Hyperloop

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Some of my best memories from college consist of sitting around a table, beer in hand, talking about about mega-projects with my engineering friends. As the condensation accumulated and dripped down our glasses and the ethanol began to flow across the blood-brain barrier our deferrals to practicality and experience gradually ebbed as talk of travel to the stars, active structures towering above the atmosphere, and bridges across wide ocean passes became more and more giddy. It's great fun, talking about the wonderful things that could be done, even if they're unlikely to come to pass until the next great civilization.

The world is indifferent to such talk from college seniors and grad students, but when a man claims that he'll use his own money to ferry goods to and from low Earth orbit, and to make electric cars cool and practical, then makes good on this talk, people tend to listen. Elon Musk is pretty busy running the show at SpaceX and Tesla, but thinks he can come up with a better way to link the biggest cities of California than a planned $68 billion high-speed rail line. The idea is Hyperloop, and the details are now online here:
Hyperloop

Musk claims Hyperloop could link Los Angeles and San Francisco faster than the terminal-to-terminal time of a subsonic airplane and at far less cost than high-speed rail or even the most efficient cars on the road today. If the system could actually be built for his price tag of $6 billion it would be a phenomenal achievement, but I doubt that things would actually turn out that rosy. A two-mile tunnel designed to bypass an unsafe section of freeway in downtown Seattle has an estimated cost of $4.25 billion, and overruns are not out of the question. Is it even remotely feasible to build a twin low-pressure, earthquake safe tunnel across most of the length of California for just $1.75 billion (less than one Curiosity) more? Color me skeptical.

Keeping the tunnel pressure reliably low enough for operation would probably be the biggest challenge, since the design pressure of 100 Pascals is a factor of 1,000 different from ambient sea level air. That's an intense vacuum, and it won't come cheap. Even though no tunnel boring machines would be required to put the tubes in place, someone powerful in California will find something to complain about when it comes to Musk's plans. Perhaps a demo project in a more technology-friendly place is in order. Houston-to-Dallas or Seattle-to-Portland would be good choices, although the latter route is short enough you might as well extend the line to Vancouver, British Columbia. Avoiding the Mount Rainier lahar zones would be nice, too.

As an aside, Musk's claim about supersonic air travel is completely bonkers. Supersonic air transports have inherently lower L/D than their subsonic counterparts since they burn extra fuel pushing against their shock waves. Maybe there's a way to coax high-speed engines to higher per-mile efficiency, but for now the subsonic high bypass turbofans are the kings of the efficiency game, and they're unlikely to be dethroned anytime soon. Let's ignore that part of his treatise.

Since SpaceX and Tesla are busy just staying alive at their tenuous businesses, it'll be up to someone else to make Hyperloop a reality. I hope someone at least gives it a shot, since the technology is challenging but workable, and the benefits would be tremendous to the cities linked. If nothing else, it'll make for some more interesting engineer bar talk while the tubes are going up along I-5.