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Ohara, C.

Publications and source records attributed to Ohara, C..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Segmented mirror coarse phasing with a dispersed fringe sensor: experiments on NGST's wavefront control testbed

A piston sensing and control algorithm for the segmented mirror coarse phasing using a dispersed fringe sensor (DFS) has been developed for Next Generation Space Telescope (NGST) wavefront sensing and control. The DFS can detect residual piston errors as large as order of a depth-of-focus and can phase the segment mirrors with an accuracy less than 0.1 micron, which is within the capture range of the fine phasing for NGST. A series of experiments has been carried out on the NGST's Wavefront Control Testbed (WCT) to validate the modeling results, evaluate the DFS performance, and systematically explore the factors that affect the DFS performance. This paper reports the testbed results for several critical issues of DFS performance, including DFS dynamic range, accuracy, fringe visibility, and the effects of segment mirror aberrations.

Space↗
NASA NTRS2002

Segmented mirror coarse phasing with white light interferometry: modeling and experiment on NGST's wavefront control testbed

A method of coarse phasing segmented mirrors using white light interferometry (WLI) has been developed for Next Generation Space Telescope (NGST) wavefront sensing and control. Using the broadband point spread function (PSF) of the segmented mirrors taken during a segment piston scan, the WLI can accurately detect small residual piston errors. WLI does not rely on any extra optics and uses only the final imaging camera. With its high sensitivity to small segment piston error WLI can be used as a complementary phasing algorithm to the dispersed fringe sensor (DFS) for NGST. The paper will present the results from modeling and experiment on the NGST's Wavefront Control Testbed (WCT).

Space↗