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Musk's Hyperloop (prattleat.us)
87 points by autotravis on Nov 19, 2012 | hide | past | web | favorite | 65 comments

It sounds like a Lofstrom loop http://en.wikipedia.org/wiki/Launch_loop

That was my leading theory, and "cross between a rail-gun and a Concorde" all but confirms it. Flight path like a Concorde, propulsion like a rail-gun. Exploit the natural vacuum above our heads without expensive tunnels.

Let's look at the attributes Elon has described publicly, and see how they compare to a launch loop:


* could be cheaper than CA high-speed rail? Check (no right-of-way).

* "theoretically fastest way" from A-B? Check.

* can't crash? Check (w/ well-designed rails).

* immune to weather? Check.

* twice as fast as a plane? Check.

* lower energy cost than a car? Check.

* self-powering with solar panels? Check.

* stores power w/o batteries? Check.


* requires aerodynamic expertise? Check.

* "ground-based Concorde – as fast as a Concorde, but on the ground"? Arguably. All weight is supported by the ground, and cars take a Concorde-like path.

* rails are not needed? BZZT!! However, he may be talking about the "right-of-way" aspect of rails here.


* leaves right when you arrive? Check (w/ individual pods).


* isn't a vac tunnel? Check.

Of all the ideas that have been kicked around, the launch loop seems to fit best. Elon would certainly have been exposed to the idea when brainstorming for SpaceX.

My only question for the past few weeks has been, "How do you build the thing?" It doesn't inertially support itself in the air until the rotor is spun up, and the rotor can only be spun up when it's fully constructed between the endpoints. Catch-22!

There are basically three ways to do it, each with their own challenges.

Build it in the air. You would need huge numbers of lifting balloons (presumably of zero-pressure solar Montgolfier design, ala ARCA), and the portions of the system in the troposphere would be incredibly susceptible to adverse weather while under construction. You would want to have the entire thing already built, then unreel it as fast as possible. Smart tethering would reduce this risk, and the whole thing would need emergency descent parachutes for operation anyway. This seems like the least unworkable scheme, imho.

Build it in the water. Ocean currents and tides are now your problem instead of wind. The requirement to survive the corrosive salt water environment puts additional constraints on material selection. Oh, and you have to shut down all boat traffic from LA to SF. And your base station either has to be mobile (to start out in the ocean) or you have to start with a big arc out from the coastline and "tip it up" vertically. Do the math on how big the rotor endpoints would be (given reasonable assumptions about bending magnets), and you quickly realize that building them in place is the only option.

Build it over land. This seems the most unworkable – all the risk of having it fall (or worse, lose containment), and now you have to build tall towers every few thousand feet and string a high-tension support cable between them. Imagine explaining to homeowners that the "rail" we're building above their house will have parts moving at 10 km/s inside before it lifts off. Ouch.

Over water seems rather reasonable considering what we can do with cable laying ships.

Whatever method is used to get it up in the air, it'll need to be safely reversible. Over water bringing it down is much easier. And you'll have to bring it down for repairs. Every five minutes it will do a full loop.. Iron is fairly ductile, but those stresses will add up. And wikipedia says the kinetic energy involved is close to a small nuclear bomb. Back of the envelope math suggests the iron cylinder would be very thin. It will wear out sooner or later.

My guess is that Musk's big breakthrough is for a cheap and reversible deployment system.

I'm double checking my numbers now (and reading the original papers) but the entire contraption might weight a lot less than we are implicitly assuming. Like, light enough that a single large plane/blimp could support the entire cable/sheath system. And a small fleet of planes could safely tow the cable through the sky. Or a fleet of blimps could support the entire cable while it was stopped for maintenance. (Both would need a large number of well trained pilots, it would make the skycrane maneuver look simple.)

edit: The original paper talks about a ribbon 5cm wide and 7.6mm thick weighing 15.6 Gg. I dropped a kilo in the back of the envelope calculations. So it would need at least 100 very large aircraft to hold up. Still feasible, but more than a little crazy.

Interesting. The linear density given is 7 kg/m, which if you wanted to lift to the tropopause (density 0.35 kg/m^3, temperature ~266 K) you would need a continuous 30 °C solar Molgolfier balloon 18 m^2 in section, or a 10 meter strip of of 15 µm HDPE. Not as bad as I thought. Still, it would be hard to roll it out before sunset.

Hydrogen is another possible lifting gas, with all its associated foibles. Obviously lifting bags would have to be isolated to prevent catastrophic failure, but you could get a lot more lift out of them.

This must take place in a La Niña year, when the jetstream is north. Reel out the track, drag it into place with two airships, join the parts and start 'er up. You could even name the airships Jupiter and Number 119. ;)

This simplified strategy that would avoid the need for aerial stations at both ends, intead using a gentle curve achieved by anchor cables and varying linear density. Acceleration would begin immediately upon departure, leaching energy from the rotor (generating eddy currents), then contributing it back by braking off the rail on the descending side.

Of course, maybe I'm just dreaming here…

When hyperloop was first mentioned I considered the criteria required and worked on a matching result. I came up with something that deviates from later info by nevertheless I came up with something that matched.

Working on the principle that the speeds and efficiency mentioned means it has to avoid the friction of travelling through a medium. Since he had said "not a vac tunnel" I set my mind considering how the problem could be solved without relying on a vacuum. I figured, 'why not move the medium as well?'. Making a tube train travelling in a fluid medium would be interesting. Make the inner surface of the tube a hydrophobic surface. Use solar power along the length of the tube to accelerate the liquid. The speed would increase until the energy lost through friction with the sides reached equilibrium of the solar acceleration. If you can reduce the surface friction sufficiently, extremely high speeds should be possible.

Comparing against the checklist you did, a Hydrophobic torus full of high speed liquid gets a fair number of hits. The same aspect applies of energy storage as kinetic. It's a better match for 'ground based' but The same ground based aspect means it would get in the way. Building the liquid filled thing would be much easier, possibly implementable at smaller scales initially.

Mostly I think this just goes to show the interesting ideas you can come up with when given a set of constraints and a goal. I seem to vaguely recall a Mike Abrash anecdote about VGA fifos that applies here too.

I think I'd be a bit disappointed if it is a Lofstrom loop(but that's what it likely is) unless there is some significant innovation extending the idea. It's just like a vac tunnel with cool inertial skyhooks.

10 km/sec. I'm still trying to wrap my head around that number. That's close to Mach 30, right?

How long would it take to safely accelerate to that speed?

The OP suggests (jokingly?) that driverless cars and Musk's Hyperloop are somehow in competition. I don't see that. Cars today are about transportation and cabin conveniences. Why can't the two be separated over time? Your "car" takes your cabin to the train that takes your cabin to the high-speed rail (Hyperloop?) that takes you from Atlanta to Kansas City. Perhaps you switch cabins based on price to transport... maybe you rented a bigger one for local travel, but don't want to pay a higher price for long range travel... lots of ifs, but to me, this and/or scenario seems more likely than driverless cars vs. Hyperloops.

> Here I was getting excited about Google's work on driverless cars.

OP here, only competing for my (unfortunately limited) excitement. There is definitely room in this world for both.

I believe that the Hyperloop is some sort of cannon. He has earlier revealed that it won't need a tube or tracks

Edit: Source to the no-tube from Elons twitter: "Will publish something on the Hyperloop in about four weeks. Will forgo patents on the idea and just open source it. Not a vac tunnel btw."

Are you sure he specifically said it wouldn't require any sort of tube? I was under the impression that Elon's Hyperloop would be a derivative of the concept of Evacuated Tube Transport - a capsule containing passengers launched inside a tube under vacuum (eliminating air resistance) and levitated using some sort of MagLev (eliminating rolling resistance).

The concept isn't entirely new but having someone with Musk's credibility and resources as a proponent may be the catalyst required to make it happen.

I distinctly recall seeing some PR material circling the internets a few months back from a consortium known as ET3.com The group claims to have been working on a similar project for the past decade.

Yeah, not a vac tube: https://twitter.com/elonmusk/status/224406502188916739

Think "cheap". The cheapest vacuum is right above us: at 35 km up there's only 1% the air pressure at the surface. It takes some energy to get there, but if you're on a rail you can recoup it on the way down.

I don´t think is a vacuum tube, it seems more like a tube with railgun like propulsion(elevated via towers, like power lines, even using the same power lines routes), but the guiding is maybe based on aerodinamics. There must be some kind of sound contention because he says it is supersonic.

He also said that it would be energetically independent so he may be using the external part of the tube to install solar cells, and the tube itself may be used for accumulation (capacitation maybe?).It doesn´t need to be air tight, just somehow sound insulated. The steering or "levitation" inside the tube may be obtained via shock waves (note his actual experience with high energy aerodinamics due to the development in spaceX).

He surely is taking advantage of the knowledge gained in the R&D of SpaceX, Tesla and Solar city.

With all the aerodynamic losses in such a system, it will use much more energy than a plane ride.

"it would cost you much less than an air ticket or car – much less than any other mode of transit – because the fundamental energy cost is so much lower" – https://www.youtube.com/watch?v=uegOUmgKB4E#t=46m03s

Oh, and he said elsewhere that you wouldn't have to wait, which implies individual cars. That means much more frontal area per person than a regular plane.

My money is on this: http://news.ycombinator.com/item?id=4806350

Well, by definition projectile used in any cannon will crash, so that's not it :)

Not if you attach a "grasshopper" to the projectile :)

And there goes my dream for a Futurama style Tube Transport System.

The cannon idea is really interesting. Musk's initiatives are all about reducing the cost of long term operation in order to disrupt the market. Most of the operational cost of air transportation is (I believe) in the take-off. If you eliminated the need for the aircraft itself to takeoff by projecting it with a rail-gun then this could theoretically reduce costs greatly. Essentially creating airline bullet gliders. Just a theory.

I would love it if this were true. I have been saying (only semi-tongue-in-cheek) for years that getting shot out of a cannon would be a great form of transportation, if only the bugs could get worked out (i.e., eliminate possibility of mid-air collisions). :-)

Forgoing patents on it is a bad idea if it means that a troll will immediately patent the idea after Musk releases it.

If only there were a GPL for patents...

Actually, the problem is that someone will immediately acquire patents on trivial upgrades and logically-related extensions of the idea. The publication of the idea itself would be prior art.

Right. So we'll all have to constructively publish as many related ideas as possible, as soon as possible :)

That's the spirit!

What about prior art?

The cynic in me is reminded of the Segway at this point. I'm not calling bullshit on this, but I'll wait to get excited when something is actually shown.

There is a segway-esque secrecy around it. However if there is one person I would give the benefit of the doubt, that person would be Elon Musk, and he said they'll open source the project.

The real question is - will you have to go through TSA first to get in it?

I'm sure people will find a way to lose my luggage.

Since there are no details, we can only speculate. There are only a few practical implementations. At the top of the list is an evacuated tube.

The linked article says it's desirable to do this without requiring a right-of-way or moving people out of their homes. So that puts the tube below ground level -- well below.

Let's say an evacuated tube, below ground level, in California, between San Francisco and Los Angeles. This really isn't going to work, because (all other considerations aside) the route crosses any number of known geological faults that are in constant relative motion -- some creep past each other, some wait and then periodically move all at once in an earthquake. You can't build a subsurface tube that crosses geological faults.

I don't think this is a practical idea. But it's a nice one in principle.

>At the top of the list is an evacuated tube.

Except for the small problem that Elon said it's not an evacuated tube: https://twitter.com/elonmusk/status/224406502188916739

Yes, I noticed since I wrote the original, but that might be smoke. It's not obvious how the system would work without some sort of dedicated pathway that remains the same day after day. The word "tube" leaps to mind. :)

This discussion may get you started: http://news.ycombinator.com/item?id=4806350

TL;DR Build a rail with a high-velocity rotor inside that inertially supports it above the atmosphere. Essentially it's a space fountain with two base stations instead of one.

So yes there's a pathway, but since it's not on the ground it requires no right-of-way.

I'm not so sure about the right-of-way issue, since we are talking about a permanent structure. The case law that weakened the old "Cuius est solum, eius est usque ad coelum et ad inferos" ("for whoever owns the soil, it is theirs all the way up to Heaven and down to Hell") rule, as far as I've seen, all involved aircraft passing over land. I'd not be surprised if a court considered that case law irrelevant when it comes to permanent structures overhanging someone's land.

Good question! I found a summary of the ruling:

>However, while the Court rejected the unlimited reach above and below the earth described in the common law doctrine, it also ruled that, "if the landowner is to have full enjoyment of the land, he must have exclusive control of the immediate reaches of the enveloping atmosphere." Without defining a specific limit, the Court stated that flights over the land could be considered a violation of the Takings Clause if they led to "a direct and immediate interference with the enjoyment and use of the land."

Would a hyperloop cause direct and immediate interference with the enjoyment and use of the land? It might if it failed!

> killing countless people daily

2.09% of deaths, according to http://en.wikipedia.org/wiki/List_of_causes_of_death_by_rate

Question: what would an Elon Musk of those even more common causes of death build?

For cardiovascular disease, how about a way to stop people stuffing their faces with greasy and fattening food?

So the Paleo Diet community (and Taubes/etc) would say that the greasy food is part of the solution (and that some perceptions of "fattening" food are wrong)

I am doing a low carb thing, and as far as my experience goes, I think they're right.

* Gene therapy to make unhealthy foods taste terrible

* Nanobots or symbiotic parasites to maintain the body [1]

[1] http://en.wikipedia.org/wiki/Parasites_Lost

A sexy, highly marketable e-cigarette.

That doesn't break very fast. My girlfriend loves e-cigarettes, but it's all fun until the endpoint (*-mizer, whatever they call it) burns out, which it does every week or three, and then there is a battery that tends to fail after around two to three months of usage. </anecdotal-evidence>

Agreed. It must be better than cigarettes in all ways: cost, convenience, aesthetics, reliability, experience, usability, availability, brand loyalty, etc. There are social factors too. Friends can't bum an e-cigarette. Proprietors may mistakenly enforce smoking bans. Bystanders may think vapor is second-hand smoke.

The solution will come with a combination of Apple-esque industrial design and Apple-esque advertising savvy. Basically, we need the iSmoke.

My father started smoking because people on building sites who smoked got smoke breaks, and people who didn't had to keep working.

If I had been of more sociable persuasion when I was in college, I might even have started smoking myself - a lot of conversations, camaraderie etc. and more occur outside pubs, where smokers are often relegated to in these days of smoking bans.

As far as I can tell (or so my girlfriend and others tell me), they're already better in most ways than normal ones - more cost-effective (though it can be vastly improved with improved reliability), more convenient, they have a big range of flavours to choose from, they get around smoking bans and, most importantly, they don't clog your lungs and don't make you stink. So it's already great, but the reliability issues are incredibly annoying. But the critical mass of popularity has not yet been achieved, so there's a need for this iSmoke you mention, with strong focus on advertising - so that you don't need to date an (non-smoking!) engineer to hear about e-cigarettes and why they're better.

> they're already better in most ways than normal ones - more cost-effective (though it can be vastly improved with improved reliability),... So it's already great, but the reliability issues are incredibly annoying.

She could also be talking about cars in the early days. Perhaps this is an indicator of untapped potential for disruption in this market?

e-cigs are already a big disrupter to the cigarette market. Until recently, these were completely detached from the tobacco companies. I think only in April of this year a tobacco company bought one of the manufacturers.

They are a massive improvement to burnable cigarettes and while the reliability of them is a pain it is improving.

Originally they all tried to look like cigarettes but that leads to compromises like small batteries. The newest models all look a lot less like "analog"s and have bigger batteries and better longevity.

What you say also has analogies with the early days of cars.

I suspect there is no hyper loop. I wouldn't put it past Elon to use his reputation to spur people to think big about these kinds of problems.

It's worked, too. The ideas people have had, just trying to "figure out" what the hyperloop might be, are very interesting and diverse.

I've never heard anything about Elon Musk that indicates he speaks lightly about things like this. He has an amazing track record and a habit of taking on huge problems. There is no reason to think that he's not working on a hyper loop.

>The ideas people have had, just trying to "figure out" what the hyperloop might be, are very interesting and diverse.

Got any links to such ideas? I would love to see what other people have come up with.

Would this possibly be using a railgun to initiate takeoff speed (reducing fuel a lot) and then some for a plane that then obtains very high speed in very high orbits to then be able to land and use existing airports.

This is only logical given the prospect to use a railgun type launcher to eliminate booster rockets or reduce fuel for space flight. So would marry in with other avenues of research and as such be less of a risk and Musk don't like risk.

This at least would fit the criteria, maybe with the initial speed a form of electric powered plane, maybe Musk and Dyson could get together and invent a good electric jet engine (yes probably be ion based but still).

In the past, it sounded like he really wanted to see someone work on the idea, but was not interested in doing it himself. Now it seems he's coming around to the idea. This is really exciting.

Elon Musk is Leonardo Da Vinci of the present times. More power to him.

" This is over 100 years after the first mass-produced automobile was sold, with the announcement of (another) successful nano-scale teleportation experiment just the other day."

So what? This is 40 years after the first Man walked on the Moon and we are still all living on Earth. It's been about 60 years we have discovered the double-helix structure of the DNA and we still have yet to see revolutions in medical practice coming from it. What is your point, exactly ? There are clear reasons why no huge technology leaps take place at once. Most innovation is progressive, iterative and it is very likely that you will not see a drastic change of technology within your lifetime.

Perhaps I am just much more impressed with the last 30 years than you. I'm not a point-by-point rebuttal man, but its very tempting. Try thinking about the massive changes if you don't limit radical progress to being in a straight line going the direction you want.

Cars were doing 100 Mph on the German autobahn in the 60's, they're not much quicker today and most drive a lot slower than that.

There is progress, but on the transportation front from a practical point of view the biggest one so far is the electric bicycle.

Fastest production car from the 60's that I can think of would do 171 mph (Lamborghini Miura). The fastest production car today will do damn close to 100 mph more than that (Bugatti Veyron Super Sport).

Certainly the top speed of either of those cars isn't practical, but the reason that the Veyron can go so much faster is that there have been massive improvements in automobile technology since the 60s, in just about every every way imaginable. Safety, efficiency, control, materials tech, aerodynamics, etc. That we still drive so slowly can be probably attributed to momentum in automotive laws and/or driver skill / lax license requirements. If we were willing to invest more in our roads and stop thinking of driving as a right instead of a privilege, we could be driving much faster today.

The biggest factor is reaction time.

Also, above 100 Mph or so the aerodynamics change substantially. There is a clear cut-off point above you are definitely in 'no mistakes' territory, even ignoring a bit of cross wind as you come out from under an overpass get get you slammed into the guardrail or driven off the road.

Add to that ice, snow, rain, night conditions, glare, low sun and so on and pretty soon the driver (automated or not) is not the limiting factor but physics and getting reliable sensor inputs is.

Anything over 140 will probably not be practical for mainstream deployment, even in Germany where there are lots of skilled drivers and it isn't rare to see an old lady do 150 Km/h there is a sharp drop-off above that point reserved for those the possession of more money than brains. It simply isn't practical from a fuel consumption and safety point of view and even the safest cars are death traps at speeds beyond that.

See 'crashedexotics.com' for the end result of that route.

Certainly when you get up into the sort of speeds things become very tricky and unpractical. The problem right now though isn't really that we aren't all driving at 100+, but that we still have all of those straight as an arrow 55/65mph roads criss-crossing fly-over country in the US. Those may have made sense at some point, but modern cars can easily do 100mph on those roads with no particularly unusual danger. Pretty much everywhere in this country speed limits are artificially low though. Most country/wooded area roads don't make any sense in cars with ABS or traction control; my limiting factor on most Pennsylvanian roads is the danger of deer, not road geometry or car capabilities.

I think with the spread of autonomous driving technology we'll be able to see even more proper, and reasonably safe, speed from cars.

I guess you are referring about the computing revolution? There are definitely impressive things about it but it has not significantly changed our lives yet. Only the communication parts and shopping, for the most. Institutions, behaviors and culture have not changed significantly yet, if not for a minority of the population. Do not take me wrong, I also think there is a tremendous potential for innovation and progress, my point is just that it takes time. I am not THAT impressed with the past 10-20 years at least where innovation has been very slow overall across all industries, in my opinion. I do not know about you, but I think the introduction of fossil fuels in the 19th and 20th century as well as the spread of electricity, radio and television were definitely MORE life-changing that what we experience nowadays.

I think you are missing the fact that the internet has allowed every human who can access it (less those under government filters) to have access to nearly the sum of all human knowledge. No, we don't precisely know what to do with this access just yet, but we have it. For instance, you can look up the intricacies of the 'Launch loop' in seconds and scan the contents of every academic paper relating to it in minutes. This immediacy of information is unprecedented in human history.

To say that only communication and shopping have been revolutionized in the past 20 years is grossly misinformed. Human interaction with each other, with ourselves, and with knowledge has been fundamentally changed for a very substantial portion of the population. No, it has not reached every corner of the globe, but neither has electricity, radio, or television.

My point is, it has not changed the world yet. Access to information is great but who cares? Do you see many people hanging in libraries instead of going drinking to the bar? No. Same at home: most people waste their evenings watching TV or on Facebook and do not spend it reading Wikipedia and getting more knowledgeable about everything. The problem has never been so much about access, but wanting to access the information. So it's like having a rocket ship when all you need is a bicycle to go where you need in everyday life. Not useful for many people.

And let me question your claims about knowledge being fundamentally changed. Kids still go to school. Still pass exams the same way as 50 years ago. Education has not changed at all, except for a pocket of people who follow coursera or other online systems. It's all very small and you are probably exaggerating the impact because you are aware of it and living in that particular tech-sphere. Not everyone read Hacker News, not everyone knows how to use computers, and most people who have computers do the same very basic things with them every single day. At least my claims are substantiated. Amazon has clearly changed shopping, and Skype/IM/email has drastically made communication cheap and led to calls being very affordable in almost every location in the world. For other things, change is not so visible and apparent.

> Access to information is great but who cares? Do you see many people hanging in libraries instead of going drinking to the bar? No.

Everyone. Because what changed is not only the amount of information, but also the immediacy of access to it. Those people going drinking to the bar quite likely found it on Google before going there for the first time. And those same people now Google up everything they want to know the moment they need it, including many practical things. "Normal" (non-tech) people, from my observation, tend to look up on-line many things in their life, for example gift ideas, travel & tourism information and practicalities ("how to do X").

You could also argue that it is the first time so many people are exposed to such a big amount of cultural work - including pirated movies, music, YouTube and Internet memes. People share common culture across the globe, and the Internet itself slowly starts to behave like a single brain.

Sounds like the Segway.


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