roll on wheels, but in transit the wheels would retract and the whole assembly would float on skis that emit a thin layer of pressurized air.
The air would come from the Hyperloop tube itself. To reduce drag on the capsules, pumps would lower the air pressure inside the tubes to 100 pascals—about the same as the pressure at an altitude of 150,000 feet. But there would still be enough air in the tubes to be scooped up by a battery-powered compressor at the nose of the capsule and sent to a pressurized storage tank, and from there to the skis.
Some of the air would also spew out the back, providing a bit of thrust, but the capsule’s real propulsion would come from a linear induction motor system. The design calls for “rotors” or aluminum fins on the outside of the capsule to provide acceleration as they pass through electrified stators attached to the inside of the tube.
The power for the stators and air pumps would come from solar panels installed along the top of the pair of tubes (northbound and southbound). The tubes themselves would be placed 20 feet above the ground on concrete pylons spaced 100 feet apart. The Hyperloop’s main footprint on the landscape, then, would be a chain of 25,000 pillars from Los Angeles to San Francisco, mostly along the median of I-5.
Musk says the capsules could travel at 300 mph along I-5’s curvy sections and a near-transonic 760 mph along the straightaways, for a total L.A.-to-San Francisco travel time of 35 minutes. Well, technically, Musk’s suggested route for the Hyperloop stops in Oakland—there is no provision for getting the capsules across San Francisco Bay. So in an apples-to-apples comparison between the Hyperloop and the high-speed rail plan, you’d need to add another 15 minutes or so for the decidedly subsonic subway ride from Oakland into San Francisco.
If anybody has offered a convincing case for the Hyperloop’s technical infeasibility, I haven’t seen it yet. Nothing Musk proposes violates the laws of physics or requires brand-new technology. It’s hard to know in advance how much energy would be required to pump air out of the Hyperloop tubes and to compress it onboard the capsules, so it may be optimistic to assume that batteries and solar panels could supply all of it. On top of that, some critics say drag and friction inside the tubes might be unmanageable, while others worry that passengers would be exposed to excessive g-forces. But such details could probably be ironed out.
So the next big question is cost. Musk says a fleet of 40 capsules could be built for $54 million, and the tube system for $4.4 billion. He figures the land required, apart from the I-5 median, could be bought for another $1 billion, for a total project cost of only $6 billion. A larger version of the Hyperloop capsule and tube system, capable of carrying vehicles or freight, specs out at $7.5 billion. If you amortized that cost over 20 years, the price of a one-way ticket would be only $20, Musk calculates.
Now, I’m neither an economist nor an engineer, but my instinct as a technology observer is that Musk has probably low-balled all of these cost estimates. Just look at the AirTrain system in New York City, an elevated railway system that carries passengers from from a subway station in Queens to JFK Airport. Like the proposed Hyperloop, the AirTrain runs along a viaduct above a highway (the Van Wyck Expressway); also like the Hyperloop, it uses linear induction motors for propulsion, and is fully automated, with no engineers or conductors on board. That system, built by the Canadian rail equipment firm Bombardier Transportation, cost $1.9 billion, and it’s only 8 miles long. At New York prices, covering the 350 miles between Los Angeles and San Francisco would cost an eye-popping $82 billion—about $14 billion more than the estimated cost of California’s high-speed rail project.
If Musk’s estimates are off by an order of magnitude, which doesn’t seem unreasonable, the Hyperloop will cost more than high-speed rail (assuming that the rail project itself doesn’t continue to explode in cost). If he’s only off by a factor of five, the Hyperloop will be cheaper. Either way, it’s too early to say whether
