent performance. Using the inertial instrument approach, jitter was reduced by as much as a factor of 43. Using the active sound barrier, an acoustic reduction of 17 dB was demonstrated. Anticipated benefits include improved performance for Airborne Laser (ABL) weapons used for theater ballistic missile defense. This experiment was funded through an SBIR Phase I contract, AF Contract No. F29601-95-C-0116, SBIR Topic AF95-113. The experimental set up and the results will be described.