For Aron: Aerogel instead of Shuttle Tiles?

Aron asked: So...I have the most insane idea for the shuttle, ever. Do you think it would be possible to strip all the tiles from the shuttle and replace it with aerogel and a thin ceramic to keep the aerogel in place. (It's insane and would increase the chance of damage to the shuttle) This could cut the weight.

It could cut the weight, in theory, given the density of aerogel. Aerogel has a density of 1.9 kg/m^3. Most of the tiles weigh in at ~144 kg/m^3 and, given that aerogel is pretty structurally strong and a great insulator, you might not even need the same volume to have the same thermal protection.

However, we might want to be careful before we get our Shuttle scrapers out and do the work.

First off, aerogel is hydrophilic (attracts and absorbs water), which means a couple of months sitting in Florida's humidity is unlikely to be good. Absorbing water not only drastically increases weight, but also cause it to deteriorate rapidly. Still, the Shuttle tiles also have to be waterproofed and there is a process for making aerogel hydroscopic (water repelling).

It's also friable which means it shatters like glass. I know it was used to gather space dust, so it can take tiny fast impacts, but I'm not sure how it would handle blunt trauma, handling, foam impact, etc.

Truthfully, we've known about aerogel for some time but I've never seen any suggestions or designs that use aerogel for a proposed spacecraft thermal protection system except early on; when the design matures, aerogel is taken off the table. I don't know why but I assume there good reasons for it. Perhaps it can't take the cold (as opposed to the heat). Perhaps it does poorly in high UV situations or is susceptible to atomic oxygen.

If whatever the problems are can be overcome (without degrading the thermal/density properties) of aerogel, perhaps some future designs will use it.

However, even if it were perfect, it might not be worth our while to change the Shuttle. As you know, there aren't many missions left for the Shuttle. Removing all the tile and replacing it (which hasn't I believe, been done in their lifetimes) would take months and probably force a recertification of the Shuttle. That's millions/billions of dollars. I'm not sure they could all be removed without potential damage to the underlying structure.

And Shuttle has some limitations - vendors no longer in business, limited spares and equipment, aging infrastructure and avionics - that replacing the tiles won't fix. Nor do I know that aerogel would better withstand foam. That makes extending the Shuttle to make the huge investment worthwhile (and to take advantage of the weight difference) a pretty bad deal I would think.

But, then, it's all speculation.