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?

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.

[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.