First, a little history: Microsoft cofounder Paul Allen funded the SpaceShipOne XPrize winner in 2004, designed by Burt Rutan and built by his company Scaled Composites. SpaceShipOne is a supersonic airplane with a rocket engine which went up over 100 km in elevation to the edge of space, a practically straight up and down "suborbital" flight. Subsequently, Scaled Composites entered a joint venture with Sir Richard Branson, called The Spaceship Company (TSC) to pursue an ambition to provide similar suborbital flights to space tourists. Orbital flights are not on the horizon. So, this website will not cover TSC or Virgin Galactic or those efforts.
Paul Allen and Burt Rutan have moved on to ambitions of providing space tourists a ride to orbital space, by attaching a rocket to another design of aircraft, whereby the rocket would detach at very high elevation and continue on to orbit, whereas the aircraft would return to Earth. Essentially, the aircraft is a reusable first stage. (The attached rocket is currently planed to be a separate 2 stages.)
To create this vehicle and provide the service, they have created the company Stratolaunch Systems. Their goal is to have the carrier aircraft testing by 2015 and the launch vehicle in a subsequent year.
Stratolaunch Services is currently planning to attach a rocket built by SpaceX and which is a derivative of the Falcon 9.
Launch of a rocket by aircraft has been done before by the Pegasus program for launch of small satellites.
This is the first design for air launching humans into orbit.
There are several advantages of air launch:
There are claims that launching a rocket from a supersonic aircraft can reduce launch costs by a factor of about 10.
This seems a longshot compared to alternative human launch scenarios, but worth keeping track of over the years.