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You can make really really really big mirrors,. Space telescopes mirrors are limited by Fairing size, so barr folding mirrors ala James Webb, there is a fairly

You can make really really really big mirrors,. Space telescopes mirrors are limited by Fairing size, so barr folding mirrors ala James Webb, there is a fairly hard limit. https://en.wikipedia.org/wiki/Extremely_Large_Telescope https://en.wikipedia.org/wiki/Extremely_Large_Telescope

marvin 7y ago
Do you know anything about development work that's been made regarding manufacturing mirrors in space? I'm not thinking assembling them from pieces, I'm thinking more about melting some raw material and using some physical process to create in space something larger.
- clmul 7y ago
  The manufacturing tolerances for large mirrors are very small, and it seems unlikely that we would be able to do this - note that barely any manufacturing has been done in space. Assembling from pieces on the other hand, is more doable.
- ceejayoz 7y ago
  I wonder if something akin to glassblowing would work in zero-G.
- HorstG 7y ago
  Gravity is an issue for mirror production. But it is far less of an issue than tension and deformation during the months- to years-long cooling of the substrate. The temperature and environment control to do that is challenging on earth, fairly impossible in space. Except with maybe a really really huge spacestation as a thermal sink, which we won't get for the next few hundred years I'd guess...
  - m4rtink 7y ago
    Aren't the terrestrial mirrors so thick due to the need to survive all the tilting under the strong terrestrial gravity ? I would assume a micro gravity only mirror could be much thinner & thus easier to cool down. Or possible alternative techniques could be used to get the needed reflective surface geometry if it does not need to take gravity and atmosphere into account.
    - HorstG 7y ago
      Yes, but stability against vibration and thermally induced warping is also important. So you could make the mirror thinner than on the ground, but not really thin.
      - petschge 7y ago
        You also need a minimum thickness and stability if you ever want to turn the mirror to point elsewhere.
  - LargoLasskhyfv 7y ago
    I've read a novel from Daniel Suarez titled Delta-v. Chapter 31, Alchemist beginning on page 175 and ending on 177 changed my assumptions about that. With not that much suspension of disbelief. It's about chemical vapor deposition at large scale, the chapter, not the whole book. That is about near term asteroid mining. edit: book -> novel
- adwf 7y ago
  A potentially more interesting solution is liquid metal mirrors, either mercury-based or some sort of ferro-silver suspension managed electromagnetically. A hollow toroid could be spun to provide force and the liquid would naturally form a parabola. There've been a few experiments on earth and it could have huge cost saving potential in space. Instead of having to launch a 8m+ solid mirror machined to perfection, you could launch a lightweight toroidal substructure with a vat of reflective liquid at a fraction of the cost.
Filligree 7y ago
That limit won't exist forever. Sooner or later we'll get space-based industry, and I'd rather that be sooner. I'm as much a fan of astronomy as anyone, but I'm not willing to let it block the best chance we currently have of becoming a space-faring species. The comm satellites aren't important, but the launch capacity scaling is.
- clmul 7y ago
  But why would you want that we become a space-faring species, at all costs? There is not much interesting to find in space, compared to what we have on Earth (especially not close to us, and I do not see us getting out of the solar system for a long time). Perhaps you could argue that we might do asteroid mining at some point, but at the moment that's very far out of reach.
  - vidarh 7y ago
    It's all always going to remain out of reach for a long time if we don't try.
    - m4rtink 7y ago
      There is also the possibility that we miss an open window of opportunity. This might be a key resource running out, a plague or global war or even an asteroid impact. That might close the window of opportunity and not give us a second chance. So better not risk it. :-)
  - short_sells_poo 7y ago
    Because we are limited in every conceivable way down here on Earth. Transportation is expensive, resource extraction is expensive, resources are limited, space is limited, pollution is a problem, energy generation runs into geopolitical, geographical and efficiency issues. And so on. Never mind the problem of us being one asteroid strike or supervolcano away from a cataclysm, and that's not an if but a when. I have a feeling that for humans to transcend the proverbial great filter, we have to tap into the vast quantities of resources and energy in the solar system, but more importantly rekindle the pioneering era that last ended with the industrial revolution. The expensive part of the space industry is lifting infrastructure from ground to space. Moving within the solar system is comparatively cheap if we avoid descending into the gravity well of other planets. Luckily, this is unnecessary for most asteroid mining. Humankind experienced incredible advances with the toppling of every transportational frontier. The wheel, seafaring, motorized transport and flight all resulted in expansions lasting a hundred years each. The next frontier is the solar system. We don't know if we'll be able to ever leave it, but that's irrelevant because it can be our home for the next billion years. Our best shot at actually preserving the habitability of Earth is exploiting resources out in space.
modeless 7y ago
That's one of the reasons I'm excited about SpaceX's Starship. It has a large diameter, so space telescope mirrors can be much bigger with less folding.
- C14L 7y ago
  And it will (hopefully) be able to fly to the moon "for cheap" and put large, land-based telescopes in the best location there is for telescopes.
njarboe 7y ago
Aren't the newest and biggest ground based telescopes made up of many mirrors that have millions of actuators on them to correct for atmospheric distortion? I don't see why you couldn't make similar multi-mirror telescopes in space. Here is a link to an article[1] that shows three of the biggest telescopes that have 7, 798 and 492 individual mirrors respectively. The biggest one has the most mirrors. [1]https://www.space.com/22505-worlds-largest-telescopes-explained-infographic.html https://www.space.com/22505-worlds-largest-telescopes-explai...
- NikolaeVarius 7y ago
  Yes. You still have to fit it in.
- ISL 7y ago
  Physics does not exclude such an instrument. Budget does. Shipping complicated physical hardware to space requires that it absolutely must work on the first try, and never require maintenance for the lifetime of the instrument. In contrast, the large earth-based telescopes can be regularly updated, maintained, and debugged. Access for such activities costs as much as a plane ticket to Chile, instead of a dedicated mission to space.

marvin 7y ago

Do you know anything about development work that's been made regarding manufacturing mirrors in space? I'm not thinking assembling them from pieces, I'm thinking more about melting some raw material and using some physical process to create in space something larger.

clmul 7y ago
The manufacturing tolerances for large mirrors are very small, and it seems unlikely that we would be able to do this - note that barely any manufacturing has been done in space. Assembling from pieces on the other hand, is more doable.
ceejayoz 7y ago
I wonder if something akin to glassblowing would work in zero-G.
HorstG 7y ago
Gravity is an issue for mirror production. But it is far less of an issue than tension and deformation during the months- to years-long cooling of the substrate. The temperature and environment control to do that is challenging on earth, fairly impossible in space. Except with maybe a really really huge spacestation as a thermal sink, which we won't get for the next few hundred years I'd guess...
- m4rtink 7y ago
  Aren't the terrestrial mirrors so thick due to the need to survive all the tilting under the strong terrestrial gravity ? I would assume a micro gravity only mirror could be much thinner & thus easier to cool down. Or possible alternative techniques could be used to get the needed reflective surface geometry if it does not need to take gravity and atmosphere into account.
  - HorstG 7y ago
    Yes, but stability against vibration and thermally induced warping is also important. So you could make the mirror thinner than on the ground, but not really thin.
    - petschge 7y ago
      You also need a minimum thickness and stability if you ever want to turn the mirror to point elsewhere.
- LargoLasskhyfv 7y ago
  I've read a novel from Daniel Suarez titled Delta-v. Chapter 31, Alchemist beginning on page 175 and ending on 177 changed my assumptions about that. With not that much suspension of disbelief. It's about chemical vapor deposition at large scale, the chapter, not the whole book. That is about near term asteroid mining. edit: book -> novel
adwf 7y ago
A potentially more interesting solution is liquid metal mirrors, either mercury-based or some sort of ferro-silver suspension managed electromagnetically. A hollow toroid could be spun to provide force and the liquid would naturally form a parabola. There've been a few experiments on earth and it could have huge cost saving potential in space. Instead of having to launch a 8m+ solid mirror machined to perfection, you could launch a lightweight toroidal substructure with a vat of reflective liquid at a fraction of the cost.

Filligree 7y ago

That limit won't exist forever. Sooner or later we'll get space-based industry, and I'd rather that be sooner. I'm as much a fan of astronomy as anyone, but I'm not willing to let it block the best chance we currently have of becoming a space-faring species. The comm satellites aren't important, but the launch capacity scaling is.

clmul 7y ago
But why would you want that we become a space-faring species, at all costs? There is not much interesting to find in space, compared to what we have on Earth (especially not close to us, and I do not see us getting out of the solar system for a long time). Perhaps you could argue that we might do asteroid mining at some point, but at the moment that's very far out of reach.
- vidarh 7y ago
  It's all always going to remain out of reach for a long time if we don't try.
  - m4rtink 7y ago
    There is also the possibility that we miss an open window of opportunity. This might be a key resource running out, a plague or global war or even an asteroid impact. That might close the window of opportunity and not give us a second chance. So better not risk it. :-)
- short_sells_poo 7y ago
  Because we are limited in every conceivable way down here on Earth. Transportation is expensive, resource extraction is expensive, resources are limited, space is limited, pollution is a problem, energy generation runs into geopolitical, geographical and efficiency issues. And so on. Never mind the problem of us being one asteroid strike or supervolcano away from a cataclysm, and that's not an if but a when. I have a feeling that for humans to transcend the proverbial great filter, we have to tap into the vast quantities of resources and energy in the solar system, but more importantly rekindle the pioneering era that last ended with the industrial revolution. The expensive part of the space industry is lifting infrastructure from ground to space. Moving within the solar system is comparatively cheap if we avoid descending into the gravity well of other planets. Luckily, this is unnecessary for most asteroid mining. Humankind experienced incredible advances with the toppling of every transportational frontier. The wheel, seafaring, motorized transport and flight all resulted in expansions lasting a hundred years each. The next frontier is the solar system. We don't know if we'll be able to ever leave it, but that's irrelevant because it can be our home for the next billion years. Our best shot at actually preserving the habitability of Earth is exploiting resources out in space.

modeless 7y ago

That's one of the reasons I'm excited about SpaceX's Starship. It has a large diameter, so space telescope mirrors can be much bigger with less folding.

C14L 7y ago
And it will (hopefully) be able to fly to the moon "for cheap" and put large, land-based telescopes in the best location there is for telescopes.

njarboe 7y ago

Aren't the newest and biggest ground based telescopes made up of many mirrors that have millions of actuators on them to correct for atmospheric distortion? I don't see why you couldn't make similar multi-mirror telescopes in space. Here is a link to an article[1] that shows three of the biggest telescopes that have 7, 798 and 492 individual mirrors respectively. The biggest one has the most mirrors. [1]https://www.space.com/22505-worlds-largest-telescopes-explained-infographic.html https://www.space.com/22505-worlds-largest-telescopes-explai...

NikolaeVarius 7y ago
Yes. You still have to fit it in.
ISL 7y ago
Physics does not exclude such an instrument. Budget does. Shipping complicated physical hardware to space requires that it absolutely must work on the first try, and never require maintenance for the lifetime of the instrument. In contrast, the large earth-based telescopes can be regularly updated, maintained, and debugged. Access for such activities costs as much as a plane ticket to Chile, instead of a dedicated mission to space.