Stratolaunch, funded by billionaire Microsoft co-founder Paul Allen, has cleared another hurdle in its goal to provide routine, low earth orbit launches of space vehicles. For the first time all six Pratt & Whitney PW4056 turbofan engines completed the first phase of testing.
Engine testing consisted of three parts. First, the engines were run as a dry motor, where an auxiliary power unit was used to charge the engine. Second as a wet motor, where fuel was introduced, and the third and final phase was to start one engine at a time and allow them all to idle. Each of the six engines functioned as expected. Additionally, testing of all six fuel tanks and fuel mechanisms was completed to ensure proper operations and sealing.
The plane will be an airborne rocket launcher, carrying a rocket weighing up to 275 tons under the central part of the wing between the two fuselages. Launching the rockets from a low orbit of 35,000 ft. as opposed to a launchpad will save fuel as well as costs associated with launch delays due to inclement weather. Stratolaunch is also reusable and takes off from a runway.
The enormous plane has a wingspan of 385 ft. (117 m) connecting two fuselages, a tail height of 50 ft (15 m) and 28 wheels to support its weight. The aircraft has a dry weight of 500,000 lb. and a maximum takeoff weight of 1.3 million pounds. To put this into perspective the Stratolaunch plane is 12 ft. shorter and has a wingspan 161 ft. longer than a Boeing 747. The maximum takeoff weight of the Stratolaunch is more than 310,000 lb., heavier than a fully-loaded 747.
The comparison to a 747 is a good one for other reasons as well. Many of the components used on the Stratolaunch have been cannibalized from 747s. The plane is utilizing 24 wheels from six sets of 747 main landing gear, as well as four wheels from two sets of 747 nose landing gear. The PW4056 engines are used on 747 jets, as well as other aircraft. The cockpit seats, as well as the controls, have also been taken. About half of the empty weight of the plane can be accounted for by compatible 747 parts.
The rest of the plane however, bears very little resemblance to a 747, or anything else flying the skies today. Scaled Composites has hand-built the body of the Stratolaunch from carbon fiber composites. Although the twin fuselages look virtually identical from the outside, the left-hand fuselage is empty and unpressurized. While the front of the fuselage has a sleek design resembling many other modern jets, the rear of the fuselages are empty and unpressurized and sport a boxier, rectangular cross-section.
Plans call for further engine testing over the next few months, at higher power levels and varying configurations. Taxi tests will follow, and if all goes as planned, a maiden flight as early as 2019.