The Hyperloop: L.A. to S.F. in 30 minutes? Imagine paying $20 and sitting down inside a Space Age capsule in Los Angeles. About half an hour later, you're in sight of the Golden Gate Bridge. Los Angeles billionaire Elon Musk, the man who made electric vehicles sexy, revolutionized the online payment business and transformed spaceflight missions for NASA, is now taking on California's public transportation system. On Monday, to international fanfare, Musk unveiled the design of his Hyperloop, a $6-billion high-speed transit system powered by solar energy. The line would travel along interstates 5 and 580 at speeds of up to 760 miles per hour and have the feel of an airliner, Musk said. Capsules would hold 28 people each. California hasn't asked for his help, and Musk's dream exists only on paper. But the state is in the middle of trying to build its own bullet train, a $68-billion project that has grown in cost and fallen behind schedule. Musk, 42, contends his system is superior - and cheaper - and that he wanted to get it into the public discussion before the state wastes more time and money on what he sees as a failed system. "How could it be that the home of Silicon Valley and JPL ... would build a bullet train that is both one of the most expensive per mile and one of the slowest in the world?" he said. It would be great to have an alternative to flying or driving, but obviously only if it is actually better than flying or driving. Musk said the answer is the Hyperloop. He might first build a prototype to prove the concept, but the plan has been published as an open-source document - ready for anyone to pick up the idea and improve it. If it were by anyone else, Monday's display probably would be dismissed as the hyperbolic ramblings of a crank. But Musk is a straight-talking modern-day industrialist cast in the mold of a young Howard Hughes. He's led numerous start-up companies in a wide range of industries and become something of a celebrity along the way. The sandy-haired South African emigrant first made millions when he co-founded and sold online payment business PayPal to EBay Inc. for $1.5 billion. Armed with his personal fortune and a Rolodex full of Silicon Valley venture capitalists, Musk started the rocket company SpaceX, or Space Exploration Technologies Corp., and co-founded electric car giant Tesla Motors Inc. in Palo Alto. Now he's declared the dawning of a fifth mode of transportation after rail, road, water and air. This one operates somewhat like pneumatic delivery systems that have been used at neighborhood banks, sending packages through pressurized air tubes. "Normally I would think this idea is borderline crackpot, but this guy has a track record," said Michio Kaku, a physicist who hosts television shows about futurist technologies. You have to take him seriously. The guy is a doer. According to Musk's design, the Hyperloop's capsules would be transported at speeds of 300 to 760 mph through a steel tube kept at low pressure. The capsules would shoot through the tube on a cushion of air (like a puck gliding on an air hockey table), accelerated by a magnetic system at points along the way. Musk said that "by placing solar panels on top of the tube, the Hyperloop can generate far in excess of the energy needed to operate." It would be an express trip across the 382 miles, connecting two stations. More stations could be added later. Musk said the system could transport 7.4 million people a year, shooting capsules as frequently as every 30 seconds. By contrast, the California bullet train system envisions a much bigger annual ridership: about 20 million at minimum. The plan, however, has been sharply disputed by outside experts who doubt that large numbers of drivers or airline passengers will be attracted to the bullet train. The Hyperloop's 57-page "alpha" design is still in its infancy - it was put together by about a dozen engineers from SpaceX and Tesla. The version released Monday was produced after an all-night Sunday session, Musk said. The California bullet train authority took Musk's criticism in stride, saying that such new technology is worth considering. But to draw a distinction between the state's project and Musk's vision, authority Chairman Dan Richard added, "If and when Mr. Musk pursues his Hyperloop technology, we'll be happy to share our experience about what it really takes to build a project in California, across seismic zones, minimizing impacts on farms, businesses and communities and protecting sensitive environmental areas and species." The plan already has drawn criticism targeting its novel design, lack of details and absence of outside review. Bill Ibbs, a UC Berkeley civil engineering professor, said Musk's idea comes up short on the economics. There's a reference to 7.4 million riders per year on this system, but there's no background, no explanation of where he comes up with that figure," he said.