I realize the shuttle uses tiles for thermal expansion reasons.

With that said, the tiles are fairly large even still. Is there a reason why NASA settled on the size it did?

I would think that smaller tiles, would provide even better thermal expansion properties while a single tile failure would result in less surface exposure. Also, why were "square" tiles used instead of triangular or diamond shaped tiles? On the otherhand, larger tiles would probably stick to the surface of the shuttle better.

One final question: I've seen it said that you could pick up a tile with your bare hands even if the bottom of the tile was super heated to the point where it glowed red...Is it really necesserry to have this degree of thermal protection? Perhaps it would be possible to design a tile or other system that offered slightly less thermal protection, but offered much greater reliability.

Too bad we in the United States have pretty much let the ball drop on developing hyper-sonic aircraft. The technologies developed on such a project would be very useful here as well.

Scott