Guest Post by Willis Eschenbach
A recent article has discussed how Elon Musk’s “Boring Company” has raised $113 million dollars in startup capital. This is the company Musk formed to drill the tunnels for his proposed “Hyperloop” transportation system. It has encouraged me to discuss some of the engineering and practical problems with his LA-to-San Francisco Hyperloop proposal. The Hyperloop concept involves a windowless “pod” traveling at just below the speed of sound in a tube with all the air evacuated from it. There’s a reasonable description of the Hyperloop at Wikipedia and a much more hyper description at their website. It all sounds so good and so 21st Century, what’s not to like?
In no particular order, the problems with the Hyperloop include:
Vacuum: The Hyperloop requires a near-perfect vacuum to run at the proposed speeds. It has been tested with a one-kilometer long test track. The test track was billed as the “second largest vacuum chamber in the world”, after the vacuum chamber of the Large Hadron Collider.
But the LA-to-SF route is 615 km. This is a huge, almost unimaginable step up in size and problems. Consider that although the LHC is carefully internally braced to keep the pressure from collapsing it, they’ve said the Hyperloop tube will be a 1″ thick steel pipe supported on pillars. There’s no way to brace it internally, the pod has to run through the middle. The day/night expansion on that much steel would be very large, and the expansion joints for that use have never been built. In addition, atmospheric pressure on the tube would be about ten tonnes per square metre … and there’s a 15-tonne “pod” running through it, putting large stresses on all bends and joints.
This means that if the vacuum is breached for any reason, say a car runs into one of the pillars, or some fool shoots an high-powered rifle round at an expansion joint, or terrorists place even a small bomb anywhere along the length of the route, or a small thermally driven “kink” in the pipe develops, or heck, a ubiquitous California earthquake, everyone in the tube would die from the instantaneous deceleration. Here’s what happens to a railroad tank car with ~ 1/2 inch (12 mm) steel walls when it is not properly vented … it collapses from nothing more than the atmospheric pressure, and that is without a near-perfect vacuum inside.
Ooogh … you don’t want to be inside if that happens.
Thermal Expansion II: A difference of only 3°C from the top to the bottom of the tube will cause differential expansion of about 25 metres from top to bottom of the pipe over the length of the SF-to-LA run … very no bueno. The pipe will tend to either lift out of its supports or bend at the expansion joints … joints with a 15-tonne pod going through them at 750 mph.
Energy: The pumps necessary to keep the tube evacuated will be quite large. Remember that each pod has to be air-locked in and out at every station. The energy cost of this constant pumping at each station is unknown, but definitely not small.
Pod Integrity: The pod will be in near total vacuum. Airplanes fly at about 33,000 feet (10,000 m). The pods will be traveling at the equivalent of 50,000 feet (15,000 m). This means that if there is the slightest leak, there will be catastrophic decompression and everyone in the pod will likely die.
Passenger Throughput: This is likely the biggest problem with the Hyperloop—for all of its speed, it is remarkably slow at actually moving people. Consider the competing technologies. Freeways typically carry 2,000 cars per hour per lane, that’s maybe 3,000 people per lane per hour. So a four-lane freeway of the type common in California will carry about 12,000 people per hour.
A subway with three-minute headways between cars will carry about 36,000 passengers per hour. The proposed and insanely expensive high-speed “Bullet Train To Nowhere”, which Governor Moonbeam is trying to build fro LA to San Francisco will carry on the order of 12,000 people per hour.
Now, Musk claims that a pod will depart SF-to-LA and LA-to-SF every 30 seconds carrying 28 people per pod. That’s the best case, and it’s only 3,300 passengers per hour.
But wait, as they say on TV, there’s more. In general, you don’t want to run cars, trains, subway cars, or Hyperloop pods so close together that they can’t stop safely in case of an emergency to the car ahead. Humans can only sustain about half the force of gravity, called “0.5 G”, for safe deceleration. Musk says the cars will be traveling about 760 mph (1225 km per hour). At that speed, it will take around 75 seconds at 0.5 G to decelerate to a stop. So the inter-pod time has to be at least 80 seconds … and that means passenger throughput drops to 1,260 passengers per hour.
And the bad news doesn’t end there. The whole system can only run as fast as the slowest segment of the Hyperloop, and that’s the stations. Remember, at every station, the pods need to be depressurized. Then passengers need to get on and get off, and the pods need to be repressurized. Musk says that up to three pods will be in the stations at once. So that means that depressurization, passenger unloading and reloading, and re-pressurization need to take place in about two and a half to three minutes … and you better hope that nobody forgets anything on a pod and has to go back to get it, or the entire system slows down.
Net result? The Hyperloop will make less than half the difference in passengers transported, and likely much less than half the difference, that would be made by adding a single lane to the LA to SF freeway …
In Short: The Hyperloop is extremely dangerous to passengers, vulnerable to a host of problems, will kill everyone inside if even a small failure happens, moves a very small number of people, and oh, I forgot to mention … what happens if the power fails, as happens these days in California all the time because of our insane renewable mandates pushed by our less-than-genius Governor, Jerry Brown. Care to think about being stuck inside a windowless pod inside a steel pipe on a hot day in the California desert, with no way to escape?
And all of that for less gain than adding a single lane to the freeway … but there is one thing we can be sure of.
Elon Musk will get even richer from government subsidies for his latest whiz-bang proposal … truly, the man is a subsidy artist. Where most of us can see nothing but government boondoggle and waste, he sees personal wealth.
My best to all,
w.
THE USUAL: When you comment please quote the exact words you are discussing, so that we can all understand your subject. In addition, rather than telling me or anyone that we are doing something wrong, please demonstrate the right way to do it.
Well so long as tax payers money is not involved!
Cheers
Roger
http://www.thedemiseofchristchurch.com
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}
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
“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.
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?
“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…
Not an argument. The TGV has derailed at (commercial) high speed. It is safe.
(The case of the Eckwersheim accident is different.)
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
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.
How long would people be able to survive in a stopped pod? Rescue could be long in coming.
should be possible to allow air in the tube on one side of the pod to move it along.
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.
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.
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?
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.
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 suitElon Musk’s Ponzi Scheme.The Ponzi family kindly requests that you refrain from using our good name in reference to Mr Musk.
If it doesn’t work….they can always turn it into this….
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.
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.
Coney Island
Ah, yes. Of course!
Coney Island’s older larger and much grander rides.
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.
The Hyperloop almost makes Jerry Brown’s toy train look good.
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.
Until their pay checks bounce, why stop working on the project?
“so many smart engineers”!? You would be surprised at how recent engineering grads are woefully deficient in fundamentals. and common sense. I know several
I’ll double that!
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.
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.
Within 15 years California will have changed in a progressive sh.thole.
Viva Calizuela!!
Calizuela! Catchy!
15 years? Lot less me thinks
Autonomous private planes (drones with people inside) will give the FAA and other organs of the national security state fits.
And supply organ donors frequently as well?
The benefits go on and on, Pop.
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/
But they will eliminate global warming; a reflective top surface, and we can welcome the next ice age.
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.
75 dollars says that won’t happen in 15 years, not even almost in 15 years.
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.
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
To you, that is a bug. To terrorists, that’s a feature.
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.
Hey, you stole that idea right out of my virtual mind.
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.
TonyL April 18, 2018 at 1:22 pm
No, I didn’t know that. As a kid I used to take the “Milk Run” train from Redding, CA, down to Sacramento. Stopped at every tiny burg along the way. It was great fun.
The good news is, now I won’t have to be nostalgic for that time …
Thanks, Tony,
w.
W. E.: ” It was great fun.”
I rode the Erie Lackawanna Railway from western PA, across Ohio and Indiana, into Chicago where, in the morning, I was catching the Santa Fe Chief.
Not much sleep time.
This was before Steve Goodman’s “City of New Orleans” song about the Illinois Central. When the song became popular via Arlo Guthrie, I felt the sadness.
Best few words: rhythm of the rails
and best line: This train’s got the disappearin’ railroad blues.
Steve Goodman was an incredible songsmith and performer.
Saw him at the Philadelphia Folk Festival before leukemia took him.
Willis, unless the passengers are expected to only travel one way in the morning and reverse direction in the afternoon, then I think two tubes should be considered. Either way, Musk’s income depends upon regular announcements of “cool” futuristic designs. Works for him.
“Good morning America how are you? Don’t you know me I’m your native son…” God that’s beautiful.
The graphic in the article shows twin tubes.
“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. 🙂
I just call it “loco.”
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.
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./CarteReseauTGV.jpg-page-001-5788b4353df78c09e99a19c8.jpg)
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).
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.
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.
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.
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…..
“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.
Bankwupt…
http://www.india.com/wp-content/uploads/2018/04/Tesla-Elon-Musk.jpg
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!
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.
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.
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 ?
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.
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 …
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?
Interesting concept, Doug, I hadn’t heard of that.
w.
Hydrogen brings to mind the hindenburg effect.
Why not just use a train and a simple acrylic-style tunnel and have fans blowing wind down it at whatever speed you want the train to move at?
This way you can run a regular bullet train at almost double the speed. All current technology. Should the tunnel be breached and windflow interrupted, the deceleration would not be catastrophic since the mass of the train itself (orders of magnitude larger than a pod) would regulate the deceleration process.
How do you provide electric power to that “bullet train”?
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.
The global supply of He is likely to increase with the onset of advanced fusion reactors.
How would changing the gas from Hydrogen to Nitrogen affect the build considerations?
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.
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.
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.
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.
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.
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.
@ur momisugly 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.
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.
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.
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?
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.
“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.
Thanks, Crash Expert. You’re correct. I’ve used conservative figures of 0.5 G and “around 75 seconds” instead of 69 … as a crash expert, surely you’d want a bit of a safety factor, no? In particular, you are assuming that the braking starts the instant the leading car stops.
In any case, thanks for checking my figures. It’s the first thing I do when I read someone else’s work, and I’m always happy when folks do it for my work. In fact, it’s one of my favorite things about the web—I’ve been prevented from wasting weeks or months on some blind alley by someone saying, “Umm … Willis … “.
All the best, keep checking,
w.
You used this bit of analysis to critique the time gap between cars with regard to the throughput of the system. Low balling the emergency stopping criteria just doesn’t seem like a necessary step to take.
The 30 second gap would require an average decel g-load of about 1.2g. Aggressive to be sure, but not outside of available techniques and not outside of the bounds of human tolerance. Particularly if you are in a rear-facing seat to distribute the load and a few seconds are used to ramp to the necessary peak rate.
30 seconds at 1.2g might be OK for you, but probably not for your eighty-year-old granny. Nor will you be in a rear-facing seat, unless they plan to turn the seats around after the pod reaches peak speed.
Yeah, killing one or two passengers will be better than killing them all, but you can’t base your normal business operations on killing a few passengers when something goes wrong.
No, wait, I did that wrong. This is one of those cases where the critical parameter in the calculation changes. The gap between the cars is defined by a time, so it’s natural to do the decel calculations with time. But, that’s wrong. That gap time is just a means to define a distance traveled at some speed, and the deceleration that follows in an emergency stop is for that distance, the length of the gap–it doesn’t matter how long it takes, so long as the car stops in that distance. Further, the deceleration time will necessarily be greater than the car’s nominal travel time at speed over that distance.
The assumed 30 second gap between cars at 760 mph (1115 ft/sec) constant speed is 33,448 feet.
a = V^2/(2D), So 1115^2 /( 2* 33448) yields 18.58 ft/s^2 or 0.58g.
Nothing particularly outrageous about that, similar to skidding your car on wet concrete pavement. Granny and the baby need to be in their seats with the belt on, but that’s not the failing criteria for the program.
Crashex April 18, 2018 at 9:02 pm
Oh, very well spotted. I’d made that mistake as well, thanks for catching it.
So now, instead of it being equivalent to half a freeway lane of passengers, it’s equivalent to a whole freeway lane full of passengers … probably just as well, it’s hard to fit cars in half a lane anyhow …
And this, folks, is why I encourage people to not trust calculations until you do them yourself … and sometimes, not even then—I did it myself and it was wrong. As my beloved grandma used to say …
Kudos to you, Crashex …
w.
Extreme roller coasters accelerate 3 to 6 g. Formula 1 cars brake at 6 g deceleration
How can roller coasters have 6 g when it’s powered by gravity that’s only 1 g? It’s the centripetal force in tight curves and loops
Willis,
I’m curious what kind of control system would reliably and instantaneously recognize a possible problem and begin full deceleration of a capsule. Position and velocity monitoring and communications would have to be very fast and sophisticated. Whatever delay detection and communications involves must be added to stopping distances. False problem detection with resultant deceleration triggering could be nearly as bad as a real fault. False trigger of a single capsules braking system could be catastrophic. And on that subject, what would the linear forces on a working tube when the high deceleration brakes activate in all the capsules in its segment. Just saying… calculating capsule timing based upon simple braking deceleration and distance is far short of necessary system safety requirements.
Assuming reasonable section lengths between stations, will there be provisions for handling and offloading capsules stranded in transit? Three capsule capacity at a station might be a little low for evacuation purposes. I can’t help but imagine sitting in one of those stopped capsules out somewhere in the tube. I doubt I’d be soothed by overhead speakers playing soft music and voice announcements that the problem was being worked on. At least in on trains and subways, there are provisions for evacuating on foot.
… 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.