NASA Finds Critical Assembly Fault in Shuttle

mzs writes "During corrosion inspection on Discovery, technicians noticed that one of the gears in a rudder actuator had been installed backwards. This particular actuator was the top-most of four that control the air brakes on the tail. As luck turns out, if it had been the bottom-most actuator, loss of the shuttle and crew would have been nearly inevitable. Plans are in place to have four spares by the time Shuttle missions resume next year."

Comments

Re:Simple solution, really.

[Lattitude]

Even better, they are going to machine them so they mechanically impossible to put in backwards.

When is a problem a problem?

[stecoop]

Discovery flew safely 30 times with the defective actuator

When does a defect become a problem? I wonder if this was really a Critical problem because shouldn't some indication have already been seen by now?

I mean since they have fixed this problem will two other problems surface that are more critical and maybe they should have left it alone?

Re:Simple solution, really.

[NeoThermic]

Or, do what they do now for computer compoments:

Colour code the connections.

From the article:
'The gear fits into the assembly both ways, but is slightly asymmetric so the teeth do not fit exactly if the gear is reversed.'

So why not have the side its supposed to go in green, and the side where its not supposed to go in red?
Simple visual solution that can be spotted quicker?

NeoThermic

Re:Should have used Java

[millahtime]

"I know NASA is conservative with technology, but using assembly in this day and age is way backwards!"

Bad Joke

Actually Assembly is a great language if your worried about efficiency and/or space. A lot of controllers in aerospace are coded that way and there is good reason for that. You can never get away from machine language for everything. Many times it is the best route to code in.

Engineering practices

[n3xup]

In engineering, it's usually good practice to design somthing that only assembles one way. That way, whoever is assembling it (no matter how intelligent they are) can only install the component the way it was meant to be.

It's strange and somewhat disconcerting that this was not the case for this shuttle component, but I haven't seen the part in question.

Re:Murphy's Law

[AlterTick]

"If there are two or more ways to do something, and one of those ways can result in a catastrophe, then someone will do it."

The important lesson here is about the design of critical parts. Nothing important should be made asymetrical and reversable. Even labeling it "THIS SIDE UP" on one side and "WRONG! DANGER! WRONG!" on the other isn't good enough. The part should either be symetrical, so it doesn't matter which way it goes, or non-reversable, so it wont fit upside down/backwards. Important thing to remember in mechanical engineering (gears|levers|*) or even eletrical parts specifications (connectors should be keyed to mate only one way: the right way).

Re:Simple solution, really.

[RealityMogul]

I'm not a mechanical engineer, but I think applying paint to such parts is not desirable.

Re:Safety is relative

[Imperator]

Why does the modern Soyuz have a better safety record than the Shuttle? Why did our old ballistic missiles have a better safety record than the Shuttle? Even the enormous Saturn V rockets never had an accident in flight.[1]

Why does the Shuttle have such a terrible safety record relative to other rockets that attain orbit?

I'll tell you why: because it was over-ambitious. Congress was sold on the idea of a re-usable (read: cheap) launch vehicle that can do cool stuff like repair satellites. The truth of the matter is that if we had stuck with traditional launch vehicles (fire-once rockets), the money we saved over the long run would have allowed us to just replace failing satellites rather than repair them. (How many satellites have we repaired anyway?) We could even have built the space station for less. (Look at how we launched Skylab. Surely we could have repeated that a few times to get as large a space station as we wanted.) The legacy of the Shuttle is that of an overpriced, underperforming safety hazard.

All manned spaceflight is dangerous. The Shuttle is just more dangerous that most.

[1] The Apollo capsule had two serious accidents, one on the ground and one on the way to the moon.

Re:Simple solution, really.

[chadjg]

In some cases stamping lettering into a stressed rotating part can lead to sudden failure. Stamping can put odd stresses into the part, and makes a slightly weaker space in the part.

I believe that the NTSB found a stamping on a rail car wheel caused a failure and derailment, but i'll be danged if I can find the incident. Maybe tonight...

Moisture could collect in the little crevices of the letters leading to corrosion. i suspect that this is not really a concern.

Silk screening or some creative powdercoating could totally avoid these issues. But what do I know. I managed to smoke my e-machine 500 last night. Nobody would hire me to be a shuttle engineer!

Re:Instead of slamming NASA

[GreyPoopon]

...but please spare me the pity party because Congress may want to save me a few BILLION dollars.

This might make sense if Congress (or any group of politicians) was actually interested in SAVING money anywhere. No tinfoil hat is needed to know that anytime a politician takes money away from one line item in the budget, they are merely diverting it to another that involves their own interests.

Re:How can a fault go unnoticed for so long?

[Ryan C.]

They found the problem before anything went wrong while checking for defects. I don't know what your definition of QA is, but that's pretty much the accepted definition.

As for horribly flawed: Compared to whom? Spaceflight is dangerous. Minor oversights that in most industries would cause a misprint in a news article tend to blow up and kill people.

Basically, until you land something off-planet, you have no room to talk. If you want to point to someone who is doing a better job of it, you pretty much have the Russians for comparison, and they have had even more problems.

-Ryan C.

Re:Why are heads not rolling?

[pz]

When the Mars Climate Orbiter was lost due to a mixup between NASA and Lockheed Martin concerning imperial vs. metric units, I recall Dan Goldin, the then-head of NASA, being asked by a reporter if heads would roll. He replied something like, "sure we could do that, but then we'd have to replace those engineers. Now we already hired the best ones we could find in the world, so where are we to get better ones?"

The Shuttle is one of the (if not *the*) most complex bits of engineering we, as a world-wide society, have achieved. I would never expect any shuttle to be manufactured/assembled/flown/controlled/maintained perfectly without flaw. I would, however, expect it to be designed to work well in the face of such problems, as does seem to be the case here. Discovery had 30 successful flights despite a part on a major control surface being installed backwards? Everyone landed safely? Tons of good science, too? Doesn't mean the problem shouldn't be fixed, but kudos to NASA for what sounds to me like a job well done.