NEWS: Cryopumping still lead suspect in foam frazzle

Article by Bill Harwood, CBS News "Space Place";

reprinted on spaceflightnow.com

TITLE: External tank modifications more complex than expected

el snippo

At the time of Columbia's destruction, NASA engineers believed a phenomenon
known as cryopumping was the most likely explanation for foam shedding. When
the external tank is fueled for launch, air trapped in voids in the
insulation or near the skin of the tank can turn into a liquid. As the
shuttle rockets away, aerodynamic heating can cause that trapped liquid to
turn back into a gas. The pressure generated by that phase transition, it
was believed, could blow overlying pieces of foam away from the tank.

The Columbia Accident Investigation Board concluded such cryopumping alone
could not explain the separation of the suitcase-size chunk of debris that
doomed Columbia. But Readdy said today additional testing shows a different
type of cryopumping can, in fact, cause such shedding.

"We've found out that the bolts and the nuts being applied to actually
construct the different areas of the tank ... before you put the insulation
on, that any kind of gap in there might be an opportunity for liquid
nitrogen or liquid air to form," he said. "And what happens is, during the
ascent environment, when the shock waves form on the external tank,
aerodynamic heating and friction occurs and as a result, even trapped air
kind of expands."

The expansion of that trapped air "imparts a velocity to that particular
piece that causes large pieces to come off and instead of (peeling) away
from the tank, actually being pushed away from the tank due to that gas
pressure behind it," Readdy said. "That is really the root cause we've been
able to discover here.

"And part of the new design is to change the bolt configuration, to actually
close those areas out so that there is no opportunity for the liquid
nitrogen or liquid air to form and close out a whole number of other areas.
The other thing is characterizing the condition of the foam application more
carefully so we have a much more controlled environment, not only in terms
of the humidity that we're able to apply this foam, but the rate at which
the foam must be applied, the surfaces near it, a whole number of other
factors."

http://spaceflightnow.com/shuttle/sts114/040220tank/

At the time of Columbia's destruction, NASA engineers believed a phenomenon
known as cryopumping was the most likely explanation for foam shedding. When
the external tank is fueled for launch, air trapped in voids in the
insulation or near the skin of the tank can turn into a liquid. As the
shuttle rockets away, aerodynamic heating can cause that trapped liquid to
turn back into a gas. The pressure generated by that phase transition, it
was believed, could blow overlying pieces of foam away from the tank.

The Columbia Accident Investigation Board concluded such cryopumping alone
could not explain the separation of the suitcase-size chunk of debris that
doomed Columbia. But Readdy said today additional testing shows a different
type of cryopumping can, in fact, cause such shedding.

"We've found out that the bolts and the nuts being applied to actually
construct the different areas of the tank ... before you put the insulation
on, that any kind of gap in there might be an opportunity for liquid
nitrogen or liquid air to form," he said. "And what happens is, during the
ascent environment, when the shock waves form on the external tank,
aerodynamic heating and friction occurs and as a result, even trapped air
kind of expands."

The expansion of that trapped air "imparts a velocity to that particular
piece that causes large pieces to come off and instead of (peeling) away
from the tank, actually being pushed away from the tank due to that gas
pressure behind it," Readdy said. "That is really the root cause we've been
able to discover here.

"And part of the new design is to change the bolt configuration, to actually
close those areas out so that there is no opportunity for the liquid
nitrogen or liquid air to form and close out a whole number of other areas.
The other thing is characterizing the condition of the foam application more
carefully so we have a much more controlled environment, not only in terms
of the humidity that we're able to apply this foam, but the rate at which
the foam must be applied, the surfaces near it, a whole number of other
factors."

http://spaceflightnow.com/shuttle/sts114/040220tank/


Well that may slow things futher and largely explain the slip to next year.
wonder if the existing tanks can be fixed?

"Hallerb" wrote in message
...

All that from a guy who just advised someone else to trim his quotes...

Well that may slow things futher

What could possibly slow your research any further?

http://spaceflightnow.com/shuttle/sts114/040220tank/

Here's another interesting bit from the above article:

The foam that doomed Columbia tore away from the so-called left
bipod ramp, an aerodynamic wedge of insulation covering the fitting
used to attach one of the shuttle's two forward attachment
struts. The ramps, in place to prevent ice buildups on the
attachment fittings, have been eliminated in favor of electric
heaters.

So the fix here is to eliminate the "aerodynamic" bipod ramp and
replace it with heaters to prevent ice formation.

This is interesting to me, because my first impression of the bipod
ramps was that they looked insignificant in terms of drag reduction
(the reason they were there in the first place). This is part of a US
philosophy that places a high value on the aerodynamics of launch
vehicles, even though they spend little time in the atmosphere.

By comparison, Russian launch vehicles have attributes that make US
aerodynamics engineers cringe.

Jeff
--
Remove "no" and "spam" from email address to reply.
If it says "This is not spam!", it's surely a lie.

Support the B Haller Memorial Scholarship Fund.
"He would of wanted it." TM (c)

First the engineers were speculating that air and moisture were getting
under the foam and getting frozen. Now the idea is that there is stuff
under the foam but it is not frozen water from outside, it is cryogenic gas
from inside the tank.

I don't buy it, because what are the odds that the cryo leak and so forth
would occur under the biggest chunk of foam on the tank? I think the foam
chunk came off because it was hanging too far out in the airstream and was
not of adequate mechanical or aerodynamic design to stay attached at Mach
one.

The tank attach point insulation is going to get a rework. No mention of it
in the press for months. Heh heh....a little amusing that the most direct
remedy, fixing the thing that actually caused the accident, is the easiest
task on their return to flight to-do list.

Support the B Haller Memorial Scholarship Fund.
"He would of wanted it." TM (c)



Hey send the money!!!! I will accept it graciously and put it to great use!

Do you want the address

"Hallerb" wrote in message
...

Support the B Haller Memorial Scholarship Fund.
"He would of wanted it." TM (c)



Hey send the money!!!! I will accept it graciously and put it to great
use!

My god, I sentence with no real typos. (I'll grant the multiple ! as poetic
license. :-)

Now we see what he's really after.



Do you want the address

jeff findley wrote:
[...]
This is interesting to me, because my first impression of the bipod
ramps was that they looked insignificant in terms of drag reduction
(the reason they were there in the first place). This is part of a US
philosophy that places a high value on the aerodynamics of launch
vehicles, even though they spend little time in the atmosphere.


Uh, ISTR discussion that the aerodynamic concern was about turbulence
turning the rest of the foam into a hazard (20-20 irony noted), rather
than drag per se.

By comparison, Russian launch vehicles have attributes that make US
aerodynamics engineers cringe.


I think Pat could cite some examples of exposed Russian piping, and
some of those grill-work intertanks were probably not exposed to
significant airflow. The Soviets weren't afraid of fat-and-wide (or
maybe didn't have any choice, given the number of engines on, say, the
N-1).

Most of the areodynamic effort on US launchers goes at the pointy end;
the Shuttle is the exception because of the aerodynamics it needed on
reentry, and even then the ET doesn't seem to be excessively
aerodynamic.

/dps

dave schneider wrote:

I think Pat could cite some examples of exposed Russian piping,

Nothing could beat a N-1 in this regard:
http://www.astronautix.com/graphics/n/n1a.jpg

and
some of those grill-work intertanks were probably not exposed to
significant airflow.

Took me forever to figure out why they used those structures on their
rockets (Korolev designs in particular)
It's because the start the engine(s) on the upper stage while the stage
below it is still attached with its motors firing to avoid ullage
problems- the truss structure lets the gas from the upper stages motor
escape before it separates. We used the same technique on Titan II,
though ours looked a bit more streamlined.
Then there are those folded aerodynamic grid flaps for the
Soyuz/Zond/LOK escape system....

Pat