Putting The Hype Back Into Hyperloop

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.

hyperloop one.png

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.

Hyperloop two.png

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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rogerthesurf

Well so long as tax payers money is not involved!
Cheers
Roger
http://www.thedemiseofchristchurch.com

Auto

Willis,
May I add a comment?
Copy & Paste:
“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. ”
Thoughts –
a 1″ wall-thickness pipe looks insufficient. Granted and agreed.
What about a 3″ wall thickness pipe? Or more
More costs – sure, but if the taxpayer is paying – I fail to see a real objection . . . . .
Joints – oil tankers have used – for more than fifty years, P/E Joints.
Again, to upgrade to <2 millibars up to Californian pressures and temperatures might add to the cost. A bit.
Thermal expansion.
Surely shading [with the shades painted white], and then enclosing and air conditioning the whole LOOP – no HYPE here! – will prevent much of the obvious problem that you highlight – here: –
Copy & Paste – again:
"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."
Anyway – as long as the Californian taxpayers stump up, I suggest many of the problems will be solved.
May be not the throughput or safety ones – but even St. Elon [is he to be our next Pope?] cannot expect the impossible.
Can he?
Auto – not /SARC this time [albeit a tad doubtful of one or two of the Papabile's claims}

rogerthesurf

Auto,
I am well aware of the impossibilities that are apparent in this project.
The most compelling reason when I express hope that tax payer funds will not be involved, is that, if this remains a private venture, it will likely die a natural death when the money runs dry and investors see the light – preferably before anyone gets hurt.
However, if governments using tax payers money get involved, the project will linger on, not only bleeding the tax payer and the economy dry, but very likely progress will be made to the point where people will actually get hurt.
Cheers
Roger
http://rogerfromnewzealand.wordpress.com

PiperPaul

What about a 3″ wall thickness pipe?
External ring reinforcement on the 1″ thick wall pipe (lotsa welding). But it’s still not gonna work.

Hugs

Thermal expansion can be traded with longitudinal pressure / drag, as is done on modern railways.
Thermal expansion turns into some thermal pressure. The earthquakes and terrorism are more like arguments. But are they more arguments than on ordinary rails?

DC Cowboy

“The earthquakes and terrorism are more like arguments. But are they more arguments than on ordinary rails?”
I’d say yes because trains on ‘ordinary’ rails don’t travel at 760mph in a complete vacuum

St. Elon, or as I call I.T. Barnum the 21st century conman…

s-t

Not an argument. The TGV has derailed at (commercial) high speed. It is safe.
(The case of the Eckwersheim accident is different.)

William Ward

Thrillionaire.
The more I learn about Musk the less I like (from a business perspective). How does someone with so many bad ideas get $5B of US taxpayer money and become a cult tech icon figure?
Thanks for the good read Willis.
William

rocketscientist

As much as I think the hyperloop is a really bad idea, mostly because it is not cost effective given the monumental engineer feats that must be accomplished (…and then a miracle occurs) several of the points made are not correct.
A human can survive very high g’s for several minutes. The Russian cosmonauts have endured over 23 g’s for several minutes when they make ballistic reentries while sustaining only chipped teeth (from the vibration). Of course they are in fitted seats and partially reclined. The orientation of the loading is important. We refer to the crew loading as “Eyeballs -in” when the force is pushing on their backs, or “Eyeballs-out” when the force is pushing on their fronts. The nomenclature refers to the direction you feel your eyes being pulled. Eyeballs-in is preferred.
If the pod is pressurized at 1 atmosphere (14.7 psi, 1 bar) and the tube is 0 bar then the pressure differential cannot exceed 1 bar. This would produce large stress on the shell of the pod, which is why it will probably only be pressurized to about .7 bar (11 psi) the standard cabin pressure of commercial airliners.
Aircraft have experienced rapid cabin depressurization without killing everyone instantly. Furthermore rapid depressurization will take more than a minor leak.

Mike G

How long would people be able to survive in a stopped pod? Rescue could be long in coming.

Bruce Ryan

should be possible to allow air in the tube on one side of the pod to move it along.

Nigel S

Like Brunel’s atmospheric railway. Problem there was rats eating the greased leather seals.
http://www.ikbrunel.org.uk/atmospheric-railway

Well thought out, and the fools errand well destroyed. Thanks Willis.

ossqss

Obsurd. Would you put your pet hamsters in the pneumatic tube at the bank? Why the need to go so fast anyhow? A bullet train would make way more sense economically, logically, and realistically. Would be interesting to be in a quake in that contraption also.

But… but… but… this would be so COOL!
That appears to be Elon’s reaction to any “investment” opportunity.
Slightly off topic, but the Tesla 3 line is shut down again. Supposedly “planned” – funny, the employees knew nothing about it. Maybe because they are going to go unpaid yet again.

MikeN

I thought the plan was to have everyone drive their cars onto a ferry, which then is closed and the ferries move very close together through the loop. What’s the need for a vacuum?

Marty

This thing has to be level or the horizontal and vertical curves need the same turning radius as a jet doing 580mph. Otherwise the inside of the car will look like the vomit comet.
The insanity is infinite.

s-t

Exactly. Slow train tracks are essentially 2D + height (with a limit on ramp angle); but fast tracks are 3D: acceleration on the vertical direction becomes relevant.
Hint: Elon Musk’s “Boring Company”. The track on pillars is a h0ax. These tracks would be almost always subterranean.

This is just the next level of Tony Stark’s Iron Man suit Elon Musk’s Ponzi Scheme.

Craig M Carmichael

The Ponzi family kindly requests that you refrain from using our good name in reference to Mr Musk.

Latitude

If it doesn’t work….they can always turn it into this….comment image

Tim.

They used to call those ‘toast racks’ in the UK. Trams pulled by horses, and you had to get out and push if the hill was too steep.

dmacleo

so horsepower and human power.
a hybrid 🙂

Willow Grove park?
That was the last wooden frame roller coaster that I know about; admittedly a very limited knowledge level.
I don’t remember one called cyclone there though.

JasonH

Coney Island

“JasonH April 19, 2018 at 7:47 am
Coney Island”

Ah, yes. Of course!
Coney Island’s older larger and much grander rides.

MarkW

6-Flags over Georgia still has one.

“MarkW April 19, 2018 at 1:56 pm
6-Flags over Georgia still has one.”

Thanks. I didn’t know (or remember) that. I’ve ridden the 6-flags over Georgia coaster, admittedly several decades ago.
I had understood that insurance costs for the wooden frame roller coasters had driven them out of operation.
An obviously flawed understanding that I read in a paper published near Willow Grove.

Tom Halla

The Hyperloop almost makes Jerry Brown’s toy train look good.

John MacDonald

This former pipeline engineer agrees fully with Willis.
If you like pretty pictures this YouTube video is good: https://youtu.be/RNFesa01llk
I find it amazing that so many smart engineers are working on Hyperloop in Nevada. They must know it isn’t practical.
Sad really…the concept is pure…the dream is admirable…but the engineering realities make it a fail at this point.

RHS

Until their pay checks bounce, why stop working on the project?

eck

“so many smart engineers”!? You would be surprised at how recent engineering grads are woefully deficient in fundamentals. and common sense. I know several

Phaedrus

I’ll double that!

Richard Smith

The power of air pressure reminds me of Von Guericke’s Magdeburg Hemispheres. These were two iron hemispheres which were fitted together and then the air inside extracted to create a vacuum. The experiment, performed before Frederick the Great if I remember rightly, demonstrated that two horses could not pull apart the two hemispheres which were held together by no more than atmospheric pressure.

Chimp

First demonstration was in 1654, before Holy Roman Emperor Ferdinand III in Regensburg. Some years later, the experiment was repeated for Frederick William, Elector of Brandenburg and Duke of Prussia, great-grandfather of Frederick the Great.

Within 15 years, autonomous vehicles will be able to pick you up at your home in LA and deposit you in anywhere in the SF Bay Area in 3 or 4 hours, likely at an adjusted cost of less 75 of “today” dollars.
Brown’s, brown bullet train will never be completed. Neither will the hyperloop. The economics of autonomous vehicles will change everything. It takes the same amount of time to drive to airport, fly, and leave airport.

Robertvd

Within 15 years California will have changed in a progressive sh.thole.

jorgekafkazar

Viva Calizuela!!

Calizuela! Catchy!

Bob boder

15 years? Lot less me thinks

Chimp

Autonomous private planes (drones with people inside) will give the FAA and other organs of the national security state fits.

Pop Piasa

And supply organ donors frequently as well?

jorgekafkazar

The benefits go on and on, Pop.

Chimp

Safer than cars.
Autonomous drones have a good “safety” record in the US military. Soon they’ll be used in fire fighting.
http://www.uavexpertnews.com/2018/01/autonomous-air-tanker-to-aid-in-firefighting/

RPT

But they will eliminate global warming; a reflective top surface, and we can welcome the next ice age.

Chimp

RPT,
Yes, if the world’s 1.3 billion ground vehicles are replaced by an equal number of private, autonomous aircraft, then they might well enhance the planet’s albedo.

Walter Sobchak

75 dollars says that won’t happen in 15 years, not even almost in 15 years.

MarkW

Add a couple of decades to that estimate.

Autonomous driving is a bad joke. Like Tesla’s Autopilot, which loves to run into parked fire trucks
and crash barriers at 65MPH, followed by a battery explosion and fire.

Chimp

Autonomous aircraft are the way to go for medium to long hauls, IMO. Granted, most of the world’s drones are still remotely piloted, but more and more of them are autonomous.
http://www.jpost.com/Business-and-Innovation/Tech/Israeli-firm-creates-autonomous-aircraft-that-goes-where-no-helicopter-dares-477334

jorgekafkazar

To you, that is a bug. To terrorists, that’s a feature.

MarkG

In fifteen years, you’ll rent a VR drone at your destination and visit from home. Not much need to move your body around when you can rent a body anywhere in the world.

jorgekafkazar

Hey, you stole that idea right out of my virtual mind.

TonyL

Just a note to the Bullet Train To Nowhere”, proposed for LA to San Francisco.
Bet you did not see this one coming:
To get the money Gov. Moonbeam has to make deals with other politicians. (Surprise!)
The price these pols want is for this super high tech, high speed wonder to serve their community along the way.
So we have now ended up with a high speed train which stops at every town along the way. In other words, it’s not high speed anymore.
It is a super expensive reinvention of Amtrak.

TA

“So we have now ended up with a high speed train which stops at every town along the way.”
We call that a “Local” on the railroads I’ve worked on. 🙂

jorgekafkazar

I just call it “loco.”

Don K

In places with functioning passenger rail, there are express trains that stop at major towns. If you want to go to a smaller town, you take an express to the nearest big town, walk across the platform, hang out for a while until a local shows up then take that to your final destination. Yes, that’s slow. But so is sitting in a monumental traffic jam at one of the I5-I405 merges.

Chimp

The TGV makes a lot of stops between Marseilles and Lyon, but fewer from there to Paris. The distance is about 100 miles longer than LA-SF.comment image

s-t

TGV is just a regular electric train (overhead) that can go fast on some segments. In the UK, a different model of TGV goes to third rail tracks too (not at high speed obviously).

Chimp

ST,
Yes, it reaches top speed only on some runs, on its special tracks. But the train of Gov. Brown’s dreams will in effect be little different. Dunno if he plans a tunnel through the Tehachapis.

Eric Stevens

Willis, an aspect you haven’t mentioned is the need for linear accuracy. At the planned speed even a minor wiggle in the direction of travel will result in significant lateral (or vertical) forces as the pod makes an almost instantaneous change in direction. This raises problems for both pod guidance and passenger restraint. The structural discontinuities at expansion joints will be particularly difficult to handle. Manufacturing and putting in place the tube will be like no other pipeline job on the planet.
Further, in the event that the wall of the tube is damaged by any sort of accident or malfunction inside, it is possible that that the shape of the tube will no longer to be able to support the external pressure with the result that the tube will collapse. Without external stiffening rings or similar the collapse is likely to expand for the whole of the length of the tube at close to the speed of sound. There is no need to comment on what will happen to the passengers in the pods in the event that such a failure occurs.

dan no longer in CA

If a crack starts in the pipe, the crack propagates at the speed of sound in the metal, but the pressure only drops at the speed of sound in air. That means the crack will extend to the nearest joint, which could be miles, and destroy any pods in that section.

Eric Stevens

dan, that’s true for internal pressure but failure due to external pressure is by buckling, as shown in Willis’s examp[les of the tank cars. Buckling from external pressure spreads at the rate at which the atmosphere can follow it up and for practical purposes that is the speed of sound in air. Stiffening rings at intervals will limit the buckling and will limit the distortion between rings. Longitudinal stiffeners have almost no value from the point of view of collapse under vacuum.
My original comment was based on the thought of a car running amok at high sped in which case it could inflict damage ovr a considerable length of the tube. It could also damage stiffening rings in the vicinity. This could be better or worse than a simple plane crash, according to how many cars became involved. Unlike a plane crash it would take out the whole system for a significant period of time.

‘Crack’ and ‘pipe’ seem to be the operative words for this project…..

Don K

“At the planned speed even a minor wiggle in the direction of travel will result in significant lateral (or vertical) forces as the pod makes an almost instantaneous change in direction.”
Do you reckon that crossing a number of active earthquake faults — including the San Andreas — might be a problem?

I think all of Musk’s best engineers went to SpaceX and his car company. This is what’s left.

icisil

Bankwupt…

icisil

And if a compressor disk fails and pieces breech the containment vessel and one pierces the fuselage killing a passenger and de-pressurizing the aircraft it will fall out of the sky, crash and kill all on board destroying the whole crazy industry.
Or maybe some smart people will, given enough time and money, figure out how to make it work. As long as it isn’t my money, I’m fine with that.

My first thought was who in their right mind wants to be sealed inside a windowless 1-inch-thick-walled metal tube? I’m not particularly claustrophobic, but, really, … this in itself is like being buried alive within a round of ammunition that you pray will not misfire.
No, the hell, thanks!

RicDre

They could put “windows” on the cars that are actually video display and project on them the illusion of looking out a window with scenery going by to help reduce the claustrophobia problem.

Sunsettommy

It would never work for me, who is very claustrophobic. I NEED to be convinced that I am NOT enclosed at all to function.
I had to be put on conscious sedation to be able to handle a MRI scan.

Robertvd

In August 2008, physicist Michio Kaku predicted in Discovery Channel Magazine that a teleportation device similar to those in Star Trek would be invented within 100 years.
(Physics students at University of Leicester calculated that to “beam up” just the genetic information a single human cell, not the positions of the atoms, just the gene sequences, together with a “brain state” would take 4,850 trillion years assuming a 30 gigahertz microwave bandwidth)
https://en.wikipedia.org/wiki/Transporter_(Star_Trek)
Any idea how many passengers per hour it can handle ?

jorgekafkazar

And with the transporter, there’s no guarantee that the “you” that appears in the destination transporter is the same “you” that left. It may look like you and act like you; it may even think it is you. But it isn’t you. You have been disintegrated permanento. You’re dead, D.E.D.

Steve in Seattle

The engineering of this matters not, it’s all about the greens, the hype and the NGO lobbyists – pay NO attention to the man behind the curtain …

Doug Jones

Mitch Clapp, George Herbert and I have kicked around an idea that seems superior to Hyperloop and may be able to address all the concerns above. Mitch first described it on Rand Simberg’s Transterrestrial Musings last year:
Mitchell Burnside Clapp
April 18, 2017 At 5:13 PM
I believe Hyperloop has made some grave technical assumptions and errors that render the system profoundly infeasible.
Specifically, I think the evacuated tube idea is an error. As an alternative, fill the tube with hydrogen at standard temperature and pressure. Several things happen when this is done:
1: The drag drops by a factor of fifteen with respect to air at standard temperature and pressure. Yes, functional vacuum has lower drag still, but seriously, is it enough lower to compensate for the hassle of maintaining an evacuated tube?
2: Mach effects are comfortably remote – the speed of sound rises by a factor of nearly four. Travel at what would be Mach 0.95 in air becomes travel at about Mach 0.25. That’s comfortably in the incompressible flow range.
3: The passenger cars become substantially simpler – they don’t even have to be pressurized in a structurally significant way, just reasonably airtight with a CO2 scrubber and other climate controls. You might pressurize the car to a tenth of a psi over the tube pressure, and the tube by a similar amount over the atmosphere, but that’s not a significant structural burden.
4: Note that the tube may now be constructed from acrylic or polycarbonate or something appealingly transparent, since it isn’t structurally loaded in the same way any more.
5: I would recommend driving the passenger cars by external means, and using an onboard magnetic levitation system. There are ways to do this simply in two axes with permanent magnets. But this could be traded around. Steel rails aren’t out of the question as long as there’s a reasonable contactless power connection by an inductive mechanism.
6: The above observation moots most of the complicated hardware on Hyperloop’s passenger cars.
7: It’s technically possible to generate the power with onboard air for the passengers and a fuel cell reacting with the hydrogen working fluid, dripping the water exhaust into a catch basin on the car as you go along, I suppose. I think that is all a little too cute for the room in my opinion and would require a supply of makeup hydrogen on a per trip basis rather than to compensate for the inevitable leakage.
8: I am astonished at myself for advocating a transportation technology that requires hydrogen. This would of course work nearly as well with helium, but I don’t think there is that much helium on the planet.
9: I am mindful of the hazards of hydrogen, of course. I will point out that the Hindenburg mishap in 1937 had 36 fatalities and 62 survivors. Most of the fatalities were *crew* – who stayed at their posts helping the passengers escape, and in an era where that was not a key portion of the job description for cabin attendants. Also, of course, the fatalities were from falling and burning diesel or fabric. The hydrogen all went upwards and no one was harmed by it.
10: A minute in vacuum will kill you faster than a minute in 1 atm, 70 F hydrogen.
Okay, is there anything fundamentally unsound about this idea, apart from calling it HydroLoop?

M Courtney

That might work. Which is something fundamentally unsound about the idea.
If it might work you might be asked to make it.
That’s no way to make money.

Chimp

The global supply of He is likely to increase with the onset of advanced fusion reactors.

RHS

How would changing the gas from Hydrogen to Nitrogen affect the build considerations?

Chimp

N2 is almost as massive as air, of which it comprises 78%. O2 and Ar are a little more massive, but make up only about 22% of air. Other trace gases, such as CO2 and H20 can be disregarded.

“A minute in vacuum will kill you faster than a minute in 1 atm, 70 F hydrogen.” More likely to kill you in a minute? Not really having a dig at you but surprised that such a half-arsed idea is better than something that found $113 million in funding.

Sounds ;like a very big cannon with people carrying bullets.

gbaikie

Put it on ocean and be 20 meter below ocean surface. Giving near constant temperature, with earthquakes not problem, but how to get out of it, if all goes wrong? Could have vacuum or H2 pipe within outer shell. Outer shell deals water pressure and way to leave it and intertube is the hyperloop.

Tim Beatty

I’d by inclined to put a turbojet engine and carry oxygen for passengers and the engine and make the car self-propelled. A direct hydrogen generator from a refinery could then be used with the turbine able to consume impurities. Cryo-pumps could accumulate water vapor. But we already have very fast tubes that move through very thin air.

“9: I am mindful of the hazards of hydrogen, of course. I will point out that the Hindenburg mishap in 1937 had 36 fatalities and 62 survivors. Most of the fatalities were *crew* – who stayed at their posts helping the passengers escape, and in an era where that was not a key portion of the job description for cabin attendants. Also, of course, the fatalities were from falling and burning diesel or fabric. The hydrogen all went upwards and no one was harmed by it.”

Burning paint exterior fabric is not the same as igniting hydrogen in a metal container.
Any oxygen contamination in the hydrogen turns the hydrogen ignition into a powerful explosion.

oldbob1231

Couple of comments regarding using hydrogen as the working fluid.
Make sure the steel tube is properly coated so the hydrogen doesn’t embrittle it.
While it burns very quickly it also burns hot (about 3000F) so we won’t have to worry about saving passengers if there is a fire.

paqyfelyc

you don’t need steel tube, as there is no pressure difference between inside and outside. You don’t need to make it round, either; for the same reason. a triangle or diamond or whatever fits best for other purpose would be just as fine.
You can double the hydrogen tube into another inert gas tube with few more hassle. Azote would be fine.

WXcycles

@ Doug
” … Okay, is there anything fundamentally unsound about this idea, apart from calling it HydroLoop? …”
—–
Fill party balloon with hydrgen, attach filled balloon to end of long stick, pass skin of balloon over lit candle.
Use ear plugs.

Not actually a big pop. You need oxygen for that and quite a bit of air to get a bang. Minimum of just under 30% air. A pretty big leak.

paqyfelyc

Planes are efficient because they cruise at reduced pressure ( ~20% of sea level).
Law of diminished return apply: you have to make much more effort to diminish the pressure from this 20% level to, say, 10%, for a much lesser gain on drag.

paqyfelyc

nice idea.
4. the tube need not even need to be round, solid, nor stiff. Could be anything reasonably non-flammable, provided it doesn’t leak (too much) hydrogen. joints won’t be a trouble.
And it could have variable size, larger for train crossing and station, for instance. Station could be has big as needed with minimal trouble
9. To cope with hydrogen fire hazard, just in-close the working tube into another tube filled with inert gas. azote would be fine.
10. Don’t bother, planes are more risky. They travel in 20% sea level pressure, -40°C temperature. And they are safe enough, so your idea is, too.
Now, I am still not convince that the game is worth the hassle.

gnomish

why not hoist passengers to the stratosphere in a balloon and drop them?
2o minutes to get up, 5 minutes to get down.
nearly half the globe is the range.
too simple?

Red94ViperRT10

Interesting adjustments, but how do you get the hydrogen from in front of the moving pod in a tube to behind the moving pod in a tube? Even that is probably solvable, but at what cost? This has been the experience of my entire engineering career, a rarely encountered an unsolvable problem, but at least 50% of the time the client was unwilling to pay for my solution.

Crashex

“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.”
I don’t disagree with your premise that the engineering issues for this are gargantuan, and likely not worth the time and money. But, I thought I’d wade in a bit to correct this bit about deceleration rates and time.
Typical passenger car deceleration rates for casual braking (0.1g), typical stops (0.15g) and hard no skid (0.35g) are comfortable levels we have all experienced. Hard maximum effort braking on dry pavement, at a tire on pavement “skid-level”, regularly yields 0.70g to 0.90g rates. Such levels are uncomfortable more for the sudden ramp up to maximum and are not hazardous. Duration is clearly an issue, but I think the 0.5 g you applied here is a bit low.
Also, I think your math went off a bit. 760 mph is 1115 feet/sec. t = V/a =1115/(0.50*32.174) = 69 sec.
With a 0.75 g rate, the time about 46 seconds.

rovingbroker

… that means passenger throughput drops to 1,260 passengers per hour.
Current and in-development single aisle jets (Boeing 737 MAX 10 and Airbus A321neo) have around 200 seats in single class configuration. This means that five aircraft flying 12 minutes apart would have the same capacity as the hyperloop.
The acceleration and deceleration rates mentioned here means that passengers would have to be seated and seat-belted for departure and arrival.

extremely dangerous to passengers, vulnerable to a host of problems, will kill everyone inside …
=========
Sounds perfect for California.
Seriously. You get a reduction in air resistance but what else? A huge capital expense along with a very demanding operating environment.
Combines the worst of air travel and rail travel. Since the system cannot overcome the speed of sound it isn’t a step up for long distance travel.

extremely dangerous to passengers, vulnerable to a host of problems, will kill everyone inside …
=========
Sounds perfect for California.
Seriously. You get a reduction in air resistance but what else? A huge capital expense along with a very demanding operating environment.
Combines the worst of air travel and rail travel. Since the system cannot overcome the speed of sound it isn’t a step up for long distance travel.

Men are not getting better… Lol

rocketplumber

Oops, link to the original discussion here:
http://www.transterrestrial.com/?p=67555
Smaller engineering issues can be handled- thermal expansion is controlled by expansion joints, and seismic events can be detected before the s-waves arrive and command an emergency stop. Emergency stops can be done at two gees- that’s what seat belts are for- and the hydrogen-filled tube is entered and exited with a section of nitrogen-filled tube to prevent mixing with air. When not moving at maximum speed, the cars can simply run in air, and fan out to multiple stations at either end (in the extreme, driving autonomously they take you door-to-door). The loading and unloading of individual cars is thus decoupled from the high speed tube scheduling.

MarkG

“Emergency stops can be done at two gees”
So you’re going to require passengers to take a medical before they get on board?

Rick C PE

Only one quibble… the pods would be at atmospheric pressure at the stations so when sealed they would not need to be pressurized. However, the station would need to be resealed and depressurized before the airlocks could be opened, so no difference in terms of time required.
Musk has shown the ability to find some amazing engineers – eg. landing Space-X rockets – and great engineers can solve some really hard problems. But great engineers should also recognize that even if they can deal with technical issues, issues of economics and safety sometimes make an idea impractical. The Hyperloop idea seems to me to be one that could not be justified on economic grounds alone. It would most likely never be built unless massive subsidies are involved.

Joe D

While, I do still see all sorts of other problems, In regards to the need to vacuum out a chamber, to insert the pod into the tube, I can see one solution. How about if there is an intermediate pod older, that can rotate out from the vacuum chamber, like a revolver gun. This intermediate pod, could be designed to hold the passenger pod, with any extra space filled with solid material.
This arrangement can, theoretically allow for passenger pod insertion/removal without pumping at all.
Some of the other technical issues may also be solvable. But, of course, the question if if it worth the cost.

Tim Beatty

Let him work it out. A similar critique of his proposal to land and reuse booster rockets on floating barges could have easily been made. Right until they did it. Also, this whole analysis presupposes that the entire loop needs to be a vacuum. That’s not true. Only the air in front of the pod needs removal and then it becomes a rate equation of how fast air can be moved and what does the work to remove it. That simplifies the initial conditions, stresses and margins.

“A similar critique of his proposal to land and reuse booster rockets on floating barges could have easily been made.”

That’s a specious strawman.
Nor is criticism about recovering boosters anything similar to the litany of safety, production and operating concerns that have been raised in Willis’s article and this thread.
Especially since both Russia and America regularly recovered and reused boosters used for space launches.
Criticism regarding recovering and reusing rocket components ignored common practice for space launches.
Let Musk build the tube. Without any use of tax payer funds!
Given Musk’s pretentiousness, Musk should build and operate the beastly thing using only renewable energy, including manufacturing the steel pipe.

s-t

“Also, this whole analysis presupposes that the entire loop needs to be a vacuum”
NO
It’s what the proposal says. (Proposals actually. There are many possible variants.)
We can only discussed what Elon Musk is suggesting. If YOU want to propose another design, than go for it. (Any change to fix one issue introduces many other issues.)

rocketplumber

The density of 0.084 kg/m3 for H2 at STP is equivalent to air at 20.2 km, or roughly 66,000 feet, so the drag on a car in the tube would be far less than for an airliner at 35,000 feet or so.
So bottom line, I agree that a vacuum tunnel is a bad idea, but a hydrogen tube could be a good idea and may be useful if someone less busy than I am can do a serious first-order design.

Tim Beatty

The entertaining part is that fossil fuels are the only economical method for extracting hydrogen.

s-t

“tube would be far less than for an airliner at 35,000 feet”
But nobody proposed “an airliner at 35,000 feet”, AFAIK.
The proposals mention 100 Pa. That’s almost empty space.

John Bell

How could ANYONE spend even a dollar on this nutty idea?

California. Nuff said.

Within 15 years, autonomous vehicles
≠============
Not sure about the date, but it is most certainly a game changer for public transit in all forms that will eliminate entire industries.
What it does mean is that roads will remain the primary means of moving people. Mass transit systems on fixed rails will make no sense when private vehicles can go out and make money for their owners. Instead of paying for parking while at work your car will be out making money to pay for fuel, insurance, maintenance, etc. End of the day after making a few hundred $ in fares it drives up to the office to pick you up and take you home.

u.k.(us)

Anybody that thinks they need to move that fast:
1) Should move closer to the hive.
2) Consider Skype, or those new video chat platforms I’m way behind on.
3) Maybe you take one trip thru the tube, just to say you felt what a 10 g acceleration felt like, and it didn’t even spill your coffee.

Andrew Cooke

As an engineer I find myself intrigued by the possibilities of the hyperloop and its various technological difficulties.
I do believe it is prohibitively expensive and the cost of construction and running the system would make the price of using the system…astronomical.
This is an example of identifying a problem and creating a solution without acknowledging the constraints that the solution must meet.
On a side note, it is quite humorous to read all the negative commentary about the Hyperloop. I am certainly not a fan, but if you were to replace the word hyperloop with airplane with all these negative comments you would assuredly be entertained.

Chimp

Self-flying aircraft will make this scheme and high-speed trains unnecessary.
Every industrial and commercial park, or large campus like Apple’s, will have its own landing strip. The planes might even be tilt-wing, so as to land and take off like helicopters, obviating the need for strips.

ironargonaut

Yeah,as soon as we change physics. I mean flying is sooo energy efficient. /sarcasm
Look up the MPG for a small plane or helicopter

Tim Beatty

My thoughts exactly. “Imagine a tube moving near the speed of sound. to achieve this, we’re going to elevate the tube to 35,000 ft to reduce drag. We will pressurize the tube to keep passengers comfortable.” Oh wait, you mean it actually works, is used everyday by millions and changed the world?

Greg Cavanagh

It works well within constraints.
1. Cost benefit for passengers, they’re the ones paying for the service.
2. Destination, the destination has to be useful to the passengers.
3. Speed Vs safety, there are other forms of transport out there, at competitive prices.
Planes work well, but the Concord was dumped simply because it’s particular need (cost-benefit) wasn’t viable.

Another Ian

An earlier go “Atmospheric Railway”
http://www.ikbrunel.org.uk/atmospheric-railway
At least you could look out the window

Pure subversion.

techgm

All the charm and risks of traveling in a submarine submerged at a depth of x-hundred feet, only a lot faster, and what’s left of you when a failure occurs can be scooped up on dry land.
Don’t forget the nifty, the-power-is-free solar panels on top of the tube sections (see 1st drawing). Surely they will have a major effect of reducing operating costs (but are really there to get government subsidies).

climatebeagle

So after an earthquake BART inspects tracks, an example here took around two or three hours, using trains: https://patch.com/california/piedmont/bart-inspects-tracks-following-earthquake
BART has 112 miles of track, though not sure if that’s distance of the routes or the actual tracks (e.g. a route typically has two sets of tracks for each direction). It also has a maximum speed of 80mph.
I wonder how much checking hyperloop would need after an earthquake & how it would be done, sensors only or running inspection cars at a lower speed through the tubes?

s-t

Elon Musk’s answer to everything: “track” (tube) inspection will be done by robots.

ChrisB

The crushed rail car is a poor example.
A tube with external steel braces (circumferential and/or longitudinal) or simply selecting a longitudinally crimped tube would be sufficient to bear the vacuum induced compressive stresses. Other engineer issues can also be solved as long as someone sprinkles money all around, a la Moon Project.
Certainly, no private investor will put money for this project which will never be a cash flow positive. Hence Musk wants government (the taxpayer) to subsidize this project.
Why should this be our government’s priority?

s-t

“Other engineer issues can also be solved as long as someone sprinkles money all around”
Probably not. You need to make the system mass transport system-safe. Not just mission to the Moon-safe.
But the project was presented with a budget. The sketchy project presented was based on existing, proven technologies. This is obviously a crook.

Before I knew anything about the technicalproblesms, I was aghast at the idea of being stuck inone of those pods, unable to escape. And the likelihood of a terrorist planting an explosive on the tube.

ResourceGuy

The elite need speed and chic and tax credits. Let the others eat carbon tax cake.

Michael Kelly

A more in-depth look at the concept was published here about 5 years ago, and it addresses each of the challenges listed above. The least of these, IMHO would be tube buckling due to atmospheric pressure. The tube radius is 65 inches, and the pressure load 14.7 psi. That’s a buckling stress of only 956 psi. Preventing buckling is simply a matter of adding external stiffening rings ever 10 feet. It’s the other loads that would dominate.
As for a cabin depressurization, this is not a much different problem from the Concorde, which cruised at 60,000 feet. Oxygen masks would be useless at that altitude, so the designers made the windows much smaller than on other jets. The pilots would go into a maximum angle dive at the first sign of cabin depressurization. If caused by a window blowout, the area was small enough to keep pressure in the livable range until the air packs could keep up with the bleed. Loss of a door, however, would have been un-survivable. The hyperloop cabin has no windows, which eliminates a lot of the problem. Elon has had a great deal of experience, no, flying a habitable cabin in space, and even with big windows and doors, Dragon has never had a problem.
The acceleration limit of 0.5 g is puzzling. Here is a list of the 9 fastest launch acceleration roller coasters in the world. Ninth is the Takabisha, at a modest 1.4 g. I’ve been on both the Xceleerator and Storm Runner (both a blast at 1.6 g). Number 1 is Japan’s Do-Dodonpa, which goes from 0 to 111.9 mph in a blazing 1.8 seconds (3.27 g). Stopping is just the inverse of starting, and I’m sure that 12.2 seconds at 3.27 g would be more acceptable to passengers than an instant stop from 760 mph.
Anyway, it’s an interesting read from the perspective of an engineer. Enjoy.
(PS: That tank car collapse was gnarly!)

Schrecken

I was thinking the same thing as well…..also having ridden many rollercoasters, including some of the launched ones like Storm Runner. There are also some that have some pretty hard stops as well (depending upon how the trains are blocked and how many can run the circuit at a time). But then again, those kinds of rollercoasters also have sophisticated restraint systems designed to keep passengers from being thrashed about too much. On public transit no one is going to want to strap in like a fighter pilot…..Probably the most that passengers would be willing to do would be to put on a seatbelt like in an airplane. That, and as the author of this article has mentioned, some people will be unwilling (or unable) to be subjected to such forces.

s-t

Also rollercoasters have a set of criteria on who can envoy the ride (“you must be that tall”).
A mass transit system cannot afford these restrictions. No public body is going to subsidize a transport system that severely restrict who can travel, especially is “protected groups” cannot use it. It’s just a non starter, from the point alone.

michael hart

Whatever one thinks about the economic prospects of Musk’s other companies, his cars do at least work, his spaceships do reach orbit, and solar city can generate some electricity on a sunny day. This hyper-loopy thing can only detract from general confidence in them, and from confidence in the person at the helm. Man will walk on Mars before this works. It would be frightening if it wasn’t so funny.
Take that back. It is frightening, despite it being so hilarious.

Bob boder

All of his successes require one thing, subsidies from the government. The one true thing he is really good at is making himself rich with other people’s money.

If we assume 1” wall thickness, 11 ft diameter, how many miles could be layed given current world steel production?
The quantity of resources needed for this is staggering.

Michael Kelly

A 500 km tube, unreinforced, would weigh 1 million tonnes. The US produced 85 million tonnes of steel in 2014, and has produced as much as 140 million tonnes in a single year (1970). I really don’t think resources would be a problem. Currently we’re utilizing 75% of our capacity, and the remaining 25% is more than enough to build the hyperloop in just one year.

Randy in Ridgecrest

And this Willis,
“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.”
is the hammer on the nail.
Thank You for encapsulating the insanity of this state in one sentence.
I do travel up and down I-5 and !-99 a few times a year, an extra lane or two would be nice.
But
I live at the junction of I-395 and I-14 at the north end of the Mojave desert. I-395 is a notorious highway of death. 2 lanes for 65 miles, and it is a major highway used by Socal to head to Mammoth etc. And a major truck road. Just last week another local couple were killed in a headon on 395. I-14 isn’t as bad but it STILL has 2 lane sections.
This idiot governor can’t be bothered about bringing the state highways into the modern age but pulls all the stops out for his stupid train.

No Name Guy

I’d respectfully submit that collapse of the tube isn’t as big of a deal as you make it out to be WE. The pressure loads are trivial compared to what subs endure. The tank car video, while entertaining, isn’t relevant since those cars are not designed for such a load.
External ring and stringer stiffeners would suffice – think of it as a standard airplane fuselage turned inside out, approximately. A simple shell “only” as the tank car video shows is wouldn’t be an ideal solution. Alternatively, an external pressure shell with internally placed ring frames and stringers as the structure, with an inner liner to define the tube way for the car might be another engineering solution. Note that I suspect submarines are built this way (certainly the WW2 vintage ones, not sure on the current types) – there is a pressure hull distinct from the external, hydrodynamic shell in WW2 boats, and there certainly could have been an inner liner hull distinct from the pressure hull just as easily.
I also don’t see the joints needed to handle thermal expansion / contraction or external imposed loads as being too big a deal. Note that simple fabric coated rubber core “P” and “Y” seals pressed into the adjoining fuselage structure are used to seal the doors of passenger airplanes to 8 PSI. Put 4 such seals (2 primary, each taking ~1/2 the load, 2 more as fail safe) in series at a “tube inside a tube” slip type joints and there you go – pressure sealed with flexibility as well. If you do this in the context of a tube-in-a-tube arrangement, the car will never encounter one of the pressure loaded slip joints, being isolated to the inner “liner” tube. Supports that impose proper section-to-section alignment across the tube section joint while allowing linear flexibility of the tube sections are trivial in concept (tube mounted rails, with interfacing support mounted rollers that constrain relative lateral displacement without constraining linear displacement).
Where I see the issue with this whole concept is simply the economics. Can the cap & running cost generate sufficient risk adjusted income to make it worth while? At this point, I’d be highly skeptical on that part.

Claude Harvey

All the vacuum Hyperloop will ever require can be generated by connecting one end of the tube to the Tesla cash-flow machine. Talk about some serious negative suck!

climatebeagle

Is the hyperloop’s capacity really an issue?
The paper Michael Kelly linked to says has a much lower hourly capacity than you calculate and states: The capacity would be on average 840 passengers per hour which is more than sufficient to transport all of the 6 million passengers traveling between Los Angeles and San Francisco areas per year.
I’m not sure about that claim of all passengers travelling is only six million per year, but 840/hour gives around 20,000 per day assuming a 24 hour day. That seems to be comparable to Southwest’s daily capacity from the Bay Area to LA area, ~28,000 (198 flights x 143 passengers/737): https://www.southwest.com/thmpg/flights-from-SFO-to-LAX.html
Caltrans seems to give average daily traffic for I5 around 38,000 in Kern county (as an example of the middle two lane (each way) portion). http://www.dot.ca.gov/trafficops/census/volumes2016/Route5-6.html
So it’s seems its daily capacity is roughly in-line with existing transportation options.

Don K

Willis – re the collapsed tank car. I believe that was done by Mythbusters in their final season, and they had a heck of a time with it.. Their first try, they steam cleaned the car, sealed it up while hot, then sprayed it with water to simulate a rainstorm after a cleaning and ill advised sealing. The tanker didn’t collapse. The tried again with an older, rusted tanker. The tanker didn’t collapse. They finally dropped a five ton block of concrete to dent the tank. Only then were they able to collapse it. There’s a description at http://www.thetvaddict.com/2016/01/16/mythbusters-recap-tanker-implosion-crushed/
Maybe 1 inch steel for the tube is enough. (and maybe not).

yes the collapsed tanker is a horible red herring. They are built to hold up agaainst a positive internal pressure

looks like you didnt read.
pylons have xy dampers
and z dampers.
you can bet the engineers do more than speculate using tankers as models of what could happen.
and yes the internal structure of the tube is different. its not purely thickness.

Russ R.

This project will not be affordable for the middle class. The infrastructure cost is an order of magnitude higher than aviation infrastructure. He can’t move enough passengers through the system to spread the cost of the system, over millions of passengers per month, so the tickets will be higher than airfare. And he is still going to need the same TSA hassles that make flying a wait-in-line experience. It has no advantages over flying. You can’t put the terminals in the city, or you will gridlock the city streets, with passengers trying to get in and out of the terminal.
And the final nail could be an increase in speed limit for automated cars. An automated car could certainly drive safely at over 100mph in the left lane of an expressway. That brings the time to drive under 4 hours.
You can overcome a problem or two, when you have no competition in the space you are trying to fill. This project has a very limited customer base, and huge start-up cost. And the rest of the country will not be riding it, so we are all going to vote for not funding it. CA has a lot of voters, but they are not going to get support from the other 49 states. LA and SFO may not even be in the same state, in 15 years!

climatebeagle

I don’t think the car speed limit is the issue on I5, there tend to be three problems on I5 in the middle 2-lane sections.
1) Trucks overtaking other trucks, causing the left lane to slow down to ~55mph
2) Drivers flying down the empty right line behind the truck being overtaken and cutting into the already compressed car traffic backed up behind the overtaking truck (from 1) causing others to break and slow even more.
3) Drivers that stick in the left lane, next to, and at the same (slow) speed as the vehicle in the right lane, thus blocking the freeway for everyone else wanting to go faster.
Maybe spending serious money on driver education and enforcement would actually allow a higher speed limit and cut the driving time.

Russ R.

The solution is to have the driving skills designed into the vehicle. The expressways could handle vastly more capacity than it does now, if the system was designed for max throughput. If we are willing to give up control, you will see a vastly different expressway system 20 years from now. Most of it is doable with today’s technology. It just needs to have a critical mass of vehicles that can take advantage of the system, and the desire to save time and money by not sitting in traffic jams.

Absolutely correct, and applies to almost all I-Slabs.
Keep the trucks in the far right lane, which is the rule in some parts of Europa. Capacity and safety would make step-change improvements.
Or, make two lanes for trucks and two others for not trucks.

climatebeagle

The claim from the doc Michael Kelly linked is:
The total cost of Hyperloop is under $6 billion USD for two one-way tubes and 40 capsules. Amortizing this capital cost over 20 years and adding daily operational costs gives a total of $20 USD plus operating costs per one-way ticket on the passenger Hyperloop.
So only $20!! Easily affordable for the middle class.
As a cost comparison, the new east span of the Bay Bridge was $6.5 billion for 3km, so that $6 billion for a 500+km project looks somewhat optimistic.

Russ R.

If you want those structures to withstand a 7.0+ earthquake without collapsing it is going to cost 5x that much. Even at that cost there will be substantial damage, from the earthquake that is going to happen. There needs to be a footing dug out, and poured. Then an earthquake force distributing attachment to the ground for everyone of those structures Then they need to keep the tube level, over un-even ground for miles at a time. And we are talking CA labor prices. $6 billion might not even get out of LA county.