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Splendid It is destined for a point in space 1.5 million kilometres from Earth — too far away for astronauts to visit and fix the telescope if something goes w

Splendid It is destined for a point in space 1.5 million kilometres from Earth — too far away for astronauts to visit and fix the telescope if something goes wrong. Hubble required an after-launch repair in 1993, when astronauts used the space shuttle to get to the Earth-orbiting observatory and install corrective optics for its primary mirror, which had been improperly ground.

gadnuk 5y ago
The whole Hubble mirror fiasco was fascinating. The before and after images of the galaxy M100 in the following link outlines the extent of the error: https://www.nasa.gov/content/hubbles-mirror-flaw https://www.nasa.gov/content/hubbles-mirror-flaw One may assume that maybe the error was simply too big and that's why the aberration. Here's the root cause and the magnitude of the error would be dismissed as nothing by most people on this planet but ultimately turned out to be huge! "Ultimately the problem was traced to miscalibrated equipment during the mirror's manufacture. The result was a mirror with an aberration one-50th the thickness of a human hair, in the grinding of the mirror."
- a9h74j 5y ago
  That's huge. Everyday profile accuracy can be spoken of in "quarter wavelength"-like terms.
  - xxpor 5y ago
    Was that true in 1979?
    - HPsquared 5y ago
      Accuracy less than a wavelength has been possible for a long time: https://en.wikipedia.org/wiki/Foucault_knife-edge_test https://en.wikipedia.org/wiki/Foucault_knife-edge_test
      - xxpor 5y ago
        Huh wow, that's brilliant! I was expecting something super complicated with extremely high tech sensors.
        a9h74j 5y ago
        Spherical-against-spherical and flat-against-flat grinding can be self-truing, so in effect centuries-old clever results required clever testing to verify. High tech in those days? Rumor I heard in the mid-1980s was that LLNL had [vertical?] lathes which could mechanically cut mirrors to optical-profile accuracy. Supposedly 100gpm liquid flows were required to keep the part temperatures uniform.
panick21_ 5y ago
The problem is that this actually makes no sense. For the price and cost of the Shuttle missions, a new even better Hubble could have been built.
- quickthrower2 5y ago
  Probably would have been bad optics to let the first one become space junk.
  - panick21_ 5y ago
    It was working fine, it could have de-orbited.

gadnuk 5y ago

The whole Hubble mirror fiasco was fascinating. The before and after images of the galaxy M100 in the following link outlines the extent of the error: https://www.nasa.gov/content/hubbles-mirror-flaw https://www.nasa.gov/content/hubbles-mirror-flaw One may assume that maybe the error was simply too big and that's why the aberration. Here's the root cause and the magnitude of the error would be dismissed as nothing by most people on this planet but ultimately turned out to be huge! "Ultimately the problem was traced to miscalibrated equipment during the mirror's manufacture. The result was a mirror with an aberration one-50th the thickness of a human hair, in the grinding of the mirror."

a9h74j 5y ago
That's huge. Everyday profile accuracy can be spoken of in "quarter wavelength"-like terms.
- xxpor 5y ago
  Was that true in 1979?
  - HPsquared 5y ago
    Accuracy less than a wavelength has been possible for a long time: https://en.wikipedia.org/wiki/Foucault_knife-edge_test https://en.wikipedia.org/wiki/Foucault_knife-edge_test
    - xxpor 5y ago
      Huh wow, that's brilliant! I was expecting something super complicated with extremely high tech sensors.
      - a9h74j 5y ago
        Spherical-against-spherical and flat-against-flat grinding can be self-truing, so in effect centuries-old clever results required clever testing to verify. High tech in those days? Rumor I heard in the mid-1980s was that LLNL had [vertical?] lathes which could mechanically cut mirrors to optical-profile accuracy. Supposedly 100gpm liquid flows were required to keep the part temperatures uniform.

panick21_ 5y ago

The problem is that this actually makes no sense. For the price and cost of the Shuttle missions, a new even better Hubble could have been built.

quickthrower2 5y ago
Probably would have been bad optics to let the first one become space junk.
- panick21_ 5y ago
  It was working fine, it could have de-orbited.