The wet Shuttle ET

A few days back, workers accidentally bumped the ET for Atlantis and
left a small scratch on it. They decided to fix this, but have noted
water is now coming out of the ET's foam that apparently got into the
foam during hurricane Katrina.
Was the tank on Discovery also at the Michoud facility during the Hurricane?
http://www.cfnews13.com/StoryHeadline.aspx?id=16685
Because if it was, and water got into the foam, and that water freezes
when they tank it up....

Pat

Pat Flannery wrote in
:

A few days back, workers accidentally bumped the ET for Atlantis and
left a small scratch on it. They decided to fix this, but have noted
water is now coming out of the ET's foam that apparently got into the
foam during hurricane Katrina.
Was the tank on Discovery also at the Michoud facility during the
Hurricane? http://www.cfnews13.com/StoryHeadline.aspx?id=16685

IIRC, it was at KSC.


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On Sun, 25 Jun 2006 15:17:30 -0500, Pat Flannery
wrote:

Because if it was, and water got into the foam, and that water freezes
when they tank it up....

Like rain doesn't get all over the Tank during the month it sits out
on the pad before launch?

Brian

Brian Thorn wrote:



Because if it was, and water got into the foam, and that water freezes
when they tank it up....



Like rain doesn't get all over the Tank during the month it sits out
on the pad before launch?



It's not supposed to soak into the tank IIRC; and that makes what
happened to the Atlantis ET worrying, as apparently water did get into
it from the hurricane. If the tanks are soaking up rain water, then you
might have one of the major causes of foam shedding - the foam gets
water in it; the water freezes when the tank is fueled, the freezing
water expands, causing cracking in the foam, and the foam sheds as the
tank warms up during ascent and the ice in the foam melts leaving gaps.
In fact, as the temperature of the ET rises during ascent and the
ambient air pressure drops, the water may actually boil, causing steam
to occur inside the foam.
The fact that water can get into the foam also leaves the possibility
that air might be coming in contact with the tank's outer surface via
the same route that's allowing the water in, and the frozen air foam
shedding problem occurring.

Pat

"Pat Flannery" wrote in message
...
It's not supposed to soak into the tank IIRC; and that makes what happened
to the Atlantis ET worrying, as apparently water did get into it from the
hurricane.

So, why can't we wrap the ET in loose plastic sheets, and pop them off right
when the solids light?

Scott Hedrick wrote:

It's not supposed to soak into the tank IIRC; and that makes what happened
to the Atlantis ET worrying, as apparently water did get into it from the
hurricane.



So, why can't we wrap the ET in loose plastic sheets, and pop them off right
when the solids light?


We have discussed that option, although considering how well it worked
for SpaceX's Falcon... ;-)

Pat

On Sun, 25 Jun 2006 19:51:16 -0500, Pat Flannery
wrote:

Like rain doesn't get all over the Tank during the month it sits out
on the pad before launch?

It's not supposed to soak into the tank IIRC;

I honestly don't see any way to avoid that. How in the world do you
keep the rainwater from soaking in after one those almost-daily
afternoon deluges Florida is famous for?

Brian

Brian Thorn wrote:

I honestly don't see any way to avoid that. How in the world do you
keep the rainwater from soaking in after one those almost-daily
afternoon deluges Florida is famous for?



I think it's supposed to have a "rind" on it the way polyurethane foam
develops a smooth water-impervious covering as it dries.
Unfortunately; that concept is at odds with the pinholes to let
liquefied air developing in any part of the foam that has gaps to vent
to the exterior during ascent, so as not to blow pieces of foam off of
the ET (this is thought to be the root cause of the foam loss) as it
goes into a gaseous state due to ascent heating.
As the tank sits on the pad in the days or weeks before launch, it will
cool at night, and contract. That cooling may cause the gas in the
foam's interior to contract, creating a suction effect through the
pinholes, and any dew that forms on the tank's exterior to get sucked
into the venting pinholes and start to wet the foam's porous interior
(simple capillary action could also cause this).
Thin as the foam covering is, if it ever started soaking up water like a
sponge it could add a huge amount of weight to the launch stack.
The wet interior foam will freeze when the tank is fueled, and this not
only could cause fracturing of the foam due to expansion as the ice
forms, but add areas of extra mass to the foam that it was not
structurally meant to stand in regards to airflow over it and launch
vibration shaking it. This problem could well be made worse as the
frictional heating of the tank during ascent causes the trapped water
(now ice) to melt back into liquid, and possibly start to boil due to
the ascent heating and lowering ambient air pressure with altitude. In
that case you could have steam performing the same function as the
vaporizing liquid air did, and shedding to occur.
It was thought that the original painting of the tank that was done on
the first few flights added both to the tank's waterproofing and foam
shedding resistance, but that was dropped to save weight and cost.

Pat

"Pat Flannery" wrote in message
...

Thin as the foam covering is, if it ever started soaking up water
like a
sponge it could add a huge amount of weight to the launch stack.
The wet interior foam will freeze when the tank is fueled, and this
not
only could cause fracturing of the foam due to expansion as the ice
forms, but add areas of extra mass to the foam that it was not
structurally meant to stand in regards to airflow over it and launch
vibration shaking it.

The answer is obvious! Immediately before fueling we fill the tank
with hot coffee!
Or tea. Or both, since we have two tanks. Then when we see the steam
no longer coming from the insulation, we drink the coffee or tea (or
both) and load the propellants. If we have the crew drink it, we also
gain productivity, since they won't be sleeping for the next couple of
weeks.

Thank you, no cheers required, just throw money...

Pat Flannery wrote in
:

It was thought that the original painting of the tank that was done on
the first few flights added both to the tank's waterproofing and foam
shedding resistance, but that was dropped to save weight and cost.

And also because there was no evidence that it helped. STS-1 and 2 had just
as many tiles replaced due to foam impacts as the flights with unpainted
tanks.


--
JRF

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