Microsoft co-founder Paul Allen and famed aerospace engineer Burt Rutan are once again teaming up for a space venture. This time they’re heading to orbit and calling in Elon Musk and SpaceX to help them get there. The project, Stratolaunch Systems, will use an air-launched booster rocket to deliver cargo, and eventually people, into low earth orbit.

The plan amounts to building the biggest airplane ever, then using it to launch rockets into space from about 30,000 feet. Allen, who reportedly is financing the project himself, announced the new company today and said it “will bring airport-like operations to the launch of commercial and government payloads.”

“By the end of this decade, Stratolaunch will be putting spacecraft into orbit,” he said.

Allen, the billionaire co-founder of Microsoft, joins super-wealthy entrepreneurs like Musk, Richard Branson and Jeff Bezos in looking to the heavens for his next venture, as NASA turns to the private sector for help getting to space.

The company will use a launch system similar to what was developed for Rutan and Allen’s SpaceShipOne project. But it will be much, much bigger.

The mothership will employ six 747 aircraft engines and have a wingspan of 385 feet — more than 120 feet greater than an Airbus A380, currently the largest commercial passenger plane in service. The airplane will have a gross weight of 1.2 million pounds, including a 490,000-pound booster rocket being developed by SpaceX.

“Paul Allen and Burt Rutan helped generate enormous interest in space with White Knight and SpaceShipOne,” SpaceX President Gwynne Shotwell said in a statement. “There was no way we weren’t going to be involved in their next great endeavor. We are very excited.”

The aircraft itself will be designed and built by Scaled Composites, the Rutan-founded company currently developing SpaceShipTwo for Virgin Galactic. The aircraft will be be designed to operate from a large airport or spaceport like Kennedy Space Center, eliminating the need for launching pads. Allen said that will cut costs and increase versatility.

The advantage of using an airplane to launch the rocket isn’t as big as it was for reaching suborbital space, according to Rutan — just 5 to 10 percent. But every little bit counts.

“It’s a small advantage to air launch,” he said, “but it’s in a world where a small advantage is big.”

Scaled will build the Stratolauncher in a hangar slated for construction at Mojave Air and Space Port in Southern California. The aircraft will require a 12,000-foot runway, and it will be able to travel about 1,200 miles.

Former NASA administrator Mike Griffin is a member of the Stratolaunch board and said the air launch system will make launching more dependable.

“We believe this technology has the potential to someday make spaceflight routine by removing many of the constraints associated with ground launched rockets,” Griffin said in a statement. “Our system will also provide the flexibility to launch from a large variety of locations.”

A first flight of the system is expected within five years. Stratolaunch will begin by launching cargo into orbit, but the company says sending people into orbit will happen once the technology is proven.

UPDATED 6 p.m. EST with additional information.

Video: VulcanInc/YouTube