The X-15's had to be repainted after every flight, because the ablative coating was designed to wear off at speed. That's a huge expense, in both time and money

The X-15's had to be repainted after every flight, because the ablative coating was designed to wear off at speed. That's a huge expense, in both time and money. Worth it for a research craft, not worth it for any practical use. In terms of materials, most of the newmake ultra fast aircraft are using inconel, which is more viable than it was back in the day. Some are using ceramic coatings of various sorts in hopes that they'll be able to develop something strong enough to be reused. And that's not to say that they won't be able to come up with something, just that nobody has done it yet, or, has done it and has talked about it.