
On Hyperloop - minikites
http://www.leancrew.com/all-this/2013/08/hyperloop/
======
jblow
Any time one is trying to have a serious argument, one must do it from the
Principle of Charity:

[http://en.wikipedia.org/wiki/Principle_of_charity](http://en.wikipedia.org/wiki/Principle_of_charity)

This article doesn't even come close. Elon Musk is in charge of the design of
rockets that have successfully delivered payloads to the ISS. It is just basic
competence of a reasoning mind to presume Elon knows some things about thermal
expansion (rockets get very hot!).

So someone who is trying to have a reasonable argument would say, okay, he
understands this issue, so I wonder what the answer is and why he doesn't
think it is a big enough deal to go into detail on this point. Or perhaps I
misunderstand something about the design (always a reasonable assumption!)

This article is about as far in bearing from that as can be. I don't find it
to be worth reading.

~~~
cousin_it
The principle of charity says one shouldn't fault other people for not
following the principle of charity ;-)

~~~
arjie
Haha, funny, but that requires an addendum: 'provided there exists an
explanation for their having abandoned it'.

------
zeteo
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."

~~~
npalli
No, his attitude is entirely appropriate. Learn your basics before you try to
reinvent stuff. As Alan Kay keeps reminding us, the programming community
doesn't really learn anything that is done in the past and is doomed to keep
reinventing stuff or working on things that have been shown not to work. For
example, if you study physics you are not going to go far if you show up to
class and start dropping apples and say this shows some magic force is
operating. Learn the basics of engineering first then try to change things.
Otherwise you will just waste everybodys time.

As for your programming example, the more appropriate case would be if someone
showed up with a revolutionary proposal to allocate memory for a GC, you see
the source code and there is a big array structure defined locally "char
memory[10000000]". There is far more things wrong here than trying to figure
out ways to scale this in production.

~~~
arethuza
"Learn the basics of engineering first then try to change things. Otherwise
you will just waste everybodys time."

So what about SpaceX and Tesla? To me those indicate that Musk must be a
pretty decent engineer, and perhaps more importantly, must be _excellent_ at
leading real hardcore engineers in complex domains.

~~~
simias
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...

~~~
jblow
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?

~~~
nonchalance
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)

~~~
ash
> key points (like the issues with thermal expansion) are legitimate
> criticisms

No, thermal expansion criticism is not careful enough. See my comment:

[https://news.ycombinator.com/item?id=6238022](https://news.ycombinator.com/item?id=6238022)

~~~
wheremiah
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.

~~~
rossjudson
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._

------
terryjsmith
I'm disappointed with the tone here; not in a "you should be nicer" kind of
way, but because he seems to assume that Musk is acting insultingly in his
proposal.

This seems to me to be the way all startup ideas start: there's a hypothesis
about X, so far I've found documentation to support that it is likely feasible
to do (there are no immediate show stoppers), here's why, and so therefore
I'll go off and build it and deal with things as they come up. I imagine this
is how Musk works and that this is how SpaceX and Tesla started. The only
difference is that this time Musk can't take it the rest of the way so he
wants the community to take over the next phase if there's ample interest.

This article reads to me as coming from someone who wouldn't take on this
endeavour themselves, and that's perfectly fine, but he instead comes across
as entirely destructive, condescending and insulted (somehow?) when he may
very well be able to contribute something.

~~~
jfb
You don't have to get into thermal expansion and FEA to know that the
Hyperloop proposal is back-of-the-napkin quality. As to why Musk did this --
dropped this hand-wavy shell of a proposal -- I don't know.

~~~
jhuckestein
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.

~~~
mcguire
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?

~~~
ameister14
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?

------
kbenson
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?

------
delinka
Someone correct my thinking: you don't have to add up all the expansions
because you don't butt each pipe against the next. You leave that 1.5" gap,
you build the gap ring out of airtight handwavium, and the tube sections don't
push each other around. Right?

This is how I read Musk's original proposal.

~~~
6ren
I think there is an inconsistency in the proposal, because he clearly
mentioned cumulative expansion (page 5 of the pdf
[https://docs.google.com/viewer?url=http://www.spacex.com/sit...](https://docs.google.com/viewer?url=http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf)):

    
    
      A telescoping tube, similar to the boxy ones used to access airplanes at airports
      would be needed at the end stations to address the cumulative length change of the
      tube.
    

If you're absorbing all the changes in length at the pylons, you don't need to
absorb cumulative changes.

Another reading is that the welded joints don't need to coincide with the
pylons - that's just how it was constructed, not how it's supported. The tube
ends up being continuous, with nothing special about the part of resting on
the pylons, and move freely on rollers or similar. However, this reading also
doesn't work, because he says of the dampers (also page 5):

    
    
      These would absorb the small length changes between pylons due to thermal changes...
    

So, there's an inconsistency. But it doesn't seem like a big one to me, and
not hard to overcome. And finding these bugs is one of the intended benefits
of open-sourcing it. I haven't looked into the second finite analysis one, but
though I looked for material consequences, it seems to be mainly a criticism
of presentation.

It amuses me that after spending his talent, time and money (he mentions at
the start that he's paying for his blog) helping Musk's proposal, this fellow
vents:

    
    
      I wouldn’t put my money, time, or talent in the hands of someone
      who takes me for a fool.
    

Musk caught him monologuing.

~~~
Gravityloss
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 ).

------
ash
Drang seems to think that Musk wants dampers (inside pillars) to handle large
thermal expansion:

> Eventually, the dampers in the pillars won’t be able to handle the movement
> because it’ll be greater than the pillar width. Eventually, the movement
> will be greater even than the distance between the pillars.

But the tube is "not rigidly fixed" to pylons. It slips past pylons during
expansion or contraction:

> By building a system on pylons, where the tube is _not rigidly fixed at any
> point_ , you can dramatically mitigate Earthquake risk and avoid the need
> for expansion joints.

In fact, the author quotes the above in the beginning of his article, but then
assumes exactly the opposite.

~~~
anologwintermut
I believe fixed and rigidly fixed have very different meanings in this
context. Your suggesting that the tube floats on the pylon(e.g on rollers).
The hyperloop paper suggests that it's attached with dampers that are, for
lack of a better term, elastic.

~~~
ash
I disagree. I think "fixed" means the tube attached to the pillar to prevent
it from jumping out of it. See rings in figure 3 (page 11):

[http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201...](http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf)

~~~
anologwintermut
Given that the proposal describes dampers used to absorb change, I think this
is wrong.

    
    
        By building a system on pylons, where the tube is not 
        rigidly fixed at any    point, you can dramatically    
        mitigateEarthquake risk and avoid the need for expansion  
        joints. Tucked away inside each pylon, you could place    
        two adjustable lateral (XY) dampers and one vertical (Z) 
        damper.
        
        These would absorb the small length changes between
        pylons due to thermal changes, as well as long form
        subtle height changes
    

(see page 11)

~~~
rossjudson
See section 4.2.3.

 _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._

------
Symmetry
The proposal was badly short on details here, but I think the author is
misunderstanding what is actually proposed. The special slip joints at the
stations have to be traversed at low speed because you're going from one tube
to another tube of a different size, having the tube slide back and forth
along the pylons might be hard engineering but I don't see any reason it
should effect the vehicle in the tube.

Also, there's no reason to think that the pretty pictures in the public
description are all the work they've done.

I do think that Musk is badly underestimating how much this is going to cost.
He's also being unfair by comparing his proposal to the legislative sausage
high speed rail that California is getting rather than the best sorts of high
speed rail you can find in France or Japan. But he isn't stupid.

~~~
vidarh
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.

------
ethagknight
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.

------
krmmalik
Here we go again.

Musk is going to invite all the same criticism and all the same premature
skepticism that all new Apple products always did. The critics never learned
and Apple never failed to exceed expectations.

I haven't studied the physics of hyperloop. Nor am I going to. I just don't
have the 'head' for it. But I've observed Musk, and if he says he can make it
work, or is going to find a way, then i'm absolutely positive he's going to
figure it out.

This is what it takes to move the human race forward. Dealing with extreme
cases of uncertainty and pushing ahead regardless. We need people like this in
our lives. The world and the human race needs it. The article says far more
about the blog author than it does about Musk.

Let it go!

~~~
dragonwriter
> But I've observed Musk, and if he says he can make it work

Even if such blind faith was justified, he _hasn 't_ said that.

Initially, he said "hey, here's this idea that would work better than CA HSR,
but I'm not going to work on it."

When the fact that he said he wasn't going to to work on it became part of the
grounds for people dismissing it, he changed tack a bit and said he would work
on a tech demonstration.

But he still has gone nowhere close to saying that he is going to make it work
as a project, or even put energy into to getting making it a real project.

> This is what it takes to move the human race forward. Dealing with extreme
> cases of uncertainty and pushing ahead regardless.

There's a difference between extreme uncertainty and certainty that basic bits
of what is necessary for what you claim a system is going to deliver are
missing. Like, in the case of a supposed SF-to-LA-faster-than-HSR system,
actually having connections into the parts of SF-to-LA where people are and/or
want to go that allow you to move between them faster than HSR would...

And not having vomit-inducing acceleration profiles...

Etc. "Uncertainty" isn't the main issue with the Hyperloop proposal; the parts
that are certain-and-wrong are a much bigger deal.

~~~
krmmalik
OK, that's a fair enough point. I can't argue with it.

------
phreeza
It is nice to see some criticism on HN. The tone of the post is a bit off but
apart from that the points made should be considered.

Personally I don't see the problem with a 150m slippage tolerance, but I think
it might have to come before the fixed base stations. basically I could
imagine the tubes transitioning into a slightly larger enclosing tube which is
able fixed to the base station. surely there are other alternatives and unlike
the OP I think the quotes from the report sound to me as if Musk hasn't
thought of this at all.

As for the FEM analysis I would tend to agree that the value does not go far
beyond being a pretty picture in its current form.

~~~
thedufer
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.

~~~
saalweachter
Is that really the only problem?

It seems to me that expecting hundreds of miles of pipe to be pushed back and
forth hundreds of feet (albeit presumably slowly) puts a heck of a lot of
stress on the self-same pipe. How is this that much different from building a
side-ways space elevator? Even if it's easier to push sideways than up, it
still adds up to quite a bit over hundreds of miles.

------
dojomouse
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?

------
jhuckestein
Well, if the problem of building a hyperloop or similar system is now reduced
to the more well defined problems mentioned in the post, we're still better of
than before the proposal.

The OP claims that the structural analysis and graphics in the proposal are
not useful and goes on "This is eyewash for the rubes, the surest sign you’re
dealing with a snake oil salesman.".

I don't think that is the most likely reason for including those bits. More
likely, this is the work of engineers from different fields taking a stab at
something new and making mistakes. If this is the case, I applaud them for
their bravery. For each point in the post, Musk can now hire a room full of
experts to work on that. I'm sure anyone who has ever picked up work in a
related but new field has made similar mistakes.

On a different note, I don't understand why this post is so petty and often
crosses into the unconstructive... If "Dr Drang" is reading this, please
consider editing your blog post and removing the parts about snake oil, other
engineers being able to do these calculations in their sleep etc. You're doing
a disservice to your otherwise very insightful post and the work that clearly
went into it.

~~~
anologwintermut
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.

------
lutorm
I don't understand the comments about snake oil and the other vitriol. Why
jump to conclusions about the author's motives instead of just taking it for
what it plainly is: a draft idea put together in the spare time by Elon and a
few SpaceX and Tesla engineers? He's not trying to get funding for it, so
what's the motivation for trying to hide some fundamental flaw?

It seems the article is more concerned about criticizing the details of the
proposal rather than the idea.

~~~
dalke
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...](http://www.time.com/time/business/article/0,8599,186660,00.html)

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.

------
Gravityloss
Valid concerns, but why does he have to write like to a five year old?

~~~
lewispollard
For people like me who have no knowledge of non-software engineering ;)

------
joyeuse6701
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.

------
acqq
For those who missed other criticisms, see also:

Musk's Hyperloop math doesn't add up

[https://news.ycombinator.com/item?id=6232573](https://news.ycombinator.com/item?id=6232573)

 _Musk 's proposal won't actually get riders to the downtowns of Los Angeles
or San Francisco. It can only carry around 10% of the capacity of the
California High-Speed Rail. Additionally, it will bypass other population
centers, like Bakersfield, Fresno, and San Jose. Building a truly workable
Hyperloop, if it's feasible at all, will be significantly more expensive than
Musk claims. It might even be more expensive than the California HSR project.
And Musk's proposal leaves a lot of questions unanswered._

And:

Loopy Ideas Are Fine, If You’re an Entrepreneur

[http://pedestrianobservations.wordpress.com/2013/08/13/loopy...](http://pedestrianobservations.wordpress.com/2013/08/13/loopy-
ideas-are-fine-if-youre-an-entrepreneur/)

 _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...](http://stopandmove.blogspot.fr/2013/08/hyperloop-proposal-bad-joke-or-
attempt.html)

    
    
            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._

~~~
dragonwriter
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.

~~~
acqq
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.

~~~
aryastark
> 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.

~~~
acqq
From the PDF:

Picture:

[http://www.rtcc.org/files/2013/08/Hyperloop-passenger-
capsul...](http://www.rtcc.org/files/2013/08/Hyperloop-passenger-capsule-
version-cutaway-with-passengers-onboard.jpg)

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:

[http://www.economist.com/blogs/gulliver/2013/08/hyperloop](http://www.economist.com/blogs/gulliver/2013/08/hyperloop)

------
simonebrunozzi
The article seems legit, and the criticism too. However, I don't want to focus
on the technical details, for once. I'd like you to notice two things: 1) A
lot of people are talking about Hyperloop; Dr. Drang, even if he doesn't want
to, is ALREADY contributing to the project. These notes will be treasured by
whoever will try to build it eventually. 2) This seems to be a very smart
strategy (no surprise, given this is Elon Musk himself) to make Hyperloop
popular and break existing barriers to execution. These barriers could be:
investors' skepticism, Government scarce interest, or else. Well played, Mr.
Musk.

One more thing: I admire Elon Musk, and have no doubts about his intelligence,
ability of execution, reputation. However, let's not forget that he does it
for money too. This approach is also a very SMART way to get a ton of free
work, and thousands of individuals who would happily work on the Hyperloop
(thus, lower wages, as there is more offer). Again, well played.

~~~
dalke
"treasured"? No.

As was written, these sorts of calculations are easy to carry out by a
"sophomore or junior year of college", and specifically the thermal expansion
calculation is something taught in high school. It's like suggesting that
someone's notes on how to implement a linked-list would be "treasured" by a
Linux kernel developer.

Anyone who 'treasures' these comments is someone who isn't able to effectively
contribute to a civil engineering project.

You also have to consider the overall net effect. People who might have
contributed, had fundamental design issues like thermal expansion been
addressed head-on, are not going to contribute, under the assumption that it's
"put[ting] my money, time, or talent in the hands of someone who takes me for
a fool."

~~~
simonebrunozzi
"treasured", in the sense that everything that comes out of the discussion
(not just this SPECIFIC critique) will benefit whoever is going to implement
it. Some things will be trivial, like you suggest, but others won't.

~~~
dalke
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?

------
dclowd9901
Maybe I don't know enough about physics or thermodynamics, but this portion
puzzled me:

> Here, I’m showing the pipe sitting on the pillars at the low temperature.
> The lines and arrows above the pipe are where it expands to at the high
> temperature.

> Now add 100′ of pipe and another piller to either end. How much movement do
> the dampers in these new end pillars have to accomodate? Just ¾″? No. They
> have to accommodate 1½″ because their lengths change ¾″ and their “starting
> points,” so to speak, also change ¾″.

I won't pretend to understand what Musk was proposing, but for the sake of
argument, can't you simply allow the ends of each portion of pipe to expand
into _each other_ , thus creating a net change of 0? All you'd need is a
tongue-in-groove connection with a small gap of .75". For sealing the
connection, just line the tongue with rubber, and for aerodynamics, just line
the resultant gap with a thin strip of material.

~~~
Gravityloss
That would be hard to seal. The air cushion that the sled rides is also
sensitive to discontinuities.

------
jccooper
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?

------
lnanek2
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.

------
nicholassmith
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".

------
JayNYC
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.

------
cookingrobot
There are alloys like Invar (64FeNi) that are designed for low thermal
expansion. [1] It's used in common products like shadow masks in cathode ray
tubes.

It has a coefficent of expansion of 0.8 [2], so if you run the numbers again
it gives a total expansion of the tube of 127', or 63' per end.

I don't know the costs or if it would be suitable for this purpose, but it
seems to be about 3x as expensive as steel for raw stock.

[1] [http://en.wikipedia.org/wiki/Invar](http://en.wikipedia.org/wiki/Invar)
[2] [http://www.engineeringtoolbox.com/linear-expansion-
coefficie...](http://www.engineeringtoolbox.com/linear-expansion-coefficients-
d_95.html)

------
michalu
>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.

------
dmak
I appreciate the time he took to write this, but I cannot say the same about
his tone.

------
robomartin
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.

~~~
moocowduckquack
" _I do have a PhD in Having Designed and Built Lots of Shit._ "

Is that from the University of Life after a time spent at the School of Hard
Knocks by any chance?

~~~
robomartin
A man holding a cat by the tail learns something he can learn in no other way.
--Mark Twain

Love that one. Just when you think you are soooooo smart something comes
around to humble you. Life kinda works that way.

~~~
moocowduckquack
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.

~~~
robomartin
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.

~~~
moocowduckquack
Sorry, I think I was in a particularly argumentative mood.

------
wodow
Knocked offline?
[http://www.downforeveryoneorjustme.com/http://www.leancrew.c...](http://www.downforeveryoneorjustme.com/http://www.leancrew.com/)

~~~
wodow
Text-only Google cache has it:
[http://webcache.googleusercontent.com/search?q=cache:http://...](http://webcache.googleusercontent.com/search?q=cache:http://www.leancrew.com/all-
this/2013/08/hyperloop/&strip=1)

------
jessaustin
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?

------
MortenK
These last few posts about hyperloop, while looking like valid criticism just
reeks of envy, jealousy and sour grapes. It become obvious when you
intersperse your arguments with descriptions of Musk as being "loopy",
"stupid", "amateur", "fraud", "snake oil salesman" and the like. It's so
typically academia, it's depressing.

Luckily guys like Musk are out actually accomplishing things, while the
professors are whining about why it can't be done.

~~~
makomk
I find accusing Hyperloop critics of whining whilst Musk's out there
accomplishing things really ironic under the circumstances. Musk has no
intention of building this - he's just done a bunch of back-of-the-envelope
calculations that he's using to take a dig at the people who are out there
actually accomplishing something with California HSR. Sure, it may not be
ideal, but they're actually doing something whereas Musk's just sniping at
them whilst sneakily handwaving away all the difficult parts of the problem.

~~~
MortenK
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.

------
taylorbuley
> 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.

------
tocomment
I agree with others. This article comes across as too negative. There's really
no reason it needs to be.

------
j2d3
I guess I didn't read Hyperloop documents correctly, but I thought that the
solution proposed for thermal expansion as well as earthquake mitigation was
tube in tube expansion system at EACH joint, and dampers in X, Y, and Z axis
under EACH pylon.

------
marze
Those are minor issues compared to the issue of the bored farm-kid with a
hunting rifle.

------
knodi123
I'd also like to see someone assess the economic impact of terrorism on these
hyperloop proposals.

Isn't that an incredibly juicy target? Hundreds of miles of tube, but bad guys
only need to blow up one piece to cripple the tube for a significant amount of
time, not to mention those poor souls who are about to be fired from the tube
like a bullet.

And let's not forget what a juicy target the capsules are, too. I anticipate
the TSA stepping in and drastically increasing both the cost and the delays,
not to mention the invasive body checks.

These kinds of attacks are a foregone conclusion, but I keep hearing people
talk about how this will be "so much more convenient than an airport, and
cheaper too!"

But airplanes are fungible- tubes are not.

~~~
zevyoura
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).

------
mnml_
Why so angry ?

------
Gravityloss
There would need to be a hyperloop wiki to list concerns of various
technological areas.

------
jredwards
Isn't "because Instagrams are incredibly low risk and Hyperloops are
incredibly high risk" a simple enough explanation?

------
orillian
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.

------
wissler
I am no expert on such things, but it seems to me that Dr. Drang has a very
basic misunderstanding or lack of imagination. He seems to assume that Musk
intended for each section of tube to physically be touching, when instead Musk
intended to leave gaps between, to account for the expansion.

~~~
lutusp
> He seems to assume that Musk intended for each section of tube to physically
> be touching, when instead Musk intended to leave gaps between, to account
> for the expansion.

Because the tube must be maintained at a near-vacuum, it can't be "gaps" \--
it would have to be expanding slip joints, maybe like those on the Space
Shuttle solid-rocket boosters. So, expanding joints in a tube that, by being
evacuated, must bear a constant load of 14.7 PSI and remain airtight?

> ... it seems to me that Dr. Drang has a very basic misunderstanding or lack
> of imagination.

Perhaps, but on present evidence he's not the only one lacking imagination.

~~~
wissler
_Because the tube must be maintained at a near-vacuum, it can 't be "gaps" \--
it would have to be expanding slip joints_

Well you're doing to me what the Dr. is doing to Musk. Obviously they'd have
to be airtight, but there would indeed be gaps _between_ the sections. Jesus.

~~~
lutusp
> Obviously they'd have to be airtight, but there would indeed be gaps between
> the sections.

I objected because you used the term "gaps". They cannot be gaps, they have to
be overlapping airtight section joints. There were no gaps between the
sections of the Space Shuttle solid-rocket boosters either, except just once,
and we all remember that day.

To understand the problem with your description, just repeat to yourself,
"airtight gaps", until the contradiction occurs to you.

~~~
wissler
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.

~~~
lutusp
> Your trifling quibbles don't matter ...

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.

~~~
wissler
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.

Please tell me you're not a programmer.

