From Slashdot: BJ_Covert_Action writes:
“NASA engineers have finally discovered the root cause of the cracks that have been found on space shuttle Discovery’s main external tank. The main tank, one of the ‘Super Lightweight Tank’ models developed by Lockheed-Martin, employs an aluminum-lithium alloy developed by Lockheed-Martin specifically for this application.
The new alloy is used in various structural stringers throughout the SLWT design. Unfortunately, the batch of this alloy used in the tank that is currently mated with the Discovery shuttle appears to be of low quality. The alloy used in the stringers has a ‘mottled’ appearance, compared to the nominal appearance typically used in the main tank stringers (see picture in article).
This appearance is indicative of a fracture threshold that is significantly lower than typical. NASA has determined, through testing, that this low grade alloy has only 65% of the fracture strength of the nominal alloy typically used.
NASA engineers have devised a potential fix to the problem that they are currently testing to ensure the repair will cause no unintended consequences. NASA plans to have the Discovery shuttle ready to launch again by February 24th, 2011.”
===========================================================
I’m reminded of another ship with low grade metal. Let’s all hope the solution they devise is sound, otherwise it may be a terrible ending for the shuttle program.
Those stringers were formed and then painted with a green zinc chromate at an outside vendor to prevent corrosion. No one would know the aluminum was aging or defective visually. I don’t recall that area of the tank having any sort of x-ray inspection either. The intertank, where these stringers are used, is a completely riveted structure. Lockheed had a lot of trouble with the aluminum-lithium alloy when I was there. Its very hard to weld without defect, and the super lightweight tank is what it is because of its extensive use of aluminum-lithium alloy.
Anthony:
Thankyou for your link to
http://www.snopes.com/history/american/gauge.asp
However, I fail to see where it “disproves” the story. In fact, it seems to confirm it, although it does say that if the Confederacy had won the Americam civil war then a different railroad gauge would have been adopted in the US.
Perhaps you would be so kind as to explain the how the story “has been shown to be false”. I have no real interest in the matter, but I would like to know as a matter of curiosity.
With thanks in anticipation.
Richard
George Steiner says:
January 15, 2011 at 3:51 pm
“There is no engineering patch for inferior material.”
I agree 100%, but they will go ahead anyway.
I had to think about the “patch work” performed on Concord that eventually caused the Paris crash when a chunk of tire separated and penetrated the left wing section puncturing the fuel tank.
Fixation to a specific problem resulted in the application of heavier reinforced tires.
No engineer had thought about the effect of heavier chunks of rubber hitting the wing surface if such a tire blows.
The risks of patchwork performed on aircraft (or spacecraft) in this case often have consequences that effect the entire design.
In the case of the main tank there could be an increase in weight resulting in a reduction of the payload. Patchwork performed on the structural parts of the tank could effect the way stress is transfered to the outer skin.
The worst scenario is a crack resulting in fuel loss during take off.
The entire project is under pressure and that is another factor that slipped into Murphy’s Law in more than one occasion.
This is still an old school space project where relative high risk factors are standard
and accepted.
In the case of Concord however the 9/11 attack and the following slump in air travel grounded the supersonic flyers for good.
New aerodynamic developments however have solved the problem of the sonic boom and when the current surge of green madness no longer obstructs progress a new generation of supersonic airliners will emerge.
http://en.wikipedia.org/wiki/Air_France_Flight_4590
***
tty says:
January 15, 2011 at 7:53 am
I think you are rather unfair to the Titanic. It was actually an outstandingly safe ship.
Even then it floated for four hours after the collision, allowing ample time for evacuation. However this, in line what had happened before, was handled with outstanding incompetence, causing many lifeboats to be launched not even half-full. Moreover most of these boats deliberately refrained from picking up survivors after the ship had sunk.
The Titanic disaster was caused by a combination of regulatory failure (specifying much smaller lifeboat capacity than needed) and an almost incredible lack of professionalism by the captain and crew.
****
I think you are insulting the professionalism of the ships officers and crew who were doing their job while knowing they were going to die.
The lifeboats were launched on a timetable, by a small crew, one after the other. The problem was that few passengers were willing to get in the initial boats, they knew the sea was going to be cold and rough in a small boat while the Titanic seemed safe. They even launched a set of (unauthorized by UK Board of Trade) canvas fold up lifeboats that people were supposed to get in while in the water (dumb design for winter North Atlantic).
There is a very good reason the lifeboats moved away from the ship (falsely explained to passengers that they thought there was another ship over there). A lifeboat is easily swamped by people trying to get aboard from freezing waters. There had been a spectacular foulup on another sinking with lifeboats sunk by passengers trying to get aboard). So the safe proceedure was to move away and let the people who jumped into the water freeze to death. When most were dead it would be safe to return to rescue a few hearty survivors. The time it took to die was very short, and most were not functional within just a couple minutes of water exposure.
Lifeboat rules can be very cruel and inhumane, but they are designed for the preservation of the maximum number of lives in a very dangerous situation. There is a reason the lifeboat captain is armed and has authority to use his weapon.
Mike Borgelt says:
January 15, 2011 at 1:12 pm
“Douglas DC, that’s either the Grumman AA1A Yankee or the Piper Tomahawk.
My wife and I had the misfortune to do our power flight training in a Tomahawk. Both of us survived. I had the advantage of over 2000 hours in gliders.”
Sorry to hear that-I had instruction time in both and they both were marginal as basic trainers. This is an example of poorly thought out design and perpetrated on the
general public. I am a fan of the old school-Piper Cub, Taylorcraft, Aeronca/Champion
Cessna 150/152,etc. Do like the Diamonds, however and some of the light sport aircraft that are now coming out. Designs whether spacecraft or light planes,
should not worry the occupants whether or not that the craft is actively trying to
kill them.
“Dave Bowman: Open the pod bay doors, HAL.
HAL: I’m sorry, Dave. I’m afraid I can’t do that.”
Fred H. Haynie says: “…Base(d) on what they have found and reported, I think this is a classic case of intergranular stress-corrosion cracking resulting from improper heat treatment….”
I’m wondering what the tank was exposed to, internally and externally. I’m reminded of the hydrostatic testing of a 6Al-4V titanium alloy space vehicle tank. After the test had been conducted with methanol as the test fluid, it was discovered that methanol was corrosive to that alloy. Who’da thunk?
http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0649187
beng says:
January 15, 2011 at 7:03 am
Because the engineer’s concerns didn’t make it to Cape Canaveral. See http://www.awesomestories.com/disasters/challenger/last-minute-pleas
“real work on climate science “
How absurd. Dump huge amounts more money to closer study random movements of huge winds in the atmosphere? Looking for a gubmint grant, are you? The Earth rotates on its axis, air has mass, inerta and viscosity. Mountains/mountain chains bull their way through the atmosphere, and the result is huge vortices of air, creating high velocity east to west or west to east moving winds, randomly varying northward and southward.
With knowledge in the fundamentals of both chemistry AND physics, statics/dynamics, thermodynamics and electrical and hydro/aero dynamics, not all that difficult to comprehend the processes, but completely impossible to model, high speed computors or nay.
Best spend money to figure out how to survive the awesome powers of natural forces . . . or find a gullible multiple billionaire to sponser you. The US taxpayer has plumb run out of money.
So how many men and women have died in the far simpler task of learning how to get relatively safe airplanes to ply the skies? The airplane didn’t go quickly from the Wright Brothers contraption to SST, and many experimental airplanes crashed and burned in the process.
Also, this is done by government contract, with schedules and spending budgets. And a fickle public and politicians to please.
It takes men and women of great courage to pilot and crew these no more than huge possible bombs, and the crews know their lives are at great risk.
I consider it to be a near miracle that the space program has worked out so well, and salute the engineers and technicians who made it happen, and the courageous men and women who knowingly risked their lives in a quest for knowledge.
But then, I am a mere civil engineer, who has managed large highway projects, both as a government-paid engineer, and a contract-to-government engineering project manager. Long since retired now.
This is what happens with “lowest bidder” contracting where no weight is given to quality of work.
George Steiner,
There is no engineering patch for inferior material.
Quite so!
There is no engineering patch for inferior thinking either. A hodge is a hodge. I have never made an engineerig change without unintended side effects. Do the job right and get the right material.
jorgekafkazar said on Worrisome engineering patches
January 15, 2011 at 6:43 pm
My guess is that it is the atmosphere at the launch pad. They are near the ocean and salt spray travels inland further than we realize. It doesn’t take much salt to increase the conductivity of condensed moisture and stimulate corrosion (especially if the rivets are cathodic to the stringers.
“another ship with low grade metal”.
An interesting and perhaps better example, is TankerSchenctedy.jpg. This should take you to the Wikipedia page which shows the tanker Schenectedy which was an early all-welded ship.
About 10 years before the war Griffith, who was an aircraft engineer, showed that if a crack developed in a brittle material it would continue across the material until it reached the edge. It was quickly found that a crack could be stopped by a properly drilled hole in it’s line of travel. The hole had the same effect as an edge.
Schenectedy must have developed such a crack, but whether or not the crew noticed it, or whether or not they knew how to stop it, I don’t know, but anyway, it is a matter of history that the ship broke, in a spectacular manner.
But Titanic was not an all welded ship. In fact I imagine that nowhere on that ship was there anything welded. The Titanic was an all riveted construction, made of steel plates. The plates could have been about 2 feet by 6 feet, perhaps and assembled with the long edge longitudinally. The entire ship, hull, bottom, inner bottom, longitudinal bulkheads, transverse bulkheads, decks, were all assembled from those huge all-rivetted steel plates. An enormous tonnage of rivets. Such a design meant that any crack would be stopped at the affected plate’s edge. Obviously then an excessive crack would be transferred from the originating plate, now failed, to the two adjacent plates, but now there would be two plates resisting the stress. And so on.
The materials would certainly allow for low temperatures, and the design would allow for the routine bending expected from alternatively being supported amidships on a wave, then supported at both ends only, which is the routine life of a ship. In fact the worst bending conditions imagine for a large ship would have been experienced during launching.
So perhaps the failure was not as simple and clear cut as the professors claim.
Nothing to do with your interesting piece, but perhaps worth noting.
Note also, Titanic was illustrated by a lurid sketch, whereas Schenectedy had a real, live photo.
Perhaps NASA wants the manned U.S. space program to go out with a bang?
It wouldn’t be the first time “end users” were sacrificed in order to secure funding for a new iteration of a defective product. Why, it’s the entire basis for the business plan of Microsoft, Inc.
The railroad story may be false. I don’t know either way. However the article http://www.snopes.com/history/american/gauge.asp provides on the subject is worse than weak. Arguments in favor of AGW are stronger and are better supported, which isn’t saying much.
DJ Meredith says: January 15, 2011 at 9:21 am
“I’m at a loss here to understand how this could happen without gross corruption in the process.
I’ve manufactured flight grade parts, both for aircraft and space vehicles. The pedigree for the metals (“Certs”, as they’re commonly called), the manufacturing processes themselves, almost to the chain of custody, it all is tracked and documented. Inspectors will come on site and check your documentation, and they’ll check your inspection tools for calibration. You guys think science is rigorous??”
The explanation is simple. That alloy is a very low production item, and some of the fabrication techniques are unique to the Shuttle. It does not have the decades of practice by hundreds of users to uncover design faults as other alloys do. If there is a design flaw, all those certifications do is ensure that every one will have the same flaws as the first one. If you want flight safety, there is no substitute for lots of flight test, of which the Shuttle had very little. Unfortunately, that’s true of all manned space flight vehicles so far. It’s hard to get 1000 test flights on a vehicle that flies 4 times a year (Shuttle orbiters) or thrown away after every flight (all other NASA vehicles to date).
The aluminum-lithium alloy usage was the result of a project to take weight out of the main tank to allow for a larger payload. Talking to some of the locals here who work at Kennedy Space Center it seems that it might have been overdone. The foam shedding was a result of getting away from a freon foam ‘expander’ to go with something a bit more ecologically sound. There had been very little or no shedding before the change, but we are all familiar with the after.
NASA seems to be at a point that no matter how much money is dumped into their hopper they always seem to come up short in their space exploration activities. I personally have given up hope that they can continue to lead the way. Rather, they seem to be on a path to follow, at great expense, companies like Space-X and Bigelow.
As far as the quality of the metal used in the problem tank, earlier comments here have not been the first I’ve heard about union activities and worker lack of focus. It is the Government, isn’t it? When I was in the Air Force the motto of the day was “Good enough for Government work.”
I need to clarify my NASA comments somewhat. The people who actually work on the shuttle are highly skilled, carefully selected people. You see license plate frames with the comment “Doing daily what others only dream of.” They love their work.
Anthony, thanks for debunking that railroad gauge story, which is a version of an old story that people adapt to their particular hobby horse.
Bridges and tunnels are not designed to the track gauge, but to the width and height of the body of the cars which always overhang the track – and probably some have been built wider and higher to accommodate even larger loads such as airplane fuselages and double-stack container railcars or automobile-carrying railcars.
As have highway overpasses (one was raised a few years ago on I-405 in the Totem Lake area east of Seattle WA, another on I-5 in Burlington WA may have been after a trucker tried to demolish it a few years ago by ignoring height information – and on the TCH east of Vancouver BC you can see scars on the lower overpasses).
Tallbloke
Aerospace structure is weight-critical.
Boeing had difficulty with stringer ends on the 787 wing structure in the wing-body, though the pieces were of composite material and IIRC the defect was an analysis problem revealed by static tests.
The disturbing problem here is a large shortfall in materials quality, as marcoinpanama suggests not noticed by anyone. Boeing has had comparable anomalies in 787 sub- assemblies that puzzle me as to why none of the supposedly skilled aviation people noticed them before final assembly.
Mark G, I think you’ll find on researching that the trend of o-ring erosion on the space shuttle was clear enough to be very concerned about risk. How clear may depend on how the data was plotted, but it should have been carefully examined given the downside risk. The big problem was political in Morton-Thiokol management – they took a vote among executives, only one of whom had technical experience. That’s “consenus”, the scam pulled by climate alarmists.
NASA too had lost visibility of risk because problems for which a fix was scheduled were no longer highlighted, despite the FMEA’s effect of dual o-ring failure: “loss of mission, loss of crew”, which tragically came to pass.
M Simon, fact is that there is a 50% overload factor in normal aircraft design – the difference between “limit” and “ultimate” cases. Everything else is either component tests or calculated. 10% sounds like a rule of thumb for thorough analysis or test cases as a margin to cover remaining imprecision in that analysis (which should have already used minimum spec part size and material strength values). We could talk about how loads are calculated of course, which is perhaps what you refer to as “G” factors. And fact is that only critical structure, like the wing, is actually tested to the required load, often to failure.