4 ms·

OTOH in zero g a mirror needn't support its own weight. A shade would eliminate temperature fluctuation. Naively I'd expect it should be practical for a very la

OTOH in zero g a mirror needn't support its own weight. A shade would eliminate temperature fluctuation. Naively I'd expect it should be practical for a very large, very lightweight telescope mirror to be built in situ in space instead of trying to launch and unfold one built on Earth. I guess the big problem for that right now is that for humans to do the building, it'd have to be in low orbit, a less-than-ideal environment for a long-lived scientific instrument. (Just kibbitzing, am not a rocket scientist.)

csunbird 6y ago
I mean the construction can be done on low earth orbit, then the satellite telescope can do a transfer to a higher orbit. Again, forgive my ignorance :)
rtkwe 6y ago
We've only built a tiny number of things in orbit and haven't yet built something that then gets sent off somewhere like a shipyard. It's all been stations that are then left basically where they [0] are so we don't really have the experience of how to do that yet. Also that takes a long time because it's just slow to move around in space. It does need to support it's own mass through during maneuvering and pointing operations as well so it can't be completely flimsy. Also you'd want to get further from the earth to avoid all that drag from a huge mirror in LEO. [0] Beyond periodic small orbit boosting burns
- abecedarius 6y ago
  Pointing needn't be at all quick, as long as you're not trying to catch a gamma-ray burst in the act or the like. Agreed about the badness of LEO. Another problem: a very large mirror is a significant target for micrometeoroids. It'd need to be made able to keep going after losing little patches.
  - rtkwe 6y ago
    Stiffness is a big problem too, it has to perfectly hold it's shape or the image will be distorted.
    - rtkwe 6y ago
      To expand the error that almost doomed Hubble was an error of 1/50th the width of a human hair on the main mirror. https://www.nasa.gov/content/hubbles-mirror-flaw https://www.nasa.gov/content/hubbles-mirror-flaw
    - abecedarius 6y ago
      Of course. I was fantasizing some form of active control, without the speed demand of in-atmosphere adaptive optics. This might be needed anyway after micrometeoroid damage.
handol 6y ago
I expect it would be much harder to put a mirror factory in orbit than a mirror.

csunbird 6y ago

I mean the construction can be done on low earth orbit, then the satellite telescope can do a transfer to a higher orbit. Again, forgive my ignorance :)

rtkwe 6y ago

We've only built a tiny number of things in orbit and haven't yet built something that then gets sent off somewhere like a shipyard. It's all been stations that are then left basically where they [0] are so we don't really have the experience of how to do that yet. Also that takes a long time because it's just slow to move around in space. It does need to support it's own mass through during maneuvering and pointing operations as well so it can't be completely flimsy. Also you'd want to get further from the earth to avoid all that drag from a huge mirror in LEO. [0] Beyond periodic small orbit boosting burns

abecedarius 6y ago
Pointing needn't be at all quick, as long as you're not trying to catch a gamma-ray burst in the act or the like. Agreed about the badness of LEO. Another problem: a very large mirror is a significant target for micrometeoroids. It'd need to be made able to keep going after losing little patches.
- rtkwe 6y ago
  Stiffness is a big problem too, it has to perfectly hold it's shape or the image will be distorted.
  - rtkwe 6y ago
    To expand the error that almost doomed Hubble was an error of 1/50th the width of a human hair on the main mirror. https://www.nasa.gov/content/hubbles-mirror-flaw https://www.nasa.gov/content/hubbles-mirror-flaw
  - abecedarius 6y ago
    Of course. I was fantasizing some form of active control, without the speed demand of in-atmosphere adaptive optics. This might be needed anyway after micrometeoroid damage.

handol 6y ago

I expect it would be much harder to put a mirror factory in orbit than a mirror.