Steven Griffin (Boeing), James Thordahl (The Aerospace Corporation), Donald Wittich (Air Force Research Laboratory), Stanislav Gordeyev (University of Notre Dame), Eric Jumper (University of Notre Dame)
Keywords: jitter, laser
Abstract:
The Airborne Aero-Optics Laboratory (AAOL) is a recently completed research effort to measure the effects of turbulent flow on the wavefront of a laser projected from an airplane in flight. The flight-test system consists of two Cessna Citation Bravo aircraft flying in formation at a distance of approximately 50 m. One aircraft projects a laser beam to the other aircraft which receives the beam using an inertially stabilized turret with a high bandwidth track loop. In addition to its benefit in providing a means for understanding and correcting optical wavefront distortion due to turbulence, AAOL also provides an ideal platform for predicting line-of-sight jitter and comparing it to measured results. AAOL has the essential elements of an airborne optical beam control system and is subject to relevant aero-loading, but operates at low power and provides a relatively inexpensive platform for collecting flight data. This paper presents the integrated AAOL line-of-sight model for prediction of optical jitter due to flight disturbances. To accomplish this, a dynamic simulation model was derived from a finite element model of the system, optical sensitivities and control loops for calculation of closed loop, line-of-sight jitter. Disturbance inputs include measured in-flight base loading and pressure loading on the turret generated from an unsteady computational fluid dynamics model. The influence of model uncertainty was also addressed by considering two separate models. The first model was based on the initial hardware design before hardware assembly. The second model was updated based on modal tests performed on the assembled flight hardware. Frequency-varying model uncertainty factors for both models required to accurately predict the measured flight data were calculated. Predicted results with and without model uncertainty factors will be compared with measured flight data from AAOL.
Date of Conference: September 10-13, 2013
Track: Adaptive Optics