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.
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.
"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.
I thought he handled that quite well, he specifically noted that his handling of thermal expansion was correct on the small scale.
Note that he mentioned that all of the renderings were correct for three pillars, but did not take into affect what happens when you expand to several thousand of them.
I would expect a rocket engineer to understand thermal expansion in an item that is 100 feet long, but I wouldn't be surprised if they did not understand what it was like when working with a 300 mile tunnel.
It seems like many people are making this thermal strain criticism of hyperloop, is it possible that the critics are posting link-bait? I only say this because few are contributing new ideas, and most are writing with substantial amounts of vitriol.
No, that's not accurate. His stockholders and/or venture capitalists do the funding -- remember that "funding" means answering a relatively simple question about risk versus reward. Someone still has to manage projects, make technical decisions. That's what Musk does.
Consider a parallel example -- Steve Jobs and Mike Markkula. Jobs made product decisions, Markkula funded them.
You are mistaking (part of) the startup world with how the real world works at large. (And to be clear, I'm not pretending that Elon has not made any direct technical decision; that, I don't know)
So that you get a sense of what can happen in the wild world, let me copy past wikipedia for you: "As of May 2012, SpaceX has operated on total funding of approximately $1 billion in its first ten years of operation. Of this, private equity provided about $200M, with Musk investing approximately $100M and other investors having put in about $100M (Founders Fund, Draper Fisher Jurvetson, ...)."
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."
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.
"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.
Tesla and SpaceX are great but I'm not aware of fundamental engineering principles they have overthrown. This is a strange religious argument you are making here. The logical conclusion to your attitude is that there is no engineering challenge that Musk and his compadres can't solve. How odd. People have been building bridges for millenia now, there is a rich history of engineering and science here. You can't just 'think out of the box' your way through some fundamental constraints.
If you feel the original article is wrong then it is worth discussing. If Musk and friends are modern day messiahs what's there to discuss?
How so? The point being made in the blog post is that Musk has a severe misunderstanding of the fundamentals of civil engineering.
That Musk runs a company that has successfully engineered cars and spacecraft in no way makes him qualified to construct the Hyperloop.
Civil engineering isn't mechanical engineering isn't chemical engineering isn't aerospace engineering. These are different disciplines. Being a talented industrialist in one (or more) of these do not imply capability in any of the others.
That's true, but all of them derive from the same set of first principles, those defined by physics.
> Being a talented industrialist in one (or more) of these do not imply capability in any of the others.
Not true -- expertise is not implied, but capability certainly is. In this specific case, to predict the behavior of an evacuated transport tube, and given that the project doesn't resemble any existing projects, one could hardly do better than have a background in spacecraft booster design.
I can't disagree more. I'm a mechanical engineering by schooling (what am I doing writing code?!) and it still routinely shocks me the sort of intriguing misconceptions I hear coming out of the mouths of very smart, very technical people.
The fact that mechanical engineering and civil engineering and aerospace engineering all derive from basic physical laws is rather meaningless - engineering isn't about first principles, it's about the extremely complex task of putting these to use.
To make an analogy to software, that's like saying "writing code for a Martian probe isn't very different from writing code for a website, it's all the same first principles".
In this case, the author's thesis is that Musk is applying analysis methods that are wholly inapplicable to civil engineering, and fails to account to the scale of the structure, and makes faulty assumptions about the validity of simulating the structure in small segments. This is the sort of thing you see when you cross someone who is an expert in one field into another where they have no expertise - but they know just enough to get started.
I write mobile apps for a living. I can probably hold a decent conversation with a kernel hacker, but I am in no way qualified to design the next uber-kernel of the future. Traditional engineering is no different.
> I'm a mechanical engineering by schooling (what am I doing writing code?!) and it still routinely shocks me the sort of intriguing misconceptions I hear coming out of the mouths of very smart, very technical people.
That's true, and I've had similar experiences, but it doesn't argue against my saying that these engineering disciplines have many basics in common.
My only reason for posting was to argue against the idea that different engineering fields have no common base. They either do, or they're not based in science, which is the common base for all engineering fields.
As to a new project that has little in common with existing projects or established engineering fields, the obvious solution is to depend on basic science rather than nonexistent engineering projects, which would be the best approach to a project like this one.
All new engineering projects teach us one thing -- no matter how many advance expectations and predictions, by the time the project is operational, all of us will be educated in new principles that no one anticipated.
For me the various engineering streams are just as different from each other as from every other non-engineering discipline. There is no way a mechanical engineer could work in the electronics, IT or biochemical engineering fields.
If you are going to label the common base as "science" then you could equally say engineering is common with psychology since they both involve "words". That makes equally as much sense.
> For me the various engineering streams are just as different from each other as from every other non-engineering discipline.
False, and that cannot be used to argue that they're not all directly derived from physics. Look at cosmology and particle physics. It's hard to imagine two fields that are less alike -- one studies nature at the largest scales, the other at the smallest. But not only are they both physical fields and share the same theories, but they attend each other's conferences and work together on common issues.
Remember that engineering is applied science. This is true for all engineering fields in which people place their trust.
> There is no way a mechanical engineer could work in the electronics, IT or biochemical engineering fields.
Same reply -- it's not relevant to the issue of their scientific underpinnings.
> If you are going to label the common base as "science" then you could equally say engineering is common with psychology since they both involve "words".
When you think of a coherent argument, post again. Psychology isn't scientific, engineering is, and the topic is science. When a psychologist uses the word "gravity", he means seriousness. When an engineer uses the word, he means spacetime curvature.
Much like a knowledge of physics is insufficient to draw conclusions about biochemistry, knowledge of basic physical laws tells you very little about the fundamentals of a practical engineering field. The theory and laws of e.g. civil engineering are typically traceable back to abstract physical principles, but are not strictly derivable from them.
As to the article's content, it's philosophy without supporting evidence (meaning it's philosophy), and its conclusions are regularly refuted by the many examples that connect physical fundamentals with everyday reality. Example? Quantum theory and computers -- as separate as the two may seem, we can't have the second without a detailed knowledge of the first.
> Much like a knowledge of physics is insufficient to draw conclusions about biochemistry ...
In the final analysis, all of biochemistry derives from biology and chemistry, each of which derives from physics. Relevant in that regard is the fact that chemistry turns out to be applied quantum physics, to a shocking number of decimal places.
> The theory and laws of e.g. civil engineering are typically traceable back to abstract physical principles, but are not strictly derivable from them.
Not true. Either civil engineering is "strictly derivable" from physics, or it's not part of reality. The behavior of concrete over time, as just one example -- we know what will become of it in the long term, and modern quantum theory tells us why.
Philosophical articles like "More Is Different" represent nothing more or less than physics envy. They're interesting and deserve to be heard, but in the reality footrace, events annoy the authors by reliably overtaking their philosophical positions.
There is a difference between reality and academic physics. It is trivial to say engineering knowledge is derived from reality, and it's wrong to say it's derived/derivable from purely theoretical/academic knowledge of physics -- especially because good engineering requires knowledge of man-made safety standards and such.
Engineering is a corpus of knowledge that has been slowly and with great difficulty hewed from the raw rock of real experience over hundreds of years. It is not just a branch of math derivable from axioms. Show some respect.
Quote: "A physical theory is a model of physical events. It is judged by the extent to which its predictions agree with empirical observations."
Read the above carefully. What it says in essence is that a physical theory is judged by the degree to which it agrees with reality. Our best physical theories agree with reality to ten decimal places.
Physical theory is a statement about reality. If reality disagrees, the theory is thrown out and replaced by a better one.
> It is trivial to say engineering knowledge is derived from reality, and it's wrong to say it's derived/derivable from purely theoretical/academic knowledge of physics ...
Engineering is applied science. Any engineering field for which this is not true has no right to exist, and doesn't deserve the public's trust.
Quote: "Applied science is typically engineering, which develops technology, although there might be feedback between basic science and applied science: research and development (R&D)."
> Engineering is a corpus of knowledge that has been slowly and with great difficulty hewed from the raw rock of real experience over hundreds of years. It is not just a branch of math derivable from axioms.
False, and you need to learn this topic. I hope you're not an engineer.
> Show some respect.
By correctly identifying engineering as applied science, I did. There is no higher praise than to say -- correctly -- that engineering is derived from scientific principles, from physics.
> How, then, do you account for the very basic and substantial errors described in the article?
Surely you don't think a single counterexample -- or a dozen counterexamples -- refute well-established principles? The argument was that various engineering disciples are independent of each other and of physics. That's very clearly false and smacks of post-modernism (i.e. that everything is a matter of opinion, not evidence), and it's hardly supported by an example -- or a dozen examples -- where someone gets the engineering wrong.
> The argument was that various engineering disciples are independent of each other and of physics.
No, actually, they were argued to be different than each other, but no one in this thread argued that they were independent of each other or that any of them was independent of physics.
Inasmuch as that's the position you are arguing against, it is a strawman.
>> The argument was that various engineering disciples are independent of each other and of physics.
> No, actually, they were argued to be different than each other, but no one in this thread argued that they were independent of each other or that any of them was independent of physics.
False. Read this quote: "The fact that mechanical engineering and civil engineering and aerospace engineering all derive from basic physical laws is rather meaningless - engineering isn't about first principles ..."
To say, as this correspondent did, that "engineering isn't about first principles", is to argue that it has nothing to do with science, because science establishes first principles.
> Inasmuch as that's the position you are arguing against, it is a strawman.
Well, since you can't be bothered to read the thread and find out what positions people have taken and that I'm arguing against, there's no point to this.
> To say, as this correspondent did, that "engineering isn't about first principles", is to argue that it has nothing to do with science
It is not arguing, as you claimed, that the disciplines or "independent of each other and of physics", especially not when, as that correspondent did, an acknowledgement is included in the same sentence which expressly acknowledges the fact (while dismissing its relevance in context) that they all derive from the same physical laws.
No one is arguing that different engineering disciplines aren't related to each other and to physics; the debate is about the extent to which how those relations (as well as Musk's connection to certain engineering disciplines through SpaceX and Tesla) are relevant in the context of the Hyperloop proposal, the criticism of it, and the treatment of Musk as an authority deserving special deference in regard to that proposal.
I was addressing your claim about this specific case:
"In this specific case, to predict the behavior of an evacuated transport tube, and given that the project doesn't resemble any existing projects, one could hardly do better than have a background in spacecraft booster design."
Seems to me that one could do a lot better than having a background in spacecraft booster design, as the fairly trivial errors pointed out in this article illustrate.
His primary argument is about thermal expansion. Are you claiming aerospace and automotive engineers make no study of thermal expansion? I could see your point if the proposal was about a dirt retaining wall or aqueduct where the other two disciplines wouldn't be well versed in the material's properties, but I am not seeing something CE specific in the thermal expansion of steel.
Yes, “stringer” is also a common word in structural engineering, especially in bridge design, but something that reinforces a tube wall is a stiffener, not a stringer. Update: I am reminded by Matthew Hunt on Twitter that “stringer” is commonly used in aircraft design. I should have remembered that.
Given this quote how do we know they aren't in violent agreement but talking past each other because they are using terms from different disciplines?
At least SpaceX actually made some quite fundamental changes in their approach to many things, since their original ideas did not work. They for example talked a lot about recovering their rockets, and none of that has worked at all. They changed from ablative to regenerative cooling. They experienced many failures (I think it is actually better to launch more often and experience some failures than launch years apart, because then you can't afford to fail at any cost and your schedule and cost will explode).
So in a sense he has this "new kid on the block" serial enterpreneur attitude where he bursts into a scene, stumbles a lot but finally seems to get something done quite right. Maybe it's him learning the tricks of the trade - or that just finding the right people takes a lot of time, or something else entirely. I at least don't know that closely what happens in these organizations.
It might be cool to read a book about something like that. I don't have high hopes of anyone getting the stories right though.
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...
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.
> Because you're good at something doesn't mean you're good at everything.
How is that statement relevant here? The criticism being responded to was that he doesn't know the basics of engineering. The response was there's significant evidence he knows a lot about engineering (and his employees who looked at this proposal probably know more). It doesn't matter whether he's good at everything.
Because in real life (as opposed to, say, Star Trek), aerospace engineering and civil engineering ain't the same ballpark, ain't the same league, and ain't even the same flipping sport. [1]
Neither are online payments, electric cars and aerospace engineering similar sports. His core competence seems to be learning new sports very quickly.
He may strike out, he may not. If he fails it's not going to be because his first paper over-reached or because he's unable to gather smart-enough experts with better civeng software.
So far, its not clear that he is attempting anything with Hyperloop other than what he is demonstrated to be very good at: selling ideas.
Its particularly clear, though, that the one thing he isn't trying to sell Hyperloop as yet (and may not be at all) is an actual project/business, as opposed to just a reason to not support CA HSR.
Why the CEO of a company selling currently selling high-end electric cars and working to expand the reach of electric cars in the market might want to sell an alternative to a project designed primarily to reduce automobile road trips (which incidentally reduces the need for automobiles) in California by improving mass transit on both the major intrastate long-distance corridor and the connecting regional/commuter mass transit systems -- either as a real system that doesn't do as much to reduce automobile demand (and even relies on transporting autos to provide door-to-door connectivity) or as a phantom system to derail the existing proposal -- is pretty obvious.
Hyperloop doesn't need to be successful as mass transit -- or even ever have $1 spent toward building it -- to succeed for Musk.
> its not clear that he is attempting anything with Hyperloop other than what he is demonstrated to be very good at: selling ideas.
While selling ideas isn't a bad skill I think you're underselling his ability to execute, somewhat.
Personally, I feel that Musk's "list of biggest risks to Tesla" has many items before "CA HSR". By the time it's built Tesla will either be (at least) a countrywide success, or not.
> While selling ideas isn't a bad skill I think you're underselling his ability to execute, somewhat.
Not my intent; I think SpaceX and Tesla both show Musk can execute in engineering quite well when his energy is behind it (or, equivalently, that he is good at putting his energy in places where he can execute.)
Part of that is the ability to sell ideas to (among others) investors, without which he wouldn't have the ability to execute.
With regard to hyperloop, Musk has been very visibly not putting the kind of intent-to-execute behind it that he has with other endeavors, making his selling ideas skill the most relevant part of his ability to execute, but I certainly did not mean to fail to recognize his ability to execute.
> Personally, I feel that Musk's "list of biggest risks to Tesla" has many items before "CA HSR".
Probably. But tossing out a "I don't plan to build this, but it would be better" diversion is a pretty low-cost way of derailing the threat. It doesn't have to be the biggest or most immediate threat to be worthy of that, from a rational viewpoint.
> By the time it's built Tesla will either be (at least) a countrywide success, or not.
This presumes HSR (including the regional/commuter transit improvements that go with that project, and are some of the earlier investments) has no effect on the market for electric cars until its fully built out. I'd question that assumption.
No, but a lot of the same types of problems surface even in all these different fields, engineering does have some rather uniquely diversified fields, but at their core they still follow ...a lot of... the same laws of physics.
arethuza ninja-edited his comment after my reply, his initial
reply was simply "So what about SpaceX and Tesla?", which didn't
make a lot of sense to me.
But my point still holds, because you're good at making rockets
and electric carcs doesn't automatically make you an expert in
high speed train infrastructure, so I don't really think that's a
valid argument.
Okay, but who is Dr. Drang? As nearly as I can tell from a web search, he is someone puts some code on Github and writes a blog. Has he sent rockets into space? Why does he feel like he gets to talk down to someone who has sent rockets into space, on the subject of engineering?
Now that's an appeal to authority. Regardless of whether this person is a doctor or a billionaire or a physicist, the key points (like the issues with thermal expansion) are legitimate criticisms. "Dr Drang" presented arguments that are within the reach of high school physics.
Now, Musk may have an answer to the issues, but he certainly didn't present them. The fact that there is no obvious resolution suggests that either Musk didn't think of them or he intentionally omitted the answer (both are damning)
Yeah, this was my initial confusion with the article and many of the comments. When I read the doc by Musk, I assumed, that the tube 'floated' over the pylons. The author seems to have assumed the opposite. The problem is that they are both assumptions.
When making an argument, sometimes it is good to make an assumption and then prove the assumption is false... sometimes it is just a straw man.
The tube does float (longitudinally) over the pylons, in the proposal.
The tube will be supported by pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion as well as dampened lateral slip to reduce the risk posed by earthquakes. In addition, the pillar to tube connection nominal position will be adjustable vertically and laterally to ensure proper alignment despite possible ground settling. These minimally
constrained pillars to tube joints will also allow a smoother ride.
> As nearly as I can tell from a web search, he is someone puts some code on Github and writes a blog.
A civil and mechanical consulting engineer [1] who also has put some code on Github and writes a blog.
> Why does he feel like he gets to talk down to someone who has sent rockets into space, on the subject of engineering?
Probably because, unlike Musk, he actually has professional qualifications in the kind of engineering at issue on the points on which he is criticizing Musk's proposal.
Tesla and SpaceX are both iterative technology. They both use existing technology and iterate improvements on it or apply it to new fields. The electric car was already proven feasible by GM and other companies or products like golf carts. It was more of a problem of the existing players being forced to build an electric car than keep doing what they've been doing to generate profits.
SpaceX still uses rockets. The new tech in SpaceX is changing the rocket design between engines so it is manufacturable in larger quantities and utilizing faster computers to create reusable rocket stages that can land with their own power back on Earth. You could say that SpaceX is leveraging computer science artificial intelligence research, the general improvement in computing (cost and speed), and sensors. For example there are many videos of software controlled quadcopters performing various aerobatic stunts by analyzing and adjusting thrust in realtime based on sensor information.
One could say there is nothing new in feedback control for vertical flight. It has even been coupled with GPS for precision motion and landing in rockets already many years ago by Armadillo Aerospace and others.
All this could have been done in the seventies, bar the GPS part, which would have required some more costly alternatives.
But even the V-2 had gyros on a free rotating platform that was connected to the thrust vectoring vanes that kept the rocket pointed to where the flight program required. The sensors weren't so good and you probably could not have throttled the V-2 to hover accurately, but maybe with radio guidance (that they actually used with some of the flights) it could have worked. Mechanical PID controllers date to late 1800s already (warship steering) so it was a totally straightforward thing to do, and was done by Goddard already. Nobody cared but the Germans...
There is very little that is novel about SpaceX / Tesla. Both were excellent executions of visions that many people had. We've had pure-electric vehicles for more than a century (For example, Detroit Electric built an electric vehicle in 1914 -- https://upload.wikimedia.org/wikipedia/commons/8/8a/EdisonEl... is a photo with Thomas Edison).
Hyperloop is different. Others have talked about it, but this is the first time he is truly laying out an idea, so I wouldn't necessarily assume that he will be successful
> 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.
Well, then, how do you explain the following?
1- Thermal expansion and contraction issues diametrically
opposed to what happens in the real world
2- Proposing that an entire 300 or 400 mile tube be a single
welded solid tube with no turns or incremental expansion
gaps. Really? In the real world? Along the 5 freeway?
3- Grotesquely underestimating seismic effects
4- Estimating a cost at least one order of magnitude
lower than what it will actually be in the real world
5- Not taking a drive down the Golden State highway before proposing
that columns be installed every 100 feet to support the tubes.
No, really, go on Google Maps and take the drive yourself.
I think these guys thought it would be a cool and possibly marketing-worthy thing to put out something like this. They put a little time into it here and there and, per the paper, a short amount of full time effort. They were probably so focused on the tube transport physics that they neglected to connect to the real world.
At some level I don't fault them for putting this out. They are obviously far more focused on building cars and rockets and that's exactly how it should be. If what came out was a fully engineered project it would have meant that they took valuable time away from Tesla and SpaceX to apply on this thing. That could border on being a breach of fiduciary duty.
At this point I am going to mark this off as science fiction simply because I am now convinced it cannot be built outside of a super-expensive short range test installation.
Why would you assume that the founder of SpaceX and Tesla "must be a pretty decent engineer"? I'm not saying Musk isn't, because I don't know much about him, but I certainly wouldn't assume that the founder of engineering-based companies must be a decent engineer. As for leading engineers in complex domains, that's more plausible, although the founder of a company doesn't need to be the person directly managing engineering teams.
If you're wondering where the conversation got derailed it was here:
> Learn the basics of engineering
Every single comment resulting from this comment has been partisan:
Side 1: Elon Musk knows the basics of engineering as evidenced by his numerous successful projects.
Side 2: Strawman: although the original comment was about _basics of engineering_ turn it into an argument about the differences between engineering disciplines.
Seriously folks, if you're going to argue about semantics, skip the strawman, he ruins the party.
Neither of those depend on the kind of engineering necessary for a large terrestrial infrastructure project (and the required engineering is more similar between SpaceX and Tesla than between either and a large civil engineering project.)
A static allocation works perfectly well. If we want a hyperloop analogy, maybe they specifically pointed out that the runtime is 3x faster if you don't have to allocate during it, and that's what they're optimizing for. Nobody cares if it's revolutionary.
On the other hand, if you're going to mock a proposal, it makes good sense to actually read it thoroughly. His criticisms on the thermal expansion issue are founded on the mistaken assumption that the tube is fixed to the pylons; this is contradicted by the first paragraph in the pylon section, which indicates that the pipe is not fixed longitudinally to the pylons. It slides.
* 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.
> 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.
Hum. I got a different impression with regards to the FEM graphs of the beams' stresses. Dr. Drang seemed more bothered by the fact that they were there because it was too amateur, and too much pretty graphs for their own sake, since any civil engineer could do the calculations in their sleep. Not because of technical problems, per se. (Honestly, that might be a social faux pas among physical engineers, and a noob move from Musk, but I'm not a civil engineer nor Musk so I don't give a shit.)
Apart from that, it seems, as I gathered from comments here, that there was a solution to thermal expansion, and that's both not fixing the tube to the pylons, and having the trajectory curve so they can bend safely under expansion. This confusion rose from the ambiguous meaning of "nearly straight tube". The Hyperloop seems to have decent tolerances for turning, so maybe that could work.
But the most solid arguments against Hyperloop, I think, come from the economics side. It's less efficient than a good HSR, like the French or the Japanese ones. It's not SF to LA, it's "somewhere near SF" to "somewhere near LA". Its cost is probably wildly underestimated. It looks as if the only failure modes are either "tubes explode causing chaos", or "crash and die horribly"; not necessarily an exclusive choice.
> any civil engineer could do the calculations in their sleep
The calculations can only be performed in Finite Element Analysis (FEA) software, doing this type of analysis (accurately) is impossible without computers.
>Its cost is probably wildly underestimated
There are also significant economic benefits to the hyperloop, in that it may be less expensive to maintain and power, while requiring much less rolling (floating?) stock. Rails are very expensive to maintain, largely because of the heavy loads they carry, and because they are entirely exposed to the elements.
I can't speak for civil engineers, but in mechanical engineering no one uses FEA to solve a cantilever beam. That's like using a supercomputer to calculate 3 times 4. Cantilever beam has bean studied for centuries and there are easy-to-use (and easy-to-prove) formulas for calculating its stress and strain.
>Hum. I got a different impression with regards to the FEM graphs of the beams' stresses. Dr. Drang seemed more bothered by the fact that they were there because it was too amateur, and too much pretty graphs for their own sake, since any civil engineer could do the calculations in their sleep.
smnrchrds, you are correct that simple structures have been studied, and equations describe their characteristics very accurately; what you are missing is that the FEMs in question were used to analyse a complex structure's response to vibration. I would challenge you to find any large bridge designed in the western world last 10 years without FEA.
> any civil engineer could do the calculations in their sleep
This sentence of Dr. Drang's article refers to FEA analysis of "applying a 1 g lateral acceleration to the three-pillar model and plotting out various stresses in the pillars". It's located directly below those plots and after his criticism of vibration analysis has finished. I agree that vibration analysis would be very hard without FEA, but applying a constant 1g lateral force to a cantilever beam could be easily done by paper and pen (well, maybe also a calculator) and is an overkill for FEA.
"(Honestly, that might be a social faux pas among physical engineers, and a noob move from Musk, but I'm not a civil engineer nor Musk so I don't give a shit.)"
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.
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.
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.
How do they deal with thermal expansion on traditional railways? Same problem no? The track needs to expand, they spread across miles and miles and I never saw a damper area (except that the tracks are disjointed by a quarter to half an inch each, which would be the same with a tube in a tube configuration)...
Most modern railroad use continuous welded rail, so there are no joints like what you're talking about. This is both stronger and quieter, but it can lead to problems when the temperature is too high or too load, because of thermal expansion.
"There are a number of ways to increase the resistance of rail to buckling. The first and most common is the use of rail anchors to limit the longitudinal expansion of the rail. Anchors come in a variety of designs, but they all apply several thousand pounds of clamping force on the base of the rail. When applied properly against each side of the crossties, the anchors prevent expansion of the rail in the longitudinal direction." - http://www.interfacejournal.com/features/03-05/track_bucklin...
The choice of Rail Neutral Temperature depends on the region. In the US Midwest and plains it's typically around 95 to 100 degrees. In the UK it's stressed to 27°C (81°F), which is the mean summer rail temperature. In neither case is it the maximum possible temperature.
You don't want it to be the maximum possible temperature for the area, because a well-laid track can be in temperatures 40 to 50 degrees above the RNT before it starts to buckle, and a higher RNT is harder to achieve.
Nor do they lay the track or heat it at the hottest possible temperature. They achieve the RNT by stressing the rail. The RNT can also change over time, for example, if winter causes a curved track to become a bit more shallow.
I agree with you and with the linked-to author: I don't see how the proposed hyperloop system can ever economically handle temperature expansion, and the lack of a good explanation or discussion makes it easy to dismiss the seriousness of the proposal.
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.
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.
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....) 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.
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.
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.
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.
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.
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.
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.
Would you attitude be different if it were some other "Bachelor of Arts in business from Wharton" proposing a rather sketchy idea and asking if you'd like to sign on to fill in the details?
Of course it would; but academic qualifications don't really play into this, do they?
Take 2 Harvard dropouts; one founded a tech company and one deals drugs from his basement. Are they interchangeable? If the former took you aside with a proposal, would you be more, or less likely to think about it than if the latter did?
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?
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?
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.
A Falcon rocket is started from flat aluminium plates, which you weld into hoops. Then you weld the hoops together into a barrel.
Similarly with hyperloop, you have to weld the tubes from much shorter barrel sections anyway, there's no way you're going to have 100 m x 12 m plate sections that you could then roll into a pipe. And you couldn't really bend any of that anyway at once. So there certainly are weld seams between pylons.
A spiral weld might be interesting if a continuous sheet could be created at some steel mill. Some big pipes are created by welding a sheet spirally. Armadillo bought such tubes from Europe for their rockets. Though for hyperloop, bends in the pipe would require a really funny shape for the sheet. Both width and orientation of the sheet would have to change, and it would require very accurate welding ).
The tube does not run in a straight line. Every curved element is an opportunity to absorb thermal expansion. Imagine bending a metal rod into a curve in your hands, which remain at fixed point, while it sits on a table. Then it gets very hot, and the metal rod has expanded. If your hands have remained at the same points, the arc of the rod has gotten slightly bigger. The pipe itself has moved laterally from its prior path. This is why the lateral and vertical dampeners assist in absorbing thermal expansion.
I think my memory is totally wonked. I remembered after reading your response that Musk mentioned the orbital seam welder. But yeah, I think there are some, uh, gaps in the plan. ;-)
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.
No. Read the pylon section. What it says is that the tube is NOT constrained in the longitudinal direction on the pylons; it's free to slide back and forth in the direction of travel. It's only constrained vertically and laterally.
Thanks, yes, he's clearer in the technical section, p.28. (I hadn't read the whole thing.)
4.2.3. Pylons and Tunnels
The tube will be supported by pillars which constrain the tube in the vertical
direction but allow longitudinal slip for thermal expansion as well as dampened
lateral slip to reduce the risk posed by earthquakes.
The "longitudinal slip" is what I assumed/guessed with "rollers or similar" (in my comment above).
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).
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.
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.
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.
I took it to mean that the tube was rigidly (or near rigidly) fixed in the vertical direction, more generously dampened in the transverse direction, and completely free to slide over the pylons in the longitudinal direction.
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
The tube will be supported by pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion as well as dampened lateral slip to reduce the risk posed by earthquake.
It says dampers absorb change. But it doesn't mean only dampers do that. Of course they couldn't handle hundred meters expansion (near ends). I don't believe Musk would make such an easy mistake and force dampers handle all of thermal expansion.
That said, the quoted text is somewhat confusing. I had to read it a few times before I got the idea.
Given that the proposal mention slip joints at the stations that needs to be long enough to handle the aggregate expansion, it is pretty clear that the tube "floats" at least to a certain degree.
'slipping past pylons' during expansion would be a pretty terrible solution though. Can you imagine how hard it would be to keep it straight and level, to the tolerances required, while not even being able to fix it to the pylons? To say nothing of the fact that some of those precast tubes are going to be precast straight, and others precast curved. They're not interchangeable.
> To say nothing of the fact that some of those precast tubes are going to be precast straight, and others precast curved. They're not interchangeable.
I don't know enough about steel and construction, but I think the tubes could all be made straight. Hyperloop curves have very large turn radius. Steel tubes are not completely rigid, they can curve a little by themselves.
Fair point - maybe that would allow the necessary flex.
The minimum bend radius they allow for the 300mph segment is 3.67km. If you made a complete circle it would have a circumference of 23km, and comprise 769 30m segments. Each segment would need to contribute 0.46deg of the 360deg curve.
To achieve this over 30m you need to deviate the end of the pipe by 24cm from where it should be... which actually sounds like a hell of a lot to me, especially if it's flexed through this range regularly (as it would be if constantly switching places with a truly straight segment).
True, but that means you're going to have some absolutely awesome bearing system that gives almost zero friction along the major axis of the pipe while also giving almost zero slop in the other axis. Which is damned hard. Adaptive maglev bearings maybe? ;-)
Why do you want zero friction along the major axis? Linear speed of pipe movement through the bearing would be very low: not more than couple hundred feet per day. And what do you mean by zero slop?
By the way, if you want to continue speculating on Hyperloop thermal expansion issue, you can join my speculations - I wrote a few comments under this blog post:
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.
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.
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.
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.
> 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.
Really? The Lisa, Apple III, Apple USB Mouse, MobileMe, and Apple TV all exceeded expectations? Most people consider that to be a list of Apple failures. How do you say they exceeded expectations?
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.
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.
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.
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.
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?
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.
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.
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.
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.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.
"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.
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.
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.
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?
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.
Yeah, I always thought the fact that the route essentially ignored the mass transit equivalent of the last-mile problem (rendering it useless as mass transit) and that virtually all of the cost savings vs. HSR came from that (to put it generously) oversight was the most important criticism.
But it doesn't surprise me to see that the civil engineering end may have equally basic problems, as well.
As I've read the proposal, I've felt like witnessing the real life Monty Python's "The Architects Sketch," the one where Cleese demonstrates his project of a residential block of flats:
This is a twelwe-storey block combining classical neo-Georgian features with the efficiency of modern techniques. The tenants arrive in the entrance hall here, and are carried along the corridor on a conveyor belt in extreme comfort and past murals depicting Mediterranean scenes, towards the rotating knives...
The tolerances a trained astronaut can accept and be prepared for one single trip aren't something you can subject normal travelers to, even with the promise of "only 30 minutes."
Riding the high speed train is pleasurable experience. You can walk to the toilet, stroll between the seats. Riding Hyperloop: once you enter the capsule, you can't even stand up from your seat. Stay put there, don't try anything for the next 30 minutes. You feel sick in the first minute? Too bad, just don't move in your seat. You can't anyway, you're in a small capsule in the same position you are while at your dentist. Only 29 minutes to go. What, you don't have your astronaut's diapers? Too bad. You can't move from your seat. Only 29 minutes to go. Enjoy the ride.
> Riding Hyperloop: once you enter the capsule, you can't even stand up from your seat. Stay put there, don't try anything for the next 30 minutes.
I kinda wish we'd get off this bullshit argument for once. To even get to the HSR or Hyperloop, you're going to be sitting in at least 30 minutes of LA or SF traffic. In a small capsule.
And I know your next comment. "You can pull over in a car!" Yeah, you don't live in LA then. Get stuck on any of the freeways and you're not pulling over and not getting out. Or did you really plan on taking a shit on the side of the freeway?
Does everyone on HN get explosive projectile diarrhea every time they step outside? Maybe Musk is missing a market for you dysfunctional people.
The maximum width is 4.43 ft (1.35 m) and maximum height is 6.11 ft (1.10 m). With rounded corners, this is equivalent to a 15 ft2 (1.4 m2) frontal area, not including any propulsion or suspension components.
Note "6.11" feet is in fact a typo, he meant at most 3.38 feet as the multiplication with 4.43 gives 15 of frontal area, and it fits with the metric units. It's very low, much less comfortable than sitting in the car. And you can be serviced in the car in the case of accident -- emergency cars reach the people in need. You practically can't interrupt the 30 minutes of supersonic ride in the capsule.
Imagine that I offer you to enter the non-moving capsule and stay there, knowing that absolutely no matter what happens to you, it won't be opened for 30 minutes. Would you enter? Would you let your grandparent enter it? Your kid?
Well my problem with Hyperloop is similar to any heavy rail solution. It only goes from two fixed points and diverting to other points is very problematic. Some larger cities have multiple airports, would they have multiple hyperloops? Either solution requires some form of transport at each end, light rail, bus, or cars.
Hence I think Tesla combined with the driverless car technology being worked on by Google and others is overall a better solution. Lanes could be added or taken from existing multiple lane roads and given over self driving cars. A network of routes could be established, with and without battery swap stations along the way, to allow people to drive from nearly any point to another all the while doing so safely and with less impact on the environment. Individual vehicles just have too much flexibility to ignore and combining them with electric power and self driving ability would provide a better solution. It could even be extended into mass transit by having buses employing the tech. With a fully protected lane these vehicles could move at much higher speeds all the while being safer.
I like Musk's idea from the standpoint that it points out the fallacy of the HSR system that is proposed, the side effect its easy to point out the fallacies of his idea as well.
The difficulties of the route did seem to be ignored in general. The environmental constraints are not some minor triviality. Even if the tracks are in the air and have a small footprint you still need to get access for large vehicles in potentially sensitive areas. Getting into dense cities tends to depend on very expensive tunnels, highly contained pinch points, or tight corners. Ultimately you have thousands of interest groups who will treat Hyperloop with the exactly the same skepticism as rail and solving those problems will cost just as much.
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.
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."
"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.
That's not what happens. It takes more time for a civil engineer to read through the myriad of blog posts and HN comments to find out this information than it would be to carry out this sort of basic analysis in the first place.
In your cost/benefit estimation, what is the contribution of this HN discussion to that project?
In your cost/benefit estimation, is there anything which touches on the topic but which is not a "treasure" and in fact is a net-negative?
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.
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?
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.
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".
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.
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.
>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.
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.
I like his, "don't let school interfere with your education"
However, to go with a line about having a "PhD in Having Designed and Built Lots of Shit" just sounds like something straight out of a Python sketch.
Besides, PhD's are not generally given out for "Having Designed and Built Lots of Shit", but more for having completed and documented an original body of research, to the standard required for submission to academic peer review.
You don't need to have a PhD to have done that, or to even be seeking a PhD when you do that. In that sense it is possible to even pick up PhD's almost by accident, if you are uncommonly curious and dedicated.
I have designed and built and fiddled with all sorts of complicated crap. I have not done a PhD however. A PhD is a different discipline. Someone who has genuinely put the work into a PhD doesn't just know a lot about the subject of their PhD, they are the authority.
Please don't take a joke on my part too far. It was just intended as a joke, nothing more. We have someone in the family with a PhD in Physics and we've had lots of very interesting conversations. We see each other several times a month in the context of family gatherings. Amazing depth of knowledge in his area (orbital mechanics mostly). Worked at JPL, etc.
He can't even assemble Ikea furniture. Does not like to exist in that world. My son and I had to go to his house and install a window air conditioner for him because he had no idea where to start and barely owns any tools. I find that odd and funny in many ways.
When it comes to real-world embodiments of theoretical constructs he checks out. He was zero experience doing anything "real". I tried to have my son work with his uncle on some of his school science projects because I want him to engage with people at various levels. Every attempt has been a complete disaster. He either does not understand reduction to practice or over complicates things beyond recognition. I find this very interesting.
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?
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.
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.
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.
> 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.
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.
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!"
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).
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.
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.
> 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.
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.
> 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.
Your trifling quibbles don't matter. It doesn't matter what you call it or how you implement it, my original point stands. The Dr. is suffering from a lack of imagination.
Trifling quibbles? It was "airtight gaps" that brought Challenger down and killed seven astronauts. If you intend to argue using words, at least learn their meanings.
You're the one who can't use words properly. A "gap" is a generic term, an "airtight gap" is a type of "gap."
You're quibbling about words, you're on the wrong side of the quibble, and on top of all that, you're not even dealing with the main point I brought up.
No. It specifically states that the pipe is not constrained to the pylons longitudinally (along the pipe direction). It slides. It's only fixed laterally and vertically, and has dampers in those movement directions.
Think of it this way -- if the pipe bent easily, you could rotate the entire hyperloop on top of the pylons, sliding it along the top.
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.