Hmm, another thought: if instead of air you maintained a sparse methane atmosphere, you could get a 140% the speed you could in air. More challenging to maintain such an environment, of course, since leaks into the pipeline would be air (unless the pipeline was surrounded by a thin methane sheath). At least it wouldn't be flammable - at such low partial pressures, there's no amount of air that could leak in that would lead to a flammable mixture.

Ammonia has similar performance to methane, but it's corrosive, so methane would probably be a better choice than ammonia. Neon also has similar performance to methane, but is way more expensive.

For the excellent performers, helium has a speed of sound 3x higher than air, and hydrogen 4x higher. But helium is rare and increasingly expensive, while hydrogen embrittles steel, leaks through almost anything, and leaks into the atmosphere have adverse consequences to the ozone layer. So I imagine both of those options are out.

If one scrubbed oxygen from the pipeline, with any sort of easily-oxidized material placed regularly in the pipeline, you should be able to get a couple percent boost in max speed, nitrogen has a slightly higher speed of sound than oxygen. But whether that would be worth it, probably not, unless the oxygen is problematic in other ways.

All of that said, I think the best option would be water vapor; at such low pressures, any water in the tube will automatically vaporize. Such a low partial pressure should pose no rust risk (that's actually very dry!), it's cheap, and most importantly, your vacuum pumps can simply discharge it and you can just feed more into the pipeline as needed, there's no need to filter it out or neutralize it first or anything. The more you approach a 100% water vapor atmosphere, the more you approach having 150% the max speed that air would give you. Instead of the 1190 kph/740 mph that the current Hyperloop design tops out at, you could potentially go upwards of 1790 kph/1110 mph. The downside is of course the increased pumping effort to try to keep the atmosphere as close to 100% water vapor.

If one could achieve a practical average 1000mph then that's 2 1/2 to 3 hours New York to Los Angeles, depending on how straight the line would be. For an express that stayed in the countryside, that is; each stop along the way would cost time. Hopefully the system would be smart enough to let passengers bundle together into "express" pods and let them bypass stations they don't want to stop at (although the lower in-town speeds would still be a hindrance)

Said who? It costs the same as a BMW 535i, yet only goes 265 miles. That's *not* revolutionary.

Given that the previous longest range before Tesla came around was in the ballpark of 40% that far and was produced by the hundreds, not the tens of thousands, and that the model S outperforms the BMW 535i, and has higher customer satisfaction ratings, and the whole teensy detail that no new US manufacturer that has anywhere near that order of sales for any type of car (let alone a radical new one) has been established since 1925... yes, that is damned impressive.

Using an engine designed by someone else

Where'd you get the impression that the Merlin was designed by someone else? Merlin is the most from-scratch engine design for an orbital launch vehicle in the US since the 1950s. It shares a few parts with older engines, such as the pintle injectors, but the vast majority of the engine is of brand-new design. The engine shares some similarities with work done at TRW, but it's not a TRW engine (doesn't even burn the same fuels). The reason that it's sometimes referred to as a descendent of work done at TRW is because TRW's former chief engineer is SpaceX's head of propulsion. He was tinkering on rocket engines in his garage that he felt he couldn't get support for at TRW when Musk picked him up; he proceeded to use his new position to create what became the Merlin series.

It's great engineering and no-nonsense construction from a company that hasn't (yet) become bloated by sucking on the DoD & NASA teats, , but that is *no* revolutionary.

Nice dodge: let me repeat: #Beating Ares 1 to the ISS for 2% of the development cost, on a rocket cheaper than the Russians and the Chinese, *without* the reuse that it was designed for": how the heck is that not bloody amazing and something to be celebrated? If it's so easy, then why hasn't everyone been doing it? And yes, people like you were all over the place here a few years ago saying they'll never get off the ground.

For it to be revolutionary, they'd have to come up with something *really* game changing, like... a fuel better than LH2/LOX which doesn't corrode everything it gets near

No, something that's "really game changing" is dramatic reductions in the price of getting to orbit, with serious potential for even more significant drops if reuse works out. That is bloody game changing if the term "game changing" has any meaning. The propellent mix is irrelevant. You can have the highest ISP fuel mix on earth and still cost a bloody fortune to get to orbit if it's not economical. The Russians beat the US for the longest time with much lower performance engines for that reason.

However, and sadly, getting a booster to land on a floating platform is "mere" engineering

Any more difficult challenge than that and you might as well just call it "magic". You don't get much harder in the rocketry world than something like that. Rocketry *is* engineering, and adding the word "mere" is just an insult.

The air on the outside is still going to *aggressively* want to rush in through any little crack.

Air is not magical. You can't put a pinprick in a partially evacuated tube and have it just suddenly equalize. Viscosity on the order of the size of small cracks highly limits the rate at which air can migrate in. A little crack or a leaky seal is simply not enough to overcome an air compressor.

To put it another way: the pressure differential here is approximately one atmosphere. Large trunk natural gas pipelines have a pressure differential of about 13 atmospheres. By your logic, a natural gas distribution infrastructure is utterly impossible because "the natural gas on the inside is still going to *aggressively* want to rush out through any little crack".

Let me see if I've got this straight: we can't build regular maglev trains because they're super-expensive (the engineering, construction and maintenance would be incredibly difficult), so... we'll just make it that much harder by wrapping a (partial) vacuum tube around it???

First off, let's make this clear. Hyperloop is not Maglev. In fact, the design document notes that they could use Maglev, but dismisses it as too expensive: "A viable technical solution is magnetic levitation; however the cost associated with material and construction is prohibitive." Hyperloop uses air bearings - skis operating in ground effect with the pipe.

Maglev trains are expensive for many reasons. The cost of having the track be able to provide forward propulsion however usually represents only the tiniest fraction thereof. First off, you have the reasons that rail is expensive, period (right of way costs, environmental reviews, and all of the other overhead). Then you have to have the entire route be able to lift up a multi-dozen to multi-hundred-tonne train. Not just propel, but actually hold it stably in the air, which is a far more difficult challenge for many reasons than propulsion - you either have to have an extremely precise computer-controlled fluctuating magnetic field in a train with hanging magnets, or you have to have the entire track be magnetized or be able to magnetize, in a manner that resists dynamic instability.

Hyperloop only involves propulsion, and the accelerators represent just a few percent of the length of the track. It's a tried and tested technology, use around the world, and their budget for it is in-line with industry norms. There are all sorts of trains today that use linear accelerators, almost all of which represent way more length of accelerator than Hyperloop needs. Examples include

                Airport Express in Beijing (opened 2008)
                AirTrain JFK in New York (opened 2003)
                Detroit People Mover in Detroit (using ICTS) opened 1987
                EverLine Rapid Transit System in Yongin (opened 2013)
                Kelana Jaya Line in Kuala Lumpur (opened 1998)
                Scarborough RT in Toronto (using UTDC's (predecessor) ICTS technology - opened 1985)
                UTDC ICTS test track in Millhaven, Ontario
                SkyTrain in Vancouver (Expo Line (using ITCS) opened 1985 and Millennium Line opened in 2002)
                Limtrain in Saitama (short-lived demonstration track, 1988)
                Nagahori Tsurumi-ryokuchi Line in Osaka (opened 1990)
                Toei edo Line in Tokyo (opened 2000)
                Kaigan Line in Kobe (opened 2001)
                Nanakuma Line in Fukuoka (opened 2005)
                Imazatosuji Line in Osaka (opened 2006)
                Green Line in Yokohama (opened 2008)
                Sendai Subway Tzai Line in Sendai, Japan (under construction, opening 2015)
                Line 4 of Guangzhou Metro in Guangzhou, China (opened 2005).[5]
                Line 5 of Guangzhou Metro in Guangzhou, China (opened 2009).
                Line 6 of Guangzhou Metro in Guangzhou, China (opened 2013).

If maglev was a good idea, it would have already been built.

1. This isn't maglev. It's a ground effect air vehicle inside a tube that simulates high altitude. Levitation works via air pressure.
2. Maglev has been built: Shanghai's Transrapid, Japan's Linimo, and there are two under construction, one in Beijing and one in Seoul.

That's not to say that there's no engineering challenges - there are. I think the biggest thing for the test track to prove will be the air bearings, to show that there's no high speed instability modes with them in a realistic tube. Most of the other stuff is pretty mature tech, however.

I don't see his Solar City work as particularly revolutionary. But SpaceX and Tesla have achieved some pretty darned impressive results thusfar which were widely ridiculed as fantasy several years ago. "Tens of thousands of annual sales of $60k electric vehicles that go hundreds of miles on a charge and getting the highest ranking Consumer Reports has ever given for a car? In your fevered dreams!" "Beating Ares 1 to the ISS for 2% of the development cost, on a rocket cheaper than the Russians and the Chinese, *without* the reuse that it was designed for? Yeah, you believe that, kool-aid drinker!"

Look, Musk is not some sort of demigod. But give the companies credit where credit is due. That's some pretty darned impressive stuff.

There are two proposals in the initial Hyperloop document. One is for a passenger-only version. The other is for a passenger + vehicle version. The passenger-only version's estimate is $6B, while the passenger + vehicle version's estimate is $7,5B.

The estimated ticket price for a seat in the passenger-only version is $20 (amortizing the $6B cost over the number of passengers). No cost for transporting a vehicle is mentioned, but we can attempt to calculate it: if they have to amortize an extra $1,5B and there's 28 passengers per pod, plus 3 vehicles per pod in the extended version (as per the proposal), then each passenger-only pod is earning $560, so the vehicles need to earn an extra $140, so about $50 per vehicle, plus $20 per passenger who comes along with their car. So about $70.

Hmm, apparently Slashdot eats "to the second power" marks also. Hooray for Slashdot's excellent unicode support!

To make the loading difference clear: here's the max loading for a 100 meter span (the spacing of the pillars) for different techs:

* Hyperloop capsule, loaded: 26 tonnes
* HSR train, loaded: Several hundred tonnes (caltrain locomotives alone weigh 190 tonnes)
* Oil pipeline: 332 tonnes (850kg/m * 100m * pi * (2.23m/2))

By spreading the loads out into many smaller, fast moving capsules, Hyperloop greatly reduces its track's required structural strength.

A high speed rail line requires steel rods -- cheaper than pipe, no?

Yes. But the cost of the steel in the track in a high speed rail project is only a tiny fraction of the total costs. BTW, you can double check Musk's tube estimate (I did), they're quite realistic compared to other "large pressuretight steel tube" project costs. He's basically building a pipeline, but instead of pumping oil or water through it, he's shooting people through it.

You could also put it on pylons if you wanted. People don't, in general, because putting it on the ground is way cheaper. There are exceptions to this -- some of the Chinese lines are elevated, I think -- but it's fairly rare.

As per my comment earlier, this is an erroneous comparison. Rail spends 99% of it's time unloaded, then for 1% of its time is loaded very heavily, an order of magnitude higher than the peak loads for Hyperloop. Consequently you have to have dramatically stronger pylons for an elevated rail line. Think monorail pylons, not conventional rail pillars.

we have a perfectly well-known technology (high-speed rail)

Unfortuantely, one of the things we know perfectly well about it is that it's ridiculously expensive. I'm not saying this to be mean, it's just a fact.

Compare this project to an oil pipeline.

* Loadings (weight) on the supports in oil pipelines will be *far, far* higher.
* Environmental approval in an oil pipeline will be *far, far* harder, and environmental constraints on construction will be far more severe.
* Oil pipelines generally move through wilderness and private land, rather than above already-prepared and already permitted land, and are often built in remote (read: expensive) areas.
* Both require the occasional pump or other regularly spaced infrastructure (honestly, an oil pipeline's is more complicated - you have to also maintain its temperature within a certain range, you require a lot more sensors, oil pumps are more expensive than vacuum pumps, etc)

We'll leave the terminals out of this for now. Given that, one would think that an oil pipeline of the same diameter would cost several times as much? Well, let's see, what's the average rate for oil pipeline construction these days. This says $200k per inch per mile, a 3-fold increase in 8 years driven in large part by "new industry regulations and practices to reduce right-of-way and minimize environmental effects" (again, reinforcing that oil pipeline should be far costlier per unit distance to build than hyperloop track). What would an oil pipeline the diameter of hyperloop this cost? $6B each way, or $12B total. Hyperloop's track is expected to cost $4B. How is this not a reasonable estimate? Even if you go with the full cost of an oil pipeline over that difference, despite the orders of magnitude difference in loading and huge difference in environmental regulations and right of way problems that have tripled oil pipeline production costs in recent years, you still end up with a hyperloop track that costs way less than HSR.

Every number in Musk's proposal that I've cross-checked I've come away feeling it's probably realistic. It looks by all standards like they consulted industry experts to come up with their figures. The only way it looks "ridiculous" is when you make inapplicable comparisons like when people claim that the cost per mile would be like the per-mile cost of a rail bridge over a canyon and whatnot.

Even more, the air in the tubes passing through the compressors is going to heat it. Now, you've got a lot of uninsulated surface area for the tube... on the other hand, air at such low pressures is itself a pretty good insulator. I wonder if you'd have a measurable impact on the air temperature? Or, if you wanted to, whether you could *deliberately* (and practically) raise the air temperature (insulated tube, etc)?

If you need to place, power, and maintain, a $100 pump every 5 meters down all of California, it is not actually cheap.

Congratulations, Citizen, I have good news! You don't have to put a pump every 5 meters all down California! Even the *pylons* are, as per the design, 100 meters apart. And the tube is only even *capable* of being opened once every several dozen kilometers. The positioning for the pumps is described as "several locations" (aka, not millions like you're picturing), and the total estimated cost for the pumps for the whole system, at current market rates, is $10m. Two tenths of a percent of the tube construction cost estimate.

There's a few reasons. But the biggest ones involve not having to use new land - not out some sort of idealist reasons, but pure economic practicality. First off, you need right-of-way. This is expensive. Also really ticks off land owners if you have to use eminent domain. These things almost always get tangled up in the courts. For in-town legs it'd be even harder. Secondly, all new projects have to go through a series of impact reviews. If you're building over a highway median, you're in an area that's already passed review - you still have to defend your incremental changes, but you don't have to pass as much of a barrier.

Also, most people overestimate the cost of the columns, comparing them to the cost of rail bridges. Just ignoring that by their very nature rail bridges are generally only built over difficult areas, and are going to be extremely price, It's important to note that one of the key cost-saving measures designed into Hyperloop vs. rail is often overlooked: weight. Hyperloop vehicles are more than an order of magnitude lighter than a passenger train, and only spend a brief period over any given segment; consequently the required structural strength is dramatically lower than for a rail bridge. I did some quick calculations, including tube mass, and found that and Hyperloop loadings should be similar to that of Disney's monorail. So think columns like this, not this.

While I do have criticisms for Hyperloop, I found that a lot of the criticisms levied against it on the net were seriously misguided, using ridiculous cost comparisons (another one is comparing the cost of Hyperloop tunnel boring to that of boring tunnels over an order of magnitude larger). I dug up "comparable" projects for each step of the project, and I really have to say, Hyperloop's numbers don't actually look to be that unrealistic. The keys of right-of-way reuse and low point loadings offer serious cost savings.

That said, I think Musk's positioning of the concept was stupid. By putting it in competition to an already-controversial high speed rail project, he both invited the rage of rail fans (who are used to feeling as if they're under attack), as well as inviting the expectation that it can do everything rail can (including, for example, making many stops along the way). It really is, as it was billed, an intermediary alternative between high speed rail and air travel - in speed, in throughput, in ability to make stops, etc. Consequently he should have proposed the first major project of it to be LA to Vegas. Then he wouldn't have encountered opposition from high speed rail fans, and the route doesn't have much population along the way to service. Plus, he could probably get tons of private backing for such a project, as Vegas is always desperate to better connect itself with customers in California.

I also think that for the current proposal, Musk should have positioned the LA station further into town. He's thinking "airport", and of course you can have local train / bus service to the station wherever it is, but airports are only on the outskirts because they *have* to be, mass transit is really ideally located more in-town. And there's no reason that he can't continue into town - the roads get a bit curvy but there's some nice straight rail lines that they could go over straight into the heart of town, and that'd probably be even easier to get approval for than for over road.

If you think this is like a pneumatic tube, then you know absolutely nothing about this.

Hyperloop is a system involving partially evacuated (not hard vacuum) tubes. The reason is that hard vacuum is much more difficult to achieve and maintain. The very low (but not vacuum) pressures offer little resistance, but do present a problem: you can't allow air to build up in front of the craft. Hyperloop solves this by a system of watercooled battery-powered compressors.

A pneumatic tube is propelled by pressurized air behind the projectile expanding, with lower pressure in front of the projectile. Hyperloop involves nothing of the sort - it involves magnetic accelerator segments for propulsion. Only a few reboosts would be needed over the length of an LA to SF run due to the low air resistance.

If you can find him while he's sleeping, you can make a goblet out of his head without having to make him get a scan.

1) Install "123D Make" on your cell phone
2) Take as many pics as you can from as many angles as you can with the sound off (up to 70) and wait for it to process (and hope it processes well... photogrammetry still isn't a mature tech)
3) If it works well then download the 3d model it produces.
4) Open it in a 3d modeller
5) Fill in any gaps
6) Replace the area that you couldn't image (the back of the head, presumably, assuming he was lying on his back) with someone else's
7) Cut the top off his head and apply a solidify/thickness modifier to turn it into a goblet
8) Upload it to anywhere that prints ceramic (for example iMaterialize not only can print in ceramic, but can even print ceramic in color).
9) Wait a bit for printing and delivery
10) Enjoy!

Bit by bit, the world is becoming an awesome place. ;)

Haha, do you mean Epic Electric Vehicles? That's Chris Anthony's company! They still exist (AFAIK - at least they did when I last checked in 2013), but they're small, as they've been going for "fun rides" market more than the "practical replacement for a gasoline car" market.

I am talking about entropy. Actual entropy, not "let's take an actual scientific concept and pretend it means something that it doesn't" entropy. I'm not making any comments about whether people are going to change DNA any time soon. I'm simply talking about the abuse of scientific terms - entropy being one of the most widely abused. To everyone who's doing it: stop.