Assembly of the Stratolaunch, the enormous air launch carrier aircraft venture backed by billionaire Paul Allen, is 76% complete, and it is being readied for engine installation and full systems testing.
“This is one heck of an ambitious undertaking. It has never been done before and is the largest wingspan aircraft ever, so that is a big deal,” says Chuck Beames, president of Vulcan Aerospace and executive director of Stratolaunch Systems. Yet, despite clear progress toward completion, the Vulcan Aerospace subsidiary building the 385-ft.-span, six-engine behemoth remains coy about when the vehicle will begin flight tests.
“When Paul kicked this thing off, he committed to have this capability on orbit by the end of decade. And of course, come hell and high water, we are on track to do that,” says Beames. “I am not at liberty to commit to any time lines right now. We will be making a series of announcements in the coming months, but we are definitely on track.” At the time of the project’s original launch in 2011, flight tests were due to start in 2015, but development has taken two years longer than expected and, given the current state of completion, flight testing now looks set to begin in 2017.
Beames, who was updating progress on the Stratolaunch project at a rare media event June 16 in Mojave, California, also emphasized the company’s continuing drive to expand into the launch market for small to medium-size low-Earth-orbit (LEO) satellites. The Stratolauncher was originally targeted at the replacement market for the Delta II medium-class launch vehicle, but with the growing focus toward smallsats and lighter payloads, the company has expanded its reach to embrace a much wider range of potential commercial and government launch opportunities.

The Stratolaunch will have 28 wheels, 24 of them attached to the six sets of former Boeing 747-400 main body landing gear legs, pictured awaiting installation. Credit: Vulcan Inc.


“Targeting the Delta II market made sense at the time, but Stratolaunch also knew then that having a larger aircraft gives you the flexibility to do lots of things. If they had shot too low, then they would have been stuck,” says Beames, who adds that future options could include carrying multiple launch vehicles on a single mission. “The nature of LEO means you can go with multiple satellites and multiple inclinations in one mission. There is no reason why you could not have a couple of different launch vehicles, for example. It is certainly feasible.”
Stratolaunch also believes the vehicle will be able to carry larger payloads than previously thought, even though the twin-boom carrier aircraft’s maximum takeoff weight of 1.3 million lb. and the maximum load capability of 555,000 lb. will remain unchanged. “Our analysis shows an even greater capability, and that is frankly due to advances in manufacturing of the launch vehicles. You get more performance. The 555,000 lb. does not change; it’s what you can do with that,” says Beames. “We have frankly conservative margins on the load-carrying capability and will do static tests. If I were a betting man, I would say we will exceed that,” he adds. 
Having earlier announced—and then quietly sidelined—launch vehicle and payload partnerships with SpaceX, Orbital ATK and Sierra Nevada Corp., Stratolaunch is equally reluctant to disclose details of potential partnerships. Reflecting the strategic shift from teaming to launch larger payloads, to a wider scope of missions now embracing everything from medium launch vehicles to small satellite LEO constellations, Beames adds: “We have decided on an architecture; we have a business plan strategy that Paul has approved.”

The vast dimensions of the 385-ft.-span wing are evident in this view across the left wing and fuselage of the Stratolauncher from near the midwing point (in foreground). Credit: Vulcan Inc.


Beames also notes that the company is “developing and fostering lots of partnerships, because this is more than just an airplane and a rocket; it is a very complex economic system.” To that end, he says, “it is important that when we go through those reveals [of partners], it makes sense from a Vulcan Aerospace perspective. No company is ruled out right now. They will be true partners and not just suppliers. So we have to be certain of the specifics of those partnerships as we go.”
While the business plan details remain closely guarded, the air carrier vehicle itself is coming into sharper focus. The aircraft is structurally complete, apart from the empennage of the right-hand tail boom. The right horizontal stabilizers are on the hangar floor awaiting mating with the 36-ft.-tall vertical tail that is nearing completion in the adjacent fabrication building. The vertical tail will stand 50 ft. high from the ground when installed. The fabrication site, which is used for the layup and assembly of the composite parts of the aircraft, will be developed into a payload preparation and integration site for customers once production wraps up this year.
Once the tail of the right boom is completed, Stratolaunch plans to quickly attach the landing gear and Pratt & Whitney PW4056 engines, all of which come from two formerUnited Airlines Boeing 747-400s that were cannibalized for parts. The aircraft will be supported by 28 wheels, 24 of which will be on six sets of four-wheel 747 main body gear assemblies, and four on a pair of 747 nose gears. Three main landing gear bays are built into the midsection of each of the aircraft’s 238 ft.-long fuselage booms. Other parts used from the 747s include the hydraulic system, including actuators, electrical system, avionics, pilot controls and flight deck. In all, about 250,000 lb. of the aircraft’s full-up takeoff weight of 1.3 lb. million will be made up of 747 components.

The nose of the left fuselage (pictured) will contain launch support equipment while the right fuselage houses the flight deck and crew. Credit: Vulcan Inc.


The cockpit, with places for two pilots and a flight engineer, is located in a pressurized section of the nose of the right fuselage. The nose of the opposite fuselage, which will not be occupied, is also pressurized and will house liquid nitrogen, compressed air, avionics and other items related to the launch systems. Customers will have the option of installing up to 2,500 lb. of support equipment in each fuselage. A composite pressure bulkhead separates the cockpit from the remainder of the vehicle, which is unpressurized.
The flight deck from the second 747 has been converted into a full-flight simulator for training the Scaled Composites flight crews who will operate the carrier aircraft for Stratolaunch. The simulator, which is programmed with flight characteristics based on load predictions from computational fluid dynamics analysis, is also currently being used to help refine control force requirements and flight control system actuation. While most of the cockpit displays are 747-400 standard units, the carrier vehicle will have a larger, centrally mounted multifunction display, modified flap/speed brake controls and a throttle quadrant with six handles.
The high-aspect-ratio wing, which weighs 260,000 lb., is configured with 12 cable-driven ailerons powered by 747 hydraulic actuators. The trailing edge supports 14 electrically signaled, hydraulically actuated split flaps which will also pivot down to act as air brakes. The center section supports the airborne support equipment pylon which provides the interface between the vehicle and payload. This is connected via five primary attachment points made from titanium, two each forward and aft, with a fifth centrally located to handle lateral loads.
The main section of the wing is made up of four continuous primary spars, each 250 ft. long, supported by four additional secondary spars. The outer sections, comprising four main spars that connect by interlocking with the main wing section, also support tip-mounted winglets, or tip-mounted strakes. The single-piece spars were assembled in the fabrication building using a specially developed expanding “concertina” oven device that cured the composite material along its entire length at 180F without the need for a giant autoclave. 

The tips of the right and left (pictured) wings were built on site and raised into position from the hangar floor. Each wingtip has six ailerons for a total of 12. Credit: Vulcan Inc.


Specially developed composite structures were also added to the aft part of each of the standard engine pylon attachments to cantilever the aircraft’s six PW4056s out ahead of the wing. Composite stiffeners were added to the upper and lower wing skins to pick up the main spar caps and take torsion loads from the engine attachments. The stiffeners extend aft over the 30-ft. chord of the wing. The wing houses six main and two auxiliary fuel tanks, with each of the main tanks located in the inboard section adjacent to a specific engine. The auxiliary tanks are located in the outer section of the inboard wing where the load-carrying structure meets the fuselage.