With the fix the astronaut performed on the belly of the shuttle today, I need to ask something about the heat tiles.
There was a ton of caution and concern conveyed about the sensitivity of the heat tiles to damage during the repair today. The way it was portrayed, if the guy so much as looked at them funny it would destroy the integrity of the tiles.
Now, these are designed to allow the shuttle to reenter the atmosphere and withstand the heat so it doesn’t burn to oblivion. OTOH, things made of solid iron, like say a meteor(ite?) burn up at an incredible rate.
I’m sure rate of decent and angle, etc play a part in this, but those tiles still must withstand an incredible amount of abuse reentering.
So how delicate are they? And judging from what I’ve heard, how the hell do they withstand reentry? In other words, how can they take the heat, but can’t take being bumped?
The surface is somewhat tougher but the tile is 80% air with the solid material being silica ceramic.
Meteorites come in at a higher speed and they are made of iron which conducts heat quite well while air and glass do so less and therefore make good insulators.
I handled one of the tiles years ago. IIRC, it seemed kinda like pumice–light and firm, but definitely not something you’d want to manhandle. I suspect the concern is that if you damage the tiles, it’d mess up the flow of gases along the surface, which you then lead in to a positive feedback loop. For a re-entering spacecraft, this would be a Bad Thing[sup]TM[/sup].
OK, this is making more sense. I always thought of them as heavy, solid tiles that just withstood heat well. If they’re more like pumice or “air-filled” ceramic, that makes a lot more sense. That, I can tell, would be VERY delicate. I think my mistake was thinking of :heat absorbing" rather then “heat deflecting”.
My family used to have two tiles that fell off the space shuttle Columbia during an early mission when I was growing up. IIRC, they withstood heat really well because they were made of silica but they could be damaged physically with metal objects pretty easily. You could place them on the stove turned up all the way and them pick them up by their edges without feeling any heat transfer at all. In addition, NASA had a problem with them just falling off during launch so it might be possible to knock one off or damage the space between the tiles.
I understand that they are pumice-like and mostly air, but still… They have to be able to withstand enormous vibrations at lift-off and reentry, and I’m sure hitting a raindrop or a dust particle at a half gazillion mph during reentry must be quite a blow.
The way they’re being portrayed right now makes it seem a miracle that they survive being sneezed on.