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.
Why would the inter-pod time increase to 80 seconds? Acceleration and deceleration time is part of travel time. At 615 km distance and speed of 1225 kph, travel time is 0.5 hour. 80 seconds x 2 is less than 3 minutes. So travel time will be 30 minutes + 3 minutes. Inter-pod time is still 30 seconds.
Why would passengers die if the tube gets pressurized to atmospheric pressure? If the tube is pressurized at the back of pod’s direction of motion, the pod will accelerate. If pressurized at front of pod, it will decelerate. Assume the tube is 3 meters in diameter.
Area = pi/4 x 3^2 = 7 m^2
atmospheric pressure = 100,000 N/m^2
Force on pod = 7 (100,000) = 700,000 N
Weight of pod = 15,000 kg
acceleration or deceleration = force/mass = 700,000/15,000 = 47 m/s^2
This is +/- 4.8 g. Like a roller coaster thrill ride but the pod has to brake before it crashes.
This is unlikely to happen because the air will lose pressure due to friction when it passes through a small hole in the tube. Turbulence will also dissipate the dynamic pressure of the air.
The supersonic pod will probably disintegrate.
“This is unlikely to happen because….”
———————-
I hate the likely part.
I calculated some simple numbers for travelling from my house in Oakland,CA to Disneyland, including items like parking, checkin, rental car etc. and came up with:
Driving: 7 hours (via In-n-Out 🙂
Flying: 4 hours 24 mins (OAK-LGB)
Hyperloop: 3 hours 6 minutes (based upon approximate station location in Hayward/Sylmar (though this location is vague in the tesla pdf)
I made some assumptions such as:
– Hyperloop terminals are smaller than an airport so parking/checkin/rental car time is faster
– Hyperloop does not require a specific departure time, you just get on the next available pod
It’s interesting that the LA terminal location means that you have to deal with the worst sections of LA traffic once you get off Hyperloop.
Because pods take passengers frequently, waiting time at the security gate should be trivial.
Just like it’s trivial in a big airport that has a plane takeoff every minute. /sarc
Well, it is less passengers, claim of 6M/year, while OAK has 13M/year and airports don’t operator 24 hours a day while the claim is the hyperloop would.
Maybe since it would be a smaller facility there would be less security gates so the security clearance would be about the same.
How many people really want to travel at 3AM?
climatebeagle, I fail to see how any of that (number of passagers) is relevant.
If the frequency of departure is extremely high, then waiting times for security are very small. Do you disagree with that?
Why do people even accept to wait a lot of time in airports? Isn’t that one of the greatest mystery of mankind?
> If the frequency of departure is extremely high, then waiting times for security are very small.
I think they might be less than an airport but they can’t be very small as you probably can’t afford a single slowdown to lead to empty/delayed pods, so you have to build some buffer time in? Also will the terminal operator want to offer the passengers shopping, so want them as a captive audience after security? Isn’t that a good revenue stream for airports?
My point with the numbers is that OAK has twice as many passengers, but has two terminals and probably has four or five security setups (X-ray, metal-detector etc.) in each terminal. How many would security setups might a hyperloop station have? Less setups mean larger lines.
“Hyperloop Test Track Under Construction In [Toulouse] France”
https://seekingalpha.com/instablog/22912651-daniel-jennings/5148235-hyperloop-test-track-construction-france
“320-meter long full-scale tube”
Yeah… impressive. In a kind of practical joke way.
Relying on pressurization in a complex system can be an issue:
From the caption on the Youtube video:
Because complex systems often have mind-bogglingly simple failure modes, what you see happen in this video is all chalked up to the accidental introduction of a small gas bubble during fueling. Details are hard to come by, but there’s a good account of what happened here:
http://www.thespacereview.com/article/1326/1
How much trouble could a small gas bubble or some similar thing cause the Hyperloop.
I was looking for the 1987 failure of a similar vehicle where I remember a cool picture of a Centaur upper stage crumpled upon itself, but I couldn’t find the picture.
There are so many great articles and analyses on this website and WUWT is one of my favorite stops for rational commentary on issues. But I’m afraid the analysis in this OP doesn’t stack up.
I am fully in agreement that the California high speed rail project has been a disastrous boondoggle. Hopefully the project will be abandoned or significantly reworked before much more taxpayer money is wasted. I also agree that there is serious question whether Hyperloop would ever be economically feasible or commercially viable. But some of the engineering critiques raised in the OP are a little off.
Let’s start with the vacuum. Yes, there are challenges in scaling up. And yes there are challenges with structural stability. But these are hardly show stoppers. A perfect vacuum is not required, and minor leaks are easily dealt with. Furthermore, it is possible to add structure stability either outside or inside the tube, particularly if the tube is enlarged and less than the entire circular surface area used for the pod. As for the catastrophic implosion risk, it was strange for a paragraph to be devoted to the risk of a leak — i.e., air getting into the tube — and then, as an example, we are shown a video of a tanker car catastrophically imploding due to too much air being pulled out of a structure that was not designed to operate with structural integrity as a vacuum.
Passenger throughput is claimed as the biggest problem for Hyperloop. The question isn’t whether it is the most “efficient” way to move people. How many planes fly from LA to, say, SF every hour? The question is whether it is a viable commute option for people who want a faster trip than driving. Again, the Hyperloop may be utterly cost-ineffective and may be a terrible investment. But the fact that it doesn’t move as many people as a full lane of traffic is not, in and of itself, a reason to abandon the project. Willis questions the every 30 seconds departure, because that is only 3,300 passengers per hour. But again, how many people are we moving by air every hour?
Then there is the deceleration claim. As others have pointed out, a 0.5G deceleration is certainly not a limit. Decelerating from 760 mph to 0 mph in 30 seconds in an emergency situation is not going to be particularly problematic, and can be further accommodated by seating backs-forward. Even turning seats around after acceleration is a very doable option. Again, there might be minor inconveniences to deal with, but there are various options and these are pretty simple engineering issues to address.
Finally, Willis is concerned about the station loading and unloading timeframe. Yes pod throughput is an issue, but easily resolved. Disneyland solved it decades ago with lots of “pods” and multiple loading/unloading points. This is an entirely trivial engineering problem to solve.
Again, Hyperloop may be a financial boondoggle. It might make little economic sense. It might be commercially nonviable. But let’s be a lot more careful about level engineering problems that are readily solvable or, in some cases, completely trivial to deal with.
Thanks for the comments, Climatereason.
Can the technical problems inherent in the Hyperloop proposal be solved?
Generally, yes. Generally, any technical problems can be solved if you throw enough money at them. My point was that there are too many such problems for too little increase in either passenger throughput or travel time to make the system economically viable.
For example. You can indeed solve the station loading and unloading timeframe in the manner that you propose, multiple pods. But with a 30-second headspace between pods, if just one station in the entire loop has a loading problem from any cause, the whole system has to slow down.
Or you could just skip loading the pod from that station and keep the whole system running … but then where do you insert the missed pod back into the system? All the pod slots in the parade are filled.
Nor is there any great decrease in travel time. Including downtown-SF to the airport, checking baggage, getting through security, flight time, and LAX to downtown-LA, it’s not hard to spend nearly as much travel time on the ground as in the air … and the proposed Hyperloop stations are further from both city centers. Remember, the actual speed of the Hyperloop is only about 60% faster than a commercial jet airplane. Flight time LAX-SFO is an hour and a half. Hyperloop is CLAIMED to be 35 minutes flight time, but real-world performance could easily be 50% longer. So the difference is likely only 45 minutes or so, a chunk of which will be eaten up in longer downtown-to-station times at both ends. So total time saved is likely to be only 15 to 30 minutes out of three hours or so… hardly impressive.
Can the tube expansion problem be solved? That one is a bit tougher. If you look at oil pipelines, every so often they have an up-and-down kink in them to solve the expansion problem. The Hyperloop engineers are rather vague about this one, saying:
However, such a device has not yet been built, and the airport version doesn’t have to maintain a near-perfect vacuum.
Next, the terrorist question. The Hyperloop will be an incredibly tempting target to a terrorist. The impact would be far, far larger than say blowing up an airplane. This one is much tougher than the technical problems because it is a human problem. How do you plan to protect hundreds and hundreds of miles of vulnerable Hyperloop pipe? A cheap and simple shaped charge could easily blow a very large hole in the pipe … what is the technical solution for that?
Finally, earthquakes. Freeways are designed so that they can move a few inches in case of an earthquake … but a tube with a pod going 750 mph in it cannot sustain such a shift. Again, is it solvable? Possibly, perhaps even probably … but again, at what cost? I don’t know if you’ve ever been out to the park north of San Francisco, where the horizontal shift in the ground from the 1907 quake was about 13 feet (4 metres). Such a shift would, of course, destroy a freeway, and might cost a few lives, perhaps a dozen, before the traffic stopped … but the same shift would rip a Hyperloop tube in half, and probably cause hundreds and hundreds of deaths. The lawsuits to follow can only be imagined, and unlike the freeways which are publicly funded and thus relatively immune to lawsuits, the Hyperloop company will have to insure against such an occurrence … again, not cheap.
Initial claims from Musk were that the system could be built for $6 billion, which seemed way low to me. Leaked docs from the company now put it at somewhere between $9 billion and $13 billion, and that’s before the first shovel has gone into the ground. Considering the problems Musk has had keeping his car costs down, it’s not encouraging.
So I fear that your “it’s all solvable” point of view, while technically valid, is very likely to drive costs up far beyond the breakeven point. Yes, it’s easy to wave your hands and say that any technical hurdles can be overcome … but a number of these are not minor issues that are “readily solvable” or “completely trivial” as you claim. They are things which have never been attempted, and those things are generally not as easy as they might seem to overcome.
Best regards,
w.
Thanks, Willis. You’ve raised some valid points and concerns about the project. Many of them deserve careful scrutiny and weighing of pros and cons: from an engineering standpoint, from a cost standpoint, from a safety standpoint. My point was simply that the idea is far from a dead end from an engineering standpoint.
It may be, for example, that something like a Hyperloop is perfectly feasible in a kind and gentle world, but that the additional expense of hardening it against terrorist attack in our current geo-political climate makes the project infeasible. This kind of analysis has to be done all the time, and I can certainly see someone raising the same concern about the latest and greatest skyscraper that goes up.
It may be, for example, that something like a Hyperloop is perfectly feasible in a more stable region that is not prone to earthquakes, but that the additional expense of hardening it against tremors makes the project infeasible. I tend to think this one is pretty solvable, even in California, but it would require some hard analysis and numbers to make the decision.
At the end of the day, it seems most all the technical difficulties can be solved pretty readily, at least for the system to fulfill its functional purpose. Then the questions become: (a) how much would it cost for the base system, (b) how much would it cost to harden it against particular risks in the world we live in and in the particular geographical region, (c) how many riders would realistically ride and at what ticket price, and so on. Once we have better answers to those questions, a rational decision can be made about whether the project makes sense. But I just want to be cautious not to take the engineering criticisms a bridge too far, at least not on functional engineering grounds. The real nail in the coffin is more likely to be social and/or commercial.
Personally, I am skeptical that it could be constructed for a commercially-reasonable cost. The $6B pricetag you mentioned is a joke — I hadn’t heard that number. If that was really the claim, then they didn’t know what they were talking about. We’re not talking about a few % points in cost overruns. It isn’t even in the ballpark.
Even the bullet train, which in many ways is an easier project to build, has now ballooned to an estimated $70B or so, last I heard. There was so much misinformation surrounding the bullet train when presented to the voters years ago, it was a real travesty. As someone who voted firmly against it at the time, when the bullet train boondoggle comes up these days all I can do is mutter under my breath to family and neighbors and anyone who will listen, “I told you so.” And $70B isn’t even right. I have full confidence that the estimate will eventually exceed $100B before any serious work is even done. And even that number will still be too low.
As someone who has to estimate project costs for my work, I’m regularly astounded at the wildly inaccurate initial estimates that some of these large public works projects throw out. An order of magnitude off in some cases.
On that point, I am firmly in agreement with you.
Best,
Thanks, Climatereason. Here’s the text from the promoters::format(webp)/cdn.vox-cdn.com/uploads/chorus_asset/file/7352899/Screen%20Shot%202016-10-26%20at%203.20.18%20PM.png)
Like you, I just laughed when I saw that …
As to the question of earthquakes, here’s the shift in the earth I was mentioning yesterday. I’ve been there, it’s about thirty miles from my house, and it’s amazing. In one place it was a total of 24 feet of lateral movement, the San Andreas is a strike slip fault … and I doubt greatly whether you can engineer a Hyperloop tube to survive that …
Best regards,
w.
As I wrote, the whole tube will be in a tunnel anyway (less costly) so the external attacks are limited.
Maybe this is a solution to limit the rate of incoming air in case of a breach: a tube inside a tube.
Which creates other complications for evacuation, arrival of safety teams, etc.
s-t April 22, 2018 at 5:39 pm
I’m sorry, but that simply is not true. Take a look at the promoters’ budget up above. There is $600 million for tunnelling (through the Tehachapi Mountains) and $2.55 BILLION for pylons. Much of the proposed line is aboveground.
w.
For the pilons based project to be viable, you would need quasi flat terrain. But then, why bother with pilons?
Willis:
The $6B cost claim is such nonsense. Front page of the San Jose Mercury News this morning indicates that extending BART to San Jose is costing $4.8B. That is for 6.1 miles and related station stops.
Granted, over open land between cities each mile isn’t going to be that expensive, but it gives us some idea of what the cost is to build a rail system through existing city infrastructure. They’re going to have that problem at both ends in spades, plus several urban stops in between.
Hyperloop from SF to LA isn’t even going to make it as far as San Jose for $6B. Perhaps barely out of SF.
The number just isn’t even in the ballpark, and it is completely irresponsible for them to claim otherwise.
The tubes should be a composite made of structural concrete with a thin steel gas barrier on the outside in order to take the atmospheric compression forces and prevent air from passing through the porous concrete. A steel sliding expansion joint should be provided every 200 m fitted with bellows seals to exclude dirt from the machined sliding surfaces and double O ring seals.
Escape from such a structure in the event of pod failure would be difficult and might be the most difficult technical problem. Earthquakes in California would be another huge problem for such a structure.