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Large payload shrouds



 
 
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  #1  
Old August 11th 05, 03:39 PM
Thomas Womack
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Default 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

  #2  
Old August 12th 05, 01:24 AM
Alain Fournier
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Default

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

  #3  
Old December 30th 05, 03:02 PM posted to sci.space.moderated
external usenet poster
 
Posts: n/a
Default 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.

  #4  
Old January 1st 06, 01:26 PM posted to sci.space.moderated
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Posts: n/a
Default Large payload shrouds

Of course the Shuttle derivative cargo lifter proposed for the future is
based on an extended External tank so presumably might be capable of
delivering large payloads.

In article ,
(Alain Fournier) wrote:

*From:* Alain Fournier
*Date:* Thu, 11 Aug 2005 20:24:04 -0400

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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