Fundamental limitations on off-axis performance of phased telescope arrays

Abstract

The sensitivity of image quality to various system and subsystem parameters has been studied in order to determine the utility of imaging phased telescope arrays to wide field of view (FOV) applications. An error budget tree is developed to include optical design errors, assembly and alignment errors, optical fabrication errors, and environmental errors. Trade studies, parametric analyses, and previous engineering experience permitted the derivation of design and engineering tolerances from error budget allocations based on known state-of-the-art performance characteristics. The FOV limitations of the residual optical design errors (off-axis aberrations) are investigated in detail. It is shown that the somewhat benign (for conventional optical systems) aberration of field curvature results in field-dependent relative phase (piston) and pointing (tilt) errors, which rapidly degrades the image quality of phased telescope arrays as the FOV is increased. Thus extremely light tolerances on residual field curvature are needed for telescope diameters larger than one meter.