The Scaled Composites Model 351 Is being built for Microsoft co-founder Paul Allen’s Stratolaunch Systems as a platform from which air-launch space missions can be staged. The aircraft boasts a wingspan of 385 feet (117 meters) which makes the 351 the undisputed wingspan champion of the world- longer than the Apollo Saturn V rockets were tall. The twin fuselages are 73 feet (22 meters) long and joined by a single wing section under which the payload(s) will be carried to launch altitude- commonly 35,000 feet (10,668 meters).
Many of the aircraft’s components are actually Boeing 747 parts, including the six Pratt & Whitney PW4056 engines, flight deck (in the starboard side fuselage), avionics, landing gear, and a few other systems. Scaled Composites went to the boneyard at Mojave and snagged two former United Airlines Boeing 747-400s, brought them to their facility at Mojave, and parted them out. A large percentage of the structure is comprised of composite materials such as carbon fiber.
Weighing in at a whopping 1,300,000 pounds (650 tons or 589,670 kilograms), and requiring 12,000 feet (3,700 meters) of runway to lift off with a payload, the 351 looks as if it is missing some pieces. There is no joinery between the tail surfaces, which is unusual to say the least. Each fuselage “boom” has its own complete tail. But when one considers that the payload will be carried aloft under the center wing section between the two fuselages it all makes sense. The project began in 2010 and the first flight of the 351 is scheduled to take place in 2017 with the first payload launch to occur in 2020.