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Large payload shrouds
Hubble, famously, has a 94-inch mirror because that's the largest that
could be put in a spacecraft that fits in the Shuttle's payload bay. The Far Infra-Red Space Telescope has a 3.5-metre (140-inch) mirror because that's the largest that fits inside the Ariane 5 payload shroud. What would be needed to build a rocket with a significantly wider payload shroud, if some space-interferometry project could be conducted much more easily with six-metre monolithic mirrors? It's presumably almost impossible, since astronomers are instead trying to figure out how to fold up mirrors, an engineering tour-de-force which I can imagine going to very great lengths to avoid -- why? Is there some sort of optimal length-to-frontal-area ratio, such that a rocket with an eight-metre-diameter shroud is obliged to be impractically large, equipped with six Vulcain 2 engines, or otherwise absurd? Tom |
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Thomas Womack wrote:
Hubble, famously, has a 94-inch mirror because that's the largest that could be put in a spacecraft that fits in the Shuttle's payload bay. The Far Infra-Red Space Telescope has a 3.5-metre (140-inch) mirror because that's the largest that fits inside the Ariane 5 payload shroud. [snip] Is there some sort of optimal length-to-frontal-area ratio, such that a rocket with an eight-metre-diameter shroud is obliged to be impractically large, equipped with six Vulcain 2 engines, or otherwise absurd? Air drag in the lower atmosphere would be horrible for an 8m shroud. The rocket wouldn't need to be longer but you would need more engines and more propellant to feed those engines. You would also need to make the structure stronger so it could survive those great air drag pressures. You couldn't just put an 8m shroud on top of any rocket. What *might* be the easiest way to launch such a thing would be to put an 8m shroud on top of the Shuttle external tank (8.4m diameter). You would put only the mirror in that shroud, the other parts of the telescope could be folded up into a more compact shape. The external tank doesn't normally reach orbit but you could change the flight profile slightly so it would. I don't think there is any chance at all to convince NASA to even consider such a thing. Alain Fournier |
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Large payload shrouds
In article ,
Thomas Womack wrote: Hubble, famously, has a 94-inch mirror because that's the largest that could be put in a spacecraft that fits in the Shuttle's payload bay. The Far Infra-Red Space Telescope has a 3.5-metre (140-inch) mirror because that's the largest that fits inside the Ariane 5 payload shroud. What would be needed to build a rocket with a significantly wider payload shroud, if some space-interferometry project could be conducted much more easily with six-metre monolithic mirrors? It's presumably almost impossible, since astronomers are instead trying to figure out how to fold up mirrors, an engineering tour-de-force which I can imagine going to very great lengths to avoid -- why? Is there some sort of optimal length-to-frontal-area ratio, such that a rocket with an eight-metre-diameter shroud is obliged to be impractically large, equipped with six Vulcain 2 engines, or otherwise absurd? Tom You can get the same effect using an array of smaller mirrors, with precision aiming and focal point, then assembling a composite of the target. -- Remve "_" from email to reply to me personally. |
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