Hyperloop technical discussion

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.

vadik | August 14, 2013

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

Bart | August 14, 2013

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.

Timo | August 14, 2013

How do you handle thermal expansion of solid metal tube?

danielccc | August 15, 2013

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.

vadik | August 15, 2013

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.

dutchstew | August 15, 2013

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?

bent | August 15, 2013

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.

Timo | August 15, 2013

@bent +1

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

mikegraham | August 15, 2013

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

Could the hyperloop be buried and follow existing easements?

Brian H | August 15, 2013

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.

danielccc | August 15, 2013

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.

vadik | August 15, 2013

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.

PorfirioR | August 15, 2013

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.

jack859363 | August 15, 2013

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.

danielccc | August 15, 2013

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.

Ocean Railroader | August 15, 2013

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.

Ocean Railroader | August 15, 2013

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

Brian H | August 15, 2013

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?

filsmyth | August 15, 2013

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.

danielccc | August 15, 2013

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.

Ocean Railroader | August 15, 2013

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.

filsmyth | August 15, 2013


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.

Timo | August 16, 2013

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.

vadik | August 16, 2013

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.

Zefeliz | August 16, 2013

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?

vadik | August 16, 2013

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.

Zefeliz | August 16, 2013

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.

vadik | August 16, 2013

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.

o2daz | August 16, 2013

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.

Timo | August 16, 2013

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.

briangilbert | August 16, 2013

feasibility of a glass tunnel is discussed above.

Armour glass is used for the iPad screen so it is available commercially as mentioned in the biography of Steve Jobs.

Glass tubing of small diameters is certainly available and widely used so that is a technical possibility.

briangilbert | August 16, 2013

Pilot model.
1. Give priority to pilot model of smallest passenger capsule as if not proven then other work would be wasted.
2. Invite universities etc to prove any concepts not yet proven to scientific standards.
3. produce a small scale model which would satisfactorily prove the overall concept.
4. Produce a full scale model limited to one tube forming a circle of minimum radius allowed in design. By allowing the capsule to circle this loop enough times it would prove that the full length Hyperloop was feasible.

Zefeliz | August 16, 2013

What's the minimum size demonstration project for HL?
It seems to me that to test reasonable curvatures at realistic speeds minimum distances are already in the 100 miles range.
Of course shorter distances would provide quite a lot of relevant info anyway, but not all.
For what I understand HL makes sense as a goods transporter also, in fact at demonstration level it almost makes more sense to prototype a purely goods moving system, especially to overcome the regulatory issues for something that isn't contemplated by any regulations yet.
What about moving goods along an already heavily trafficated highway?

briangilbert | August 16, 2013

TO Zefeliz
1.Minimum size demo. A minimum curvature is mentioned in the Hyperloop Alpha pdf but I don't think the figure is given. If you can find that out in degrees, then you can calculate the minimum area needed for the demo/pilot.

2. The goods market is probably limited to those needing high speed. This should appeal to courier services that charge extra for high speed delivery. The operator could also offer a lower price for 'ballast'. That would be the price at which it was more profitable to carry the goods than leave space in the capsule.

briangilbert | August 16, 2013

The hyperloop alpha spec comes up blank on my iPad but is readable at this address

I even tried clicking on the iBook legend which appears in the top rh corner but that did not work

b1berns | August 16, 2013

I'm a great admirer of Elon Musk, supporter of Tesla, electric car converter from an ICE vehicle, an auto mechanic/tinker, multiple business owner, an American citizen and I wish for nothing less, but to see the Hyperloop a reality in the near future.

However, since all ideas are welcome, I wish to share some of my recent thoughts:

My concern is a possibility of an earthquake during Hyperloop operation.

I know that the tube and pylons are designed to withstand earthquakes, but how much of an earthquake can it handle?

We all know that State of California is known for frequent earthquakes and how unexpectedly one can strike.

Imagine, traveling in the capsule at 760 MPH and suddenly, a violent shaking occurs...

The loaded capsule is heavy and would start moving back and fourth inside the tube, traveling at a high rate of speed and possibly scraping sides of the tube.

The momentum may overpower air cushion support protection and throw it in a violent, spark emitting spiral, that can end up with fire and disintegration.

This is by no means a criticism, but merely an attempt to help to prevent any possible setbacks. I would appreciate a comment that would alleviate my suspicions.

GeekEV | August 16, 2013

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

@vadik - Go with a spoke and hub design. Straight shot from LA to SF, get out at SF and hop in another pod for a SF - Sacto trip. Still *much* faster than driving, flying, etc...

GeekEV | August 16, 2013

@b1berns - Earthquakes are addressed in the PDF and easily addressed in a design such as this by "floating" the tube on the pylons instead of bolting them directly to it, etc.

b1berns | August 16, 2013

GeekEV - You are correct, the pylons are not connected to the tube with hard connections, but my
concern is: while shaking pylons during the earthquake, pushing the tube up and down and throwing
passing capsule into the tube wall: will the air cushions have enough support to prevent the capsule
from touching walls of the tube?

My take on the junctions: The tube will have a Y section that will have an electronic linear motor control to change direction of the capsule, the speed will most likely be reduced at the junction.

briangilbert | August 16, 2013

Moderator. I suggest a thread devoted to rebuttals. A link should be given to the criticism accompanied by comments in rebuttal.

briangilbert | August 16, 2013
Criticism: They have to acquire 1100 pieces of land.
Rebuttal: That was for the railway. The route proposed is alongside Interstate 5.

Croticism: Local communities will demand extra viaducts and tunnels.
Rebuttal: Not applicable to existing Interstate 5 route

Criticism: Local communities will demand a terminal.
Rebuttal: If they demand a terminal that can be provided as a spur. It would be an extra benefit of the project and it is up to them to pay the cost.

Critiicism: The project will be too costly:
Rebuttal:: No figures supplied to support this criticosm. Has a formal costing been provided yet by Elon Musk?

Criticism: The whole technology is unproven.
Rebuttal: No project os proven until it is completed. Some ideas are expected to be disproven and the project changed.

Criticism; He is not Henry Ford.
Rebuttal: Not a valid criticism.

Brian H | August 17, 2013

The cost is given, about 10% the level of Moonbeam's Mistake.

Zefeliz | August 17, 2013

The Demo
I propose a thread devoted to the demo project where the discussion would focus on proposals which assume all HL Alpha assumptions as valid.
I don't want to read about Tesla, Paypal, Elon Musk net worth and the need for windows and toilets any more, let newspaper blogs deal with it.

TimC | August 17, 2013

In regard to earthquake concerns, probably one of the most critical stretches of the proposed route is near the southern terminus through the Newhall Pass. In both the '71 and '94 earthquakes, the Newhall Pass was the site of major damage. Driving through there and observing the terrain, it's clear to see that the Newhall Pass is a major geological stress point.

briangilbert | August 17, 2013

Earthquake risk raised above by b1berns.
Elon Musk will have considered the earthquake risk, but given the small size of this forum can also be expected to become aware of the points you raise.
The design and pilot models will have to pass tests for earthquake resistance and so the project could not be completed if despite changes to the design it could not pass them.

briangilbert | August 18, 2013


by Don Tuite

Yet the propulsion method in a railgun is still a LIM. Since one of the major challenges in any electric motor is minimizing the air gap, getting the car around curves is challenging. (I can’t help but think of the famous Tehachapi Loop.)

Rebuttal: The Hyperloop Alpha pdf says that ' Linear Induction Motors will only be needed for 1 per cent of the length.'
so can be placed on straight stretches

briangilbert | August 18, 2013

Criticism: Many sources
Rebuttal: Relatively appalling conditions are tolerated on rush hour subway trains in UK and Japan.

briangilbert | August 18, 2013

To Moderator.
In my previous comment I omitted to say that project is widely criticised as being too uncomfortable for passengers and has no provision of toilets. Please can you amend it.

Brian H | August 18, 2013

Moderation/administration is virtually non-existent here. None of your mod requests will be followed up.

briangilbert | August 18, 2013

To: BrianH
Thanks.. BG