The Next Space Shuttle: Hybrid Engines Make Runway-To-Orbit Missions A Reality

A disembodied jet engine, attached to a hulking air vent, sits in an outdoor test facility at the Culham Science Center in Oxfordshire, England. When the engine screams to life, columns of steam billow from the vent, giving the impression of an industrial smokestack. Engineer Alan Bond sees something more futuristic. “We’re looking at a revolution in transportation,” he says. For Bond, the engine represents the beginning of the world’s first fully reusable spaceship, a new kind of craft that promises to do what no space-faring vehicle ever has: offer reliable, affordable, and regular round-trip access to low Earth orbit.

Bond and the engineers at Reaction Engines, the aerospace company he founded with two colleagues in 1989, refer to the future craft as the Skylon. The vehicle would have a fuselage reminiscent of the Concorde and take off like a conventional airliner, accelerate to Mach 5.2, and blast out of the atmosphere like a rocket. On the return trip, Skylon would touch down on the same runway it launched from.

Bond’s Synergistic Air-Breathing Rocket Engine (Sabre)—part chemical rocket, part jet engine—will make Skylon possible. Sabre has the unique ability to use oxygen in the air rather than from external liquid-oxygen tanks like those on the space shuttle. Strapped to a spacecraft, engines of this breed would eliminate the need for expendable boosters, which make launching people and things into space slow and expensive. “The Skylon could be ready to head back to space within two days of landing,” says Mark Hempsell, future-programs director at Reaction Engines. By comparison, the space shuttle, which required an external fuel tank and two rocket boosters, took about two months to turn around (due to damage incurred during launch and splashdown) and cost $100 million. Citing Skylon’s simplicity, Hempsell estimates a mission could cost as little as $10 million. That price would even undercut the $50 million sum that private spaceflight company SpaceX plans to charge to launch cargo on its two-stage Falcon 9 rocket.

The engine produces incredible heat as it pushes toward space, and heat is a problem. Hot air is difficult to compress, and poor compression in the combustion chamber yields a weak and inefficient engine. Sabre must be able to cool that air quickly, before it gets to the turbocompressor. In November, Reaction Engines hit a critical milestone when it successfully tested the prototype’s ability to inhale blistering-hot air and then flash-chill it without generating mission-ending frost. David Willetts, British minister for universities and science, called the achievement “remarkable.”