A new concept for launching payloads into orbit was unveiled this week in Seattle. In a press conference, Microsoft billionaire Paul Allen and aviation legend Burt Rutan wowed attendees with a model and a video of what will be the biggest airplane in the world, which will be used as a launch platform for a modified SpaceX Falcon rocket slung underneath it. The event occurred just one day short of Thursday’s twenty-fifth anniversary of the takeoff of the Voyager, a Rutan-designed aircraft that made the first non-stop flight around the world without refueling. First flight of the airplane is estimated to be about four years from now, with first launch into space a year or so after that.
How big will it be? The current contender, at least in terms of lift capability, is the Russian Antonov-225 (though Howard Hughes’ Spruce Goose had a larger wingspan). The new aircraft will dwarf both of them, with a planned wingspan of 385 feet, larger than a football field, and over three times the length of the first flight of the Wright Flier (whose 108th anniversary is on Saturday).
Air launch is not a new concept — as former NASA administrator Mike Griffin, who is on the new venture’s board of directors, pointed out. It goes back over sixty years to Chuck Yeager’s flight of the X-1 in 1947 that first successfully flew supersonic after being released from the bomb bay of a B-29. It was followed by the space-bound (though only suborbital) X-15s in the fifties and sixties that were dropped from a B-52 bomber, and an anti-satellite rocket was developed that was designed to launch from an F-15 fighter. Since the 1980s, Orbital Science Corporation has been launching the solid-fueled Pegasus launcher (another design by Rutan) from under the wing of a modified Lockheed L-1011 Tristar, delivering about a thousand pounds to orbit. But this will be by far the largest space vehicle ever launched from an aircraft: about half a million pounds, with an orbital payload capability of several tons.
One of the problems of air-launch concepts is that the size of the launcher is constrained by the size of the carrier aircraft, and this design seems to push the limits. The aircraft itself will be developed by Rutan’s former company, Scaled Composites, at the Mojave Air and Spaceport. Aircraft size, in both dimension and weight, is limited by the characteristics of the runway on which it takes off and lands. Mojave’s longest is over 12,000 feet, with a 200-foot width, so that will put an upper limit on the width between the gear, assuming some margin. If the wings exceed this width, as they do, then there are issues with ingestion of foreign material in the engines of the part of the plane that hangs over the grass (or in the case of Mojave, desert sand). Judging by the model, they apparently plan to deal with this problem by hanging all the engines from the high wing, keeping them, including those outboard, relatively far from the ground