Stuck Knob Causes Serious Window Damage To Atlantis 291
FTL writes "While in orbit a metal knob floated between a window and the dashboard of Atlantis. Once back on Earth, the shuttle contracted, wedging the knob firmly in place and damaging the window. Initial attempts to free the knob have failed and engineers may need six months to disassemble that section of the orbiter. Given that the shuttle program will probably end next year anyway, such a delay might mean scrapping Atlantis early rather than repairing it. Efforts to remove the knob using less invasive techniques continue."
Re:physics (Score:2, Insightful)
Why not just apply extremely localised extreme heat to critical areas on the knob, collapse it and remove the new shape?
Why not just pull it really hard?
Why not chisel it really hard ...etc.
You and me could think of a bunch of stuff; NASA could think of a bunch of stuff and properly assess how likely it is to work vs how likely it is to damage the shuttle vs how much it will cost and so on.
Re:Blow it up (Score:3, Insightful)
Re:Aren't the windshields replaced all the time? (Score:2, Insightful)
Or is that only an outer protective layer? .... I just assumed they were made to be easily replaced.
No, sadly, the knob's outer, protective layer can not be easily replaced (cf circumcision).
Leave it till next time. (Score:1, Insightful)
I wonder if they could just leave it in there until the next mission. It should come loose on orbit right?
Here's a lesson, never make parts that can break off out of something you can't easily cut. If the knob were
made of some kind of plastic a little acetone might have fixed the problem.
Re:physics (Score:2, Insightful)
That's the problem: many armchair rocket scientists have lost faith in NASA's ability to accomplish anything of value. They're a big money sink in a time when the budgets could be far more beneficially applied elsewhere. Do people give a flying fuck about Mars ? Not when there are innumerable large-scale problems here on earth.
Re:physics (Score:3, Insightful)
As someone else earlier suggested, why not dissolve it? There are acids with high enough electronegativity differences to dissolve just about anything. If the acid were brushed on to the a sufficiently narrow part of the knot, and all collected as it dripped down, it would in time etch that part of the metal away enough to break it and hence dislodge the knob. Of course, it would have to be secured first so it doesn't collapse when it shouldn't. But that seems less invasive if more time-consuming. However, it needn't even be so expensive -- the acid can after all simply be re-circulated. No matter how time-consuming, though, it's simple enough that there's not much overhead -- so it could be done in weeks instead of 6 months.
And yes, I don't see this option discussed anywhere in the article. Several other options with immediately visible flaws are discussed and rejected, but this isn't.
Re:Aren't the windshields replaced all the time? (Score:5, Insightful)
Excellent and informed analysis. However, I think it is unlikely that "metal" knob could scratch glass. See the Moh hardness scale.
Hmm. You're saying you know what the knob is made of, and what the surface treatment of that material is? If, for example, it's aluminum with an anodization (as it looks to be in the photo), it may well scratch the glass. Scratching isn't the only issue, though, as if sufficient pressure has been applied, localized microscopic deformation might have occurred as well. If the compression layer of the tempered glass has been breached, the glass will fail. If it has been damaged beyond the stated engineering guidelines, as described in the article, the window will need to be replaced. The close up image in the article shows what appears to be damage to the glass at two points where the glass contacts the knob.
It's a simple problem that many of us have faced in one situation or another where something small has managed to get wedged where it shouldn't, and requires extraction. The difference here is that there are serious, and potentially highly costly, either in dollars or in human life, or both, potential ramifications to performing the extraction badly.
Re:This reminds me of my dashboard ... (Score:3, Insightful)
I have found the that the main difference between a $20K car and a $50K car is that the $0.20 parts get replaced with $0.50 parts. Not shaving every possible penny on every possible part seems to help a lot quality-wise. I just wish I could buy the $21K car with just those parts upgrades!
Re:NASA forgot low tech approaches? (Score:3, Insightful)
Magnets for aluminum. Sure.
I'm know I'm not smarter than nasa, but... (Score:3, Insightful)
why can't they put postive pressure inside the orbiter and pop it out?
but a better question perhaps, is why the hell is there junk rolling around inside the space shuttle?
Re:Aren't the windshields replaced all the time? (Score:3, Insightful)
Cutting would obviously be done by hand, or with a very slow speed reciprocating saw, which produce minimal vibration. They'd probably encase the whole thing in epoxy first to further reduce vibration.
Movement of the knob against the glass, no matter how slow, is potentially going to grind the glass away. Encasing the knob in epoxy isn't going to help unless the epoxy is also adhering to the glass to prevent relative motion between the knob and glass. And, in that case, there's the difficulty of removing the epoxy afterward. Could be done, but probably not a very good approach, and certainly not without risk.
If scratches can lead to "spontaneous catastrophic failure" in the window material then obviously there is zero risk because the window must have a strong scratch-proof covering, probably a thin layer of plexiglas or similar. Otherwise trivial incidents over the course of the shuttle's working life would pose an unacceptable risk--anything breaking loose on re-entry, in particular, could scratch the surface if it was not heavily protected.
The article (you did read the article before spouting off, right?) does not describe any coating that I saw. It does, however, describe the minimum acceptable damage to the outer stressed layer of the glass. Recall this is thermally stressed (aka Pyrex) glass, and if the outer compression layer is breached, it can, and does, lead to spontaneous catastrophic failure. That's why there are guidelines as to how deep a scratch is acceptable. Also recall that the compression layer is not one atomic layer, such that the glass can sustain some damage before failing. Note that this would still be true if there were any sort of plastic coating as well -- there would still be some limit of acceptable damage before risk of failure is too high.
More importantly, if the choice is a) scrap the shuttle early for sure or b) risk having to scrap it due to damage done during knob removal, the choice is so obvious that only a NASA engineer could get it wrong.
[snip]
Personally, I'm wondering why engineers rather than machinists are working on this problem. Engineers don't have the appropriate hands-on skills to deal with it. Machinists do.
Did you learn somewhere that there are no machinists working on the problem? Do you know engineers working at NASA, so you have the experience to make blanket statements about their ability like that? It just so happens that I do know engineers at NASA, and at some of their subcontractors. One can argue whether they are absolutely the very best in the world or not, but they are certainly world-class, and a damned sight better than any run-of-the-mill engineers around. Listen, these aren't stupid people. It is rocket science, and rocket science is hard. If you have never been to Johnson, I highly recommend it. And you can bet that if you or I had an idea after cogitating for 2 minutes about the extraction problem, someone who's job depends on it, who likely has a degree in aero-astro from MIT, who realizes the potential ramifications of screwing up, and who has spent many hours thinking about it non-stop, has already come up with it. Like asking a machinist for his thoughts.