This video, produced by NASA, may not be quite as stunning as some of the other space shuttle tile videos, but it does a nice job explaining why the tiles are needed, how they're made, and what the other options are.
Oh, and I know my quote source here is Wikipedia, but I've read in a number of places that the explanation of friction being the cause of heating of the shuttle (and other objects) upon reentry to the atmosphere is incorrect. Rather, most of the heating is due to compression of the air.
Direct friction upon the reentry object is not the main cause of shock-layer heating. It is caused mainly from isentropic heating of the air molecules within the compression wave. Friction based entropy increases of the molecules within the wave also account for some heating....but Randall Munroe has my back, too...
Things get really hot when they come back from space. This isn’t because of air friction, strictly speaking—it’s because of air compression. The air can’t move out of the way fast enough, and gets squished in front of the spaceship/meteor/steak. Compressing air heats it up. As a rule of thumb, you start to notice compressive heating above about Mach 2 (which is why the Concorde had heat-resistant material on the leading edge of its wings).
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