Prepegs offer (even) lower weight, higher strength, less wasted (squeegeed out) epoxy and most importantly… Can survive much higher temperatures without deforming or melting. Something to which SpaceShip2 might appreciate. The downside is that you NEED an autoclave and they don’t make those things very big… SpaceShip1 was made in small parts so it could be autoclaved but that added complexity and weight.

That material could be very useful, especially for people like me that like to do big composite projects that tend to sit in the sun (requiring white paint jobs to reduce heat buildup) and can’t afford an autoclave…