Spatial frequency selective error sensing for space-based wide field-of-view multiple-aperture imaging systems

摘要

High-resolution space-based imaging applications are limited by the difficulty of placing large monolithic mirrors in space and by technology limitations on the diameter achievable in monolithic mirrors. Multiple-mirror imaging systems can overcome these limitations but require precise alignment-error sensing and correcting schemes to maintain all elements in phase. When a wide field of view is desired, the complexity increases substantially since significant error terms will be a function of field angle. Approaches which can reduce the complexity of the error sensing/correcting schemes are thus of great interest. By sampling selected spatial frequencies, representative of both the individual subapertures and errors between subapertures, measurement of all error terms except absolute piston can be achieved. A technique which places a nonredundant mask in the compacted pupil plane of a phased-array imager and senses the selected spatial-frequency magnitude and phase in the focal plane has been analyzed. This technique can reduce complexity in the local error-sensing system while accounting for all tilt, geometry, magnification, and relative piston errors.