More cracked ribs on Discovery ET

On Jan 4, 6:29*pm, Brian Thorn wrote:
On Tue, 4 Jan 2011 06:15:40 -0800 (PST), "

wrote:
it appears they will add stifners to the entire tank...

wouldnt it be wierd if the aged pad were somehow to blame,

Yes. Very weird. Remember, they *have* seen these cracks before... at
the factory. That makes the chances of the pad being to blame
ridiculously low.

Brian

perhaps but this is the most cracks ever found, and the first to be
found at the pad after fueiing. dont forget many tanks have been
fueled repeatedly for a long list of reasons.

theoritically these cracks at the pad should of been found before...

something else may be at work.......

" Yes. Very weird. Remember, they *have* seen these cracks before... at
the factory. That makes the chances of the pad being to blame
ridiculously low.

Again, a slight wording difference may apply - they *have* seen cracks LIKE
these before at the factory.

The factory cracks appear to have been produced by stresses resulting from
some process variation during manufacturing - or maybe a parts manufacturing
tolerance issue. But there are obviously other processes that could also
create similar cracks.

This tank was delivered without such cracks. They formed during processing
on the pad. No cracks appear to have occured on other tanks that underwent
even more cycles on the pad.

So what changed here - there's nothing that indicates the tank itself is
unique. The processes seem the same - yet all of a sudden cracks appear
while on the pad. So if the tank is the same - and the processes are the
same - the finger kind of points at something on the pad may have changed.
In some respects hard to believe a structure that size just shifted - but
it's been exposed to the elements for decades - real question is how would
you check it.



Val Kraut

..

In article ,
says...

This tank was delivered without such cracks. They formed during processing
on the pad. No cracks appear to have occured on other tanks that underwent
even more cycles on the pad.

So what changed here - there's nothing that indicates the tank itself is
unique. The processes seem the same - yet all of a sudden cracks appear
while on the pad. So if the tank is the same - and the processes are the
same - the finger kind of points at something on the pad may have changed.
In some respects hard to believe a structure that size just shifted - but
it's been exposed to the elements for decades - real question is how would
you check it.

The latest reports on this seem to point at a materials problem.

stringer investigation boosted by potential root cause find
http://www.nasaspaceflight.com/2011/...investigation-
boosted-potential-root-cause/

Jeff
--
"Had Constellation actually been focused on building an Earth-Moon
transportation system, it might have survived. The decision to have it
first build a costly and superfluous Earth-to-orbit transportation
system (Ares I) was a fatal mistake.", Henry Spencer 1/2/2011

On Jan 5, 11:25*am, Jeff Findley wrote:
In article ,
says...



This tank was delivered without such cracks. They formed during processing
on the pad. No cracks appear to have occured on other tanks that underwent
even more cycles on the pad.

So what changed here - there's nothing that indicates the tank itself is
unique. The processes seem the same - yet all of a sudden cracks appear
while on the pad. So if the tank is the same - and the processes are the
same - the finger kind of points at something on the pad may have changed.
In some respects hard to believe a structure that *size just shifted - but
it's been exposed to the elements for decades - real question is how would
you check it.

The latest reports on this seem to point at a materials problem.

* *stringer investigation boosted by potential root cause find
* *http://www.nasaspaceflight.com/2011/...investigation-
boosted-potential-root-cause/

Jeff
--
"Had Constellation actually been focused on building an Earth-Moon
transportation system, it might have survived. *The decision to have it
first build a costly and superfluous Earth-to-orbit transportation
system (Ares I) was a fatal mistake.", Henry Spencer 1/2/2011

Exactly, whereas instead as of decades ago we could have had Clarke
Station or at least the Boeing OASIS parked within Selene L1 at
roughly 10% the cost of those useless and/or dubious Apollo missions,
and in less than half the time.

~ BG

On Jan 4, 5:23*am, Sylvia Else wrote:
On 3/01/2011 3:03 AM, Pat Flannery wrote:

* I'm still trying to figure out what they mean by that; either the
launch is necessary, in which case they should either fix the tank or
swap it with another one ASAP, or the launch isn't necessary, in which
case they should just cancel the last two flights and save a lot of
time, effort, and money.

Pat

The expression is used again in the article you orignally cited: "a key
element in developing flight rationale showing the tank is structurally
sound".

IMHO it needs to be interpreted along the lines of believing that a
justification exists for thinking that the risks of flight are
acceptable. Clearly, if you can't explain why the cracks are occurring
in the first place, then you can't claim any certainty about the
behaviour of the tank after modifications are made.

Sylvia.

Our NASA uses conditional laws of physics, plus a need-to-know policy
and plenty of applied obfuscation so that perfectly rational logic
like that just doesn't fly, especially when it's not your butt getting
put at risk.

~ BG

On 1/4/2011 8:40 AM, Glen Overby wrote:
Pat wrote:
I can't really picture the cracks getting past the Michoud inspection
team before they foamed and shipped the tank, Or the cracked foam not
being spotted during assembling or transporting the stack to the launch
pad, so to me this sounds like something wrong with the ribs themselves
that got past the part manufacture's inspection process, or, more
likely, something that happened to the Shuttle stack after it was moved

They have pictures of that area of the tank before the shuttle was rolled out,
and there is no indication of the foam being cracked.

But that's exactly what I said; whatever it was apparently happened once
it was on the pad.

Pat

On 1/4/2011 3:29 PM, Brian Thorn wrote:

Yes. Very weird. Remember, they *have* seen these cracks before... at
the factory. That makes the chances of the pad being to blame
ridiculously low.

Yeah, but that assumes the rib fractures were unnoticed and foamed over
at Michoud, or formed at some point after it left Michoud...but didn't
cause the foam to crack till they started fueling it on the pad.
Back when Boeing were designing the 777, they were going to incorporate
aluminum-lithium alloy into it to save weight, but found out that
hairline cracks formed around holes drilled in it, so ditched the concept:
http://www.entrepreneur.com/tradejou...109220586.html
The stringer fractures emanate from the holes where they are attached to
the bottom of the LOX tank structure, so maybe they haven't solved that
problem yet, and hairline cracks that aren't visible at Michoud grow in
size with time, or when any stress is put on the stringers.
BTW, The launch has now been moved back to late February:
http://spaceflightnow.com/shuttle/sts133/110106delay/
And it looks like the stringers may have been made from a defective
batch of alloy from 2002.

Pat