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  • MECHANICAL ENGINEERING  (6)
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  • 1
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    Development of lightweight, glass mirror segments for the Large Deployable Reflector (1986)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Accomplishments in the development of lightweight, honeycomb-core, sandwich mirror blanks made of borosilicate and high-silica glasses at the University of Arizona for the Large Deployable Reflector program are described. In this paper, work spanning the last 2 years is reported, highlighting a new mirror blank fabrication technique that permits the fabrication of the honeycomb core integrally with the front and back plates of the blank in a single furnace cycle. Two types of mirror blanks made by this method, an off-axis, aspheric segment and a smaller Vycor circular piece, are described. The fabrication of two off-axis, aspheric mirror segments is also described. Cryogenic test results are included on the test of a 38-cm diameter, lightweight, honeycomb core, sandwich mirror made of Pyrex.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 2
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    Steps toward 8m honeycomb mirror blanks. III - 1.8m honeycomb sandwich blanks cast from borosilicate glass (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-07-27
    Beschreibung: 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.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Advanced technology optical telescopes II; September 5, 6, 1983; London
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  • 3
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    Steps toward 8m honeycomb mirrors IV - Some aspects of design and fabrication (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-07-27
    Beschreibung: 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.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Advanced technology optical telescopes II; September 5, 6, 1983; London
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Thinning and mounting a Texas Instruments 3-phase CCD (1986)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Thin CCDs with precise control of thickness and surface quality allow astronomers to optimize chips for specific applications. A means of mechanically thinning a TI 800 x 800 CCD with an abrasive slurry of aluminum oxide is presented. Using the same techniques, the abrasives can be replaced with a chemical solution to eliminate subsurface damage. A technique of mounting the CCD which retains the high quality surface generated during thinning is also demonstrated. This requires the backside of the chip to be bonded to a glass window which closely matches silicon's thermal expansion properties. Thinned CCDs require backside treatment to enhance blue and UV quantum efficiency. Two methods are discussed which may be effective with this mounting system.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 5
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    Steps toward 8 m honeycomb mirror blanks. II - Experiments with waffleplate and honeycomb casting (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: 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.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 6
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    Honeycomb mirrors of borosilicate glass (1982)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: 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.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: In: Scientific importance of high angular resolution at infrared and optical wavelengths; Proceedings of the Conference; Mar 24, 1981 - Mar 27, 1981; Garching
    Format: text
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