Microsoft co-founder Paul Allen is indulging his enthusiasm for space travel with a new project: a giant aircraft designed for mid-flight rocket launchers.

And he doesn’t think small: under a new company, Stratolaunch Systems, Allen plans to put together the “biggest airliner ever built” using six 747 engines to haul SpaceX rockets carrying payloads, satellites and – if SpaceX can get human-rated – people into low-Earth orbit.

There’s a certain patriotic thread to Allen’s announcement: “For the first time since John Glenn, America cannot fly its own astronauts into space,” he is quoted as saying by AFP.

Finding airstrips will also be non-trivial, since the lifter would need around 3.65 Km of runway to get airborne. It will weigh around 544,000 kilos and have a wingspan of 117 meters (1.2 million pounds and 380 feet, respectively).

Allen said the project will cost more than his SpaceShipOne craft, which achieved sub-orbital flight after a $US25 million investment.

The airplane-based launcher would, Allen said, be more flexible than ground-based rocket launches, and would also be cheaper. Allen says that Soyuz manned launches will soon cost around $US63 million per seat, enough to give him confidence that he can compete on price. ®