Hyperloop

I have long been a fan of Elon Musk, the Internet entrepreneur who has made the difficult jump into hardware with his successful SpaceX company, which sends cargo (and soon passengers) to the International Space Station.

He also co-founded Tesla, the company that proved that electric cars can be sporty.

But SpaceX is just an iteration on existing technology: that is not to denigrate what they have done, but at the end of the day it is just a long tube of fuel sitting on top of rocket motors, just as all rockets have been since Sputnik 1 first orbited the earth. And Tesla also uses proven technology, albeit in a novel way.

It is therefore with interest that I note that Mr Musk and his team have come up with the Hyperloop, a solution for mass transit between Los Angeles and San Francisco.

The Hyperloop is a tube running between the two cities. A partial vacuum is maintained in the tube whilst a linear induction motor fires off a pod containing passengers (and in some designs cars) through it. The partial air pressure is sucked in at the front of the pod, compressed, and used to levitate the pod on a cushion of air (so-called 'air bearings'). Occasional linear induction motors continue to accelerate the pod to account for the small amount of friction and aerodynamic drag; for most of the time the pod coasts. One pod can be fired off every 30 seconds, and they travel at high subsonic speeds (to a maximum of 760 MPH).

The tube is supported on pylons above ground, and is covered with solar panels which will provide the power for the system. The pods contain batteries that run the compressors that provide the lift air.

The whole scheme is described in the following link:
http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf

I have read the paper, and the following issues come to mind. None of these are necessarily game changers, but will need addressing:

• Crashworthiness: The energies involved at high-subsonic travel are immense. What happens if a component breaks off and is left in the tube to be hit by the next vehicle? Or if the vehicle makes contacts with the sides somehow, imparting great energies to the tube and pod? Even a 5 gram nut has significant energy when hit at over 700 MPH.
• Evacuation: If there is a problem and people need to evacuate, how does that happen? Remember, the tube is sealed and in a partial vacuum. And as the tube is intended to be supported on pylons above ground, how do passengers get from the tube to the ground?
• Life support: the air pressure within the tube (i.e. outside the pod) will be harmful to human life. The pods will have to maintain a pressure that we can survive in, and all hatches and seals will have to be foolproof. They have addressed this in the document, but I'm not sure they have the whole answer, especially with hatches and seals that will have to be repeatedly used over a period of days, months or years. Will the air inside the pod be at normal sea-level atmospheric pressure, or reduced as in aircraft?
• Claustrophobia: the passenger-only vehicle appears rather cramped. Claustrophobia may be a significant problem for many passengers - airplanes are bad enough for some people. This effect may be worsened by G-forces, which will be considerably more than is the case for high-speed rail.
• Breakdowns: With one pod every 30 seconds, what happens if one breaks down mid-tube and away from one of the accelerator areas? The paper says there will be deployable wheels that can be driven along using electric motors; this is not only extra complexity, but the power required may be significant if a long way away from an accelerator area. In addition, there is no mention of gradients. If the tube has a significant gradient, the amount of energy required to take a pod up slope will be large. And what happens if the emergency wheel system fails?
• Construction: in the paper, I fear the team underestimate the costs and complexities of construction. They have designed the route on Google Earth to follow existing transport corridors where possible (for example Interstates). This takes no account of ground conditions: if the line passes through an area of soft or difficult ground, the costs of constructing the pylons will grow significantly. As the route will be passing through an area that can exhibit significant seismic activity, the pylon foundations will have to be designed to cope with liquefaction and other effects.
• Braking and signalling: If a car does stop, how do the others get messages to stop? What sort of signalling system will be used, and how fail-safe will it be? The proposed system of braking is simply referred to as 'emergency mechanical braking system' What is this, and how does it work?
• Pointwork: One of the deal breakers with Maglev systems is pointwork. With one pod leaving every 30 seconds, there will be many pods at the stations unloading and loading. The paper suggest that there may be branch lines to other cities in the area. How are the pods transferred to different tubes or tracks at the stations (or indeed into depots or maintenance areas)? If this is done in tubes, you will need moving tubes and/or walls, preferably whilst keeping a low pressure vacuum. Not an easy task.
• Charging: the on-board batteries will need charging every few journeys. How is this done during intensive usage of the pods?
• Fire: all mechanical and electrical systems suffer from the risk of fire, and those risks need managing. Being in a sealed pod with a fire, and a vacuum outside, is not necessarily healthy. In addition, there are the risks of smoke for other pods further down the line. Fire and smoke management are very costly in similar tube-like systems such as the Channel Tunnel, which has a service tunnel and refuges at regular intervals.

I could be wrong about all of this, and could end up sounding like Doctor Dionysius Lardner who in the 1830s said the following:

Rail travel at high speed is not possible because passengers, unable to breathe, would die of asphyxia.

On a positive note: engineering-wise, it is perfectly feasible to construct a partially-evacuated tube that is supported by pylons. The propulsion system also appears feasible at first glance, as is the air-cushion support mechanism. Engineering difficulties will happen, but if you throw enough money at it, it should work.

However, getting such a system to work reliably and safely is a whole different matter, and I am unsure that anywhere near enough thought has been put into this.

Another view on the Hyperloop's feasibility is at the Ambivalent Engineer blog. The costings are explored at the New York Times. The New Statesman is sceptical.

And the Daily Mash has its own take on the Hyperloop....