The new plane has a 385-foot wingspan and, powered by six Pratt & Whitney engines used on Boeing 747 aircraft, has a maximum takeoff weight of 1.3 million pounds.

The Stratolaunch's wingspan is the largest in history and is bigger than fellow billionaire Howard Hughes’ Spruce Goose by 65 feet.

Vulcan Aerospace says its Stratolaunch airplane will have an operational range of 2,000 nautical miles. Serving as a reusable first stage for rocket launches, the Stratolaunch system will be capable of delivering payloads to multiple orbits and inclinations in a single mission.

The company moved the Stratolaunch aircraft out of its hangar at the Mojave Air & Space Port in the eponymous California desert. This was first time it had been moved outdoors, and Allen said the purpose was to conduct a "fuelling test". This event marked the completion of the construction phase, the company later said, and the beginning of ground and eventually flight tests.

Allen wants to lower the cost of access to space through reusability. Vulcan has released few details about the launcher's capacity, but in October it did announce a partnership with Orbital ATK by which the Dulles, Virginia-based company would provide "multiple" Pegasus XL air-launch vehicles for use with the Stratolaunch aircraft.

These rockets can launch small satellites weighing up to 1,000 pounds into low Earth orbit. With this concept and capacity, Stratolaunch is competing with companies such as Virgin Orbit, which plans to launch rockets from a modified Boeing 747-400.