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What is the practical limit for a size and weight of an object that we can realistically put into space now? I imagine that a, for example, 10meter wide lens wo

by yoz-y 9y ago

What is the practical limit for a size and weight of an object that we can realistically put into space now? I imagine that a, for example, 10meter wide lens would be extremely heavy and can not be really split into pieces for shipping. How much smaller space telescopes are for the same performance?

dredmorbius 9y ago
The James Webb Space Telescope is an example of a segmented-mirror optical scope. The deployment video (simulation) is fascinating to watch: https://m.youtube.com/watch?v=v6ihVeEoUdo https://m.youtube.com/watch?v=v6ihVeEoUdo It has a 6.4m (21ft 4in) primary mirror. Which, from a pragmatics standpoint, answers your question. Though I suspect mission plans could be drafted for a larger scope yet. https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope
- ExactoKnight 9y ago
  Fascinating video, but honestly the only thought that kept going through my head is: they've overcomplicated this. Despite it's impressive number of steps, this does not look like good engineering. Instead, it looks like a design by committee, with engineers going drunk on complex parts coming together rather than dumbing down the unfurling of this telescope down to its most basic possible mechanism, with the fewest moving parts possible (where failure is chronically always possible). Seeing how overcomplicated this is, it's no surprise it cost $10 billion to build.
  - dredmorbius 9y ago
    I strongly suspect they aren't. You're looking at a high-precision instrument, that's being fit inside a distinctly finite space and mass budget, that will have to operate for years (possibly decades), and which is beyond reach of any conceivable service mission for a very long time. Movement, thermal control (the Webb operates in the low end of the visible spectrum, through the infrared, so its temperature itself is critical), alignment, and drift, all matter. And every piece of equipment has to be tested and trialed to the maximum extent possible. Yes, it's a bit Rube-Goldbergish, but then, so is the specification.
tim333 9y ago
Space X's Falcon Heavy is supposed to launch in november with a 57 ton payload. I'm not sure how big the payload can be. I wonder if you could make one with a few bits of lens that fold out? They'd have to be positioned more accurately that one wavelength of light (to ~100nm say or a 10,000th of a mm) which is tricky on earth but might be doable in space where you don't have gravity making things flop?

by yoz-y 9y ago

dredmorbius 9y ago

The James Webb Space Telescope is an example of a segmented-mirror optical scope. The deployment video (simulation) is fascinating to watch: https://m.youtube.com/watch?v=v6ihVeEoUdo https://m.youtube.com/watch?v=v6ihVeEoUdo It has a 6.4m (21ft 4in) primary mirror. Which, from a pragmatics standpoint, answers your question. Though I suspect mission plans could be drafted for a larger scope yet. https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope

ExactoKnight 9y ago
Fascinating video, but honestly the only thought that kept going through my head is: they've overcomplicated this. Despite it's impressive number of steps, this does not look like good engineering. Instead, it looks like a design by committee, with engineers going drunk on complex parts coming together rather than dumbing down the unfurling of this telescope down to its most basic possible mechanism, with the fewest moving parts possible (where failure is chronically always possible). Seeing how overcomplicated this is, it's no surprise it cost $10 billion to build.
- dredmorbius 9y ago
  I strongly suspect they aren't. You're looking at a high-precision instrument, that's being fit inside a distinctly finite space and mass budget, that will have to operate for years (possibly decades), and which is beyond reach of any conceivable service mission for a very long time. Movement, thermal control (the Webb operates in the low end of the visible spectrum, through the infrared, so its temperature itself is critical), alignment, and drift, all matter. And every piece of equipment has to be tested and trialed to the maximum extent possible. Yes, it's a bit Rube-Goldbergish, but then, so is the specification.

tim333 9y ago

Space X's Falcon Heavy is supposed to launch in november with a 57 ton payload. I'm not sure how big the payload can be. I wonder if you could make one with a few bits of lens that fold out? They'd have to be positioned more accurately that one wavelength of light (to ~100nm say or a 10,000th of a mm) which is tricky on earth but might be doable in space where you don't have gravity making things flop?