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  • 1
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    Steps toward 8m honeycomb mirror blanks. III - 1.8m honeycomb sandwich blanks cast from borosilicate glass (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The design, fabrication techniques, and equipment used for producing two 1.8-m honeycomb sandwich blanks, eventually leading to production of 8-m blanks, are reported. The procedure employed 85 cast hexagonal tiles at the bottom section, affixed against flotation by SiC bolts. The two plano concave mirrors are 1.83 m thick, weight 500 kg, and are each designed for 19 supports of astatic-lever type. Both blanks are of high quality and with an adequately low bubble content; one is to be figured to high-precision 0.25-arcsecond images, and is to be tested on the Multiple Mirror Telescope. Construction of a spin-casting facility based on the same principle is being planned for test-fabricating spin-cast mirrors on a smaller scale.
    Keywords: MECHANICAL ENGINEERING
    Type: Advanced technology optical telescopes II; September 5, 6, 1983; London
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    NASA TECHNICAL REPORTS
  • 2
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    Steps toward 8m honeycomb mirrors IV - Some aspects of design and fabrication (1984)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The tolerances in glass homogeneity, thermal control, and support of the blank, necessary to meet the requirements of telescopes in the best ground-based sites, are defined for a hypothetical 8-m honeycomb mirror spin-casting facility. Homogeneity in expansion coefficient of 10 to the -8th/C and thermal equilibration to 0.1 C are estimated. Laboratory measurements show that both can be met by a ventilated honeycomb of borosilicate or similar glass. Adequate resistance to wind pressure and buffeting can be achieved by an axial support that responds to pressure on the three defining points. Annealing of the blank at the peak cooling rate of 20 C/day will take about six weeks, leading to a temporary stress of 15 kg/sq cm.
    Keywords: MECHANICAL ENGINEERING
    Type: Advanced technology optical telescopes II; September 5, 6, 1983; London
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  • 3
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    Manufacture of large glass honeycomb mirrors (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The problem of making very large glass mirrors for astronomical telescopes is examined, and the advantages of honeycomb mirrors made of borosilicate glass are discussed. Thermal gradients in the glass that degrade the figure of thick borosilicate mirrors during use can be largely eliminated in a honeycomb structure by internal ventilation (in air) or careful control of the radiation environment (in space). It is expected that ground-based telescopes with honeycomb mirrors will give better images than those with solid mirrors. Materials, techniques, and the experience that has been gained making trial mirrors and test castings as part of a program to develop 8-10-m-diameter lightweight mirrors are discussed.
    Keywords: OPTICS
    Type: International Conference on Advanced Technology Optical Telescopes; Mar 11, 1982 - Mar 13, 1982; Tucson, AZ
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    NASA TECHNICAL REPORTS
  • 4
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    Steps toward 8 m honeycomb mirror blanks. II - Experiments with waffleplate and honeycomb casting (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A technique for fabricating large low-cost light-weight borosilicate-glass mirrors for ground and space-based astronomy is described. This technique involves the remelting of glass into complex molds for vacuum-formed ceramic fiber and is used to cast in one piece either waffleplate or full honeycomb sandwich blanks. The construction of molds and the cycle for melting and annealing are described in detail. A 1.1-m square blank with a 22.4-cm-thick face and 1.6-cm ribs, 15-cm deep on 15-cm squares, has been cast, and a 1.8-m circular blank of full honeycomb construction is scheduled for production. The casting of blanks of up to 8-m in diameter is anticipated, with densities of 200 kg/sq m (like that of the ST mirror) being typical of casting.
    Keywords: MECHANICAL ENGINEERING
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  • 5
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    Optical matching for fiber optic spectroscopy (1984)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Single silica fibers of the type developed for communications are useful in the design of astronomical spectrographs. They can be used to couple light from many objects over a wide field to a single spectrograph, or to eliminate wavelength errors from image motion and gravitational flexure. For many applications it will be advantageous to use small lenses to make the most efficient coupling into and out of a fiber. If the telescope pupil is imaged on the fiber core, an efficient coupling can be made that preserves image size over a certain range. This method is demonstrated by a laboratory test using sapphire spheres as coupling lenses.
    Keywords: OPTICS
    Type: Instrumentation in astronomy V; Sep 07, 1983 - Sep 09, 1983; London
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  • 6
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    Honeycomb mirrors of borosilicate glass - Current results and plans for 7-8m diameter (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The making of large astronomical mirrors with borosilicate glass honeycomb structure is discussed. Particular attention is given to a single casting technique for making borosilicate honeycomb mirror blanks up to 7 meters in diameter. Current work on the development of this technique involves the casting of blanks 60 cm in diameter which have the full thickness (33 cm), cell size (15 cm), and faceplate thickness (2.5 cm) needed for a 1.8-m mirror.
    Keywords: OPTICS
    Type: Instrumentation for astronomy with large optical telescopes; Sep 08, 1981 - Sep 10, 1981; Zelenchukskaya; USSR
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    NASA TECHNICAL REPORTS
  • 7
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    Honeycomb mirrors of borosilicate glass (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The fabrication of different types of honeycomb mirrors with various kinds of borosilicate glass is discussed. Borosilicate glass is much less expensive to make than zero expansion glass, and can be used for ground-based applications. A mirror 60 cm in diameter made with a slotted strut or egg-crate honeycomb of 6 mm polished Pyrex plate is shown. The faceplates are 12 mm thick, laminated from the same 6 mm sheet. The result of an interferometric test is shown, with residual errors of about wavelength/8 RMS. An alternative fabrication technique for very large mirrors which require high quality bonds between separate sheets of thick Pyrex is described. The result of a recent test casting of a 60 cm honeycomb structure made in a mold with towers 14 cm square and 6 mm gaps between is shown, and methods to cast an entire mirror in one operation are discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: In: Scientific importance of high angular resolution at infrared and optical wavelengths; Proceedings of the Conference; Mar 24, 1981 - Mar 27, 1981; Garching
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