On Hyperloop
leancrew.com
leancrew.com
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.
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.
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.
Consider a parallel example -- Steve Jobs and Mike Markkula. Jobs made product decisions, Markkula funded them.
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, ...)."
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.
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."
> 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.
That makes it very hard to take his criticism seriously, and doubly so when the tone is so condescending.
- 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.
The author missed the "not rigidly fixed" part when he was analyzing thermal expansion issue. My comment:
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.
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.
>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.
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.
Besides, it's the idea that's important.
"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...
For more, and pictures, see http://en.wikipedia.org/wiki/Rail_stressing .
The UK had problems this summer because of buckling: http://www.dailyecho.co.uk/news/10549015.Rail_delays_as_trac... .
Then when it cools it pulls very hard, but because it has a tons of anchors on the ground it is able to handle the stress.
But it requires a very strong railway track. With the hyperloop the tube is not made that strong, and would tear.
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.
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.
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.
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...
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.
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)
No, thermal expansion criticism is not careful enough. See my comment:
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 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.
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.
[1] See, e.g., http://www.codeproject.com/Articles/582981/A-Coder-Interview...
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.
edit: fixed typo and added emphasis
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.
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]
[1] with apologies to Pulp Fiction.
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.
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.
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.
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.)
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
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?
No, but it is a pretty good claim to show an understanding of the basics that they supposedly haven't learned.
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.
More is different (PDF link: http://robotics.cs.tamu.edu/dshell/cs689/papers/anderson72mo... ).
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.
What? A link to a paywalled article with no abstract? That was constructive. Here's a real link:
https://www.tkm.kit.edu/downloads/TKM1_2011_more_is_differen...
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.
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.
"Academic physics" describes reality. It is the closest thing to an accurate description of reality that we have.
http://en.wikipedia.org/wiki/Theoretical_physics
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.
http://en.wikipedia.org/wiki/Applied_science
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.
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.
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.
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.
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.
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.
"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.
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.
> 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.
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.
How so? By insisting on their connection with established scientific principles? Astrologers would love for me to do that, as would psychologists.
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?
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.
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.
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...
So I guess the point is, apparently persistence counts for something.
How ? By hiring people who know how to easily build a SpaceX and Tesla.
> 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.
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.
http://pedestrianobservations.wordpress.com/2013/08/13/loopy...
From this article:
* Redefining SF and LA to Hayward and Sylmar allows the Musk proposal to make an extremely unfair trip time comparison, and, moreover, Musk's proposal can't easily do a "real" SF and LA because unlike HSR the Hyperloop can't repurpose infrastructure.
* At the speeds and course plotting Musk alludes to, the Hyperloop will make its passengers very motion sick.
* The costs Musk projects are unrealistic; for instance, if the Hyperloop can really construct elevated tracks at 1/10th the per-mile cost of existing viaducts, that cost improvement alone would be an equally important advance. Similar problems exist for the tunneling cost projections, and are exacerbated by the fact that a realistic course for the Hyperloop would probably require even more tunneling than projected.
There's a good MeFi thread on this too.
*I'm not an engineer however I did stay at a holiday inn express last night.
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.
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.
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?
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?
This is how I read Musk's original proposal.
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.
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.
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.
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...
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.
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 ).
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. ;-)
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.
> 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.
http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201...
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
That said, the quoted text is somewhat confusing. I had to read it a few times before I got the idea.
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.
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.
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).
Tubes are fixed to the pylons, just not rigidly (in longitudinal direction).
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:
http://blog.rongarret.info/2013/08/everything-you-need-to-kn...
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.
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.
Let it go!
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 was a statement more about leadership than about the products in themselves.
So, do you agree with me that your statement "Apple never failed to exceed expectations" is incorrect?
If so, then if Apple can have failures under Jobs' leadership then surely Musk can fail, even with great leadership.
If not, how did Apple exceed expectations?
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.
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.
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?
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.
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.
It seems the article is more concerned about criticizing the details of the proposal rather than 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.
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.
Musk's Hyperloop math doesn't add up
https://news.ycombinator.com/item?id=6232573
Musk's proposal won't actually get riders to the downtowns of Los Angeles or San Francisco. It can only carry around 10% of the capacity of the California High-Speed Rail. Additionally, it will bypass other population centers, like Bakersfield, Fresno, and San Jose. Building a truly workable Hyperloop, if it's feasible at all, will be significantly more expensive than Musk claims. It might even be more expensive than the California HSR project. And Musk's proposal leaves a lot of questions unanswered.
And:
Loopy Ideas Are Fine, If You’re an Entrepreneur
http://pedestrianobservations.wordpress.com/2013/08/13/loopy...
The proposed relationship between curve radius and speed in the Hyperloop standards is for a lateral acceleration much greater than 4.9 m/s^2 in the horizontal plane: 480 km/h at 1,600 meters is 11.1 m/s^2. This only drops to 5 m/s^2 after perfectly canting the track, converting the downward 9.8 m/s^2 gravity and the sideways acceleration into a single 14.8 m/s^2 acceleration vector downward in the plane of the capsule floor, or 5 m/s^2 more than passengers are used to. This is worse than sideways acceleration: track standards for vertical acceleration are tighter than for horizontal acceleration, about 0.5-0.67 m/s^2, one tenth to one seventh what Musk wants to subject his passengers to. It’s not transportation; it’s a barf ride.
The barf ride that is as expensive as California HSR and takes as long door-to-door is also very low-capacity.(...) The proposed headway is 30 seconds, for 3,360 passengers per direction per hour. (...) HSR can do 12,000 passengers per direction per hour: 12 trains per hour is possible (...) But even 30 seconds appears well beyond the limit of emergency braking.
And also:
Hyperloop proposal: Bad joke or attempt to sabotage California HSR project?
http://stopandmove.blogspot.fr/2013/08/hyperloop-proposal-ba...
High Speed Rail between downtown LA and downtown SF:
2 hours, 28 minutes
Hyperloop trip between downtown LA and downtown SF:
1 hour from LA to Sylmar via Metrolink
20 minute transfer
35 minutes to Dublin
20 minute transfer
1 hour 10 minutes from Dublin to SF via BART
Total: 3 hours 25 minutes
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.
But it doesn't surprise me to see that the civil engineering end may have equally basic problems, as well.
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.
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.
Picture:
http://www.rtcc.org/files/2013/08/Hyperloop-passenger-capsul...
Description:
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?
And finally:
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.
Another option is personal rapid transit grids: http://www.skytran.net/
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."
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?
> 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.
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?
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'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".
Very few invest in real hardware these days. I am looking for money for my own start up. Diabetes field. No Chance.
It has a coefficent of expansion of 0.8 [2], so if you run the numbers again it gives a total expansion of the tube of 127', or 63' per end.
I don't know the costs or if it would be suitable for this purpose, but it seems to be about 3x as expensive as steel for raw stock.
[1] http://en.wikipedia.org/wiki/Invar [2] http://www.engineeringtoolbox.com/linear-expansion-coefficie...
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.
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.
Is that from the University of Life after a time spent at the School of Hard Knocks by any chance?
Love that one. Just when you think you are soooooo smart something comes around to humble you. Life kinda works that way.
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.
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.
having had a negative run-in with musk in the mid-90s I have _never_ been under this illusion, at least wrt musk in particular.
Luckily guys like Musk are out actually accomplishing things, while the professors are whining about why it can't be done.
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.
Isn't that an incredibly juicy target? Hundreds of miles of tube, but bad guys only need to blow up one piece to cripple the tube for a significant amount of time, not to mention those poor souls who are about to be fired from the tube like a bullet.
And let's not forget what a juicy target the capsules are, too. I anticipate the TSA stepping in and drastically increasing both the cost and the delays, not to mention the invasive body checks.
These kinds of attacks are a foregone conclusion, but I keep hearing people talk about how this will be "so much more convenient than an airport, and cheaper too!"
But airplanes are fungible- tubes are not.
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.
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.
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.
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.
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 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.
Please tell me you're not a programmer.
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.