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Hyperloop technical discussion

Hyperloop is supposed to be open source, meaning we engineering types can talk about and solve issues. Here is one:

The cooling of the compressed air is to be supplied by water. The water is to be heated and turned to steam that is stored on the vehicle. So I ran some numbers....

The total water on board is 290 kilograms. It is to be turned into steam at 400 Kelivins. To get water to boil at that temperature it has to be pressurized to 260kPa. (Its not clear if it is intended to boil the water at elevated pressure, but as will be seen the issue I'm bringing up is worse the lower the pressure.) At 260 kPa and 400K stream has a density of 1.4 kg/cubic meter. 290 kg of this steam would require a storage tank with a volume of 207 cubic meters. At lower pressures the volume is greater.

I do not see room on the pod for such a tank. Given the pods frontal area of 1.3 square meters the tank would have to be 160 meters long, 4 to 5 times longer than the current design.

How to fix this? First, do not boil the water. Start with water-ice slush, say 70% ice, and let it cool by melting and heating to 400K. It will absorb only 25% or so of the heat as we would get by allowing it to boil, so we will have to carry 4 times as much water. But no steam tank is needed.

Next, see what we can avoid cooling. The bypass air may be left hot for example. Not cooling the bypass air has several advantages: The heat exchangers are smaller, we cut the water requirements in half, and when discharged it will create about twice as much thrust. The disadvantage is the bypass pipe will need to be larger and insulated from the passengers.

Another question, how would you handle junctions? How would a switch point look like? Any hints?

In the other thread it was suggested that switching be done vertically. A second tube would branch off angled slightly down and the floor of the tube would be hinged to allow for either tube to be accessed as needed.

How do you handle thermal expansion of solid metal tube?

You know, the technical issues are interesting. But my first impression is that the current design has a major human factors problem.

It's a small, enclosed, windowless capsule in an enclosed, windowless tube.

People don't feel comfortable more than about a minute in an elevator, let alone half an hour, and that without being able to move from your seat at all.

Through the journey there will be odd noises and substantial accelerations. Incidents would really suck, as you would spend well over an hour, maybe several, in this extremely cramped environment.

Since I made a billion miles in underground trains I can't even relate to the 'human factors pproblem' daniel is talking about.

But since this thread evolves to a hyperloop questions dump, I just want to get rid of another one.

Is it technically possible to substitute concrete for steel? Seems cheaper eg for tunnels.

I was thinking about Elons proposal for an air pump to suck the air out of the way to reduce drag. This link demonstrates the principle of entrainment. A small directed movement of air attracts a proportionately larger body of air with it for no extra energy cost.
A pump could be designed with this concept in mind to either reduce the power of the pump required or maximise the volume of air removed.

Another question

Could a breathable air mixture that differs from regular air but has less mass or density be put in the tube?

The document suggests that "beautiful landscapes" will be displayed to the passengers in the cabin. Whether this is enough of a substitute for windows seems uncertain. I would go for the bigger "people + vehicles" tube myself if for no other reason that you could then make roomier accommodations for the passengers.

@bent +1

I too am concerned of the apparent cramped space of the smaller tube.

This reminded me of pipeline pigs, tools sent through pipelines to inspect condition of walls.

Could the hyperloop be buried and follow existing easements?

HD vid etc. in each seat would suffice for holding attention for a half hour or more.

The tunnel would be a soft vacuum, about 1% of a Martian atmosphere, which is about 1% of Earth's. Even with that little pressure, managing it is a serious issue, such that the capsule trains must suck-compress air in front and expel it from the rear. It's barely sub-sonic in the straight stretches.

I am not dumping on the concept. I am pointing out an obvious issue.

I ride the subway every day, it is not the same thing by a very long shot. The doors open every couple of minutes, there are windows, the cars are much bigger and you can walk around, or in many systems between cars.

The passenger only version of the hyperloop is really very small, and you are strapped to your seat the whole time. It's not a plane ride, it's more like a space ride, except with no view.

I think windows could be added, though the cost would be substantial. Because it moves so fast, you don't need many windows on the tube. At half speed (600 km/h), you are doing 10 km per minute, or about 160 meters per second. This means that, on the tube, a window every five meters would yield an view with a 32 Hz refresh. If each window is just one foot wide, it would be like wearing sunglasses with 7% light transmission.

At 1200 km/h, the cruise speed, the "image" of the landscape would refresh at 64 Hz. Smaller windows closer together would raise the refresh rate, but might cost more, or not, I am not sure.

Windows on the vehicle would add some weight but be comparatively trivial.

It would be awesome to see the landscape go by at 700 MPH. I think the effect would be surreal.

A few problems with this though. One is that the tube is structural, and here you are introducing holes, though well spaced. A slightly thicker tube wall might be required to compensate.

Cost is significant. The number of windows would be huge, over 90,000 per side (so if just one side per tube, that's over 180,000). At $500 per window (wild order of magnitude guess, since I know it won't be $100 and won't be $1,000), that's $90,000,000. Not trivial but not a deal breaker on a $2 billion project.

A second problem is that the tube becomes much more vulnerable to attack. Glass, even laminated gorilla glass, is no match for the nearly 1" steel wall thickness specified. The steel is totally bullet proof and could handle small explosives. The glass could be cracked or broken by a rifle shot.

Maintenance costs would be higher, since periodic cleaning would be required. A window cleaning machine would have to travel the tube every few days. There would need to be several, since the segments would have interruptions such as tunnels and so on.

One advantage is that emergency evacuation would be easier since the windows could be broken with a blunt object.

A ride on an 330 kmh ICE train in Germany made me vomit whenever I looked out the window. I better bring my own porn.

My two cents on some comments:

" you would spend well over an hour, maybe several, in this extremely cramped environment.."

Not so. Under the concept proposal, the pod's subsystems would not even last 45 minutes before needed a recharge. The proposal is for 35 minutes of travel time. The times shown on page 41 of the alpha paper are cummulative.

By the way, it usually takes 35 minutes to travel the channel-tunnel in Europe (34 miles underground or underwater) and: a) there isn't much to see; b) it is cramped, loud, and uncomfortable; and c) people do it routinely.

IMHO, the cramped conditions and lack of visual references would be no much different than flying in a private jet on a dark night. Granted, there are people who can't even do that but, the hyperloop is the *fifth* mode of transportation, there are four others.

"...substitute concrete for steel..."
Air on concrete would have higher drag coefficient. Page 27 of the alpha design even discusses special boring/polishing process to keep the inner surfaces of the metal tube smooth. It would be tough to replicate that with concrete unless you lined it with something.

"...breathable air mixture that differs from regular air..."
Somebody smarter than me can do these calculations but I believe that, whatever gains you make by using a less dense mixture, you lose by the increased complexity and management. For instance, you could not simply evacuate the tube directly to the outside atmosphere as you may need to recycle the mixture to maintain its supply. You may also need to incorporate a different compressor and air bearing design. The advantages of a lower density gas might also be so marginal at that low pressure that it might be easier to simply try for a slightly lower pressure using regular air and the current design.
My guess is that, if hyperloops take off, vacuum pumps and associated systems would get better.

I read the entire brief of the hyperloop alpha pdf and the concept is really interesting. My job is currently forecasting failures and one fundamental problems I see is the "spin" factor. To demonstrate this, imagine the pod as the bullet, and the tube as the barrel of the gun. Whenever you fire a gun at very intense speeds, the tendency of the bullet is to spin. Since it is floating on air, and only held by the linear motors, there is a great probability that it would spin out of control and jump of the electromagnetic tracks.

This can be mitigated I believe placing extended parts (at least 2 at the sides) that follow an electromagnetic path. Thus, instead of the linear motors (which are placed at the bottom or top), then there are 2 guide wings that can stabilize the whole cabin. Adding this feature would also mitigate slowing down at turns.

Porfirio, my "several hours" was a reference to what can happen in an emergency, where the tube is pressurized and the pods move on wheels at much slower speeds, almost certainly quite a bit less than 100 MPH. We are talking about California and a loss of vacuum is a possible scenario.

We all know that under normal use the trip is 35 minutes.

The Chunnel has full-sized trains, way larger than the hyperloop pods.

Jack, lateral stabilization is mentioned and would be done by reaction wheels, compressed air thrusters, or a combination of both.

This is what the Hyperloop reminds me of it's like a updated version of the Beach Pneumatic Transit system idea system. The Hyperloop and the Beach Pneumatic Transit system both had trains running as giant cylinders running though giant steel tubes while being pushed along with air or running in a air tight tube. This is sort of a back to the Future Idea in that Beach would most likely be very happy right now with the Hyperloop idea.

The question I have is that if this idea can work could they try building a O scale model of the hyperloop system at the Tesla factory and have it run from one end of the factory to the other as a working model. If a working model could built then that would be very cool to see it in action. Or to take the Hyperloop idea to the next level maybe they could build a 500 foot long Test track section much in the same way Beach built his Pneumatic Transit project experiment.

Here is another news story with the Beach Pneumatic Transit system being compared to the Hyperloop

I think the HD screen directly in front of each passenger will have to substitute for windows. Views of the passing landscape could be displayed there, simulated from external cameras, of course. Maybe with individual digital zoom and pan controls?

The smaller passenger-only version has to go. The seating is simply too confined.

Some research will have to be done to see how often people will want to travel Hyperloop with their vehicles, but I get the feeling that those who don't bring vehicles along will not want to be in a capsule with other people's vehicles, if they have a choice.

Then there's the question: If you bring your vehicle, do you ride inside it? Probably not. I'm guessing vehicle occupants will be required to ride in the passenger cabin. How many passengers in addition to 3 vehicles is not made clear. 28? That's 3 full Model Xes, 5 or 6 other passengers, and 1 or 2 Hyperloop employees (at least at first, passengers are going to want human representatives along for the ride). Oh, and there'd better be a lavatory, just in case -- which would not be an option with the smaller version.

Perhaps this should be scaled down a bit, to accommodate 1 or 2 vehicles and/or cargo -- but let's put that aside for a moment...

Going with the larger tube means larger passenger-only capsules, one would think, and not only passenger-plus-vehicle capsules. What is the optimal passenger capacity in this larger format? Do we just make them the same size & shape, and replace the vehicle area with seating? They would still have different specifications, but being able to share a basic frame and most of the bodywork would reduce cost.

...Then you see where scaling it down a bit might make sense.

By the time the initial route could be completed, we can expect vehicle automation to have made great strides. The advent of the fully-automated vehicle brings a variety of usage options, ranging from a taxi-like one-time ride to a rental, along with subscription services, town car and limousine services, shuttles and timeshares. Once these transportation options are available, the desirability of ferrying a vehicle on the Hyperloop becomes diminished.

This needs to be taken into account when deciding how many of each type of capsule to build, a ratio that should lean more toward passenger-only capsules over time.

I think a good place to start would be with a less ambitious "superloop", a 200 MPH urban transport, with car carriers, for travel within large cities like LA.

It would have a single acceleration stage and cover distances in the order of 20 miles.

That would be nice to take your car with you in that you wouldn't have to worry about renting one and if you go into a rural area you could do a lot more with your car with you.


A 20-mile trip at 200MPH (average) would take 6 minutes. Loading and securing a single vehicle on such a transport, then unloading it, would likely take longer than the trip itself. Unless the operation is extremely well-coordinated, the wait times involved could easily cancel out time saved in transit.

However it does sound like a good idea for passenger travel.

Subway. In here it's no hassle system that does that distance in just about 30 minutes and stops in about every 2 minutes. If it would make less stops it would make that trip a lot faster. Transfers tens of thousands of people every day. I think hyperloop would be too much hassle for short trips like that.

I think taking cars with you is not really a must.

I know at least several carsharing schemes where you look up a car parked all over the city on the smartphone and just take it automatically paying per minute.

Hyperloop station being a natural place for a bunch of them waiting.

I am curious about the optimization of the max speed of hyperloop. Lower max speed would presumably lower the cost but possibly not significantly, how does the construction cost/ maxspeed curve look like?

I would love to participate to further developments of this idea, as a retired scientist I would donate my time. Does anybody knows how?

Zefeliz, I know how.

Hyperloop as it is is a freaking large up front investment.

Find a breaking point in terms of shortest possible tube for Hyperloop to be built to technically and physically make sense.

This should pave the way to the pilot launch.

Just make a chart at what speeds and distances the underlying physical characteristics of Hyperloop kick in.

Post the results here, by then you are a part of global public discussion of Hyperloop and your work is not in vain. I assume it is a day's work.

Vadik,thanks for replying.
My first question is a simple one, I am interested in how the cost of the hyperloop depends on max speed for the proposed SF to LA route. I guess I could work it out myself given that they have already priced the individual items and I could guess the associated scaling laws but I wanted to know the "official" considerations in picking this specific max speed.
Somewhere it says that going over mach 1 is very hard but why did they choose mach .91?
It's possible that since 70% of the cost is in the tubes, to reduce the speed, and the resulting reduction of throughput, doesn't make any difference in the ticket price.

I am an intensely unofficial person in case you are wondering.

But your direction of thinking is wrong.

LA-SF hyperloop is much more a social project (which happens to make economic sense) than a for profit venture. For the society as a whole it is vital to have the highest possible throughput for this system, right at the edge of physically sound.

Whenever you start optimizing against the dollars, here marginally less speed here marginally less throughput, you end up sending Greyhounds up the interstate.

Motivating a pilot project in the frame I pictured above does serve to advance hyperloop in my opinion. I cannot imagine California approving without seeinga pilot working first.

I think transparent glass tubes is still a posibility if they find a way how to create diferent diameter tube type glass. Then the glass can be tempered and laminated in any thickness needed and provide explosion, impact safe solution.

Also it would allow to laminate solar panel films between the glasses and create solar power ready tubes.

I work in the glass business and I haven't seen tube type glass, but I know that it must be possible to produce them.

Somewhere it says that going over mach 1 is very hard but why did they choose mach .91?

I would guess to avoid shockwave from going thru sound barrier inside a metal tube.

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