DESIGN ASPECTS OF FUTURE VERY LARGE TELESCOPES (HONEYCOMB MIRRORS).

Persistent Link:
http://hdl.handle.net/10150/183998
Title:
DESIGN ASPECTS OF FUTURE VERY LARGE TELESCOPES (HONEYCOMB MIRRORS).
Author:
Cheng, Andrew Yuk Sun
Issue Date:
1987
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Research has been carried out on three major difficulties in designing efficient and economic telescopes with 8m f/1 lightweight mirrors. These problems are polishing f/1 aspherics, thermal distortion of borosilicate glass mirror and mirror seeing. Viable solutions to all three have been developed. Solving the fundamental problems allows future very large telescopes to use such mirrors as the basic elements in the design which will reduce the cost. Accurate mirror figure together with good pointing stability given by the short focal length will enable the telescope to form images as sharp as that permitted by nature on the ground. A new technology of polishing f/1 aspherics with a computer controlled stressed lap will give very accurate figure because the lap is changed accurately to adapt the desired figure. Design parameters and performance specifications for a 0.6m aluminum stressed lap for polishing a spun cast 1.8m f/1 borosilicate glass honeycomb mirror have been developed. These can be readily scaled up for polishing 8m f/1 mirrors. Stressed lap polishing also requires accurate material removal over the entire mirror surface. An optimization algorithm using the theory of material wear has been developed to search for the polishing strokes suited for uniform or other desired removal rates. Direct casting of lightweight mirrors requires that the glass be borosilicate. The figure distortion caused by the expansion of borosilicate glass requires the mirror be isothermal to less than 0.1°C for image degradation not to exceed 0.1 arcsecond. The problem of thermal interference by air and the environment has been investigated. A method of injecting well controlled air into the cells that forces the mirror to be isothermal to within 0.1°C has been discovered. Mirror seeing caused by temperature difference between the mirror and ambient air can degrade the telescope performance, but can be reduced by careful thermal design. A simple theoretical thermal model is used to select the glass thickness of a honeycomb structure mirror. Under air ventilation thermal control, the mirror responds to changing air temperature in less than an hour, reducing mirror seeing also to 0.1 arcsecond for telescopes at good seeing sites.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Telescopes -- Design.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Astronomy; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Angel, J. Roger P.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleDESIGN ASPECTS OF FUTURE VERY LARGE TELESCOPES (HONEYCOMB MIRRORS).en_US
dc.creatorCheng, Andrew Yuk Sunen_US
dc.contributor.authorCheng, Andrew Yuk Sunen_US
dc.date.issued1987en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractResearch has been carried out on three major difficulties in designing efficient and economic telescopes with 8m f/1 lightweight mirrors. These problems are polishing f/1 aspherics, thermal distortion of borosilicate glass mirror and mirror seeing. Viable solutions to all three have been developed. Solving the fundamental problems allows future very large telescopes to use such mirrors as the basic elements in the design which will reduce the cost. Accurate mirror figure together with good pointing stability given by the short focal length will enable the telescope to form images as sharp as that permitted by nature on the ground. A new technology of polishing f/1 aspherics with a computer controlled stressed lap will give very accurate figure because the lap is changed accurately to adapt the desired figure. Design parameters and performance specifications for a 0.6m aluminum stressed lap for polishing a spun cast 1.8m f/1 borosilicate glass honeycomb mirror have been developed. These can be readily scaled up for polishing 8m f/1 mirrors. Stressed lap polishing also requires accurate material removal over the entire mirror surface. An optimization algorithm using the theory of material wear has been developed to search for the polishing strokes suited for uniform or other desired removal rates. Direct casting of lightweight mirrors requires that the glass be borosilicate. The figure distortion caused by the expansion of borosilicate glass requires the mirror be isothermal to less than 0.1°C for image degradation not to exceed 0.1 arcsecond. The problem of thermal interference by air and the environment has been investigated. A method of injecting well controlled air into the cells that forces the mirror to be isothermal to within 0.1°C has been discovered. Mirror seeing caused by temperature difference between the mirror and ambient air can degrade the telescope performance, but can be reduced by careful thermal design. A simple theoretical thermal model is used to select the glass thickness of a honeycomb structure mirror. Under air ventilation thermal control, the mirror responds to changing air temperature in less than an hour, reducing mirror seeing also to 0.1 arcsecond for telescopes at good seeing sites.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectTelescopes -- Design.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineAstronomyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorAngel, J. Roger P.en_US
dc.identifier.proquest8709888en_US
dc.identifier.oclc698372257en_US
All Items in UA Campus Repository are protected by copyright, with all rights reserved, unless otherwise indicated.