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Segmented Mirror Image Degradation Due to Surface Dust, Alignment and FigureIn 1996 an algorithm was developed to include the effects of surface roughness in the calculation of the point spread function of a telescope mirror. This algorithm has been extended to include the effects of alignment errors and figure errors for the individual elements, and an overall contamination by surface dust. The final algorithm builds an array for a guard-banded pupil function of a mirror that may or may not have a central hole, a central reflecting segment, or an outer ring of segments. The central hole, central reflecting segment, and outer ring may be circular or polygonal, and the outer segments may have trimmed comers. The modeled point spread functions show that x-tilt and y-tilt, or the corresponding R-tilt and theta-tilt for a segment in an outer ring, is readily apparent for maximum wavefront errors of 0.1 lambda. A similar sized piston error is also apparent, but integral wavelength piston errors are not. Severe piston error introduces a focus error of the opposite sign, so piston could be adjusted to compensate for segments with varying focal lengths. Dust affects the image principally by decreasing the Strehl ratio, or peak intensity of the image. For an eight-meter telescope a 25% coverage by dust produced a scattered light intensity of 10(exp -9) of the peak intensity, a level well below detectability.
Document ID
20020043302
Document Type
Other
Authors
Schreur, Julian J. (Texas A&M Univ. Kingsville, TX United States)
Date Acquired
August 20, 2013
Publication Date
October 1, 1999
Publication Information
Publication: 1999 NASA/ASEE Summer Faculty Fellowship Program
Subject Category
Optics
Funding Number(s)
CONTRACT_GRANT: NGT8-52874
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.