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

Once designed and tested, the vehicle will also set the parameters for operational runways after development, but there are several possibilities (almost any field that can handle a B-52 would work), and the company has already reportedly been in discussions with Kennedy Space Center to use the Shuttle runway.

What are the advantages of air launch over a fixed launch pad? There are at least two.

First, the performance of a given launch vehicle is increased, not only because it gets a slight “head start” into orbit by leaving from altitude and with some ground speed, but because the rocket nozzles can be optimized for space, since it doesn’t have to operate at sea level. This allows a significant improvement in fuel efficiency.

But more important is the increase in operational flexibility. A fixed launch pad can’t avoid weather. It is also restricted in launch azimuth (the direction that the launch takes) because of geographical overflight constraints. Moreover, an aerial launch platform can fly to the precise location needed to allow an injection into an orbital plane at just the right place and time to allow a rendezvous and docking with an orbiting object (such as the International Space Station, or a tourist hotel) within a few hours, rather than a day or two, which is typical for a launch from a more constrained pad.

This would be a huge benefit for current space travelers whose nominal, standard experience is worse than being tortured by an airline with hours on the tarmac, with no toilet facilities whatsoever. For people who want to get quickly to their destination, rather than sitting in a cramped capsule for days, as is currently the case on Soyuz, and would be the case for the SpaceX Dragon or Boeing CST or other commercial fixed-pad providers, it would dramatically open up the market.

There are some interesting regulatory issues that weren’t addressed in the press conference. Orbital operates its Stargazer L-1011 under a standard FAA aviation certification and license, though it also has to get a launch license for the Pegasus from the FAA’s space office, FAA-AST. It’s likely that the carrier aircraft for this new venture will as well. The cost estimate provided was about an order of magnitude above what Mr. Allen spent on winning the X-Prize with Burt Rutan’s SpaceShipOne, which has been reported to be about thirty million dollars. That means it will be at least three hundred million, which is still far shy of the billions that traditional NASA/Air-Force cost models would generate for such a project.

But it’s unclear whether this includes the cost of FAA certification. Years ago, Burt built a prototype of a very small business jet for a couple million dollars. The estimate to get it certified for commercial use by the FAA aviation branch was a couple hundred million dollars. The difference in this case won’t be as bad, at least in terms of the ratio, but it could still add hundreds of millions in cost. On the other hand, there may be markets for the largest aircraft in the world other than as a launch carrier, so the cost of certification may be a good investment. Regardless, given that the project has an investor with very deep pockets and a clear commitment to it, we’re in for an interesting decade.