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Not having any insulation on the ET



 
 
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  #1  
Old August 1st 03, 05:57 PM
Bill Bonde
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Default Not having any insulation on the ET

Since it obviously is an issue that the insulation on the external tank
of the Shuttle tends to fall off, why not just completely do away with
the insulation?

Some sort of rapidly removed insulation could detach from the ET while
it is on the pad just before lift off. This should save weight as a side
benefit. If the heat generated in flight is too much, perhaps the
insulation in some parts of the tank could be left off and the
insulation needed for the actual flight made more robust.

Has anything like this been considered?
  #2  
Old August 2nd 03, 06:34 PM
Bill Bonde
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Default Not having any insulation on the ET



jeff findley wrote:

Bill Bonde writes:

Since it obviously is an issue that the insulation on the external tank
of the Shuttle tends to fall off, why not just completely do away with
the insulation?

snip
Has anything like this been considered?


Read the Columbia Loss FAQ:

http://www.io.com/~o_m/home.html

Look for this question and read the answer:

Why is the ET insulation on the *outside*?

I've quoted the text you refer to at the bottom. It doesn't really
address what I'm talking about. I wasn't suggesting not having
insulation while the tank was on the ground, just having some means to
remove it immediately before lift-off. I don't think this is *that* wild
of an idea. A two piece foam form that is well supported and
mechanically moved from a position insulating the tanks away to allow
lift-off would eliminate ice build up problems and too much boil off
while Shuttle is on the ground. I don't have any idea whether heat
generated during the flight would cause problems by too rapidly heating
the liquid fuels or heating them in the wrong places too much.



#begin quote from URL provided
The insulating foam that was seen to break off the ET was able to do so
because it is on the outside of the tank. This is in contrast to the
design of other large launch vehicles, such as the Saturn 5, where the
insulation was on the *inside* of metal-walled tanks.

The reason for this is that the ET insulation is doing a somewhat
different job on the Shuttle ET than is the case for other launchers.
On, for instance, the Saturn 5, the internal insulation was purely to
reduce the rate of boil-off of cryogenic (ultra-low temperature)
propellants. It did not totally insulate the tanks, so the outer metal
walls still became extremely cold; cold enough that water vapor from the
air condenses and freezes into ice on the side of the launcher. At
launch, such ice breaks free, often in quite large chunks. This is very
clearly and spectacularly visible in many of the close-up films of
Saturn 5 launches.

For the Saturn, this was not a problem, as the ice fell straight off the
side of the launcher. There was little for it to hit on the way, and
what there was was part of an expendable rocket anyway. On the Shuttle,
the situation is very different. As is now well known, anything falling
off the ET can hit the Orbiter on the way and potentially cause serious
damage to the delicate TPS tiles. As such it is important to prevent the
build-up of ice on the ET. For this reason the insulation is on the
*outside*, and as well as helping keep the propellants cold, it also
stops the outer layer of the ET from chilling so far that ice forms on
it. Whatever the hazards posed by fragments of foam insulation breaking
off and striking the orbiter, the hazards from chunks of ice would be
far worse.

One other thing to keep in mind is this: a very significant advantage of
external insulation is that metals get stronger at low temperatures,
meaning the walls of the tank can be thinner than if the insulation were
on the inside.
#end quote
  #3  
Old August 2nd 03, 07:57 PM
Jorge R. Frank
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Default Not having any insulation on the ET

Bill Bonde wrote in
:

I wasn't suggesting not having
insulation while the tank was on the ground, just having some means to
remove it immediately before lift-off. I don't think this is *that*
wild of an idea. A two piece foam form that is well supported and
mechanically moved from a position insulating the tanks away to allow
lift-off would eliminate ice build up problems and too much boil off
while Shuttle is on the ground.


It sounds extremely wild to me. The forms would necessarily be complex
shapes due to the need to accommodate the SRBs and orbiter, so the removal
would not be a straightforward translation-motion. The removal would also
be a time-critical process that must work perfectly every time, else
catastrophic results could ensue. It seems much easier to me to simply
reformulate the foam so it doesn't fall off in the first place, or failing
that, to prevent the big pieces from coming off and recertify the orbiter
(hardening the TPS as necessary) to handle impacts from smaller pieces.

I don't have any idea whether heat
generated during the flight would cause problems by too rapidly
heating the liquid fuels or heating them in the wrong places too much.


It would. In fact, protection from ascent heating was the original reason
for having the foam on the outside of the tank - the ice formation problem
was not appreciated until the mid-to-late 1970s.

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  #4  
Old August 2nd 03, 11:36 PM
gbaikie
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Default Not having any insulation on the ET

"Jorge R. Frank" wrote in message ...
Bill Bonde wrote in
:

I wasn't suggesting not having
insulation while the tank was on the ground, just having some means to
remove it immediately before lift-off. I don't think this is *that*
wild of an idea. A two piece foam form that is well supported and
mechanically moved from a position insulating the tanks away to allow
lift-off would eliminate ice build up problems and too much boil off
while Shuttle is on the ground.


It sounds extremely wild to me. The forms would necessarily be complex
shapes due to the need to accommodate the SRBs and orbiter, so the removal
would not be a straightforward translation-motion. The removal would also
be a time-critical process that must work perfectly every time, else
catastrophic results could ensue.


How about a cold dry helium balloon covering, the balloon is over
pressurized and shatters as shuttle clears launch tower. The balloon
fits over ET and it can made reflective of solar energy. The balloon
strength would mainly have to be strong enough to withstand a windy
day and it's helium pressure would be low. The total weight of balloon
could be a few pounds.

It seems much easier to me to simply
reformulate the foam so it doesn't fall off in the first place, or failing
that, to prevent the big pieces from coming off and recertify the orbiter
(hardening the TPS as necessary) to handle impacts from smaller pieces.

I don't have any idea whether heat
generated during the flight would cause problems by too rapidly
heating the liquid fuels or heating them in the wrong places too much.


It would. In fact, protection from ascent heating was the original reason
for having the foam on the outside of the tank - the ice formation problem
was not appreciated until the mid-to-late 1970s.

  #6  
Old August 5th 03, 03:16 AM
Tony Rusi
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Default Not having any insulation on the ET


How about a cold dry helium balloon covering, the balloon is over
pressurized and shatters as shuttle clears launch tower. The balloon
fits over ET and it can made reflective of solar energy. The balloon
strength would mainly have to be strong enough to withstand a windy
day and it's helium pressure would be low. The total weight of balloon
could be a few pounds.

You should get a patent lawyer on this!
 




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