Air cushioning: That's the high-concept technology behind the high-speed transit concept that billionaire Elon Musk calls the Hyperloop.
Musk—who already plays leading roles in the SpaceX rocket venture, the Tesla electric car company and the SolarCity solar-energy company—unveiled what he has called the "alpha" version of the Hyperloop plan in a blog post on Monday. It runs to 57 pages as a PDF file.
The plan is aimed at cutting the travel time between San Francisco and Los Angeles to 30 minutes at a price that's less than an airline ticket. Musk said the Hyperloop arrangement could be implemented between any pair of cities situated up to, say, 900 miles (1,500 kilometers) apart. For longer distances, air travel probably would be more efficient, he said.
Musk said he came up with the plan out of frustration with the shortcomings of California's $68 billion high-speed rail project, which is just getting started.
How the Hyperloop would work
The Hyperloop would send travelers through low-pressure tubes in specialized pods that zoom at high subsonic speeds, reaching more than 700 mph (1,100 kilometers per hour). That compares with typical speeds of 110 to 300 mph for high-speed rail travel.
Musk's plan would rev up the pods from their stations using magnetic linear accelerators, but once they're in the main travel tubes, they would be given periodic boosts by external linear electric motors. The pods would also have electric compressor fans mounted on their noses that would transfer high-pressure air from the front to the rear. The journey would be nearly frictionless, thanks to a cushion of air between the cars and the tube's inner surface.
The whole system would be powered by solar panels installed onto the tubes.
"By placing solar panels on top of the tube, the Hyperloop can generate far in excess of the energy needed to operate," Musk wrote.
The tubes would be elevated on pylons, and generally follow Interstate 5 between San Francisco and L.A. Musk says that would cut down on the cost of land acquisition and rights of way. He said the whole system would cost several billion dollars to build.
"Even several billion is a low number when compared with several tens of billion proposed for the track of the California rail project," he wrote.
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This combination of technologies is what led Musk to describe the Hyperloop last month as a "cross between a Concorde, a rail gun and an air-hockey table." The hints that he dropped along the way sparked a flurry of speculation about schemes ranging from "Jetsons"-like people movers to underground vacuum tunnels.
One of the closest guesses came from a self-described "tinker" named John Gardi, who laid out a plan for a turbine-driven pneumatic system. "This story has been a classic case of the media not having a clue," Gardi said in a Twitter update just before Musk's big reveal. "I had to come out of semi-retirement to write a GOOD article."
Who'll build the Hyperloop?
Musk says he won't be able to build the Hyperloop himself, because of his duties at SpaceX and Tesla. For now, he's leaving it to others to build upon his initial open-source concept. But if no one picks up the idea and runs with it over the next few years, he might return to the task.
It's possible that the Hyperloop could be held back by technical as well as political and economic issues. Transportation policy experts say that high-speed transit in the United States has been stymied not so much by technological challenges as by the challenges of acquiring rights of way and getting enough money for the required infrastructure.
Nevertheless, high-speed transit projects are beginning to gain traction. California, for example, is continuing with its next-generation rail system, and other states are proceeding with their own high-speed rail initiatives.
—By Alan Boyle, Science Editor, NBC News