Guest Post by Willis Eschenbach

A recent article has discussed how Elon Musk’s “Boring Company” has raised $113 million dollars in startup capital. This is the company Musk formed to drill the tunnels for his proposed “Hyperloop” transportation system. It has encouraged me to discuss some of the engineering and practical problems with his LA-to-San Francisco Hyperloop proposal. The Hyperloop concept involves a windowless “pod” traveling at just below the speed of sound in a tube with all the air evacuated from it. There’s a reasonable description of the Hyperloop at Wikipedia and a much more hyper description at their website. It all sounds so good and so 21st Century, what’s not to like?

In no particular order, the problems with the Hyperloop include:

Vacuum: The Hyperloop requires a near-perfect vacuum to run at the proposed speeds. It has been tested with a one-kilometer long test track. The test track was billed as the “second largest vacuum chamber in the world”, after the vacuum chamber of the Large Hadron Collider.

But the LA-to-SF route is 615 km. This is a huge, almost unimaginable step up in size and problems. Consider that although the LHC is carefully internally braced to keep the pressure from collapsing it, they’ve said the Hyperloop tube will be a 1″ thick steel pipe supported on pillars. There’s no way to brace it internally, the pod has to run through the middle. The day/night expansion on that much steel would be very large, and the expansion joints for that use have never been built. In addition, atmospheric pressure on the tube would be about ten tonnes per square metre … and there’s a 15-tonne “pod” running through it, putting large stresses on all bends and joints.

This means that if the vacuum is breached for any reason, say a car runs into one of the pillars, or some fool shoots an high-powered rifle round at an expansion joint, or terrorists place even a small bomb anywhere along the length of the route, or a small thermally driven “kink” in the pipe develops, or heck, a ubiquitous California earthquake, everyone in the tube would die from the instantaneous deceleration. Here’s what happens to a railroad tank car with ~ 1/2 inch (12 mm) steel walls when it is not properly vented … it collapses from nothing more than the atmospheric pressure, and that is without a near-perfect vacuum inside.

Ooogh … you don’t want to be inside if that happens.

Thermal Expansion II: A difference of only 3°C from the top to the bottom of the tube will cause differential expansion of about 25 metres from top to bottom of the pipe over the length of the SF-to-LA run … very no bueno. The pipe will tend to either lift out of its supports or bend at the expansion joints … joints with a 15-tonne pod going through them at 750 mph.

Energy: The pumps necessary to keep the tube evacuated will be quite large. Remember that each pod has to be air-locked in and out at every station. The energy cost of this constant pumping at each station is unknown, but definitely not small.

Pod Integrity: The pod will be in near total vacuum. Airplanes fly at about 33,000 feet (10,000 m). The pods will be traveling at the equivalent of 50,000 feet (15,000 m). This means that if there is the slightest leak, there will be catastrophic decompression and everyone in the pod will likely die.

Passenger Throughput: This is likely the biggest problem with the Hyperloop—for all of its speed, it is remarkably slow at actually moving people. Consider the competing technologies. Freeways typically carry 2,000 cars per hour per lane, that’s maybe 3,000 people per lane per hour. So a four-lane freeway of the type common in California will carry about 12,000 people per hour.

A subway with three-minute headways between cars will carry about 36,000 passengers per hour. The proposed and insanely expensive high-speed “Bullet Train To Nowhere”, which Governor Moonbeam is trying to build fro LA to San Francisco will carry on the order of 12,000 people per hour.

Now, Musk claims that a pod will depart SF-to-LA and LA-to-SF every 30 seconds carrying 28 people per pod. That’s the best case, and it’s only 3,300 passengers per hour.

But wait, as they say on TV, there’s more. In general, you don’t want to run cars, trains, subway cars, or Hyperloop pods so close together that they can’t stop safely in case of an emergency to the car ahead. Humans can only sustain about half the force of gravity, called “0.5 G”, for safe deceleration. Musk says the cars will be traveling about 760 mph (1225 km per hour). At that speed, it will take around 75 seconds at 0.5 G to decelerate to a stop. So the inter-pod time has to be at least 80 seconds … and that means passenger throughput drops to 1,260 passengers per hour.

And the bad news doesn’t end there. The whole system can only run as fast as the slowest segment of the Hyperloop, and that’s the stations. Remember, at every station, the pods need to be depressurized. Then passengers need to get on and get off, and the pods need to be repressurized. Musk says that up to three pods will be in the stations at once. So that means that depressurization, passenger unloading and reloading, and re-pressurization need to take place in about two and a half to three minutes … and you better hope that nobody forgets anything on a pod and has to go back to get it, or the entire system slows down.

Net result? The Hyperloop will make less than half the difference in passengers transported, and likely much less than half the difference, that would be made by adding a single lane to the LA to SF freeway …

In Short: The Hyperloop is extremely dangerous to passengers, vulnerable to a host of problems, will kill everyone inside if even a small failure happens, moves a very small number of people, and oh, I forgot to mention … what happens if the power fails, as happens these days in California all the time because of our insane renewable mandates pushed by our less-than-genius Governor, Jerry Brown. Care to think about being stuck inside a windowless pod inside a steel pipe on a hot day in the California desert, with no way to escape?

And all of that for less gain than adding a single lane to the freeway … but there is one thing we can be sure of.

Elon Musk will get even richer from government subsidies for his latest whiz-bang proposal … truly, the man is a subsidy artist. Where most of us can see nothing but government boondoggle and waste, he sees personal wealth.

My best to all,

w.

THE USUAL: When you comment please quote the exact words you are discussing, so that we can all understand your subject. In addition, rather than telling me or anyone that we are doing something wrong, please demonstrate the right way to do it.

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