Trains, Planes, Cars, Boats and ... Pods
In Elon Musk's world, the Hyperloop will become a "fifth mode" of transportation, standing beside planes, trains, automobiles and boats in the pantheon of mechanized movement. Musk envisions people traveling through the Hyperloop in pods that whiz through steel tubes mounted on pylons, or pillars, designed to withstand California's earthquakes. Those pylons, made of reinforced concrete, would be spaced every 100 feet (30 meters) or so and stand 20, 50 and 100 feet (6, 15 and 30 meters) high, depending on the terrain [source: SpaceX].
How exactly does Musk plan to accomplish this amazing task of physics? Well, he looked at several possibilities. Most, he said, fall short for a variety of reasons. For example, the Hyperloop might be able to use powerful fans to push the pods, much like pneumatic tubes that offices use to shove mail from one building to another. Musk says while it's possible to construct such behemoth fans, it's impractical because a 350-mile (563-kilometer) -long column of air moving so rapidly would create an enormous amount of friction inside the tube, making the type of speed he hopes to achieve impossible [source: SpaceX].
The entrepreneur has also ruled out moving the pods through vacuum tubes using electromagnetic suspension, the same technology that maglev trains use. Musk explains that it's difficult to create a perfect vacuum in the tubes, especially with thousands of pods entering and exiting every day. Moreover, the aluminum tubes might crack or leak, letting the air out of the system.
"All it takes is one leaky seal or a small crack somewhere in the hundreds of miles of tube and the whole system stops working," Musk wrote in his initial Hyperloop report.
Another technical problem centers on the pod moving through a tube containing air. Musk says if the walls of the tube and pod are close together, "the capsule will behave like a syringe." In other words, the pod would push the entire column of air in the system instead of letting it flow past. The result is that the pods would have to travel very slowly, or engineers would have to build a massive tube to make traveling quicker. In that case, riders would be traveling several thousand miles per hour, subjecting their bodies to crushing G-forces when going around the slightest bend [source: SpaceX].