Air pressure is the Hyperloop’s biggest energy issue. Wind resistance can slow a vehicle of any kind down significantly, and force it to use more energy to get around. As a result, the Hyperloop tube is designed to be a partial vacuum. A perfect vacuum would be ideal, but those are very difficult to produce in ideal circumstances. Pulling a perfect vacuum in a tube that is hundreds of miles long and contains many entry and exit points is as close to impossible as you can get with current technology.
Still, a partial vacuum created and maintained by a series of pumps along the track will allow the hyperloop to meet both its speed and efficiency targets. There is still one major issue, and that is known as the “Kantrowitz Limit.” Even in a partial vacuum, there is still air to be compressed. The Hyperloop capsule traveling down the tube has the potential to act like the plunger in a syringe, compressing the air in front of said capsule until it gets dense enough to slow everything down. Over short distances, there isn’t enough air to cause a problem, but over hundreds of miles it’s a serious problem.
Where there’s a problem, there is a solution. Currently Tesla believes that the best way around the Kantrowitz Limit involves installing an air compression which will suck the sparse air from in front of the capsule and distribute it behind the vehicle as needed.