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I don't believe that an experimental tube is going to be somehow magically cheaper and easier to route and build than train tracks.

Do you really think the special interests that are making HSR so difficult and expensive would say, "Oh, do whatever you like with your tube."?

These are extremely important issues that advocates seem to be glossing over. Putting the guideway on pylons doesn't magically eliminate land issues, you will still have to deal with visual impacts, along with any number of anticipated and unanticipated problems.

Musk should do what the Germans did with the TR0x series of maglev vehicles, build a 10-20 mile test section someplace and demonstrate that is analysis is sound.

(perhaps more in the future--why wouldn't California design with this goal [350 km/h] in mind?)

There are a variety of reasons, but one important reason I have to deal with is that the speed of shear waves through soil is only on the order of a couple of hundred miles per hour. When a train exceeds the shear wave speed, ground-borne vibration waves "build up" in a manner similar to the shock wave created in air when a plane exceeds the speed of sound, causing a ground-borne vibration equivalent of a "sonic boom" that can cause problems for wayside structures. I believe the French have started to experience this with some of their higher-speed TGV experiments and we don't have a good way to handle this yet.

> When a train exceeds the shear wave speed, ground-borne vibration waves "build up" in a manner similar to the shock wave created in air when a plane exceeds the speed of sound...

Putting the railway or tubes on pylons would give you an opportunity to dampen or otherwise transform those vibrations wouldn't they?

Putting the railway or tubes on pylons would give you an opportunity to dampen or otherwise transform those vibrations wouldn't they?

Maybe, maybe not. Guideway supports (pylons) are typically founded into the bedrock which does reduce vibration somewhat, but the vertical motion of the pylon moving against the soil will still generate shear waves.

This is why a demonstration project would be useful.

I recall reading that the pylons had vertical and horizontal dampers to protect against earthquakes (among other minor natural changes), so wouldn't those dampers be able to cancel out the shear waves?

No. Well, I suppose you could design an active vibration system to (almost) completely cancel the vertical vibration motion, but know you're talking about a powered system in each pylon of incredible complexity.

Passive resilient systems could help with higher frequency vibration (above say 100 Hz or so, depending on the forces and weights involved), but for lower frequency vibration (especially below 20 Hz), the resilient elements would have to be so compliant that even a gentle breeze would create very high vibrations in the guideway itself, which would be incompatible with the speeds of the cars inside.

You could make the pylons so massive that the forces from the vehicles couldn't move it, but again you're talking about higher construction and material costs, as well as visual impacts.

Ah! Note that the pods are far lighter than trains, being more like a lightweight aircraft. This would reduce the effect considerably.

Vibration from trains is proportional to the unsprung weight of the vehicle (basically the axle, wheels and traction motors) rather than the vibration of the whole vehicle (which is isolated by the primary and secondary train suspensions). For a heavy rail transit vehicle (NYC transit, MBTA Red Line, CTA vehicle, etc), you're talking about 2,700 kg. I don't have numbers handy for HSR trainsets.

The air cushion isolates the entire vehicle... perhaps making the "unsprung" weight 0?

No. That would only be true if the vehicle was buoyant.

The plan uses an air bearing partly because an air bearing is exceptionally stiff. It's not like a hovercraft, with all that ability to squoosh up and down. So the unsprung weight might be the weight of the entire vehicle.

edit: though, mind you, the whole capsule also has mechanical suspension

> Musk should do what the Germans did with the TR0x series of maglev vehicles

Musk has already given more than enough for the world and done more than enough. Somebody should do it, but we should not expect him to do it.

We shouldn't expect him to demonstrate his idea?

He says he won't do it himself for a long time. He's busy with other things.

I think tesla motors releasing an affordable car would benefit the world a lot more than the hyperloop. But it's nice that he is presenting the idea so the world can do their own analysis and even implement it before he has the chance.

>>I think tesla motors releasing an affordable car would benefit the world a lot more than the hyperloop.

Specifically, an affordable Tesla car could benefit the entire world, whereas the Hyperloop would (at least initially) only benefit people living in LA and SF.

What are the benefits to the world market of an affordable Tesla compared to, say, a modernized version of the Volkswagen Lupo, or a plug-in Up! ?

They both benefit the world. Fact is, there is no modernized 3-Liter-Lupo, and I've heard no rumors that there ever will be (?). Until there is, Tesla will be the one who demonstrates what is possible.

Really specifically, an affordable Tesla would (at least initially) benefit only those who were able to buy an affordable Tesla given the still significant cost and Tesla production constraints.

They both have the potential to be hugely beneficial to the entire world. Although in Tesla's case it's more of a certainty... fortunately we can have both :-)

He noted (just today!) that he'll be working on a subscale demonstration of the technology.

Link?

http://www.theverge.com/2013/8/12/4615378/elon-musk-will-pro...

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Wow. I'm an Elon Musk fan too but this is a bit much. He didn't give anything to the world. He is a businessman-he gets paid very handsomely to do the things he does.

That is an absolutely disgusting attitude.

True innovators carry all of humanity on their backs, and give massively to all of humanity, present and future.

The fact that they get some monetary compensation doesn't entitle you to not be grateful and to not recognize their heroism.

It does not entitle you to imply, as you have, that they deserve the same level of praise as any person who is paid for any work whatsoever.

You are, by implication, equating Elon Musk to the teenager flipping burgers, or any other menial laboror.

That is moral treason.

Without innovators, we would all be dying in pestilence-ridden Stone Age villages. In my opinion, those who claim that innovators do not deserve the highest of possible praise _deserve_ that fate.

No wo(man) is an island.

Musk would have a hard time innovating if he had to build his own house, grow his own food, knit his own clothes, etc. etc...

We all rely on each other to provide our basic standards of living.

Without our basic needs being satisfied, we don't have a platform from which to focus on innovation.

Yes, innovation is great, but don't act like they are the entire backbone of humanity.

Elon Musk is probably at least millions of times more productive than the average human.

If you were to calculate the sum of gains and losses between Elon Musk and humanity, it would balance out that Elon Musk is overwhelmingly the creditor, and humanity is overwhelmingly the debtor.

As with the great-grandparent of this comment, your comment is a massive moral equivocation.

At very least, it is in society's best interest to socially reward people working on solving big problems instead of doing lucrative things that just exploit people.

> one important reason I have to deal with is that the speed of shear waves through soil is only on the order of a couple of hundred miles per hour.

Perhaps a stupid question, but the shock wave forms because the trains is moving continuously over the ground? So if you put the entire thing on stilts, there would be one wave formed at t0, x0 when the train reaches pylon 0 and the next wave would be at t1, x1 etc. So the interference pattern for the waves would look vastly different. ( This holds of course only for point like trains... )

Yes, rather than a line-source, you have multiple incoherent point sources, but those point sources are being excited along a line at a rate faster than the shear wave speed. So yes, it somewhat different, but also similar.

A test segment would go a long way to determining if/how much of a problem this might be in a hyperloop system.

The pod is basically flying. Although its weight of course is still ultimately borne by the pythons, perhaps it's mushed out and dampened in a way that reduces the ground-boom effect? But it sounds like one of the (many) bugs that must be worked out. spaceX wasn't all smooth sailing.

Can you elevate rail as easily? We're talking a lot more weight being carried by the pillars in that case. Plus you don't get the same natural banking off the walls he talks about, which is relevant at these speeds. While rail could bank, you better be going at the right speed when doing so, too slow and you just fall laterally off the tracks.

Can you elevate rail as easily?

The short answer is, "yes." I've ridden on it. The slightly longer answer (as another commenter has pointed out) is that it depends on the weight of the train versus the weight of the hyperloop. I see no fundamental reason to assume that the hyperloop is lighter than the train. It could be so, but then, we could make smaller and lighter trains, too (light rail).

Plus you don't get the same natural banking off the walls he talks about, which is relevant at these speeds. While rail could bank, you better be going at the right speed when doing so, too slow and you just fall laterally off the tracks.

This is a problem even when you are at grade. The solution is known: tilt-trains. The track is banked such that the train will not fall over if it has to stop on the curve. The passenger cabin then tilts with respect to the wheels so that it always feels like the floor is "down" regardless of the speed that the train goes around the curve. The radius of curve sets the maximum speed the train can travel around it.

"I see no fundamental reason to assume that the hyperloop is lighter than the train."

Did you actually read the PDF?

It doesn't carry its motor with it. That's a pretty big reason. Nor does it need the heavy-duty (and heavy!) trucks of a standard rail car.

A bigger factor is that the efficiency of a train depends on having all the cars connected to each other. With the hyperloop, the pods are spaced out, so there's no need for the structure to bear the load of a bunch of them at once.

Turn down the nastiness. It's totally non-obvious that this isn't overshadowed by the weight of the tube. And it does carry a motor with it, just not one that's responsible for initial acceleration or for large air resistances.

Sorry if you perceived that as "nasty".

The motor that it carries with it is about 146 horsepower. That's less than a Kawasaki Ninja street bike.

The General Electric E60 locomotives currently in use on Amtrak crank out 6,250 hp (4,660 kW) and weigh 423,000 lb (192,000 kilograms).

The weight of the tube doesn't really enter into it.

The weight of a 10' diameter steel tube with 1" wall thickness is 125,000 lbf per 100 feet. Note that does not include the reinforcing braces, that is just the plate. The actual weight could be easily 2-4x greater. It also doesn't include the weight of the solar array.

My bet is that it's not significantly different to compare a light rail (subway-like) system to a hyperloop in terms of weight.

The weight of the track ballast alone is more than that. Gravel is about 100 pounds per cubic foot, and you need about 12 cubic feet of ballast per foot of track, or 127,500 pounds.

Then you get to add the rails and ties (or concrete sleepers), plus the vastly more heavy rolling stock.

The reason I said that the weight of the tube doesn't enter into it is because the tube isn't moving. The only thing that matters in terms of energy use is the rolling stock.

The weight of the track ballast alone is more than that.

? You don't need to use ballast & tie track on elevated structure, in fact it's rare to do so on modern rail structures.

Flippant comments like "Did you actually read the PDF?" are exactly the kind of needless small escalations that destroys the tenor of commentary at HN. Any time you write that, you could be writing "It's discussed on page XX". If the comment doesn't deserve a cordial response, then just downvote and move along.

He responded to your points about the linked article. You went back to discussing why his language was out of line. Now you're destroying the tenor of commentary. Just append the etiquette suggestion to your previous post.

...now I'm contributing to this thread -- shoot!

You can't edit a comment that's more than an hour or so old. Reasonable people can have disagreement about the ground rules for online discussions, and it's helpful to get everyone in the same page in a constructive way.

You can't just make lighter trains; heavy rail is heavy because it has high capacity. These vehicles can be much lower-capacity per vehicle because the speed is very high, which means you get equivalent throughput even with much smaller per-vehicle capacity. It's just like how you can get the same amount of water through a high-pressure, low-diameter pipe as through a low-pressure, high-diameter pipe.

So yes, you could make the rail lighter, but in order to match the proposed passenger throughput, it would have to go 700mph. Good luck with that.

I would be very surprised if the numbers really work out the way you claim: that the weight for carrying a passanger is similar for trains and a tube, and that the weight advantage of a tube comes essentially from 3x speed allowing for a one third the linear density of passengers. Do you have a cite?

No, this is just back-of-the envelope, admittedly. But the three factors that determine how many people you can move past a given point per unit of time are the frequency of the vehicles, the capacity of the vehicles, and the speed of the vehicles, so if you want to match the throughput of the proposed Hyperloop, but with rail traveling at 164mph, you have to either make the vehicles more frequent or higher-capacity, or both. I would expect rail to be much less frequent, at least if typical rail conventions are followed, meaning you'd need much higher-capacity vehicles, combined with the engines to bring them up to speed (which move along with the train). It doesn't take that much weight to get past what you could reasonably support on a pylon in a median... there's a reason inter-city rail isn't built this way.

> the three factors that determine how many people you can move past a given point per unit of time are the frequency of the vehicles, the capacity of the vehicles, and the speed of the vehicles

Why is speed relevant?

Because it's per unit of time. The faster you go, the higher throughput you'll have.

The frequency already accounts for the time component.

(People/Car)*(Car/Hour) = (People/Hour) = Throughput

At a constant frequency and higher speeds, you will simply have less trains on the track at the same time.

Yes, I guess you're right, but the maximum frequency is bounded by vehicle length and speed (you can't have a vehicle pass every thirty seconds if it takes more than thirty seconds for a single vehicle to pass a given point).

The longest TGV and Shinkansen consists are around 400 m, so they pass a given point in 30 seconds at about 50 km/h (30 mph). Of course there's spacing for safety and so on, but 50 km/h is so low that it's really a factor in practice unless you also have non-HSR traffic on the line.

A bigger factor in practical capacity is loading and offloading people and switching near termini.

> But the three factors that determine how many people you can move past a given point per unit of time are the frequency of the vehicles, the capacity of the vehicles, and the speed of the vehicles

As a matter of fact, only the frequency and the capacity matter. Speed matters to passengers but not to the amount of people you can move.

The hyperloop as proposed actually has fairly low throughput; conventional rail systems, particularly of inter-metro variety where high throughput is most important, best it easily. 28 passengers per capsule at a capsule every 30 seconds makes 3360 pph during rush hours. RER line A averages 30000 passengers per hour over the entire year, with rush hour capacity being much higher.

And if someone would like a long-distance example, at its busiest the line between Tokyo and Osaka sees up to thirteen trains per hour each capable of carrying around 1300 people.

The hyperloop passenger capsule is estimated at 15,000 kg, while a TGV weighs 400,000 kg.

[1] https://en.wikipedia.org/wiki/TGV

Edit: I had the wrong numbers before, thanks to Shiffern for the correction.

The actual number for the hyperloop capsule is 15,000 - 26,000 kg. Still much less than the TGV, obviously.

The tube is not nearly as wide or heavy as a traditional train, so I don't know that it's fair to say that you can just as easily put a train up on pylons as you could this tube.

It's interesting to think about, but also there are probably much higher costs associated with a completely untested system like this than estimated. I wouldn't be surprised if this system, if it actually worked at all, ended up being more expensive than a HSR proposal through California that actually made sense.

But why make it a traditional train? Just build a lightweight train if it gets you all of the hyperloop's cost advantages without the additional costs and complexity of a tube?

On trains the cars have to be connected to each other. The structure has to bear the load of all of them at once. Not the case with hyperloop.

It's totally implausible that that's the primary factor.

Why? You've given no explanation.

Nor has jim-greer.

The reason we have to run long, heavy trains is it's unsafe to run two passenger capsules at 300kph a minute apart. I find it hard to believe regulations will permit that even when they're in a tube.

Traditional trains have wheels and engines, which are quite heavy. And with a traditional train you're trying to minimize losses due to air resistance, which is not an issue in a low pressure tunnel.

Above a certain speed wheels present huge issues, which means you need to change your drive mechanism and suspension mechanism.

Also, drag is a huge killer of efficiency and hence overall economics. Even at 500kph the drag on a train at sea level is enormous. At 1000kph it's 4 times bigger again, and you've got the sound barrier to worry about. Trying to do the same with multiple small capacity trains is astronomically worse. So, better to have reduced drag... and by now you've basically got the hyperloop.

My bet is that Elon could build the Hyperloop closer to budget than the state of California could build a traditional train. Leadership matters.

It's not clear to me that he is interested in being the one to build it. I think he wants somebody else to.

I'm sure he'd prefer someone else do it but then again he might have preferred that someone else would have conceived of and designed it -- or something similar. There's a chance, as with the leadership of Tesla, that no one else with the capability (or position/reputation) to execute will be found, and I'd be surprised if he were not heavily involved in seeing it through.

From what I understand he still sort of wants out of Tesla in the long term. SpaceX is his baby and he's only running Tesla because he feels that he has to. I suspect he isn't receptive to spreading himself out over a third project (he apparently doesn't do much work himself for SolarCity).

My bet is that people in the middle who don't get any benefit from it will prove just as obsrtuctive as they are towards any other large scale infrastructure project.

>>However, the answer, to my mind, is to do it properly rather than propose a wild experiment with hand-wavy arguments as to why it would be politically easier to do. Do you really think the special interests that are making HSR so difficult and expensive would say, "Oh, do whatever you like with your tube."?

Even when done properly, HSR has most of the limitations stated by Musk. And while it is possible that special interest groups would make the construction of Hyperloop more difficult than it is, I don't think that's an argument against giving it a try.

Steel tube is inherently far more structurally stable than rail. This should make elevation easier/cheaper.

Edit: apparently, the weight of the train/car/etc matters more.

> For example, you can put railway tracks up on pylons, too, with very little impact on the ground.

Out of curiosity (I'm not at all familiar with HSR)—does the Hyperloop plan increase the distance between columns or the cost to build the columns (due to materials or any other factors)?

The basic issue the hyperloop overcomes is the energy waste in train transportation, especially at high speeds. This is primarily about aerodynamics, and secondarily about carrying with you the propulsion system. Third, it overcomes the "chunkiness" of the rail system, where passangers needs to be assembled and grouped into train-sized lots for transportation, rather than being able to depart continuously. You get superior energy economics, speed and convenience. I cannot see how that would be disappointing.