Adaptive optics for airborne platforms—Part 2: controller design

Abstract

In an airborne platform adaptive optics application, the inbound (beacon) and outbound (high-energy laser) wavefronts propagate through different regions of the atmosphere at different time instants, that is, spatial and temporal anisoplanatism cannot be neglected. Measurements in an airborne platform system are from the inbound (beacon) wavefront and therefore, the outbound, high-energy laser's wavefront phase distortion Zernike expansion coefficients must be estimated. Once the said estimates are available, these values are used by a linear quadratic regulator to drive the actuators of the deformable mirror. The controller, which consists of a Kalman filter estimator in tandem with the regulator, provides commands to the piezoelectric actuators of the deformable mirror. Thus, the estimated conjugate phase is applied to the mirror and, hence, to the outbound high-energy laser wavefront, such that at the aim point on the target, the high-energy laser wavefront distortion is minimized. In other words, the high-energy laser is correctly pointed to the aim point and the Strehl ratio is maximized. In this way, the correct deformation is applied to the deformable mirror and the benefits of adaptive optics are realized in an airborne platform application. In Part 2 of this paper, the design of the controller, that is, a Kalman filter and regulator, is addressed. The theoretical derivations are validated in extensive simulation experiments.