Challenger disaster and Boeing 757
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Challenger disaster and Boeing 757
I've been reading a bit into the Challenger disaster recently, we all know the bullet points of course.
A TV documentary a few years ago claimed that a Boeing 757 overflew Cape Kennedy about half an hour before the launch, and had a short but unpleasant encounter with a layer of wind (referred, I suspect incorrectly given the latitude, by the documentary as a jetstream) about 300kph, which would be about 160 knots in real money. The documentary claimed, with some reasonable arguments, that this was what finally precipitated the disaster, the O-ring seals not having catastrophically failed at either launch or max-Q as might have been more likely expected.
First I'd come across that particular snippet, and I can't see anything about it in various books I've got at home or websites I've gone through. The Rogers Commission report describes "wind shear" higher than usual but within design limits, but not where that information came from.
The documentary had claimed that this wasn't observed by NASA sonde balloons because they'd drifted 40odd miles away, which in the conditions of the day doesn't seem particularly unlikely.
Does anybody know anything specific about those wind observations, what airline it was, whether they reported it whilst still airborne, or anything else about it really?
G
A TV documentary a few years ago claimed that a Boeing 757 overflew Cape Kennedy about half an hour before the launch, and had a short but unpleasant encounter with a layer of wind (referred, I suspect incorrectly given the latitude, by the documentary as a jetstream) about 300kph, which would be about 160 knots in real money. The documentary claimed, with some reasonable arguments, that this was what finally precipitated the disaster, the O-ring seals not having catastrophically failed at either launch or max-Q as might have been more likely expected.
First I'd come across that particular snippet, and I can't see anything about it in various books I've got at home or websites I've gone through. The Rogers Commission report describes "wind shear" higher than usual but within design limits, but not where that information came from.
The documentary had claimed that this wasn't observed by NASA sonde balloons because they'd drifted 40odd miles away, which in the conditions of the day doesn't seem particularly unlikely.
Does anybody know anything specific about those wind observations, what airline it was, whether they reported it whilst still airborne, or anything else about it really?
G
From memory I thought it was standard practice for a dedicated “weathership” to flown through the area prior to launch (possibly/usually an astronaut flown T-38).
I’ll see if I have anything relevant tucked away in print at home.
I’ll see if I have anything relevant tucked away in print at home.
Challenger was a case study in my first masters, but all the notes are somewhere in the loft. I remember the "wind shear" being discussed along with the other aspects, but I don'r remember it being given any particular significance. But I do remember that there had been evidence of the SRB seals (O-rings, membrane and refractory putty) leaking right from the very first launch. It was the subject of an on-going investigation from that time and it was still not concluded 25 launches later.
There was evidence of seal blow-by on other launches as well. In fact I *think* I remember it being said that there was evidence of seal failure on all 24 launches that preceded STS-51-L. If it wasn't all then it was certainly the majority. These failures were randomly distributed between segments and around the circumference of the booster. One investigator concluded that the boosters leaked on every flight and that STS-51-L was simply the first time one of the hot gas leaks happened to impinge on the fuel tank.
PDR
There was evidence of seal blow-by on other launches as well. In fact I *think* I remember it being said that there was evidence of seal failure on all 24 launches that preceded STS-51-L. If it wasn't all then it was certainly the majority. These failures were randomly distributed between segments and around the circumference of the booster. One investigator concluded that the boosters leaked on every flight and that STS-51-L was simply the first time one of the hot gas leaks happened to impinge on the fuel tank.
PDR
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I remember there was discussion of jetstreams mixing above Kennedy that day, and that the SRB gimbals were working hard to steer the stack as a result.
And the sondes weren't much help in detecting because their vertical measurement intervals were too long, something like that, which was already a known problem but again one that warranted a shrug.
And the sondes weren't much help in detecting because their vertical measurement intervals were too long, something like that, which was already a known problem but again one that warranted a shrug.
Re a dedicated “weathership” best I can find at the moment is this, part of a much longer piece about John Young in airspace mag:
AFAIK the weathership pilot’s main job was checking conditions at low and medium altitude, primarily to make sure conditions were Ok for a Return To Launch Site (RTLS) abort, so Young might not have ventured up to the sort of altitude the shear was encountered.
https://www.airspacemag.com/space/spaceman-7766826/
The day of the Challenger launch, Young was flying the weather plane, circling the pad, keeping an eye out for storms, wind, and temperature changes. From his aerial perspective, he saw it all happen. “We were holding at 20,000 feet and watching them lift off, and I got a picture of the whole thing blow—coming apart,” he says.
https://www.airspacemag.com/space/spaceman-7766826/
Having just posted the above, found this:
https://www.wunderground.com/blog/24...-disaster.html
There is mention of sonde data, there is no mention of pilot reports from a 757, but there is this:
“ Prior to liftoff, pilots conducting test flights reported some vertical wind shear earlier that morning, but it was within acceptable limits. Obviously, vertical wind shear must have dramatically increased after 12Z (conditions were considerably worse during liftoff). According to the President's Commission Report:
"At approximately 37 seconds, Challenger encountered the first of several high-altitude wind shear conditions, which lasted until about 64 seconds. The wind shear created forces on the vehicle with relatively large fluctuations. These were immediately sensed and countered by the guidance, navigation and control system.”
https://www.wunderground.com/blog/24...-disaster.html
There is mention of sonde data, there is no mention of pilot reports from a 757, but there is this:
“ Prior to liftoff, pilots conducting test flights reported some vertical wind shear earlier that morning, but it was within acceptable limits. Obviously, vertical wind shear must have dramatically increased after 12Z (conditions were considerably worse during liftoff). According to the President's Commission Report:
"At approximately 37 seconds, Challenger encountered the first of several high-altitude wind shear conditions, which lasted until about 64 seconds. The wind shear created forces on the vehicle with relatively large fluctuations. These were immediately sensed and countered by the guidance, navigation and control system.”
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What I heard was that the Challenger wasn't in a fully serviceable condition but it had the female teacher amongst the crew and it was the case that any delay to the launch was unacceptable.
The Rogers Report makes it clear that none of the issues that contributed to Challenger not being flight-ready were things that could have been rectified while the astronauts sat there twiddling their thumbs.
What I heard was that the Challenger wasn't in a fully serviceable condition but it had the female teacher amongst the crew and it was the case that any delay to the launch was unacceptable.
Fundamentally there was a political/management need from within NASA to launch but that was almost entirely down to the fact that Senior management wanted to show that the Shuttle programme, aka the Space Transport System (STS), had evolved from an experimental project into a reliable transport system that could operate to a schedule with pretty much fixed, predictable launch dates (edit to add - and they were struggling..as PDR correctly points out below there had already been multiple delays to the flight..management were feeling the pressure). There has never been any suggestion that they launched simply because Christa McAuliffe was there.
As far as the shuttle not being serviceable when launched, well there were relatively, in the scheme of things, minor niggles (what would probably be called “allowable deferred defects” in airline speak ) but of course the major issue was launching outside demonstrated limits (temperature) and a questionable design feature.
Rogers report below:
https://spaceflight.nasa.gov/outreac...ion_report.pdf
Last edited by wiggy; 12th Feb 2018 at 11:53.
Details here. which also discusses the "wind-shear" effects and the actual booster seal leaks (which were visible from 0.678 seconds after lift off, before the shuttle had lifted past the gantry and well before any "wind-shear" effects had become apparent.
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I recall thinking when watching and listening to the endless replays, that there was a high probability that the references to SRB gimbal activity between the crew and mission control may have been erroneously ascribed to wind-shear, when (unknown to both at the time) they were largely caused by the ever increasing breach in the wall of the RH SRB causing asymmetric loss of thrust in that booster's nozzle, let alone thrust from the developing plume at almost a right angle to the normal thrust line and causing the SRB gimbals to work hard to steer the stack, rather than jetstream mixing and upper level winds that were described as high but within limits.
A few back-of-fag-packet scribbles give me a (very) rough estimate of total vehicle mass ~70 secs after launch (ie the time of the explosion) of some 1,300,000kg. The article I linked about talked about the initial catastrophic failure being the hydrogen/oxygen burn in the external fuel tank blasting off its lower dome producing a thrust of "2,800,000lbs" (~1,300,000kgf).
60-70secs after lift-off is close to the point of max dynamic pressure, so the acceleration is throttled down a bit to about 1.5G. At that point the aft dome is blown off and there is a short burst of another 1G, which must have been quite dramatic.
PDR
60-70secs after lift-off is close to the point of max dynamic pressure, so the acceleration is throttled down a bit to about 1.5G. At that point the aft dome is blown off and there is a short burst of another 1G, which must have been quite dramatic.
PDR
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My take on it, from various reading, is that there were three major reasons why launching was a bad idea...
(1) Significant presence of ice on the spacecraft and surrounding launch structure, with unknown effects.
(2) The known problems with the O-rings at low temperatures, which had been under investigation at Morton Thiokol for about 7 months. It's well documented that the engineers at MT had made it clear that the launch "go" should not be issued, and that they were overruled by politically minded management in that company.
(3) That in the Atlantic, in the booster recovery area, the two recovery ships were in an "Extreme survival condition", and completely incapable of doing anything beyond stay upright(ish) in 50-70kn winds, 100ft seas, and routinely 30° pitch attitude changes.
The reasons these were ultimately disregarded are much debated - but clearly the desire to prove that they could launch the Challenger *at-all*, the high profile nature of the mission with Christa MacAuliffe on board, and increasing presidential scrutiny were clearly all in the mix. It seems highly unlikely that it was any one single factor.
My interest in the wind-shear / B757 issue is mainly that if reported to NASA it would have been *another* reason to cancel. However, I suspect strongly that it probably never was.
G
(1) Significant presence of ice on the spacecraft and surrounding launch structure, with unknown effects.
(2) The known problems with the O-rings at low temperatures, which had been under investigation at Morton Thiokol for about 7 months. It's well documented that the engineers at MT had made it clear that the launch "go" should not be issued, and that they were overruled by politically minded management in that company.
(3) That in the Atlantic, in the booster recovery area, the two recovery ships were in an "Extreme survival condition", and completely incapable of doing anything beyond stay upright(ish) in 50-70kn winds, 100ft seas, and routinely 30° pitch attitude changes.
The reasons these were ultimately disregarded are much debated - but clearly the desire to prove that they could launch the Challenger *at-all*, the high profile nature of the mission with Christa MacAuliffe on board, and increasing presidential scrutiny were clearly all in the mix. It seems highly unlikely that it was any one single factor.
My interest in the wind-shear / B757 issue is mainly that if reported to NASA it would have been *another* reason to cancel. However, I suspect strongly that it probably never was.
G
(2) The known problems with the O-rings at low temperatures, which had been under investigation at Morton Thiokol for about 7 months. It's well documented that the engineers at MT had made it clear that the launch "go" should not be issued, and that they were overruled by politically minded management in that company.
Anyway, so NASA's response to 17 refusuals is to refuse to accept the decision. But when at the 17th time of asking (with no actual change in the data) MT finally say "OK" they just accept it and press the go button. No one subjects a "go" decision to anything like the scrutiny and due diligence that they applied to the "nogo" decision, thereby proving that NASA had lost its way, and was no longer a fit and proper organisation to hold and engineering or flight-safety governance authority. They had no safety culture, and finance was able to trump engineering science.
That was the real problem IMHO. MT carry some blame, but NASA carry much, much more. That was the conclusion I came to after a few weeks studying the engineering and human iissues involved for that module of that masters.
€0.000005 supplied,
PDR
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You could argue that he shouldn't have caved.
As a Chartered Engineer I have signed up to a code of professional ethics which says I would refuse and resign in such circumstances - I can only hope that if I ever find myself in that position I would have the integrity to put my family into dire economic straights and resign. I tell myself I would, but I've never asked myself to prove it...
G
Last edited by Genghis the Engineer; 12th Feb 2018 at 17:37.
PDR
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These are the things we know: Warnings from the MT SRB engineers were overruled by management. That is the widely accepted reason we lost Challenger. According to NASA and the accident investigation, wind shear was within mission limits and the control systems responded to flight path deviations up until the moment of (unplanned) SRB separation. However, failure of the joint seal and stresses from wind shear on the SRB were not part of the investigation as far as I know.
A timeline with communication transcripts and visual observations is available along with links to various NASA media and the accident report here at Spaceflight Today - Challenger timeline.
A timeline with communication transcripts and visual observations is available along with links to various NASA media and the accident report here at Spaceflight Today - Challenger timeline.
The timeline merges telemetry beamed down from the shuttle, NASA recordings of the flight director's loop in mission control at the Johnson Space Center, the NASA-Select audio circuit heard by the public and a transcript of crew cabin intercom conversations released by NASA after the accident.
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There was some 'arrangement' in later years in which Thiokol took a reduction of program profits ( by quite a lot, tens of millions ) instead of paying compensation or accepting blame. Rather a one-sided arrangement given the information mentioned above about NASA pressure.
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I take your point, but I think that you are probably poking the wrong (engineering) manager in the chest there. The guilty party at MT seems to me to be Joe Kilminster.
G
Perhaps. But I still think NASA should accept a fair amount of the blame because they did use commercial pressure to influence an engineering decision - that's a professional foul IMHO. As people from *any* discipline (engineering, QA, Safety, Procurement, Legal, Finance, Commercial, Manufacturing, Logistics or WHY) get more senior in a company they will become necessarily more and more responsible for "the whole business" rather than their particular specialism. Equally NASA is an "intelligent customer" so if they apply pressure to suggest that they feel a particular technical risk in a sub-system is an acceptable risk for the whole system there will always be the thought as to whether their view should be given weight.
But as I said before - the really BAD issue was the way NASA ticked off their Launch Readiness Review on the basis that an investigation was "in-progress" rather than "complete with findings implemented". To my mind if there is to be a lynching (which I'm not necessarily saying there should be) the person who said it was OK to do that should be the first in the queue for the noose!
PDR
But as I said before - the really BAD issue was the way NASA ticked off their Launch Readiness Review on the basis that an investigation was "in-progress" rather than "complete with findings implemented". To my mind if there is to be a lynching (which I'm not necessarily saying there should be) the person who said it was OK to do that should be the first in the queue for the noose!
PDR