Aiming to return to a time when the U.S. can fly its own astronauts into space — or anyone else with money enough to buy a ride — Microsoft co-founder Paul Allen and his SpaceShipOne partner, experimental aircraft designer Burt Rutan, plan to use the equivalent of two 747-400s to airlift a Falcon 9 derivative launcher for drop-launches into orbit by the end of the decade.

“Since the success of SpaceShipOne, I have thought a lot about how to take the next big step, a private orbital system,” Allen says. SpaceShipOne was the suborbital X-Prize winner that Rutan’s Scaled Composites built with Allen’s financial backing.

Rutan has since sold Scaled Composites to Northrop Grumman, but the company will again give Allen’s dream a ride aloft.

The carrier aircraft they are to build will have a 385-ft. wingspan — a 747-400’s is a mere 212 ft. — and use twin fuselages. No technical data are being provided, beyond a weight of 1.2 million lb.

But the aircraft will be made of composites, so even though it will use a -400’s engines, flight deck, landing gear and systems, it will be a substantially different aircraft.

With a wingspan longer than a football field, Rutan emphasizes that the proposed carrier aircraft will easily rank as the world’s largest airplane.

Space Exploration Technologies (SpaceX) is developing a Falcon 5 or 6 two-stage liquid-fueled derivative of its Falcon 9 booster for the Stratolaunch Systems venture. Initial customers are expected to be either government or civil satellites. Stratolaunch aims for a 13,500-lb. payload-to-orbit capacity.

It will be an unmanned expendable launch system for satellites. Rutan said the human-rated Falcon system will fly the “feathered” low-drag re-entry profile he used for SpaceShipOne.

Huntsville, Ala.-based Dynetics will build the mating and integration system for the carrier aircraft to be able to carry the Falcon launcher. An onboard crew will conduct the launch, says Stratolaunch President and Chief Executive Gary Wentz, former chief engineer at NASA’s Marshall Space Flight Center. What type of thermal protective system the human-rated, winged Falcon will require is unclear.

Rutan provided few details, insisting they are competition-sensitive. Nor would Allen say how much he will need to invest over the coming decade, saying only that it will be “an order of magnitude” greater than his investment in SpaceShipOne, which is estimated at $25 million.

Former NASA Administrator Michael Griffin, a Stratolaunch board member, says the emphasis initially will be on customers to use Stratolaunch as a self-contained system, whether for manned or unmanned flights. He does not rule out the possibility of delivering cargo or astronauts to the International Space Station, but notes that its safety requirements for docking operations are formidable, “as they should be.”

The first test flight of the carrier aircraft is planned in 2015 from Scaled Composites’ home in Mojave, Calif. An operational base for the Stratolauncher has not been selected.