Abstract
We present progress on our development of edge control for fabrication of mirror segments potentially for the European Extremely Large Telescope (E-ELT). Zeekoś Bonnet polishing technology has been adopted to achieve the form correction target. Like other Computer Numerical Controlled (CNC) polishing, accurate and stable tool Influence Functions (IFs) are important. Particular challenges arisen when polishing up to edges where the geometry of the IFs created by a bonnet changes. We described a model based on measured IFs data that allowed us accurately to predict the edge profile. To obtain IFs at the edge, data from interferometers and profilometers have been stitched. Numerical models with empirical Ifs as input data have been used to predict edge profiles with some preliminary success.
Highlights
This paper reports on part of a development programme on fabrication of mirror segments for the European Extremely Large Telescope (E-ELT) using Zeekos IRP polishing machine
The primary mirror of the proposed 42m aperture E-ELT consists of 984 off-axis aspheric hexagonal segments, each of 1.4 metres wide, but only 50mm thick
The demand for an edge figuring process is seen in parallel projects such as the Giant Magellan Telescope (GMT) and the James Webb Space Telescope (JWST) [1], [2]
Summary
This paper reports on part of a development programme on fabrication of mirror segments for the European Extremely Large Telescope (E-ELT) using Zeekos IRP polishing machine. The demand for an edge figuring process is seen in parallel projects such as the Giant Magellan Telescope (GMT) and the James Webb Space Telescope (JWST) [1], [2] This is because the total length of the edges of these segmented optical systems is much longer than those of the conventional system with one mirror. It means that spot size of tool must to be less than half of bandwidth of surface error in order to remove a certain frequency feature). It has proved possible by such techniques to maintain the entire surface right up to the extreme edge with slopes within the dynamic range of the full-aperture interferometer
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More From: Journal of the European Optical Society-Rapid Publications
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