All that stands between the world and an engine that can propel a craft into low Earth orbit, with no expendable booster rockets, is $3.6 billion dollars. That's the amount of money aerospace company Reaction Engines needs to raise to finish funding Sabre, or the Synergistic Air-Breathing Rocket Engine. This engine, writes PopSci, is the key to the Skylon, a single-stage spacecraft Reaction Engines hopes to build. Unlike NASA's retired Shuttle, the Skylon would take off and land horizontally, and could conceivably make return trips to space within two days of landing.
"Sabre has the unique ability to use oxygen in the air rather than from external liquid-oxygen tanks like those on the space shuttle," writes PopSci. "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."
Reaction Engines predicts the Skylon could make trips to space for as little as $10 million, far cheaper than the $100 million it cost to launch the space shuttle--with a two-month turnaround. A SpaceX launch costs around $54 million.
Reaction Engines' breakthrough is its ability to convert extremely hot air into air cool enough for the engine to use. PopSci elaborates: "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.' "
This isn't a new concept, but there is reason to be excited about Sabre's prospects.
What's groundbreaking is how Reaction Engines engineer Alan Bond and his team managed to instantly cool that air in a heat exchanger that is, all things considered, incredibly light: "When air strikes an engine at five times the speed of sound, it can heat up to nearly 2,000 degrees Fahrenheit. Bleeding off that heat instantly, before the air reaches the turbocompressor and then the thrust chamber, was the most onerous technical challenge for Reaction Engines engineers. Bond’s solution is a heat exchanger that works by running cold liquid helium through an array of tubes with paper-thin metal walls. As the scorching-hot air moves through the exchanger, the chilled tubing absorbs the energy, cooling the air to minus 238 degrees Fahrenheit in a fraction of a second. Bond says his exchanger could handle about 400 megawatts of heat (equivalent to a medium-size natural-gas plant). 'If it were in a power station, it would probably be a 200-ton heat exchanger,' he says. 'The one we’ve built is about 1.4 tons.' "
Bond estimates that the entire Skylon craft would weight 358 tons and be capable of carrying 16.5 tons of payload, making it far lighter than other rockets but capable of delivering a similar payload. Unfortunately, though Reaction Engines needs to raise another $3.6 billion to fund the engine, building the craft that houses it will cost another $14 billion. But that figure may not be impossible to reach. If the engine proves as effective as they hope, it could enable supersonic aircraft to circle the globe in four hours. That would be just as revolutionary for air travel as it would spaceflight.
Check out the rest of PopSci's profile, which delves into the history of developing single-stage spacecraft. If it succeeds, the Skylon will be the culmination of decades of work and research.