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  • Didn't know they need adaptive optics in space telescopes

    From RichA@21:1/5 to All on Sat Sep 16 03:34:00 2023
    https://phys.org/news/2023-09-large-space-telescopes.html

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  • From Martin Brown@21:1/5 to Quadibloc on Sat Sep 16 13:11:13 2023
    On 16/09/2023 12:59, Quadibloc wrote:
    On Saturday, September 16, 2023 at 4:34:03 AM UTC-6, RichA wrote:
    https://phys.org/news/2023-09-large-space-telescopes.html

    Up until now, space telescopes didn't use adaptive optics.

    The article claims that if a space telescope were launched with a 6.5
    metre mirror made from a single borosilicate glass blank, though, it
    would be needed. Since there's no atmosphere to worry about, I suppose
    the culprit is thermal expansion of the mirror itself.

    More likely differential thermal expansion of the support structure as
    it goes in and out of the Earth' shadow. Pre HST launch much of the
    knowledge about those thermal effects were highly classified.

    --
    Martin Brown

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  • From Quadibloc@21:1/5 to RichA on Sat Sep 16 04:59:46 2023
    On Saturday, September 16, 2023 at 4:34:03 AM UTC-6, RichA wrote:
    https://phys.org/news/2023-09-large-space-telescopes.html

    Up until now, space telescopes didn't use adaptive optics.

    The article claims that if a space telescope were launched with a 6.5
    metre mirror made from a single borosilicate glass blank, though, it
    would be needed. Since there's no atmosphere to worry about, I suppose
    the culprit is thermal expansion of the mirror itself.

    John Savard

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  • From RichA@21:1/5 to Quadibloc on Sun Sep 17 23:08:52 2023
    On Saturday, 16 September 2023 at 07:59:48 UTC-4, Quadibloc wrote:
    On Saturday, September 16, 2023 at 4:34:03 AM UTC-6, RichA wrote:
    https://phys.org/news/2023-09-large-space-telescopes.html

    Up until now, space telescopes didn't use adaptive optics.

    The article claims that if a space telescope were launched with a 6.5
    metre mirror made from a single borosilicate glass blank, though, it
    would be needed. Since there's no atmosphere to worry about, I suppose
    the culprit is thermal expansion of the mirror itself.

    John Savard

    Changes to Beryllium (what the Webb has) with temperature are probably more than borosilicate glass. But the Webb has its heat shield.

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  • From Quadibloc@21:1/5 to RichA on Sun Sep 17 23:14:09 2023
    On Monday, September 18, 2023 at 12:08:54 AM UTC-6, RichA wrote:

    Changes to Beryllium (what the Webb has) with temperature are probably
    more than borosilicate glass. But the Webb has its heat shield.

    Yes, but:

    - The Webb space telescope is kept at a constant, and very low, temperature
    to avoid it glowing at the very wavelengths it is to observe;

    - It has a segmented mirror, not a monolithic one; and

    - Beryllium, being a metal, conducts heat more effectively than borosilicate glass, so temperatures within it are more uniform.

    So there are multiple reasons why it would be less in need of adaptive optics - which, in a sense, it has, since the individual mirrors were brought into position
    to make it work - than a telescope with one large glass mirror.

    John Savard

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