Beyond the hype of Hyperloop: An analysis of Elon Musk’s proposed transit system

“It’s a cross between a Concorde, a rail gun, and an air hockey table.”

Now that the media kerfuffle surrounding Elon Musk‘s Hyperloop transit system proposal has settled down to a dull roar, it’s a good time to step back and consider in detail some of the real innovations and difficult issues raised through analysis of the 57-page Hyperloop plan.

The shortest description of the Hyperloop is Musk’s own bon mot: “It’s a cross between a Concorde, a rail gun, and an air hockey table.”

A slightly more complete description of the concept is that of an elevated, reduced-pressure tube that contains pressurized capsules driven within the tube by a number of linear electric motors. These capsules move with very little friction or drag owing to air bearings that ride on the inner surface of the tube, and a combination of active and passive means to reduce the negative effects of choked airflow on the transportation system.

In this article I am only considering the science and engineering aspects of the Hyperloop. While acknowledging that political issues may actually determine its fate, what concerns us here is whether or not it could work.

A Quick Overview

A reaction many people have to the Hyperloop is that there is nothing new here. While it’s fair to say that all inventors are standing on the shoulders of giants to a certain degree, there are in fact very real innovations in Musk’s proposal.

The Hyperloop has essentially no relationship with the old pneumatic tube transports beyond a certain similarity of appearance. There is, however, quite a bit of overlap with earlier proposals for reduced pressure or vacuum-tube transports. In particular, the early theoretical and experimental work of Robert Goddard, the inventor of the liquid fuel rocket, appears to have the greatest overlap with the Hyperloop.

Goddard’s notes about reduced pressure transports sat in storage for over 30 years, only surfacing after his death in 1945. In US patent 2,511,979, he describes nearly every major feature of the Hyperloop save for the use of linear electric motors for propulsion (he preferred using reaction motors for propulsion), and using special apparatus to minimize the detrimental effects of choked airflow around the capsules. Goddard also described the use of air bearings, but of a very different sort than proposed for the Hyperloop. Many others, of course, have suggested the use of linear electric motors.

To sum up, it would appear that the main innovations in the Hyperloop proposal are the type of air bearings used to reduce friction forces on the moving capsules, and design elements that avoid the limitations encountered when the airflow around the capsules is choked. Let’s take a closer look at these additions.

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