Originally Posted by
Dont Hang Up
Not even that. The mothership launch technology has not yet overcome the technology hurdle to achieve anything better than a brief parabolic excursion beyond the atmosphere. That is why the experimental craft of sixty years ago did not progress further and the space programme reverted to vertical launch rockets. Early ideas that the Space Shuttle might work this way were also quickly abandoned.
For a real technology progression using this launch method a true hybrid engine would be needed - a combination jet and rocket that can transfer gradually from air-breathing to purely reactive as the air density decreases. And that is a development programme which is probably beyond even Mr Branson's deep pockets.
Even a true hybrid engine would not help much, because of elementary energy balance constraints. You need to impart the craft with a certain amount of kinetic energy (Mach 25 or so). There is a hard physical limit on specific impulse of rocket fuel, and the weight of fuel necessary per unit of useful load goes up exponentially as the ratio of target speed to specific impulse. A typical surface-launched rocket with enough payload to get a few humans into orbit has to weigh at least 300 tons.
Launching from a mothership in a two-step fashion, the way Virgin does, assuming that you can add a good ramjet on top of their existing designs, lets you save some money because the mothership is fully reusable, and lets you save some weight because you don't have to carry all oxidizer that you burn up to a certain speed. But even if you can get the "spaceship" out of the atmosphere and up to, say, Mach 3 before you switch to rocket engines, you still need to go from Mach 3 to Mach 25, which means that you still need to carry a heck of a lot of fuel and only a small amount of payload.
SpaceShipTwo reportedly weighs ~10 tons (constrained by the lift capacity of the mothership), and payload to fuel ratio is way too high. You need to scale the mothership by a factor of 10, somewhere to the size of a 777, and you need to turn SpaceShipTwo into something that looks more like a classic rocket (with large separating first stage), and then it would approach being useful for actual space flight. In the present form it's firmly stuck inside Earth's gravitational well.