21 ms·

On Hyperloop

• Gravityloss 13y ago
  Valid concerns, but why does he have to write like to a five year old?
  • lewispollard 13y ago
    For people like me who have no knowledge of non-software engineering ;)
  • cowsandmilk 13y ago
    you may feel like it is written "like to a five year old", but this style is very similar to what I see every day in communication between PhDs.
• zeteo 13y ago
  I'm very ambivalent about this article. On the one hand, it's the first serious criticism of Hyperloop that I've seen on HN. The author has dived to the deepest levels of one section of the proposal, understood them, and found a serious problem. On the other hand, I'm disappointed with his attitude. It's the equivalent of "This open source project is very ambitious and planned in good detail. I'm an expert on memory management so I looked at the code there and had a good laugh. This will never scale to production levels because of X, Y and Z. You can probably fix it with sufficient development time. But I won't tell you how, because I think a problem with such important code shows you're dishonest and stupid."
  • mrt0mat0 13y ago
    I agree with your assessment. I did appreciate the feedback he gave on Musk's idea, but I think he went about it all wrong. i think he should have proposed the problems as flaws to Musk's work and let someone in the spacex or just the growing hyperloop community come up with a solution to perfect the concept, not condemn it. no idea pops out of the head of someone perfected. that's naive. Now if anyone does respond to his points based on this article, they'll probably attack back with a equally negative tone, ruining the full concept of what the hyperloop is.
  • parhamn 13y ago
    > The author has dived to the deepest levels of one section of the proposal > This open source project is very ambitious and planned in good detail Through reading the article I think his opinion is far from that. The vibe I got was along the lines of "this is so bad that a high school physics student knowing the thermal expansion laws, and a sophomore college student who knows how cantilever beams work could tell you this project is fundamentally fishy". Considering this perhaps his snarky comments are warranted. Musk dropped this project as a critical piece against current plans for this infrastructure and on a very basic level it comes off as 'snake oil'. Expecting a high level of polish doesn't seem too much of a requirement to me.
    • vidarh 13y ago
      The problem with taking that tone is that it is by no means obvious that the article poster actually understood the part of the proposal he is criticising. That makes it very hard to take his criticism seriously, and doubly so when the tone is so condescending.
      • nickff 13y ago
        I have seen less criticism from the engineering community than from other groups, thought this may be due to a general reluctance of engineers to go on the record unless obligated.
    • austinz 13y ago
      This. On one hand, we hate credentialism and criticize those who arrogantly wave their diplomas around as a substitute for making good arguments. On the other hand, we're enamored enough with SpaceX and Tesla to give Musk the benefit of the doubt, even though: - The Hyperloop is a very different type of engineering compared to anything Musk and his engineers have done before (competency in one field does not guarantee competency in a very different field), - The analysis has some serious issues. A trivial example: the thermal expansion issue in this blog post has been brought up in user discussion several times in previously posted Hyperloop articles on HN, and nobody was able to post a good response or justification.
  • 6d0debc071 13y ago
    I suspect the objection was more that it had such basic flaws that he takes it to have been designed to trick the naive more than as a serious project. On that assumption, investing his time in it would be a waste.
  • npalli 13y ago
    No, his attitude is entirely appropriate. Learn your basics before you try to reinvent stuff. As Alan Kay keeps reminding us, the programming community doesn't really learn anything that is done in the past and is doomed to keep reinventing stuff or working on things that have been shown not to work. For example, if you study physics you are not going to go far if you show up to class and start dropping apples and say this shows some magic force is operating. Learn the basics of engineering first then try to change things. Otherwise you will just waste everybodys time. As for your programming example, the more appropriate case would be if someone showed up with a revolutionary proposal to allocate memory for a GC, you see the source code and there is a big array structure defined locally "char memory[10000000]". There is far more things wrong here than trying to figure out ways to scale this in production.
    • arethuza 13y ago
      "Learn the basics of engineering first then try to change things. Otherwise you will just waste everybodys time." So what about SpaceX and Tesla? To me those indicate that Musk must be a pretty decent engineer, and perhaps more importantly, must be excellent at leading real hardcore engineers in complex domains.
      • simias 13y ago
        What's your point? Because you're good at something doesn't mean you're good at everything. That being said, I agree that the tone of the article is a bit too harsh for my taste, but then again Linux Torvalds is revered here for this kind of tone. It's always good to think outside of the box and bring new ideas to the table. Even if they're dead ends, they keep the brains working, if only to form counter proposals. N.B.: american friends, pretty please, consider including metric values alongside imperial, I have no idea what 1030feet means. Fortunately we have google for unit conversion...
        • Dylan16807 13y ago
          A foot is about a third of meter, and a mile is about a kilometer and a half. That's all you really need to remember. Heck, in a discussion like this you could pretend a mile equals a kilometer and be fine. Oh, and a pound is about half a kilogram. I won't expect you to remember all the stupid volume units, but those three tiny conversions are worth knowing.
  • deleted 13y ago
    [deleted]
  • tptacek 13y ago
    This article is also a serious criticism of the Hyperloop, and makes a largely non-overlapping set of points; it has also been on HN: http://pedestrianobservations.wordpress.com/2013/08/13/loopy-ideas-are-fine-if-youre-an-entrepreneur/ http://pedestrianobservations.wordpress.com/2013/08/13/loopy... From this article: * Redefining SF and LA to Hayward and Sylmar allows the Musk proposal to make an extremely unfair trip time comparison, and, moreover, Musk's proposal can't easily do a "real" SF and LA because unlike HSR the Hyperloop can't repurpose infrastructure. * At the speeds and course plotting Musk alludes to, the Hyperloop will make its passengers very motion sick. * The costs Musk projects are unrealistic; for instance, if the Hyperloop can really construct elevated tracks at 1/10th the per-mile cost of existing viaducts, that cost improvement alone would be an equally important advance. Similar problems exist for the tunneling cost projections, and are exacerbated by the fact that a realistic course for the Hyperloop would probably require even more tunneling than projected. There's a good MeFi thread on this too.
  • kenrikm 13y ago
    What strikes me is that author of the article did not take into account key data about the proposed Hyperloop system which in itself is lacking data. I wonder if this article would ever have been written if the author had talked to any of the engineers that had worked on the proposal for even a few minutes to ask how they expected to work around some of the issues he's attempting to hi-light. For example the fact that it's "mostly evacuated" or that it's covered in solar panels which have been shown to keep structures cooler (http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1094 http://www.jacobsschool.ucsd.edu/news/news_releases/release....) taking many small details into account could have drastic effects on his "1030 feet" of expansion estimate. I'm sorry but this article smells of intellectual laziness just for the sake of having a counter opinion* I'm looking for honest criticism and in my opinion this is not it. *I'm not an engineer however I did stay at a holiday inn express last night.
  • Tloewald 13y ago
    If you start from the assumption that Musk is awesome then you probably won't like the article. If you read the article you will likely come to the conclusion that Hyperloop is half-baked and the proposal includes "detail" that is little more than flim-flam. My problem with Hyperloop is that it's trying to solve the wrong problem. In less than twenty years the transportation landscape is going to be very different. The younger generation is not wedded to cars the way the last several generations were, and new transportation methods, such as self-driving vehicles are emerging. Assuming any kind of sane public policy, energy is going to get more expensive, speed of travel is going to become less of a concern, and connectivity will go through the roof. Why will I care about a fast tube for going from LA to SF? Whay's so great about fast? An inconvenient method for traveling really fast that doesn't let me chat or work might be far less desireable than a convenient method that is slow but doesn't disrupt my day.
  • etler 13y ago
    I kinda felt that the hyperloop proposal was made in a know it all fashion, like "oh look how easy it is, why hasn't this been done yet?", so I feel like this response is appropriate to that tone.
• jessaustin 13y ago
  I understand the tone is troubling to us mere mortals, but surely a Titan of Awesome like Elon Musk can ignore the tone and just forward these concerns to his civil and structural engineers?
• phreeza 13y ago
  It is nice to see some criticism on HN. The tone of the post is a bit off but apart from that the points made should be considered. Personally I don't see the problem with a 150m slippage tolerance, but I think it might have to come before the fixed base stations. basically I could imagine the tubes transitioning into a slightly larger enclosing tube which is able fixed to the base station. surely there are other alternatives and unlike the OP I think the quotes from the report sound to me as if Musk hasn't thought of this at all. As for the FEM analysis I would tend to agree that the value does not go far beyond being a pretty picture in its current form.
  • thedufer 13y ago
    The problem with a 150m slippage tolerance is that it means the horizontal dampers on the pylons near the end have to deal with movements of up to 150m, which is significantly larger than the distance between pylons. Maybe that's feasible (seems unlikely, but I'm no engineer), but it's the kind of point that ought to be addressed explicitly.
    • phreeza 13y ago
      I think the proposal says explicitly there are no longitudinal dampers on the pylons, only horizontal transverse, but thermal expansion shouldn't be a problem for those.
    • saalweachter 13y ago
      Is that really the only problem? It seems to me that expecting hundreds of miles of pipe to be pushed back and forth hundreds of feet (albeit presumably slowly) puts a heck of a lot of stress on the self-same pipe. How is this that much different from building a side-ways space elevator? Even if it's easier to push sideways than up, it still adds up to quite a bit over hundreds of miles.
• mnml_ 13y ago
  Why so angry ?
• delinka 13y ago
  Someone correct my thinking: you don't have to add up all the expansions because you don't butt each pipe against the next. You leave that 1.5" gap, you build the gap ring out of airtight handwavium, and the tube sections don't push each other around. Right? This is how I read Musk's original proposal.
  • clarkmoody 13y ago
    I believe you're correct. May I add that the air bearings on each capsule will be lined with an alloy of anti-handwavium to achieve the desired fly-height above said airtight fittings.
  • phreeza 13y ago
    Handwavium just made my day. Thanks for that.
  • dspeyer 13y ago
    Airtight handwavium that meets the other specs may be hard to come by. I can't think of a precedent. And the original design called for all the space at the ends to avoid needing that (which doesn't work).
  • nether 13y ago
    You use expansion joints like these: https://en.wikipedia.org/wiki/File:Flanged_Rubber_Bellows.jpg https://en.wikipedia.org/wiki/File:Flanged_Rubber_Bellows.jp... They're made of rubber, fiberglass and other flexible but strong materials. I don't know how well they'd handle the vacuum stresses but I don't think it'd be too extreme.
    • ars 13y ago
      That won't work because the capsule has to ride on the pipe wall. Any bump will destroy the capsule.
  • 6ren 13y ago
    I think there is an inconsistency in the proposal, because he clearly mentioned cumulative expansion (page 5 of the pdf https://docs.google.com/viewer?url=http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf https://docs.google.com/viewer?url=http://www.spacex.com/sit...): A telescoping tube, similar to the boxy ones used to access airplanes at airports would be needed at the end stations to address the cumulative length change of the tube. If you're absorbing all the changes in length at the pylons, you don't need to absorb cumulative changes. Another reading is that the welded joints don't need to coincide with the pylons - that's just how it was constructed, not how it's supported. The tube ends up being continuous, with nothing special about the part of resting on the pylons, and move freely on rollers or similar. However, this reading also doesn't work, because he says of the dampers (also page 5): These would absorb the small length changes between pylons due to thermal changes... So, there's an inconsistency. But it doesn't seem like a big one to me, and not hard to overcome. And finding these bugs is one of the intended benefits of open-sourcing it. I haven't looked into the second finite analysis one, but though I looked for material consequences, it seems to be mainly a criticism of presentation. It amuses me that after spending his talent, time and money (he mentions at the start that he's paying for his blog) helping Musk's proposal, this fellow vents: I wouldn’t put my money, time, or talent in the hands of someone who takes me for a fool. Musk caught him monologuing.
• Symmetry 13y ago
  The proposal was badly short on details here, but I think the author is misunderstanding what is actually proposed. The special slip joints at the stations have to be traversed at low speed because you're going from one tube to another tube of a different size, having the tube slide back and forth along the pylons might be hard engineering but I don't see any reason it should effect the vehicle in the tube. Also, there's no reason to think that the pretty pictures in the public description are all the work they've done. I do think that Musk is badly underestimating how much this is going to cost. He's also being unfair by comparing his proposal to the legislative sausage high speed rail that California is getting rather than the best sorts of high speed rail you can find in France or Japan. But he isn't stupid.
  • vidarh 13y ago
    It's pretty clear even from the quoted portions that what you describe is what Musk proposed, coupled with dampers per pylon to control smaller movements.
• wodow 13y ago
  Knocked offline? http://www.downforeveryoneorjustme.com/http://www.leancrew.com/ http://www.downforeveryoneorjustme.com/http://www.leancrew.c...
  • wodow 13y ago
    Text-only Google cache has it: http://webcache.googleusercontent.com/search?q=cache:http://www.leancrew.com/all-this/2013/08/hyperloop/&strip=1 http://webcache.googleusercontent.com/search?q=cache:http://...
  • masnick 13y ago
    Yep. I was able to read it by manually adding the post's URL to http://instapaper.com http://instapaper.com and then looking at the text version.
• nicholassmith 13y ago
  I don't think we need to worry about the tone upsetting Musk, he'll either respond with vitriol or not care. I'm not sharp enough with physics to understand how much of it is accurate but Dr. Drang certainly seems to have nailed it down pretty quickly, but Musk does have a team of aerospace engineers he can forward these concerns to and see if they go "Well, you just jiggle that over there, and use that material, and change that and done".
• terryjsmith 13y ago
  I'm disappointed with the tone here; not in a "you should be nicer" kind of way, but because he seems to assume that Musk is acting insultingly in his proposal. This seems to me to be the way all startup ideas start: there's a hypothesis about X, so far I've found documentation to support that it is likely feasible to do (there are no immediate show stoppers), here's why, and so therefore I'll go off and build it and deal with things as they come up. I imagine this is how Musk works and that this is how SpaceX and Tesla started. The only difference is that this time Musk can't take it the rest of the way so he wants the community to take over the next phase if there's ample interest. This article reads to me as coming from someone who wouldn't take on this endeavour themselves, and that's perfectly fine, but he instead comes across as entirely destructive, condescending and insulted (somehow?) when he may very well be able to contribute something.
  • jfb 13y ago
    You don't have to get into thermal expansion and FEA to know that the Hyperloop proposal is back-of-the-napkin quality. As to why Musk did this -- dropped this hand-wavy shell of a proposal -- I don't know.
    • jhuckestein 13y ago
      I see only benefits to releasing something like this proposal. Even if absolutely nothing comes of it, we all learned some interesting Physics, Musk learned what happens when you publish your unfinished proposals, others may start thinking about the problem and come up with a different solution and finally, the cynics can point out how bad the idea was to begin with. Of course the cynics won't realize that working on these ideas and in this case even publishing the work are the reason that Elon Musk runs Tesla and SpaceX and they don't.
      • jfb 13y ago
        Yeah, I don't want to worry about motivation; the proposal itself is prima facie unserious. Perhaps Musk was just tired of being asked about it all the time. Perhaps he has a nefarious motive. Ultimately, I don't know or care.
• jblow 13y ago
  Any time one is trying to have a serious argument, one must do it from the Principle of Charity: http://en.wikipedia.org/wiki/Principle_of_charity http://en.wikipedia.org/wiki/Principle_of_charity This article doesn't even come close. Elon Musk is in charge of the design of rockets that have successfully delivered payloads to the ISS. It is just basic competence of a reasoning mind to presume Elon knows some things about thermal expansion (rockets get very hot!). So someone who is trying to have a reasonable argument would say, okay, he understands this issue, so I wonder what the answer is and why he doesn't think it is a big enough deal to go into detail on this point. Or perhaps I misunderstand something about the design (always a reasonable assumption!) This article is about as far in bearing from that as can be. I don't find it to be worth reading.
  • kybernetikos 13y ago
    My understanding of his reasoning is that he does credit Musk with knowing things about thermal expansion, and it's precisely that combined with the hand-wavy treatment of it in the proposal that makes him believe that the whole thing is likely to be snake oil. He's not really trying to have a reasonable argument, he's describing his thought processes around whether this is a project that is worth him getting involved in. There are a lot of bad ideas out there, and geniuses (if that is what Musk is) are no stranger to them (c.f. Einstein's wing design). It's perfectly reasonable when faced with a huge number of proposals that take a significant amount of effort each to make an initial determination based on surface details. Sure you'll have some false negatives, but you'll have a bit more time to address the ones that really have a chance of going somewhere.
    • nobodysfool 13y ago
      "Snake oil" is a term to be used when describing someone selling you something you don't need, and knows it doesn't work. It claims that it will fix a problem you have, but in the end the result is to part you from your money. This is not "Snake Oil". This is a design, and one that is open. Elon is not asking for money for the idea, he's wanting engineers to help design this thing and have an open discussion about it.
• taylorbuley 13y ago
  > In short, Silicon Valley has killed major innovation. Whether I agree with this statement or not, it to me sounds like postmodernism. A technological extension to Baudrillard's "death of the real": To wit, we present modest technological change as "innovation," thus stifling actual innovation through a redefinition of what is actually rather status quo.
• dmak 13y ago
  I appreciate the time he took to write this, but I cannot say the same about his tone.
• ash 13y ago
  Drang seems to think that Musk wants dampers (inside pillars) to handle large thermal expansion: > Eventually, the dampers in the pillars won’t be able to handle the movement because it’ll be greater than the pillar width. Eventually, the movement will be greater even than the distance between the pillars. But the tube is "not rigidly fixed" to pylons. It slips past pylons during expansion or contraction: > By building a system on pylons, where the tube is not rigidly fixed at any point, you can dramatically mitigate Earthquake risk and avoid the need for expansion joints. In fact, the author quotes the above in the beginning of his article, but then assumes exactly the opposite.
  • anologwintermut 13y ago
    I believe fixed and rigidly fixed have very different meanings in this context. Your suggesting that the tube floats on the pylon(e.g on rollers). The hyperloop paper suggests that it's attached with dampers that are, for lack of a better term, elastic.
    • ash 13y ago
      I disagree. I think "fixed" means the tube attached to the pillar to prevent it from jumping out of it. See rings in figure 3 (page 11): http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201...
      • anologwintermut 13y ago
        Given that the proposal describes dampers used to absorb change, I think this is wrong. By building a system on pylons, where the tube is not rigidly fixed at any point, you can dramatically mitigateEarthquake risk and avoid the need for expansion joints. Tucked away inside each pylon, you could place two adjustable lateral (XY) dampers and one vertical (Z) damper. These would absorb the small length changes between pylons due to thermal changes, as well as long form subtle height changes (see page 11)
• ethagknight 13y ago
  A bit ironic to politely decline helping with the Hyperloop only after criticizing the Hyperloop. Acting as a critic helps Musk in his noble quest. I have enjoyed the Hyperloop discussion as a thought experiment, and I appreciate that Musk is willing to throw around crazy ideas that challenge conventional thinking. Regarding thermal expansion, the change in length must be dissipated through the curves and changes in vertical alignment. The hyperloop is mostly straight, not perfectly. Oil and gas pipelines are almost perfectly straight, thus needing an expansion bend. The Hyperloop changes bearing frequently. Being mostly straight is a major item to overlook, as any pylon near any change in direction will have to deal with thermal expansion, not the end tubes. A 20 mile arc with a 20 mile radius will absorb a significant change in tube length with only modest pylon deflection. Musk's pylons could handle the strain with smart structural engineering. At a glance, I would design the pylons to pivot on a hinge portion with pretensioned steel and (viscous fluid) dampers to control vibration, letting the tubes push the pylons to modestly reduce or increase the curve radii. The major difference in Musk's design is that the tube would need to be periodically anchored in various dimensions to discourage the end-station movement and force the tubes to use the pylons' flex rather than snaking the whole length of tube.
• acqq 13y ago
  For those who missed other criticisms, see also: Musk's Hyperloop math doesn't add up https://news.ycombinator.com/item?id=6232573 https://news.ycombinator.com/item?id=6232573 Musk's proposal won't actually get riders to the downtowns of Los Angeles or San Francisco. It can only carry around 10% of the capacity of the California High-Speed Rail. Additionally, it will bypass other population centers, like Bakersfield, Fresno, and San Jose. Building a truly workable Hyperloop, if it's feasible at all, will be significantly more expensive than Musk claims. It might even be more expensive than the California HSR project. And Musk's proposal leaves a lot of questions unanswered. And: Loopy Ideas Are Fine, If You’re an Entrepreneur http://pedestrianobservations.wordpress.com/2013/08/13/loopy-ideas-are-fine-if-youre-an-entrepreneur/ http://pedestrianobservations.wordpress.com/2013/08/13/loopy... The proposed relationship between curve radius and speed in the Hyperloop standards is for a lateral acceleration much greater than 4.9 m/s^2 in the horizontal plane: 480 km/h at 1,600 meters is 11.1 m/s^2. This only drops to 5 m/s^2 after perfectly canting the track, converting the downward 9.8 m/s^2 gravity and the sideways acceleration into a single 14.8 m/s^2 acceleration vector downward in the plane of the capsule floor, or 5 m/s^2 more than passengers are used to. This is worse than sideways acceleration: track standards for vertical acceleration are tighter than for horizontal acceleration, about 0.5-0.67 m/s^2, one tenth to one seventh what Musk wants to subject his passengers to. It’s not transportation; it’s a barf ride. The barf ride that is as expensive as California HSR and takes as long door-to-door is also very low-capacity.(...) The proposed headway is 30 seconds, for 3,360 passengers per direction per hour. (...) HSR can do 12,000 passengers per direction per hour: 12 trains per hour is possible (...) But even 30 seconds appears well beyond the limit of emergency braking. And also: Hyperloop proposal: Bad joke or attempt to sabotage California HSR project? http://stopandmove.blogspot.fr/2013/08/hyperloop-proposal-bad-joke-or-attempt.html http://stopandmove.blogspot.fr/2013/08/hyperloop-proposal-ba... High Speed Rail between downtown LA and downtown SF: 2 hours, 28 minutes Hyperloop trip between downtown LA and downtown SF: 1 hour from LA to Sylmar via Metrolink 20 minute transfer 35 minutes to Dublin 20 minute transfer 1 hour 10 minutes from Dublin to SF via BART Total: 3 hours 25 minutes The project also doesn't even attempt to price the connection into LA or SF. That's where the high costs are. Amusingly enough, the California HSR budget for the Central Valley is under $10 billion. Ie, in the same ball-park as this proposal. The reason the HSR project is going to cost $60 billion is because it has to face an uncomfortable truth; actually getting to LA and SF is expensive. Very expensive. Is Elon Musk's s mega-announcement really just a last-ditch attempt to sabotage the California High Speed Rail (HSR) project, rather than a serious proposal to revolution travel? Something smells very fishy.
• wissler 13y ago
  I am no expert on such things, but it seems to me that Dr. Drang has a very basic misunderstanding or lack of imagination. He seems to assume that Musk intended for each section of tube to physically be touching, when instead Musk intended to leave gaps between, to account for the expansion.
  • lutusp 13y ago
    > He seems to assume that Musk intended for each section of tube to physically be touching, when instead Musk intended to leave gaps between, to account for the expansion. Because the tube must be maintained at a near-vacuum, it can't be "gaps" -- it would have to be expanding slip joints, maybe like those on the Space Shuttle solid-rocket boosters. So, expanding joints in a tube that, by being evacuated, must bear a constant load of 14.7 PSI and remain airtight? > ... it seems to me that Dr. Drang has a very basic misunderstanding or lack of imagination. Perhaps, but on present evidence he's not the only one lacking imagination.
    • wissler 13y ago
      Because the tube must be maintained at a near-vacuum, it can't be "gaps" -- it would have to be expanding slip joints Well you're doing to me what the Dr. is doing to Musk. Obviously they'd have to be airtight, but there would indeed be gaps between the sections. Jesus.
      • lutusp 13y ago
        > Obviously they'd have to be airtight, but there would indeed be gaps between the sections. I objected because you used the term "gaps". They cannot be gaps, they have to be overlapping airtight section joints. There were no gaps between the sections of the Space Shuttle solid-rocket boosters either, except just once, and we all remember that day. To understand the problem with your description, just repeat to yourself, "airtight gaps", until the contradiction occurs to you.
        • wissler 13y ago
• robomartin 13y ago
  I've written about this before. The problem is that any critique of Musk on HN is met with extreme opposition. Almost like the other HN meme: all corporations and CEO's are greedy except for Apple and Jobs (and probably Tesla/SpaceX/Musk). Well, I'm glad people are now seeing that this is not a serious proposal. I actually think this is an elaborate marketing move. Not much Tesla news lately. While I don't have a PhD in Physics, I do have a PhD in Having Designed and Built Lots of Shit. I have touched enough disciplines outside of my EE training to have a pretty good reality meter when it comes to engineering. Thermal expansion, earthquake survivability, cost and plausibility were probably the first few issues that stood out to me. Thermal expansion is a huge problem. It is also a first year college physics problem. What is not mentioned in this article is thermal shrinking! I am surprised the author did not focus on that a bit. And then there's the more complicated problem of differential thermal effects. Put another way, you can have a portion of the tube pushing while another portion would is pulling. The bottom line is that there's a need for tube-to-tube gaps bridged with compliant material. This would localize thermal effects to a single tube and prevent propagation up and down the system. Welding is out of the question. The superficial treatment of earthquakes is also of concern. Many years ago I devoted a non-trivial amount of time to understanding earthquake physics because of a large project I was heading that required earthquake survivability. I learned just how serious these events can be. There are at least four effects to deal with: ground acceleration, structure resonance, amplification of acceleration magnitude within structures (resonant "snap"). This isn't the right venue to discuss this at length. You'd have to design for ground accelerations in excess of 5 g, ground displacement in the one to five meter range and "snap" accelerations in the 10 to 50 g range (guessing the high end). And do so for six degrees of freedom (xyz and the respective rotations). Just yesterday I drove along a 100 mile stretch of the Golden State freeway. I took note of the viability of installing support columns every 100 ft. Let's just say the very idea does not align with any imaginable reality. Great marketing though. No need to deliver anything real. Thise not equipped to understand the real engineering and business problems will surely elevate Musk to even greater genious status and recoil at the very idea of criticizing him. My prediction is that somwhere in Washington someone is trying to figure out how to throw a few hundred billion dollars at this and use it for political gain as well.
  • 13y ago
• kbenson 13y ago
  It seems to me there's an awful lot of people with engineering knowledge getting all uppity about how (in a presentational sense) the proposal was presented, along with what was presented. Criticisms about what the proposal claims are useful. Criticisms about how it's redundant to mention that a diagram is magnified or that a slightly less common term is used to describe an element is used are unconstructive and puerile. I'm interested in criticisms of hyperloop, but all the ones I've seen so far have seemed to carry some bias, if the manner of the criticism is to be taken into account (and to a layperson without the ability to accurately and quickly check their assertions, how can it not?). How are we to know if this perceived bias is affecting the more coherent criticisms or not?
• dclowd9901 13y ago
  Maybe I don't know enough about physics or thermodynamics, but this portion puzzled me: > Here, I’m showing the pipe sitting on the pillars at the low temperature. The lines and arrows above the pipe are where it expands to at the high temperature. > Now add 100′ of pipe and another piller to either end. How much movement do the dampers in these new end pillars have to accomodate? Just ¾″? No. They have to accommodate 1½″ because their lengths change ¾″ and their “starting points,” so to speak, also change ¾″. I won't pretend to understand what Musk was proposing, but for the sake of argument, can't you simply allow the ends of each portion of pipe to expand into each other, thus creating a net change of 0? All you'd need is a tongue-in-groove connection with a small gap of .75". For sealing the connection, just line the tongue with rubber, and for aerodynamics, just line the resultant gap with a thin strip of material.
  • Gravityloss 13y ago
    That would be hard to seal. The air cushion that the sled rides is also sensitive to discontinuities.
• tocomment 13y ago
  I agree with others. This article comes across as too negative. There's really no reason it needs to be.
• JayNYC 13y ago
  This is totally true. I remember having read an article where the author states, that in 20 or 30 years we may look back this time as a time with very little innovation (due to the internet start-ups). Very few invest in real hardware these days. I am looking for money for my own start up. Diabetes field. No Chance.
• knodi123 13y ago
  I'd also like to see someone assess the economic impact of terrorism on these hyperloop proposals. Isn't that an incredibly juicy target? Hundreds of miles of tube, but bad guys only need to blow up one piece to cripple the tube for a significant amount of time, not to mention those poor souls who are about to be fired from the tube like a bullet. And let's not forget what a juicy target the capsules are, too. I anticipate the TSA stepping in and drastically increasing both the cost and the delays, not to mention the invasive body checks. These kinds of attacks are a foregone conclusion, but I keep hearing people talk about how this will be "so much more convenient than an airport, and cheaper too!" But airplanes are fungible- tubes are not.
  • zevyoura 13y ago
    Trains, and especially HSR, have the same problem. A derailment of a long train can be disastrous, and can kill many passengers (arguably even more than the Hyperloop, since each train carries many more people).
• jhuckestein 13y ago
  Well, if the problem of building a hyperloop or similar system is now reduced to the more well defined problems mentioned in the post, we're still better of than before the proposal. The OP claims that the structural analysis and graphics in the proposal are not useful and goes on "This is eyewash for the rubes, the surest sign you’re dealing with a snake oil salesman.". I don't think that is the most likely reason for including those bits. More likely, this is the work of engineers from different fields taking a stab at something new and making mistakes. If this is the case, I applaud them for their bravery. For each point in the post, Musk can now hire a room full of experts to work on that. I'm sure anyone who has ever picked up work in a related but new field has made similar mistakes. On a different note, I don't understand why this post is so petty and often crosses into the unconstructive... If "Dr Drang" is reading this, please consider editing your blog post and removing the parts about snake oil, other engineers being able to do these calculations in their sleep etc. You're doing a disservice to your otherwise very insightful post and the work that clearly went into it.
  • anologwintermut 13y ago
    But it's not reduced to that problem. It's just screwed by it. Even if you could build the pylons, you still need to make the tube smooth to within 2mm for hundreds of miles. This says nothing about the overblown cost reduction. Being able to build the hyperploop at 6bn dollars implies being able to build a slower (say 200 mph) but same weight trolly on that runs on the same pylons. This seems dubious.
• lnanek2 13y ago
  Doesn't seem like an intellectually honest article. It starts out saying 300 miles of pipe creates too long of an expansion to handle at either end and that the design doesn't address this. Although even then the expansion is well within the realms of an airport runway, for example. But the whole proof by contradiction at the start is proved wrong when he quotes the design document saying there is expansion provisions at the stations, not just the very start and end. So his entire first calculation that is supposed to prove the design untenable is erroneous based just on the parts of the design he himself quotes.
• krmmalik 13y ago
  Here we go again. Musk is going to invite all the same criticism and all the same premature skepticism that all new Apple products always did. The critics never learned and Apple never failed to exceed expectations. I haven't studied the physics of hyperloop. Nor am I going to. I just don't have the 'head' for it. But I've observed Musk, and if he says he can make it work, or is going to find a way, then i'm absolutely positive he's going to figure it out. This is what it takes to move the human race forward. Dealing with extreme cases of uncertainty and pushing ahead regardless. We need people like this in our lives. The world and the human race needs it. The article says far more about the blog author than it does about Musk. Let it go!
  • dragonwriter 13y ago
    > But I've observed Musk, and if he says he can make it work Even if such blind faith was justified, he hasn't said that. Initially, he said "hey, here's this idea that would work better than CA HSR, but I'm not going to work on it." When the fact that he said he wasn't going to to work on it became part of the grounds for people dismissing it, he changed tack a bit and said he would work on a tech demonstration. But he still has gone nowhere close to saying that he is going to make it work as a project, or even put energy into to getting making it a real project. > This is what it takes to move the human race forward. Dealing with extreme cases of uncertainty and pushing ahead regardless. There's a difference between extreme uncertainty and certainty that basic bits of what is necessary for what you claim a system is going to deliver are missing. Like, in the case of a supposed SF-to-LA-faster-than-HSR system, actually having connections into the parts of SF-to-LA where people are and/or want to go that allow you to move between them faster than HSR would... And not having vomit-inducing acceleration profiles... Etc. "Uncertainty" isn't the main issue with the Hyperloop proposal; the parts that are certain-and-wrong are a much bigger deal.
    • krmmalik 13y ago
      OK, that's a fair enough point. I can't argue with it.
  • dalke 13y ago
• joyeuse6701 13y ago
  The tone seems to give off an inferiority complex. It intertwines emotion with logical analysis and projects his distaste for Musk, taking a public paper and considering it a personal attack. This guy has a serious serious ego.
• lutorm 13y ago
  I don't understand the comments about snake oil and the other vitriol. Why jump to conclusions about the author's motives instead of just taking it for what it plainly is: a draft idea put together in the spare time by Elon and a few SpaceX and Tesla engineers? He's not trying to get funding for it, so what's the motivation for trying to hide some fundamental flaw? It seems the article is more concerned about criticizing the details of the proposal rather than the idea.
  • dalke 13y ago
    Because the only way to get the idea is through the details. If the details don't work, then how long should we pursue the idea? My idea is that we redevelop our city centers so they are more pedestrian and bicycle friendly. My idea is that we build a bridge (or a tunnel) across the Strait of Gibraltar. My idea is that we develop a fleet of ekranoplans for medium-speed cargo delivery. My idea is that we have nuclear bomb powered rockets so we can get from Earth to Mars in a single stage. All of these are great ideas. Abstractly. All of them have had people spend serious time developing the ideas. "What's the motivation for trying to hide some fundamental flaw?" Do you remember the Segway hype? Kamen said that it would be "will be to the car what the car was to the horse and buggy." ... "In the future he envisions, cars will be banished from urban centers to make room for millions of "empowered pedestrians"--empowered, naturally, by Kamen's brainchild." - http://www.time.com/time/business/article/0,8599,186660,00.html http://www.time.com/time/business/article/0,8599,186660,00.h... He really believed it, and he spent more than $100 million developing the Segway to make that idea happen. I bring this up to point out that you can believe in an idea so much that you overlook or brush over details, because your heart is pure and you have such noble dreams. Sadly, noble dreams don't have a high tensile strength.
  • mcguire 13y ago
    "It seems the article is more concerned about criticizing the details of the proposal rather than the idea." Normally on HN, you'll find many people repeating a mantra, something about execution being more important than ideas. Ideas are cheap and easy. Actually making them work usually isn't. The thing about the hyperloop is that the proposal is the only thing anyone has to go on. Unfortunately, it has the same problems as many other proposals familiar to HN'ers, including excessive details in some areas while cheerfully breezing over important issues.
• jredwards 13y ago
  Isn't "because Instagrams are incredibly low risk and Hyperloops are incredibly high risk" a simple enough explanation?
• orillian 13y ago
  First I'd like to start by saying I'm not an engineer, so this post regarding the thermal expansion issues of the Hyperloop brought up by Drang are not meant to be a criticism of his analysis, but more a platform to ask and raise a number of question I personally have regarding the Hyperloop, that I don't feel Drang addresses, or for that fact have been fully addressed by Musk. I will be using Drang's article as a springboard for my thoughts and comments. While I agree that thermal expansion does pose a problem, one thing that I've not seen addressed by his article and anywhere else is the amount by which the total "POTENTIAL" expansion of the loop will be negated by the following points. 1) Type of steel. Different types of steel expand differently. I ploughed around the net and the library and found some references for common steel with a value as low as 5.5 for its linear temperature expansion coefficient, also some steels that were as high as 9.6. 1b) Also the rate of temperature change in steel will also dictate the rate of expansion. So, does that not mean that the mean temperature coefficient can change dependant on how fast the steel is heating up and or cooling down? 2) Overall temperature changes across a 300 mile length of pipe. This means different portions of the pipe will be cooling and heating at different rates. So while some areas will expand, some will in fact be contracting. Hint: sections tunnelled into the ground will generally be contracting. See more thoughts about tunnels in point 5. 3) The environment inside the tube. Would the pressurization and air flow inside the tube not affect the thermal expansion of the steel as well? Especially if the air is moving it would wick heat out of the steel reducing the thermal expansion. 4) All 11 of those curved portions of track seen in the image on page 44 of the pdf. (Ya, I know it's a proposed route. But having curves makes a difference over assuming it's one straight pipe as those curves will act in a similar fashion to the expansion loops Drang talks about in his post. Is there anything that one could read to get a better idea as to how much bend you need in a tube to compensate for a set amount of thermal expansion? I found nothing that was useful in that regard. 5) Tunnels. The potential to have some sections of the loop hard anchored, especially in locations where the loop needs to tunnel through something. Note: There is only minimal talk about tunnelling but apparently he has looked at something that makes him think tunnelling will be required as there is a $600-700 million dollar price tag added in for tunnelling operations. Also: is there a good reference out there regarding the cooling factor tunnelling underground has on things like steel tubes? I've been in a lot of tunnels and mines and even at the half a mile mark it can get rather cold down under the earth, especially in a straight tube that has a good amount of air flow. 3) Slip joints. Telescoping end points similar to the telescoping air plane ramp are noted in the pdf. This can be done much easier along the ground, and with the capsules already slowed right down even a 500foot long telescoping tube is feasible. Also if in the last couple miles the overall speed of the capsule is reduced enough multiple slip joins could be put in place to compensate for some of that expansion. Anyway I could be completely off base here, but it seems that if as Drang states a 3/4" of expansion over 100' can add up to be a lot, a lot of the points I make above could add up to being a lot of reduction on his initial 1030' estimate...or they might make it even worse, but in either case, making a case for or against the Hyperloop based on 300miles of tube and the difference in temperature of Fresno seems, a bit off. That stated, I get the impression from reading the Hyperloop pdf, that Musk has more information available to him that was not added into the initial brief, whether for brevity, for simplicity, or to hide pain points I do not know.
• simonebrunozzi 13y ago
  The article seems legit, and the criticism too. However, I don't want to focus on the technical details, for once. I'd like you to notice two things: 1) A lot of people are talking about Hyperloop; Dr. Drang, even if he doesn't want to, is ALREADY contributing to the project. These notes will be treasured by whoever will try to build it eventually. 2) This seems to be a very smart strategy (no surprise, given this is Elon Musk himself) to make Hyperloop popular and break existing barriers to execution. These barriers could be: investors' skepticism, Government scarce interest, or else. Well played, Mr. Musk. One more thing: I admire Elon Musk, and have no doubts about his intelligence, ability of execution, reputation. However, let's not forget that he does it for money too. This approach is also a very SMART way to get a ton of free work, and thousands of individuals who would happily work on the Hyperloop (thus, lower wages, as there is more offer). Again, well played.
  • dalke 13y ago
    "treasured"? No. As was written, these sorts of calculations are easy to carry out by a "sophomore or junior year of college", and specifically the thermal expansion calculation is something taught in high school. It's like suggesting that someone's notes on how to implement a linked-list would be "treasured" by a Linux kernel developer. Anyone who 'treasures' these comments is someone who isn't able to effectively contribute to a civil engineering project. You also have to consider the overall net effect. People who might have contributed, had fundamental design issues like thermal expansion been addressed head-on, are not going to contribute, under the assumption that it's "put[ting] my money, time, or talent in the hands of someone who takes me for a fool."
    • simonebrunozzi 13y ago
      "treasured", in the sense that everything that comes out of the discussion (not just this SPECIFIC critique) will benefit whoever is going to implement it. Some things will be trivial, like you suggest, but others won't.
      • dalke 13y ago
• michalu 13y ago
  >I wouldn’t put my money, time, or talent in the hands of someone who takes me for a fool. When Musk said he makes it "open source" and "invites everyone to contribute" I thought he meant exactly this. People finding flaws and ways to do things better so in the process the flaws are eliminated and you end up with some workable design. I don't understand why some people react arrogantly, or feel offended with the hyperloop design I have a suspicion that if Musk wasn't labeled as "billionaire" people would react differently. He kind of lost me with his comments such as the one above, but that doesn't change anything about the quality of his arguments.
• MortenK 13y ago
  These last few posts about hyperloop, while looking like valid criticism just reeks of envy, jealousy and sour grapes. It become obvious when you intersperse your arguments with descriptions of Musk as being "loopy", "stupid", "amateur", "fraud", "snake oil salesman" and the like. It's so typically academia, it's depressing. Luckily guys like Musk are out actually accomplishing things, while the professors are whining about why it can't be done.
  • makomk 13y ago
    I find accusing Hyperloop critics of whining whilst Musk's out there accomplishing things really ironic under the circumstances. Musk has no intention of building this - he's just done a bunch of back-of-the-envelope calculations that he's using to take a dig at the people who are out there actually accomplishing something with California HSR. Sure, it may not be ideal, but they're actually doing something whereas Musk's just sniping at them whilst sneakily handwaving away all the difficult parts of the problem.
    • MortenK 13y ago
      Whether he builds the hyperloop or not is entirely irrelevant to the argument. Musk has already built several huge companies all based on the engineering of extremely advanced technology. And here is some guys calling him an amateur, a fraud and even straight stupid. You should look for the irony in that.
• Gravityloss 13y ago
  There would need to be a hyperloop wiki to list concerns of various technological areas.
• dojomouse 13y ago
  It's beyond me why the Hyperloop team missed the bus on the thermal expansion thing. It occurred to me immediately when I read it, and the several people I've mentioned it to since (engineers or not) have immediately realised why it won't work. I guess that's what happens when you pull multiple all-nighters. A tube that slides through the pylon joints won't work either. Some of the sections will be cast straight; others curved. They're not interchangeable... to say nothing of trying to keep the overall assembly true to within millimeter tolerances while taking up the slack and extra length over the 360mi length. There's another solution though. I don't know why you're so negative in tone though. I'm doing other work on the Hyperloop, and I've found some other aspects which I think need addressing, and I absolutely plan to get in touch with the Hyperloop team and try to work with them. Why? Because I want this thing to be built, and I want it to work. I'm sure as hell not going to be able to raise funding for a fundamentally new technology and billion dollar transport project off my own bat. Musk, on the other hand, probably can. Ease up on the scorn; these aren't a bunch of talentless hacks. Tesla and SpaceX have disrupted two transport industries. They deserve a bit of respect. Have you never made a mistake?
• jccooper 13y ago
  Railroads have thermal expansion problems with new-style all-welded rail, even with a variety of ameliorative techniques and lots of history and experience. And rail doesn't need to maintain sub-mm tolerances. Is the Hyperloop construction going to somehow pre-stress the tubes like they do with welded rail? That's a big big tool. It's a legitimate problem. I don't think slip joints at the end is going to be the only solution. Over a single day you might experience 40 degrees in temperature change, and thus 250 ft movement over the course of a day. I bet you could see it move. That's scary, and I can't believe it wouldn't create kinks or local bends that would be bad at even 300mph. I think it'd have to have some sort of local expansion joint. More complicated than proposed--but isn't it always?
• j2d3 13y ago
  I guess I didn't read Hyperloop documents correctly, but I thought that the solution proposed for thermal expansion as well as earthquake mitigation was tube in tube expansion system at EACH joint, and dampers in X, Y, and Z axis under EACH pylon.
• marze 13y ago
  Those are minor issues compared to the issue of the bored farm-kid with a hunting rifle.
• cookingrobot 13y ago
  There are alloys like Invar (64FeNi) that are designed for low thermal expansion. [1] It's used in common products like shadow masks in cathode ray tubes. It has a coefficent of expansion of 0.8 [2], so if you run the numbers again it gives a total expansion of the tube of 127', or 63' per end. I don't know the costs or if it would be suitable for this purpose, but it seems to be about 3x as expensive as steel for raw stock. [1] http://en.wikipedia.org/wiki/Invar http://en.wikipedia.org/wiki/Invar [2] http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html http://www.engineeringtoolbox.com/linear-expansion-coefficie...