With all the news and media surrounding the recent Columbia disaster, one thing that seems to be coming up in conversation is the heat sheild tiles. This is not the first time I recall hearing about this important shuttle parts. Early on in the shuttle program I recall NASA and news outlets occationally talking about them, even comminting that one or two even fall off occationally. And of course, we all know that each one is unique in size, and that there are a whole buch of them (did someone say 30,000)?
So why do we use these things still? Why would we not want to manufacture one large peice, or a few large piece(s) of this material? With it’s larger surface area to attach with (and perhaps even enough area for a few mechanical fasteners?), wouldn’t larger tiles, (or one large piece) of heat shielding material be a better idea?
And I suppose while I’m asking, why not make the stuff out of aerogel too?
IIRC–The tiles are designed to flake off as they ablate during re-entry. One big piece would not allow the flaking to occur. If the damage they are suspecting caused the accident really did cause it, it had more to do with the wing than the tiles.
I am not a Ceramic Engineer, but as far as I know, one of the reasons the ceramic tiles are used is the fact that they handle the heat buildup extremely well when traveling at high speeds and through the atmosphere, etc.
My guess about why several tiles are used instead of “one big one”, is that the one piece would not last long. If you watch a video of a shuttle blasting off, you will see thousands of little ceramic pieces falling off the shuttle from all the vibrations at ignition. I don’t know for sure, but I would think if there was only one piece of ceramic, it would crack/break apart or what have you.
I’m sure someone else can come along and shed a lot more light on this than I can.
The shuttle, like any aircraft of that size flexes, expands and contracts as it experiences changes in loading pressure and temperature. One large piece of shielding would probably not be flexible enough and would be prone to cracking. And with many small tiles it is easier to replace damaged ones. In addition the tile must be bonded solidly to the underlying structure, the larger it is the more difficult this becomes. These tiles represented a major breakthrough in material science when they came out, it was probably not possible at that time to make large panels of the stuff. Remember that this design dates to the 1970s.
BTW: I am almost positive that it is not ceramic that is falling off the shuttle at launch but ratehr ice and other stuff as hoses disconnect from the orbiter when it launches.
One problem with mechancal fasterers probably is that you might have just reintroduced an element of heat convection back into the aircraft, thus negating the full efficiency of the tile.
Actually, that is what I thought that debris was as well… ice on cabling and on the exterior of the rocket boosters. Sure, all that stuff gets hot once the engines are fired, but up until that point, they could be awfully cold.
A bit ago I saw on TV a demonstration of the heat qualities of these tiles, and it was pretty amazing.
I had thought, apparently wrongly, that when they said ceramic tile, they were hard, thin and heavy. That doesn’t seem to be the case. Obviously there is some sort of tough skin, but the tiles seemed to be pretty thick, like 3-5 inches, very light in weight, more like foam.
I have always wondered why the designers did not use a non-repeating tesselation patern to avoid strips of tiles coming off (not that I am saying that was the cause of the accident). It would seem that if a tile came off in a regular, repeating pattern that would put pressure on the next tile ‘down-wind’ from that tile to also peel off.
A Penrose tesselation uses the same shape tiles that sit easily and snugly together. You do not need to make sure they line up, however I think you need at least two different shaped tiles.
I suppose they engineers thought of this, but I don’t know why the idea would have been rejected.
Aside from any other considerations, the economics of the situation provide a huge incentive to stick with the small tiles. It’s much cheaper to replace a few small tiles at a time than it would be to replace the whole nose section. One chip or crack would be enough to require the replacement of the entire nose, if it were all one piece.
Also, I don’t believe it’s currently possible to produce such a large, complex shape in traditional ceramics. It might be possible if, as someone suggested, these tiles are actually produced from some type of foam.
I think Penrose tiling was first mentioned in the mid 70’s and the tiling ideas in eth early 80’s. That might be a little late for shuttle applications.
Cool idea though, wonder if they’d every use them?
