# Hyperloop : pie in the sky or is it time? **URL:** \ **Category:** Factual Questions\ **Created:** [August 13, 2013, 6:37am UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116 "2013-08-13T06:37:17Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 13, 2013, 9:49pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/41 "2013-08-13T21:49:17Z")
> [@Exapno\_Mapcase](#): > > He requires 100% capacity and availability with not an empty seat or a moment of downtime for maintenance in both directions! That’s how he gets his 20-year return. The paper doesn’t advocate a ticket price of $20. That’s just the price of paying for the infrastructure with his optimistic estimates. Obviously the price won’t be that low–why would it? It is superior to plane travel in virtually every way and so can justify a ticket price at least as high–somewhere in the $100-$150 range. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 13, 2013, 9:54pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/42 "2013-08-13T21:54:17Z")
> [@Exapno\_Mapcase](#): > > “They laughed at Columbus” is the single dumbest point that can ever be made in favor of something. Likewise, “it’s never been done before, therefore it can’t be done” is the stupidest point that can be made against something. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 13, 2013, 10:00pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/43 "2013-08-13T22:00:47Z")
> [@Dr.Strangelove](#): > > Likewise, “it’s never been done before, therefore it can’t be done” is the stupidest point that can be made against something. Good thing nobody’s saying that. ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [August 13, 2013, 10:03pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/44 "2013-08-13T22:03:32Z")
> [@Habeed](#): > > There’s a huge aluminum blade sticking out the bottom of the tube car. However, in order to handle turns, the car has to be able to bank so that the G force of the turns is oriented downwards relative to the passengers. This is an essential element of the design, apparently, high speed trains have big problems with curves because passengers don’t like side-ways Gs. > > The banking is done either by using a huge control moment gyroscope in the tube car that causes the entire car to tilt sideways, or reaction thrusters that send a constant stream of compressed air out a rocket nozzle to achieve the same effect. (the original paper says it’s one or the other, but he didn’t figure out which method would be better) > Anyways, since it can bank, there’s a risk that it could be in a “banked” configuration when it reaches a part of the track that has one of those linear motors. The massive aluminum blade would slam into the iron cores of the stator coils embedded in the track, at possibly 800 mph. > > That sounds bad. Well, if I were designing it, I’d put the car on a central longitudinal axis pivot and allow the attitude control stuff to act on it, and have the power and tube-relation stuff on a fixed-orientation frame. The linear motor pickup never has to shift orientation with respect to the tube. That moves the mechanical failure risk to the bearings between tube-following frame and car, but at least it’s not a Mach 1.1 collision with the linear motor track. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 13, 2013, 10:16pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/45 "2013-08-13T22:16:03Z")
> [@Exapno\_Mapcase](#): > > Good thing nobody’s saying that. Many of the comments are morally equivalent. Simply objecting, and saying that it will take 10x the cost, or that it’s too dangerous, or whatever, without the slightest shred of evidence, is a vacuous statement. It’s content-free. In short, while we might learn something from the types of cost overruns we see in different projects, for the most part history doesn’t tell us anything about the success of a new technology. That goes both ways. Many technologies were vastly more successful than anyone could have predicted. And some were utter failures. Anyway, I’m not even disagreeing with you in the end. Build a prototype section and see how it works. The idea is worth that much, at least. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [August 13, 2013, 10:17pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/46 "2013-08-13T22:17:19Z")
> [@Exapno\_Mapcase](#): > > “They laughed at Columbus” is the single dumbest point that can ever be made in favor of something. Correct me if I’m wrong, but didn’t they laugh at Bozo the Clown, too? ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 13, 2013, 10:23pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/47 "2013-08-13T22:23:36Z")
> [@gnoitall](#): > > Well, if I were designing it, I’d put the car on a central longitudinal axis pivot and allow the attitude control stuff to act on it, and have the power and tube-relation stuff on a fixed-orientation frame. The linear motor pickup never has to shift orientation with respect to the tube. > > That moves the mechanical failure risk to the bearings between tube-following frame and car, but at least it’s not a Mach 1.1 collision with the linear motor track. It also makes sense to have a retractable blade. The blade only extends when it detects that the car is lined up correctly. If the car misses the blade, it will have to coast for the next section, but that’s not a catastrophic failure. The gyros/thrusters don’t have to do a whole lot of work. The bulk of the banking effort will be handled simply by having a center of mass below the tube center. The extra control is only necessary for damping oscillations and providing fine control. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 13, 2013, 10:38pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/48 "2013-08-13T22:38:21Z")
> [@Dr.Strangelove](#): > > Many of the comments are morally equivalent. No, they’re really not. They are quite properly pointing out various flaws in the proposal. And Musk has been backing away from the proposal at nearly the speed of his pods. He realized that he overpromised and cannot back up anything he says because it simply doesn’t exist yet. Not a demonstration project, not a prototype, not a proof-of-concept. Nothing but lab specs. You cannot defend technology that doesn’t exist. If you allow his proposal to stand without opposition, then what can you criticize? Every proposal of every kind by every person becomes sacrosanct. > [@](#): > > Anyway, I’m not even disagreeing with you in the end. Build a prototype section and see how it works. The idea is worth that much, at least. Which is of course what he should have done. Even Dean Kamen did that with the Segway, which while overpromised was an excellent piece of technology that people could evaluate. But I will guarantee here in print that his cost estimates are low. You know that, too. Cost estimates on unknown, unbuilt technology and projects are always too low. That’s how you get people to sign on. If you start by saying it’ll cost a trillion dollars, no one will ever pay attention. If Robert Goddard had told the Smithsonian that getting a rocket up to space would cost literally a billion dollars, they’d have committed him. But start low and you can creep the price up and up. I haven’t checked, but I guarantee that Musk’s original numbers and timelines for Tesla and Space-X are already laughable. There are no exceptions and I would be astonished - and would apologize here - if you could name one unbuilt technology that cost less than or equal to the first estimate. ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [August 13, 2013, 10:41pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/49 "2013-08-13T22:41:20Z")
The Segway was supposed to be The Next Big Thing, too. It now seems to be used mainly by security guards, and as a toy. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 13, 2013, 11:12pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/50 "2013-08-13T23:12:00Z")
> [@Exapno\_Mapcase](#): > > And Musk has been backing away from the proposal at nearly the speed of his pods. He realized that he overpromised and cannot back up anything he says because it simply doesn’t exist yet. Not a demonstration project, not a prototype, not a proof-of-concept. Cite, please. In [this](https://soundcloud.com/kqed/musk-mp3) radio interview he says he’s planning on using his own money to build a demo project at some point. > [@Exapno\_Mapcase](#): > > Nothing but lab specs. You cannot defend technology that doesn’t exist. If you allow his proposal to stand without opposition, then what can you criticize? Every proposal of every kind by every person becomes sacrosanct. You criticize it on technical grounds. Projects fail for specific reasons. The California HSR project has ballooned in cost for reasons such as land right of way and terrain leveling. Musk’s proposal avoids these to a large extent, but may have other problems. If you have objections, name them–but be specific. Otherwise you are worse than what you accuse him of (with regards to handwaving some numbers). > [@Exapno\_Mapcase](#): > > Which is of course what he should have done. Even Dean Kamen did that with the Segway, which while overpromised was an excellent piece of technology that people could evaluate. You’re missing the point. This is a design proposal which Musk has from the very beginning said is only a starting point for discussion, and that many details still need to be fleshed out. If anyone was expecting the kind of 100,000 page document you’d need to _really_ complete the design, they were badly misled and should have been paying attention to what Musk said and not what some journalist said about him. It was never intended to come out fully formed. > [@Exapno\_Mapcase](#): > > There are no exceptions and I would be astonished - and would apologize here - if you could name one unbuilt technology that cost less than or equal to the first estimate. Well, I suspect I could find one, but that we’d be stuck in some semantic morass of what it really means to have an unbuilt technology. The more important point is that just because cost overruns happen, you don’t get to arbitrarily declare a 10x factor. I could point out that the Apollo program had a cost overrun of [less than a factor of four](http://science.ksc.nasa.gov/shuttle/nexgen/Nexgen_Downloads/Butts_NASA's_Joint_Cost-Schedule_Paradox_-_A_History_of_Denial.pdf) from the original budget. Surely if we can get to the moon with that level of budget bloat, we can get from SF-\>LA, right? No; it would be as ridiculous for me to claim that as you with 10x. It’s not wrong to look at other programs for insight, but if it’s going to be useful at all they need to be comparable. The Keystone pipeline would be a good start (for the infrastructure parts of the project) if there were a breakdown of where the costs went. I find it likely that the high-tech parts of the project are actually the least risky piece. The cars are not high technology. The basic components are mostly stuff that Tesla and SpaceX do already. They haven’t been immune to cost overruns, but they still have a pretty good record. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [August 13, 2013, 11:12pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/51 "2013-08-13T23:12:01Z")
> [@Habeed](#): > > Every section is supposed to be cleanly seam-welded to every other section, so it’s supposed to be a continuous mass of steel tube from one end to the other. Hopefully nowhere for it to leak except at the airlocks, pumps, etc. How do you handle expansion and contraction due to temperature then? One of the most common causes of train derailment is track buckling due to thermal expansion of the rails. I see Musk did some hand-waving about putting thermal expansion joints at each station, but that doesn’t nearly cover it. I just did some quick math using the coefficient of expansion of a steel pipe, and if we assume that it would be designed to handle a minimum temperature of 0F and a maximum of 120F, then tube between LA and San Franscisco would need to be capable of dealing with a change in length of about 1386 ft! Even if you design it to handle a temperature fluctuation of only half that, you still need to be able to handle a change in length of almost 700 feet. Musk breaks the route into four sections - two really long ones and two short ones. Those long ones have bends in them. That means the track is going to slide not just back and forth, but from side to side. The curved sections of tube are going to move hundreds of feet back and forth, meaning the whole shape of the track will change. I don’t see how you can build a curving multi-hundred kilometer tube without expansion joints. For one thing, every concrete pylon fitting would have to be on bearings to allow the tube to slide back and forth or all those pilings would be torn apart on the first day. And if the track isn’t perfectly straight, the expansion would cause every section of the track to move laterally, too. You can look at this yourself - if you plan for a 120 degree possible temperature change, then you have to handle a track that will expand/contract about 47 inches per mile. So let’s say you go 10 miles east, then curve and go north. That curved section of track is going to move out of position by 39 feet as the temperature changes. That means the whole north section of the track will be displaced by 39 feet. So you would have to put the whole thing on pilings that are at least that wide, and the whole thing would have to be on sliding bushings. However… The northern section of track is also expanding, and it’s over 100 miles long. So your east-west section is going to be displaced north/south by as much as 390 feet. Are you going to build concrete pilings 400 feet wide to handle that? Musk doesn’t handle this at all - his pilings are curved on top to hold the tube snug, which means they can’t tolerate any lateral displacement at all. I don’t see how that can possibly work unless each section of tube has an expansion joint so that the overall length stays the same. At the very least, you would have to have something like a station before each direction change, and handle a significant amount of linear expansion/contraction there. I suppose the tube could be on bearings and move back and forth on them. Two stations 100 KM apart would then each have to be able to handle a tube that is moving back and forth at maximum of about 200 ft, and on a typical day with maybe a 50 degree change in temperature between day and night about half of that. I can imagine a set of overlapping tubes on some kind of sliding joint, with the car going through them very slowly. But that kind of defeats the whole point - you simply couldn’t have high-speed curves at all because you’d have to have expansion joints on either side of the curve. You might as well just slow the car down and then turn it tightly inside the station. Heck, expansion would be significant even inside the curve. For example, Musk calls out one curve with a radius of 2.81 miles. It’s a shallow curve, so let’s say the length of that curved section is 4 miles. The curve itself would change in size by 15 feet, displacing the entire track and changing the location of the tube with respect to the pilings all along its length. More to the point, since the bend radii would change with temperature, the curved steel tubes would bend and buckle unless they are very elastic. Over time they would weaken from constant bending. > [@](#): > > Onboard each capsule are some compressed air tanks that feed air through regulator valves to the individual skis. The jet turbine is to reduce drag and keep these air tanks full. If the turbine fails, the car is going to slow to a stop gradually - most air will bypass the car because it isn’t “tight” against the tube walls like a syringe, about 40%-60% of the frontal area is empty space. (I wasn’t able to determine which, maybe you can) I was going to nitpick about the energy required to compress the gas into tanks and the problem of heating the gas as it compresses, but it looks like Musk has considered that and added intercoolers and steam vents to cool the compressed gas and reclaim the heat when the car stops. I don’t know if his math is right or not, but I do know that compressing gas causes it to heat up substantially so these cars will have significant thermal management issues. I also think he underestimates the cost of maintaining a near-vacuum in a volume so huge. > [@](#): > > If a tube section catastrophically fails in that someone blows it up, people will probably be killed. But that failure mode is present in the alternative methods of transportation. No, it really isn’t. In other transportation systems like a railroad track, a bad section of track affects only the train that hits it. A catastrophic re-pressurization of the tube would effect every car. Granted, with proper sensors and the length of time it would take the pressure wave to move down the tube you could start emergency-braking vehicles and get the further ones stopped before the pressure wave hit them. I’d be interested to see a model of what exactly would happen, though. Can you imagine the forces involved when 350 miles of tube with a 14.7 PSI pressure differential suddenly opens up? More quick math: The volume inside the ‘small’ tube would be 222,816 cubic feet per mile. That’s about 18,000 lbs of air per mile that would be sucked out of the tube system - all of which would come rushing back in if the tube failed. Just how fast do you think that would be going after a mile or two of acceleration inside the tube if it was breached? My guess is that the pressure wave would rise to near transonic speeds and smash everything in its path. Maybe you’d have to design it with explosive panels situated along the length so that you could rapidly equalize the tube if there was a breach or something like that. Those are the kind of little engineering problems that crop up once you get past the ‘handwaving’ stage of the design. > [@](#): > > There are some tricky bits totally unaddressed in the paper. For instance, how do you build “junctions” in the system, to where there are 2 tubes that a onrushing car could go down…how do you force the car to go down one tube or the other? (and never under any circumstances slam into the dividing wall) Why do you need junctions? Once the cars get to the end and through the airlock, you can just wheel them around into the return tunnel and send them on their way, can’t you? I don’t think there’s a scenario where the cars need to pass each other. The problem is what do you do with trapped cars if the ends of the tunnel are damaged? I know Musk designed them with emergency air and the ability to travel under their own power at a slow speed, but I don’t know that this really helps. For example, if a breach caused an explosive wreck at one end of the tunnel, a car near the end would have to backtrack 350 miles. I think you’d have to plan for emergency exits. Maybe every few miles there’s a special section of the tube that can be opened up to remove trapped passengers - that might also be designed to blow open if that humongous pressure wave comes flying down the tunnel, helping to release the energy before it smashes the pods into confetti. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [August 13, 2013, 11:31pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/52 "2013-08-13T23:31:41Z")
> [@gnoitall](#): > > Well, if I were designing it, I’d put the car on a central longitudinal axis pivot and allow the attitude control stuff to act on it, and have the power and tube-relation stuff on a fixed-orientation frame. The linear motor pickup never has to shift orientation with respect to the tube. > > That moves the mechanical failure risk to the bearings between tube-following frame and car, but at least it’s not a Mach 1.1 collision with the linear motor track. That’s an excellent idea! The pressurized part of the car that holds the passengers would need an independent suspension from the undercarriage. Musk was proposing that the individual “skis” will have suspensions to dampen out vibration, but instead putting that those dampeners between the passenger section and the undercarriage is a better idea. So, not only would it have a suspension, but an electric motor would be able to twist the passenger module to an orientation different from that experienced by the undercarriage. Second, there would be guidance groves in the track itself that the “skis” would be forced to follow. Basically, the skis would be trapped in these indentions in the track. This would lock the transit car into following only one possible path. Junctions would take advantage of this, though, I only have a rough idea in my head of how to use this. Active control systems may be cool, but a design that doesn’t need them is superior. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 13, 2013, 11:32pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/53 "2013-08-13T23:32:31Z")
> [@Sam\_Stone](#): > > No, it really isn’t. In other transportation systems like a railroad track, a bad section of track affects only the train that hits it. And when that happens, [80](http://www.cnn.com/2013/07/30/world/europe/spain-train-crash/index.html) or [100](http://en.wikipedia.org/wiki/Amagasaki_rail_crash) people die, or maybe [500](http://en.wikipedia.org/wiki/Bihar_train_disaster) if you live in the wrong country. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [August 13, 2013, 11:41pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/54 "2013-08-13T23:41:53Z")
So, essentially, you need thermal expansion joints every mile or so to keep from having to handle extreme changes in lengths. Well, the simplest such joint sounds like a bigger section of tube that fits over the two inner sections, with huge O-rings inside it to reduce air leakage. And, then, somehow the inner surface of the tube has to retain a nice smooth surface for the parts of the tube that the skis will travel along. I’m thinking 4 sets of skis- 2 horizontal ones and 2 near the ground at 45 degree angles with respect to vertical. The horizontal ones will take the load in a curve. This is the kind of useful feedback I was hoping for. That’s a huge problem, it’s hard to think of a thermal expansion joint that doesn’t leak air. ---
**Author:** ![Backwater\_Under\_Duck](https://avatars.discourse-cdn.com/v4/letter/b/ba8739/32.png) [@Backwater\_Under\_Duck](https://boards.straightdope.com/u/Backwater_Under_Duck)\ **Post date:** [August 13, 2013, 11:51pm UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/55 "2013-08-13T23:51:31Z")
> [@Habeed](#): > > So, essentially, you need thermal expansion joints every mile or so to keep from having to handle extreme changes in lengths. > > Well, the simplest such joint sounds like a bigger section of tube that fits over the two inner sections, with huge O-rings inside it to reduce air leakage. And we know exactly how reliable O-rings are. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 14, 2013, 12:02am UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/56 "2013-08-14T00:02:43Z")
> [@Dr.Strangelove](#): > > Cite, please. In [this](https://soundcloud.com/kqed/musk-mp3) radio interview he says he’s planning on using his own money to build a demo project at some point. I can’t play that now, but in [this article](http://www.slate.com/articles/health_and_science/transportation/2013/08/elon_musk_s_hyperloop_a_realistic_alternative_to_high_speed_rail.html), he’s clearly indicating that any future is “if,” “maybe,” “someday,” and “I’ve got to learn to think before I speak.” > [@](#): > > You criticize it on technical grounds. You can equally validly criticize it on political, economic, or social grounds. All are part of the reality that technology lives in. > [@](#): > > You’re missing the point. This is a design proposal which Musk has from the very beginning said is only a starting point for discussion, and that many details still need to be fleshed out. And we are indeed discussing it. But the discussion does not have to be positive. > [@](#): > > I could point out that the Apollo program had a cost overrun of [less than a factor of four](http://science.ksc.nasa.gov/shuttle/nexgen/Nexgen_Downloads/Butts_NASA's_Joint_Cost-Schedule_Paradox_-_A_History_of_Denial.pdf) from the original budget. You could, but I would hope for your sake that you wouldn’t. The Apollo project came along more than four decades into serious liquid-fueled rocket research. The Germans spent far more than a mere 10X projections to get the V-2 into reality. Goddard never had more than $100,000 or five orders of magnitude less than he needed. Rocketry is a very, very bad example for your side. If you want to play a game of fantasy tech, have all the fun you want. You can play this with anything: a space elevator, engineering the oceans to prevent global warming, putting a dome over Manhattan. But if you do play the game of Musk’s toy train, remember that I always have a trump card: it doesn’t exist and no one in the world is actively working on it. That beats any argument you can make. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 14, 2013, 12:03am UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/57 "2013-08-14T00:03:01Z")
> [@Habeed](#): > > This is the kind of useful feedback I was hoping for. That’s a huge problem, it’s hard to think of a thermal expansion joint that doesn’t leak air. For whatever system you come up with on the inside, the outside could be a welded metal accordion. No sliding joints or rubber seals or anything. Obviously you need to design it so as not to generate stress cracks, but steel has an infinite fatigue limit, so it’s perfectly reasonable to design a bending structure that lasts “forever”. I’m thinking a sawtooth-like gap on the inside might work well. An annular gap of several inches is a bit much for the air bearings to cleanly glide over, but if the gap could be angled relative to the travel path, the effective gap width could be reduced. ---
**Author:** ![aNewLeaf](https://avatars.discourse-cdn.com/v4/letter/a/ac91a4/32.png) [@aNewLeaf](https://boards.straightdope.com/u/aNewLeaf)\ **Post date:** [August 14, 2013, 12:15am UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/58 "2013-08-14T00:15:22Z")
> [@Backwater\_Under\_Duck](#): > > And we know exactly how reliable O-rings are. Used correctly and according to manufacturer specs, quite reliable. We saw a case once where these guidelines were not followed and learned a lesson. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [August 14, 2013, 12:21am UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/59 "2013-08-14T00:21:51Z")
> [@Sam\_Stone](#): > > I just did some quick math using the coefficient of expansion of a steel pipe, and if we assume that it would be designed to handle a minimum temperature of 0F and a maximum of 120F, then tube between LA and San Franscisco would need to be capable of dealing with a change in length of about 1386 ft! Even if you design it to handle a temperature fluctuation of only half that, you still need to be able to handle a change in length of almost 700 feet. First, we’re talking SF to LA. SF has a record high of 103, and a low of 27. LA’s max was 113, minimum was 28. So, the range is a little smaller than you’re looking at, but that does mean we might not be able to make one that covers Chicago to St. Louis, and the Twin Cities is just screwed… How does your analysis change if we assume there will be an expansion joint at the center of each pylon? ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 14, 2013, 12:27am UTC](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116/60 "2013-08-14T00:27:48Z")
> [@Exapno\_Mapcase](#): > > And we are indeed discussing it. But the discussion does not have to be positive. Sure. But it’s handy if the discussion involves concrete criticisms (Sam Stone has raised some very good points). > [@Exapno\_Mapcase](#): > > You could, but I would hope for your sake that you wouldn’t. The Apollo project came along more than four decades into serious liquid-fueled rocket research. And here we have the semantic morass of what it means to have an unbuilt technology. Obviously, I wasn’t talking about rockets, I was talking about the moon program. > [@Exapno\_Mapcase](#): > > The Germans spent far more than a mere 10X projections to get the V-2 into reality. When did I mention the Germans? At any rate, as I already said, this game of adding arbitrary multiplicative factors to a budget is useless on its own. > [@Exapno\_Mapcase](#): > > But if you do play the game of Musk’s toy train, remember that I always have a trump card: it doesn’t exist and no one in the world is actively working on it. That beats any argument you can make. I see; the “na na na, I win and you lose” method of debate. Did the GQ rules change? [Previous page](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116.md?page=2) [Next page](https://boards.straightdope.com/t/hyperloop-pie-in-the-sky-or-is-it-time/666116.md?page=4)