Use of updated material properties in parametric optimization of spaceborne mirrors

Hull, Tony; Westerhoff, Thomas; Weidmann, Guenter; Kirchhoff, Rule

doi:10.1117/12.2234269

Cited by 2 publications

(3 citation statements)

References 5 publications

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“…With marking the earlier published literature data point for ZERODUR together with the new point achieved with narrower CTE tolerances, the improvement reveals to be outstanding. 42,44,45 Fig. 21 Solar telescope GREGOR 1.5-m diameter × 161-mm-thick primary mirror, 420 pockets 8-mm rib thickness, and 65% weight reduction.…”

Section: Suitability Of Zerodur Extremely Lightweight Mirrors For Space Missionsmentioning

confidence: 99%

“…Materials: beryllium (Be), silicon (Si), silicon carbide (SiC), fused silica (FS), titanium-doped fused silica (ULE), aluminum (Al), molybdenum, and ZERODUR ® . 42,43 Progress in machining requires measurement equipment with higher accuracy. A new coordinate measuring machine at Schott accredited by the German National Bureau of Standards (DAkkS) provides versatile measuring capabilities in a volume of 5 m × 6 m × 2 m (see Fig.…”

Section: Large Blanks With Sophisticated Geometrical Featuresmentioning

confidence: 99%

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Glass ceramic ZERODUR®: Even closer to zero thermal expansion: a review, part 2

Hartmann

Jedamzik

Carré

et al. 2021

J. Astron. Telesc. Instrum. Syst.

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Observational astronomy has sought better telescopes with higher resolution from its beginning. This needs ever-larger mirrors with stable, high-precision surfaces. The extremely low-expansion glass ceramic ZERODUR ® has enabled such mirrors for more than 50 years with significant improvements in size and quality since then. We provide a survey of the progress achieved in the last 15 years. Equally important as the thermal expansion coefficient CTE is its homogeneity. The CTE variation in 4-m mirror blanks lies below 5 ppb∕K in radial and axial directions on large and short scales. Improved measurement capabilities allow reduced bias, which in the past made variations look greater than they were. Isotropy and uniformity of ZERODUR are outstanding. A method for lifetime calculation increases reliability considerably with respect to mechanical loads. The production and metrology capability and capacity are greatly extended. Surface figure and texture of large blanks allow starting directly with polishing. Filigree structures with up to 90% weight reduction are well-suited for space mirrors. The progress with low thermal expansion and its measurement, the insensitivity of ZERODUR against ionizing radiation in space, and outstanding application examples are presented in the first part of our review. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: Suitability Of Zerodur Extremely Lightweight Mirrors For Space Missionsmentioning

confidence: 99%

Section: Large Blanks With Sophisticated Geometrical Featuresmentioning

confidence: 99%

Glass ceramic ZERODUR®: Even closer to zero thermal expansion: a review, part 2

Hartmann

Jedamzik

Carré

et al. 2021

J. Astron. Telesc. Instrum. Syst.

Self Cite

View full text Add to dashboard Cite

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“…The key property of the glass ceramic ZERODUR ® is its extremely low-thermal expansion. 1 Equally and sometimes even more important is the very high homogeneity of this property throughout the total volume of very large items. 2 Both together are the essential criteria deciding on the application of the material.…”

Section: Introductionmentioning

confidence: 99%

Minimum lifetime of ZERODUR® structures based on the breakage stress threshold model: a review

Hartmann

2019

Opt. Eng.

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Increasing demand for using the glass ceramic ZERODUR ® for optical elements with high mechanical loads called for strength data based on statistical samples larger than 20 specimens. The data now available for a variety of practical surface conditions (ground, lapped, and etched) allow stresses by factors 4 to 10 times higher than before. The larger samples revealed that breakage stresses of ground surfaces follow the threeparameter Weibull distribution. The threshold parameter of this distribution reflects the existence of an upper limit for the microcracks depth within such surfaces. It is equivalent to a minimum strength below which breakage probability is zero. Its use in the well-established crack growth theory allows calculating minimum lifetimes including fatigue using the stress corrosion constant for the prevailing environmental humidity. Long-term loading tests have confirmed the validity of the model. For fully etched surfaces, the Weibull statistics fails because in such cases failure mechanism is not unique anymore. Nevertheless, ZERODUR ® with fully etched surfaces that are free from other damages still exhibit minimum breakage stress above 100-MPa tensile stress. The successful satellite mission LISA Pathfinder has confirmed the possibility to apply ZERODUR ® for utmost precision experiments together with high mechanical loads.

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Use of updated material properties in parametric optimization of spaceborne mirrors

Cited by 2 publications

References 5 publications

Glass ceramic ZERODUR®: Even closer to zero thermal expansion: a review, part 2

Glass ceramic ZERODUR®: Even closer to zero thermal expansion: a review, part 2

Minimum lifetime of ZERODUR® structures based on the breakage stress threshold model: a review

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