In a blog post today, Elon Musk revealed plans for an alpha version of his much-anticipated Hyperloop, an innovative transportation system that would move passengers from Los Angeles to San Francisco in less than 30 minutes. According to the plans (PDF), the Hyperloop would transport passengers in aluminum pods traveling up to 800mph, mostly following the route of California's I-5. The estimated cost would be $6 billion for the passenger-only model, or $7.5 billion for a larger model capable of transporting cars. On a following conference call, Musk said he expected a prototype unit might take only three or four years to complete given the right project leader, including a couple years to acclimate themselves to the project. "If it was my top priority, I could probably get it done in one or two years."

The biggest puzzle was how Musk's low-power loop would maintain such high speeds without tremendous power losses to friction. According to a Businessweek article, published with the post, the solution is keeping the interior of the Hyperloop at low pressures, which lowers friction without risking the dangers of a full vacuum. "I think a lot of people tended to gravitate to one idea or the other as opposed to thinking about lower pressure," Musk told Businessweek. "I have never seen that idea anywhere." The system would also reduce friction by mounting compressor fans on the front and rear of each pod, actively transferring air from the front of the pod to the back.

In addition to following existing highways, the Hyperloop would minimize its physical footprint by elevating the tubes on columns 50 to 100 yards apart. Much of the route could be constructed on the median of California's I-5, but where the hyperloops path diverges, the pillar system would allow tubes to be built over private land with minimal disruption to existing structures.

Musk encourages observers to weigh in with ideas

The crafts would travel over air bearings, which Musk described as "the same basic principle as an air hockey table, which would allow them to travel at supersonic speeds with extremely low friction. For acceleration, the Hyperloop would use a linear accelerator — essentially the railgun promised in Musk's initial descriptions of the system, accelerating the pod through a traveling electromagnetic pulse. As the pod nears its destination, the process will be reversed, slowing the pod through the same electromagnets and absorbing the kinetic energy back into the system.

It's not a coincidence that Musk chose Los Angeles and San Francisco as a test route; the Hyperloop is apparently designed for city pairs that are roughly 900 miles apart. Shorter distances don't allow enough acceleration time, while over longer spans, the document speculates that supersonic planes may end up being both faster and cheaper.

The result would be impossible to crash or derail, and the internal pod would be immune to outside weather conditions like fog and snow. As a result, the only safety concern is maintaining the integrity of the track itself. The plans called for many expansion joints to deal with thermal shifts, and tube thickness of nearly a full inch to prevent buckling. On the call, Musk acknowledged the design isn't indestructible, especially given southern California's potential for earthquakes. "If all of LA falls down [in an earthquake], then I guess the Hyperloop would too."

Musk had announced earlier that he has no immediate plans to build the device, citing commitments to his Tesla and SpaceX businesses, but on today's call said he was considering building a prototype model. "What happens is, you start building a prototype and you encounter a whole series of ideas you have to work around. It happened with SpaceX and it happened with Tesla."

Already, Musk is encouraging observers to weigh in on the designs, requesting ideas and improvements be sent to hyperloop@teslamotors.com or hyperloop@spacex.com. The documents are available here.