Achieving something that has never existed in manned spaceflight and that is high volume and public access.
Burt RutanTo allow public access to orbit, we would need breakthroughs that would lower the cost by a lot more than an order of magnitude and increase safety by a factor of 100 as compared to every launch system used since the first manned space flight. I think airborne launch will be a significant part of the safety solution.
Burt Rutan