Review of Hyperloop Alpha

Written by Casey Tilton

In August 2013, Elon Musk, the CEO of SpaceX and Tesla Motors, officially unveiled his theoretical plans for a new mode of ground transportation called the Hyperloop. In a 57-page white paper, Musk describes in detail each of the technical systems that make up the Hyperloop. He explains that the impetus for releasing the report was the announcement of the plan to build the California high speed rail system, which has a budget of over $60 billion and an average speed of 164 mpg. According to his calculations, this Hyperloop system could be built between San Francisco and L.A. for around $6 billion, which is less than 10 percent of the proposed cost for the high-speed rail system between the two cities.

The Hyperloop is essentially a set of two long tubes that will run in opposite directions between distant cities. They will have passenger pods with up to twenty eight people that depart at regular intervals between 30 seconds and two minutes. The innovation that makes this mode of transport unique is that the tubes operate under very low pressure. This allows for the capsules to travel at high speed with very low air resistance, similar to why airplanes travel high in the atmosphere where the pressure and air resistance is low.

The capsules levitate in the tube with a system called air bearings. Compressed air will shoot out of holes throughout the bottom of the capsule to create a cushion of air that will allow it to glide safely at high speeds. This is very similar to how air hockey tables work.

One of the most challenging problems that engineers will face when creating this new technology is overcoming a law nature called the Kantrowitz limit. If the walls of the tube and the capsule are too close together, the system will behave like a syringe with the capsule being forced to push the entire column of air in front of it. Musk’s novel idea to combat this is to add an air compressor to the front of the pod that transfers the air to a release valve at the back of the capsule. Some of the compressed air, however, is stored and used for the air bearing system.

The capsule is propelled by a set of linear induction motors that are placed at certain locations along the tube. Each capsule has a “rotor” mounted to it that runs between a magnetic track called a stator that is mounted to the tube. Powerful electrical pulses push the rotor forward to accelerate the capsule, and it can run in reverse to slow the capsule down. According to Musk, a system of solar panels that run along the entire length of the track should provide ample energy to power this propulsion system.

Musk also describes in detail the methodology his team used to map the proposed route between Los Angeles and San Francisco. They took great pains to make sure the route is as straight as possible to avoid subjecting passengers to uncomfortable g-forces while turning. During areas where turns are more necessary, the capsules will travel at approximately 300 mph; only when the route runs along the long stretch of highway called the I-5 corridor between Los Angeles and the Bay Area can the capsule reach the top speed of 760 mph.

When Musk originally unveiled his white paper in 2013, he didn’t have any immediate intentions to actually build the Hyperloop. However, on January 15, 2015 he announced on Twitter his plans to build a five mile test track so that companies and students can test passenger pod prototypes.

-by Casey Tilton

Musk, Elon. “Hyperloop Alpha.” Aug. 2013. http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf

Image credit: Hyperloop Alpha. http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf 

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