Failure at PAL Ramp Removal?

At the moment its not clear whether it will be removed. But if it
turns out to be a mistake to remove the PAL-Ramp, what would be the
worst case effect inflight? A structural failure of the ET, some
picture like Challenger?


## CrossPoint v3.12d R ##

wrote in :

At the moment its not clear whether it will be removed.

It has already been removed.

But if it
turns out to be a mistake to remove the PAL-Ramp, what would be the
worst case effect inflight? A structural failure of the ET, some
picture like Challenger?

The PAL ramp contributes nothing structurally to the ET; it protects the
LOX feedline, repress lines, and cable trays from aero forces. Failure of
the LOX feedline or repress lines would be nasty but wouldn't cause
strucural failure of the tank.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

In article ,
"Jorge R. Frank" wrote:

But if it
turns out to be a mistake to remove the PAL-Ramp, what would be the
worst case effect inflight? A structural failure of the ET, some
picture like Challenger?

The PAL ramp contributes nothing structurally to the ET; it protects the
LOX feedline, repress lines, and cable trays from aero forces. Failure of
the LOX feedline or repress lines would be nasty but wouldn't cause
strucural failure of the tank.

Hmm? LOX feedline failure - SSME shutdown - SRBs tear loose from tank?

At the moment its not clear whether it will be removed.

It has already been removed.

? You mean they already decided to launch without it? Or is there some
other ET available in case they decide to need the ramp?

But if it
turns out to be a mistake to remove the PAL-Ramp, what would be the
worst case effect inflight? A structural failure of the ET, some
picture like Challenger?

The PAL ramp contributes nothing structurally to the ET; it protects the
LOX feedline, repress lines, and cable trays from aero forces. Failure of

I`m aware of that but not of the possible consequences

the LOX feedline or repress lines would be nasty but wouldn't cause
strucural failure of the tank.

JRF

Sure? If the cables were cut (or some shorted) before seperation, how
would it affect the electric and computer systems of the orbiter?

The ET structure is pressure stabilized. If the internal pressure drops
below some margin the ET will collapse inflight. According ET managment
that was the case with the Challenger ET. Well, I heard two other
interpretations too: Failure of upper loadstructure or rocket effect
as LH2 bottom was lost. Nevertheless it seems certain that ET pressure
is crucial for its structural stability. If you lose a feedline or
the repress line...

If the LOX feed gets air in, how will the turbine react?
If the feedline gets suddenly ruptured the turbine will explode and destroy
the whole aft section of the orbiter. No chance for crew survival.

If the LOX feedline fails (and the turbine has time to shut down) what
could be the fate of the orbiter? No chance to reach ISS but almost
certainly a destroyed TPS.

Assume the engines shut down before SRB seperation. What follows would
be less demanding than a real reentry. But could the orbiter still
reenter and land with large scale damage in the TPS?



## CrossPoint v3.12d R ##

wrote in
:

the LOX feedline or repress lines would be nasty but wouldn't cause
strucural failure of the tank.

Sure? If the cables were cut (or some shorted) before seperation, how
would it affect the electric and computer systems of the orbiter?

Go back and re-read what I wrote. I said it would be nasty. ET structural
failure isn't the only way to have a bad day.

The ET structure is pressure stabilized. If the internal pressure
drops below some margin the ET will collapse inflight. According ET
managment that was the case with the Challenger ET. Well, I heard two
other interpretations too: Failure of upper loadstructure or rocket
effect as LH2 bottom was lost. Nevertheless it seems certain that ET
pressure is crucial for its structural stability. If you lose a
feedline or the repress line...

I believe you're mistaken. The ET is not a "balloon tank" like the Atlas;
I've seen photos of workers inside one without breathing apparatus. ET
failure on 51L was not due to loss of pressure; it was due to the failed
RSRB aft seal allowing hot gases to burn through the LH2 tank and the aft
SRB attach strut, which allowed the RSRB to pivot about the forward
attach strut and penetrate the LOX tank.

If the LOX feed gets air in, how will the turbine react?
If the feedline gets suddenly ruptured the turbine will explode and
destroy the whole aft section of the orbiter. No chance for crew
survival.

Go back and re-read what I wrote. I said it would be nasty. ET structural
failure isn't the only way to have a bad day.

If the LOX feedline fails (and the turbine has time to shut down) what
could be the fate of the orbiter? No chance to reach ISS but almost
certainly a destroyed TPS.

Go back and re-read what I wrote. I said it would be nasty. ET structural
failure isn't the only way to have a bad day.

Assume the engines shut down before SRB seperation. What follows would
be less demanding than a real reentry. But could the orbiter still
reenter and land with large scale damage in the TPS?

Go back and re-read what I wrote. I said it would be nasty. ET structural
failure isn't the only way to have a bad day.

--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

The ET structure is pressure stabilized. If the internal pressure
drops below some margin the ET will collapse inflight. According ET
managment that was the case with the Challenger ET. Well, I heard two
other interpretations too: Failure of upper loadstructure or rocket
effect as LH2 bottom was lost. Nevertheless it seems certain that ET
pressure is crucial for its structural stability. If you lose a
feedline or the repress line...

I believe you're mistaken. The ET is not a "balloon tank" like the Atlas;
I've seen photos of workers inside one without breathing apparatus. ET

The air pressure load during ascent is much higher than the static
load at the ground. It needs internal pressure to survive the airload.
You may look in this historicaly quite interesting paper:

http://www.nasa.gov/pdf/2241main_shu...son_021030.pdf
Myron A. Pessin: "Lessons Learned - A Technical History of the External
Tank" Report prepared for the Marshall Space Flight Center details the
technical history of developing the space shuttle external tank and
lessons learned from the effort. Oct. 30, 2002

On page 23 about Challenger: "Then the tank wall failed and the tank,
which is pressure stabilized in flight, lost pressure and structural
stability, and the accident proceeded from there."


failure on 51L was not due to loss of pressure; it was due to the failed
RSRB aft seal allowing hot gases to burn through the LH2 tank and the aft
SRB attach strut,

yes

which allowed the RSRB to pivot about the forward
attach strut and penetrate the LOX tank.

From the wreckage there was evidence that a fragment of the ET from near
the LOX tank had contact with the right SRB nose. From that on Newspapers
(or even the Rogers Commission?) concluded that the SRB nose pivoted
inside the tank. Of course it was the opposite. After collapse of the
forward ET a fragment hit the SRB. This SRB pivot myth was already debunked
in 1986 by the Congress investiation, but its very persistent. I mentioned
this Congress report several times in the past. Its more compact and to
the root causes than the Rogers report. Rogers seemed more interested
to support the cover up at NASA. I recently found an online version
of the Congress report:

http://www.gpoaccess.gov/challenger/64_420.pdf
HOUSE OF REPRESENTATIVES Report 99-1016
INVESTIGATION OF THE CHALLENGER ACCIDENT
OCTOBER 29, 1986. - Committed to the Committee of the Whole House on the
State of the Union and ordered to be printed

p.75f: "The right Solid Rocket Booster without the attachment strut to
the External Tank, rotated around its long axis (41a). In so doing, it
may have jammed the upper Solid Rocket Booster to the External Tank
attachment structure and caused it to fail. That structure is located
on a large cross beam in the intertank which in turn possibly damaged
the cross beam."

"(41a) It should be noted that the right Solid Rocket Booster did not
swing outward at the bottom and cause the nose of the booster to collide
with the External Tank as had originally been thought. For this to have
happened, the right Solid Rocket Booster would have extended outward at
the bottom at a wide angle that is not supported by any of the
photographic or telemetric evidence."

If the LOX feed gets air in, how will the turbine react?
If the feedline gets suddenly ruptured the turbine will explode and
destroy the whole aft section of the orbiter. No chance for crew
survival.

Go back and re-read what I wrote. I said it would be nasty. ET structural
failure isn't the only way to have a bad day.
....

Seems we agree it could be a risky mission. Lets hope it wont be nasty.


## CrossPoint v3.12d R ##

In article ,
wrote:
The ET structure is pressure stabilized. If the internal pressure
drops below some margin the ET will collapse inflight...
I believe you're mistaken. The ET is not a "balloon tank" like the Atlas;
I've seen photos of workers inside one without breathing apparatus...

The air pressure load during ascent is much higher than the static
load at the ground. It needs internal pressure to survive the airload.

That's correct, but speaking of it as "pressure stabilized" without
qualification remains wrong -- that term, without qualifications like
"in flight", is normally applied only to Atlas-like tanks that need
pressure at all times.

Even the qualified form "pressure stabilized in flight" isn't seen often,
because it's the normal state of affairs -- almost all rocket tanks rely
to some extent on internal pressure for strength in flight.

which allowed the RSRB to pivot about the forward
attach strut and penetrate the LOX tank.

From the wreckage there was evidence that a fragment of the ET from near
the LOX tank had contact with the right SRB nose. From that on Newspapers
(or even the Rogers Commission?) concluded that the SRB nose pivoted
inside the tank. Of course it was the opposite.

The evidence was just a bit stronger than that. Notably, the SRBs have
their own gyros, and at T+72.204 (a second or so before breakup started),
the SRB gyros started to disagree -- the right SRB was rotating
independently of the stack in both yaw and pitch. Moreover, both the nose
of the right SRB and the right side of the ET intertank ring show crush
damage, which is absent on the left. Likewise, there is a dent in the
orbiter wing and burn damage to orbiter surfaces, again only on the right.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

which allowed the RSRB to pivot about the forward
attach strut and penetrate the LOX tank.

From the wreckage there was evidence that a fragment of the ET from near
the LOX tank had contact with the right SRB nose. From that on Newspapers
(or even the Rogers Commission?) concluded that the SRB nose pivoted
inside the tank. Of course it was the opposite.

The evidence was just a bit stronger than that. Notably, the SRBs have
their own gyros, and at T+72.204 (a second or so before breakup started),
the SRB gyros started to disagree -- the right SRB was rotating
independently of the stack in both yaw and pitch. Moreover, both the nose
of the right SRB and the right side of the ET intertank ring show crush
damage, which is absent on the left. Likewise, there is a dent in the
orbiter wing and burn damage to orbiter surfaces, again only on the right.
....


Whats not unusual because the failure of the load structure happened
on the right side. First the burn through of on SRB attachment strut,
then the overload of the remaining one. That may caused destruction
in the intertank area and created an asymetrical collapse of the ET.
Nothing far fetched.

But this pivot myth I still saw a few years ago in a TV documentary
again. To get the effect it looked like a pivot angle of 10 degree or
more was necessary. The SRB had to pivot such an angle against the high
air pressure (it was just seconds after max-q). And it had to pivot back
within a second as it came out of the ET cloud on straight course. Once
imagined the timing and the forces/masses involved one need no back
of the envelope calc to dismiss it. It was such a rediculous scenario
that I considered it in 1986 as usual journalist fast written trash.
It was annoying to hear it from the Rogers report and much later
documentaries.


## CrossPoint v3.12d R ##

wrote:

But this pivot myth I still saw a few years ago in a TV documentary
again. To get the effect it looked like a pivot angle of 10 degree or
more was necessary. The SRB had to pivot such an angle against the high
air pressure (it was just seconds after max-q). And it had to pivot back
within a second as it came out of the ET cloud on straight course.


Actually it went through the burning cloud of LOX and LH2 and came out
on the opposite side it started from, as the close-up photos of the
vehicle break-up show:
http://www.aerospaceweb.org/question...ns/q0122.shtml
.....in fact, the pivot angle is very severe on the damaged SRB, as these
photos from that page show:
http://www.aerospaceweb.org/question...hallenger7.jpg

Once
imagined the timing and the forces/masses involved one need no back
of the envelope calc to dismiss it. It was such a rediculous scenario
that I considered it in 1986 as usual journalist fast written trash.
It was annoying to hear it from the Rogers report and much later
documentaries.



The photos don't lie- it's very easy to see which SRB is damaged, and
how it ends up on the opposite side of the break-up event* from where it
started at, due to pivoting inwards as it detached.

* No, I'm not going to call it an "explosion"- we don't need to start
_that_ all over again. :-)

Pat