Air pressure is the Hyperloop’s biggest energy problem. Wind resistance can slow down any type of car, forcing it to use more energy in turns. As a result, the Hyperloop tube is designed to be slightly thinner. A good vacuum would be nice, but this is very difficult to create in good conditions. Pulling a good vacuum through a tube that is hundreds of miles long and has many inlets and outlets is about as difficult as possible with current technology.
However, a small vacuum created and maintained by several pumps along the route allows the hyperloop to meet its demands and speeds. There is also one big issue, which is known as the “Kantrowitz Limit.” Even in a partial vacuum, there is still compressed air. A Hyperloop capsule traveling down a tube can act like a plunger in a syringe, compressing air in front of the capsule until it’s thick enough to slow everything down. On a short trip, there isn’t enough air to cause a problem, but over hundreds of miles it’s a big problem.
Where there is a problem, there is a solution. Currently Tesla believes that the best way to get around the Kantrowitz Limit involves installing an air compressor that sucks a small amount of air from the front of the capsule and distributes it to the rear of the car as needed.