phelan said:
...To me the only reason they wouldn't want to repair/replace the tile is if they think the repair is riskier than leaving it alone. Sure they trained for this after Columbia, but they haven't ever proven it works.
While I'm not Paul, I do know quite a bit about the tile repair techniques. I was a spacesuit engineer at JSC for 8 years and just recently moved on to other endevours. I supported many of the tile repair tests and saw all the options.
One of the main issues with repairing the tile is that its on the belly of the Orbiter and there are no hand-holds or foot restraints down there. Prior to the Columbia accident, there was no way to even inspect down there. They now have a long boom that attaches to the end of the shuttle robotic arm (RMS) so they can inspect and repair if needed. The main issue with the boom is that its aluminum and flexes quite a bit. If someone is on the boom and pushes on something (like the belly of the shuttle), the boom will start swaying. It could bring the astronaut into contact with the belly tiles and do more damage than is already there. The tiles are very fragile and can't take much of an impact. You can also input enough force to slip the brake on the joints of the RMS. This causes another whole series of problems. Lets just say they don't want to do this unless they absolutely have to.
One of the tile repair methods is to put a high temp RTV substance in the cavity. This goo (that's what we called it) is in 2 parts in a gun type apparatus. To mix the goo, there is a static mixer in the barrel. The goo works very well at resisting the temperature but has other issues. The main one is that they don't know if it will adhere to the tiles. If it comes out, not only is the cavity not protected but the clump of goo will do more damage as it bounces down the belly during re-entry. Needless to say, they don't want to use this method of repair unless they absolutely have to.
Another technique is to fill the cavity with small insulation "Pills" and then screw a carbon fiber overlay over the damage. There are a lot of issues with this technique. Some of the questions are: will the overlay stick up too much and trip the boundry layer? Will the augers that attach the overlay keep it on or will it just blow off? There are more issues that I can't think of right now.
"I thought for sure they would do the repair just as an excercise to see how well it worked. At least then they would have some actual real-world results to base future decisions on."
They have practiced these techniques many times in the pool (NBL), KC-135 and C-9 (zero-g), on an air bearing floor, in glove boxes and vacuum chambers, and many other places. They have practiced every way possible except during a real EVA. Now "the powers that be" must decide if the risks of more damage outweigh the risks of doing nothing. I'm kind of surprised but not totally surpised that they will leave it alone
As for the gloves, each (EVA) crewmember has two sets of gloves, prime and backup. Rick damaged his prime gloves. He will use his backup for any additional EVAs.
There has also been talk of the MMOD strike on the window. This occurs fairly regularly. The window are 5 layers (I think) of different materials. It would take a pretty severe hit to actually break a window to the point of leaking. The crew does a "survey" of the window at regular intervals to look for strikes and evaluate the damage. I'm not surprised they found a strike and it appears to have done minimal damage.
Enough rambling for now...
Karl (former EMU Guru)
