The Scaled Composites Model 351 Stratolaunch is an aircraft built for Stratolaunch Systems by Scaled Composites to carry air-launch-to-orbit rockets. It was announced in December 2011 and rolled out in May 2017. The aircraft features a twin-fuselage design and the longest wingspan ever flown, at 385 feet (117 m), surpassing the Hughes H-4 Hercules flying boat of 321 feet (98 m). The Stratolaunch is intended to carry a 550,000-pound (250 t) payload and has a 1,300,000-pound (590 t) maximum takeoff weight. It should release its rocket at 35,000 ft (11,000 m).
The aircraft flew for the first and so far only time on April 13, 2019, and shortly thereafter, the company announced it would halt development of its air-launched family of launch vehicles following the death of Stratolaunch founder Paul Allen in October 2018. The company ceased operations the next month, and placed all company assets, including the aircraft, for sale for US$400 million by June 2019. Cerberus Capital Management acquired Stratolaunch Systems including the Stratolaunch aircraft in October 2019. Stratolaunch announced in December 2019 that it would now be focusing on offering high-speed flight test services.
Stratolaunch has a twin-fuselage configuration, each 238 ft (73 m) long and supported by 12 main landing gear wheels and two nose gear wheels, for a total of 28 wheels. The twin-fuselage configuration is similar to the Scaled Composites White Knight Two. Each fuselage has its own empennage.
The pilot, co-pilot and flight engineer are accommodated in the right fuselage cockpit. The flight data systems are in the left fuselage. The left fuselage cockpit is unmanned with storage space for up to 2,500lb of mission specific support equipment. Both fuselage cockpits are pressurized and separated by a composite pressure bulkhead from the remainder of the unpressurized vehicle.
At 385 ft (117 m), it is the largest plane by wingspan, greater than a 300 ft (91 m) American football field. The main center section is made up of four primary composite spars supported by four secondary spars. The center section of the high-mounted, high aspect ratio wing is fitted with a Mating and Integration System (MIS), developed by Dynetics and capable of handling a 490,000 lb (220 t) load. The wing houses six main and two auxiliary fuel tanks, with the main tanks located inboard adjacent to an engine. The auxiliary tanks are located in the inboard wing where the load-carrying structure joins the fuselage.
Stratolaunch is powered by six Pratt & Whitney PW4056 engines positioned on pylons outboard of each fuselage, providing 56,750 lbf (252.4 kN) of thrust per engine. Many of the aircraft systems have been adopted from the Boeing 747-400, including the engines, avionics, flight deck, landing gear and other systems, reducing development costs.
It will require 12,000 ft (3,700 m) of runway to lift-off. It should release its rocket at 35,000 ft (11,000 m). It will carry a 550,000 lb (250 t) payload. With a Pegasus II, it could deliver up to 13,500 lb (6.1 t) satellites to LEO or 4,500 lb (2.0 t) to a 15° GTO. It could launch a Dream Chaser small spaceplane capable of transporting astronauts or payloads within 24 hours. The stated goal is to carry up to three Orbital ATK “Pegasus XL” rockets for high-altitude launches by 2022.