Getting back to Earth

Watching the space shuttle having its heat shield 'repair' live this week got me thinking. NASA has always spent a certain amount of money on engineers trying to think up innovative ways of doing space things, so how much thought has gone into building a better heat shield?

First some NASA info on the current heat shield is here. It says an average of 50 tiles are replaced between every mission, although there is lots of other work done on it every time it is refurbished for the next flight.

I think I read once (years ago in a science magazine) that they had to check the bonding of almost every tile between flights, but I haven't found a reference to that on the internet (yet).

As for the history of heat shields generally, this article briefly summarises it, and contains this interesting snippet of information:

"China developed recoverable spacecraft that reputedly used wood as an ablative material. While this may seem primitive, wood (in some cases cork) is actually used as an ablative material for some American rocket engine areas and payload shrouds, which heat up as the rocket flies through the atmosphere."

It also mentions an advanced idea:

"One promising idea that has been proposed for the future is the use of a plasma torch to form an artificial shockwave in front of a reentry vehicle. Just as the shockwave generated by a blunt body can protect a spacecraft by keeping hot gasses away from the skin of the vehicle, the plasma shockwave could theoretically protect a vehicle traveling at hypersonic velocity (Mach 6+) for sustained periods of time. But there is as yet no demand for such a thermal protection system and it remains only a laboratory experiment."

Pity if it went out suddenly though.

Inflatable shields also get an article here.

Not so long ago, using water as part of a shield was discussed in New Scientist.

So, seems there are limited options to explore for future heat shielding. Maybe I'll just wait for a space elevator to be built.

Update:

More googling has revealed that in fact the cancelled X 33 project involved a new metal based thermal protection system, that did get some testing before the whole project was cancelled. See links here, and here. In fact, one NASA media release indicates it was fully tested and ready for flight.

A more recent (2002) article about metallic reentry shields generally is here.

And while wandering around the Web, I found the forgotten (by me anyway) story of the Air Force's Lenticular Reentry Vehicle, a proposed nuclear powered, flying saucerish bomber from the dawn of the Cold War. The Popular Mechanics story on the link has a Brisbane connection too.

Gee, those 1950's boffins knew cool looking design, didn't they...