Allen confirmed that he was the sole investor behind aerospace engineer and entrepreneur Burt Rutan's SpaceShipOne suborbital commercial spacecraft on October 4, 2004.
The craft was developed and flown by Mojave Aerospace Ventures, which was a joint venture between Allen and Rutan's aviation company, Scaled Composites.
SpaceShipOne climbed to an altitude of 377,591 feet (115,090 m) over the Mojave Air and Space Port and was the first privately funded effort to successfully put a civilian in suborbital space.
It won the Ansari X Prize competition and received the $10 million prize.

On December 13, 2011, Allen announced the creation of Stratolaunch Systems, based at the Mojave Air and Space Port.
The Stratolaunch is a proposed orbital launch system consisting of a dual-bodied, 6-engine jet aircraft, capable of carrying a rocket to high altitude; the rocket would then separate from its carrier aircraft and fire its own engines to complete its climb into orbit.
If successful, this project would be the first wholly privately funded space transport system.
Stratolaunch, which is partnering with Orbital ATK and Scaled Composites, is intended to launch in inclement weather, fly without worrying about the availability of launch pads and to operate from different locations.
Stratolaunch plans to ultimately host six to ten missions per year.
On April 13, 2015, Vulcan Aerospace was announced.
It is the company within Allen's Vulcan Inc. that plans and executes projects to shift how the world conceptualizes space travel through cost reduction and on-demand access.

On April 13, 2019, the Stratolaunch aircraft made its maiden flight, reaching 15,000 ft (4,600 m) and 165 kn (305 km/h) in a 2 h 29 min flight.
 Stratolaunch CEO Jean Floyd offered this comment: "We dedicate this day to the man who inspired us all to strive for ways to empower the world's problem-solvers, Paul Allen.
Without a doubt, he would have been exceptionally proud to see his aircraft take flight".

As of the end of May 2019, Stratolaunch Systems Corporation is closing operations.
Allen confirmed that he was the sole investor behind aerospace engineer and entrepreneur Burt Rutan's SpaceShipOne suborbital commercial spacecraft on October 4, 2004. The craft was developed and flown by Mojave Aerospace Ventures, which was a joint venture between Allen and Rutan's aviation company, Scaled Composites. SpaceShipOne climbed to an altitude of 377,591 feet (115,090 m) over the Mojave Air and Space Port and was the first privately funded effort to successfully put a civilian in suborbital space. It won the Ansari X Prize competition and received the $10 million prize.
On December 13, 2011, Allen announced the creation of Stratolaunch Systems, based at the Mojave Air and Space Port. The Stratolaunch is a proposed orbital launch system consisting of a dual-bodied, 6-engine jet aircraft, capable of carrying a rocket to high altitude; the rocket would then separate from its carrier aircraft and fire its own engines to complete its climb into orbit. If successful, this project would be the first wholly privately funded space transport system. Stratolaunch, which is partnering with Orbital ATK and Scaled Composites, is intended to launch in inclement weather, fly without worrying about the availability of launch pads and to operate from different locations. Stratolaunch plans to ultimately host six to ten missions per year. On April 13, 2015, Vulcan Aerospace was announced. It is the company within Allen's Vulcan Inc. that plans and executes projects to shift how the world conceptualizes space travel through cost reduction and on-demand access.
On April 13, 2019, the Stratolaunch aircraft made its maiden flight, reaching 15,000 ft (4,600 m) and 165 kn (305 km/h) in a 2 h 29 min flight.  Stratolaunch CEO Jean Floyd offered this comment: "We dedicate this day to the man who inspired us all to strive for ways to empower the world's problem-solvers, Paul Allen. Without a doubt, he would have been exceptionally proud to see his aircraft take flight".
As of the end of May 2019, Stratolaunch Systems Corporation is closing operations.
Paul Allen