Stuck Knob Causes Serious Window Damage To Atlantis

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."

Comments

Re:Aren't the windshields replaced all the time?

[pz]

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.