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The recent NASA press release Primary Mirror for NASA’s Roman Space Telescope Completed states:

While it’s the same size as the Hubble Space Telescope’s main mirror, it is less than one-fourth the weight. Roman’s mirror weighs only 410 pounds (186 kilograms) thanks to major improvements in technology.

What are the "major improvements in technology" that would allow for such a drastic reduction in weight?

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    $\begingroup$ Interesting question! I was going to guess that they used silicon carbide like these instead of glass, but the article says they used glass. $\endgroup$
    – uhoh
    Sep 5 '20 at 22:14
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    $\begingroup$ Every article I read parrots that exact same phrase, but never gives any detail. Annoying. $\endgroup$ Sep 6 '20 at 19:12
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    $\begingroup$ @OrganicMarble there are some images here. It's a complicated Three-mirror anastigmat and so 1) doesn't look at all like Hubble, 2) has two more pretty big mirrors, 3) has a giant hole in the primary, and (4?) I don't know but there might be actuators in one of the other elements to actively compensate for small thermal drifts. Until recently it was called WFIRST so that may be a helpful search term. $\endgroup$
    – uhoh
    Sep 7 '20 at 0:52
  • $\begingroup$ A more fair, or at least interesting comparison would be the payload mass of RTS vs HST. RTS's telescope itself may not be lighter than HST's telescope for example. $\endgroup$
    – uhoh
    Sep 7 '20 at 0:56
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    $\begingroup$ @OrganicMarble - That this satellite is an NRO hand-me-down may well explain why details are so hard to find. As I've said before, the US Department of Defense would classify $F=ma$ as TS/NOFORN if they had their druthers. $\endgroup$ Sep 9 '20 at 7:44
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WFIRST stands for Wide Field Infrared Survey Telescope. The fabrication technologies used to construct the PM blank include abrasive water jets to reduce the core's weight and a proprietary glass-to-glass fusing technology to bond the faceplates to the core. HST had much thicker face plates and thicker ribs in the core.

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    $\begingroup$ Interesting! Have you found any sources that go more into depth on this? $\endgroup$
    – IronEagle
    Dec 18 '20 at 3:54
  • $\begingroup$ PM = primary mirror, since you only use it once the space saved by using an acronym is small and the possibilities that readers will not recognize it larger. Maybe just spell it out? $\endgroup$
    – uhoh
    Dec 18 '20 at 9:37

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