China: Cute Hyperloop Elon, now watch how it's really done Elon Musk might have popularized the idea of a Hyperloop transport system, but the Chinese have taken up the idea and plan to make it better – with 4,000km/h (2,485mi/h) bullet trains planned for the Middle Kingdom. The Chinese concept is for a "supersonic flying train," with the carriage floating on magnetic levitation tracks …
Seriously, El Reg? You know better than that.
1000 km/h is only 278 m/s. If you accelerate at a perfectly comfortable (assuming you're facing forwards) 0.5g, you'll be going that fast in little over a minute. Even at a barely noticeable 0.1g, it'd be about five minutes. Fighter piloting this ain't.
No, the casualties will happen when there's a breach in the tube - whether caused by terrorism, faulty construction or just dodgy maintenance.
And pressure suits are not worn to combat gee forces anyway. That would be a "gee suit" which compresses only the leg areas while under high gees, to maintain blood flow in the brain. Of course that only works when the legs are "lowest" in relation to those high gees.
I suppose those tubes make bends now and then, and at 2000km/h there might be significant side gee forces. Probably the entire vehicle carriage would rotate in such cases to put passenger feet at the "bottom."
But my guess is the engineers won't be allowed to make such tight turns. Those tubes will be like Roman roads, going thru any and all obstacles in their way, regardless. Might have to move a couple more big cities, but the Chinese must be getting used to that by now. ;-)
Why move the cities, plough right through them!
China is making more progress towards environmentaly sound travel than any other country...
On my most recent trip to Xi'an, all the busses I saw running were electric, all of the small bikes/trikes I saw were electric.
Taxis are all LPG, and I expect they will be the next thing to be converted to Electricity (harder to do than busses)
The metro is being being expanded for mass transit.
In other words, they are doing better than london with its congestion charge that hurts the average person but still allowing diesel busses!
Electric buses are lovely, but not really environmentally sound when most of their power is generated initially by dirty coal, which I understand is currently the case in China.
When are they going to start trotting out the thorium / liquid salt reactors they were supposed to be working on?
They're using dirty coal for now, but as they build wind/solar/nuclear facilities they can eventually phase out the dirty coal plants. It also allows efficiency boosting stuff like regenerative braking which is very effective for all the start/stop cycles of buses in cities.
"They're using dirty coal for now"
And they've effectively banned the building of any new coal stations. The ones under construction are the last ones which will be built.
As for china's nukes: it doesn't matter about thorium or not. They _WILL_ roll out nuclear technology with what's available now and when thorium is ready it can eat the waste.(*)
(*) Amongst other things thorium reactors can digest depleted uranium, which prevents it falling into the hands of the likes of North Korea - depleted uranium being both a nasty environmental toxin(**) and a critical component of Teller-Urlam (hydrogen(***)) bombs which gives the final massive "boom"
(**) as in heavy metal poisoning/lead poisoning. Seeing kids crawling all over dead iraqi tanks which had been strafed with depleted uranium and are covered in uranium dioxide is a bad thing.
(***) modern miniature "Hydrogen bombs" are only partly fusion bombs and the vast majority of the boom comes from fissioning of U238
There is another country (Norway? Netherlands?) that may beat China to a functioning LFTR reactor. There was a recent story.
The "dirty coal" story is the chant of the ignorant. A coal fired electric plant is many times cleaner than an equivalent power output collection of small internal combustion engines. China's problem is that they have become the manufacturing center of the world so pollution that might have been generated in the US and Europe is now spewing out over the middle kingdom with far fewer (if any) regulations.
"China's problem is that they have become the manufacturing center of the world so pollution that might have been generated in the US and Europe is now spewing out over the middle kingdom with far fewer (if any) regulations."
Chinese power plants are pretty clean. One of the bigger chinese problems is that across the country most building heating systems use coal (not oil or gas) and have rotten furnaces. They've been tightening regulations recently (and are trying to eliminate such systems entirely in urban areas) but it will take years to clean up.
The air in Shanghai is frequently acrid. I'm glad I don't go there much.
"China is making more progress towards environmentaly sound travel than any other country..."
Yep. That is because they are a polluted mess. The same could have been said about the U.S. decades back. It seems the will to make progress is stronger when you can't breath.
The problem is not a but x distance travelled.
x=distance - metres
v=initial velocity - in this example 0
a=acceleration - metres/second^2
x=v*t+a*t*t/2
v=a*t
so for v=0 to v=550 m/s (1980 km/hr)
a=1 m/s^2 (10.2% of gravity)
t=550 s (9.2 minutes)
x=151 km
now you have stop so repeat the calculation
thus to accelerate to 1980 km/hr and stop takes 300 km
Re: distance to accelerate - this why there are different top speeds depending upon the distance travelled. The train just keeps up a modest acceleration, uninhibited by air friction, until it reaches the half-way point and then starts to decelerate. The further you go, the greater the maximum speed reached. Over very long distances an arbitrary top speed is reached.
This system, if practical, would take a very large capital investment and so would be worth while only on routes between very large population centres.
> a very large capital investment and so would be worth while only on routes between very large population centres.
I give you the last supersonic transport system between large population centres on this planet, viz. Concorde. It didn't sustain itself, and give rise to successor systems, because not enough people (need | want) & can afford to travel that far that quickly.
Also the physics is a bit dicey. If you're accelerating a train at 0.5g, as others have suggested you need to do to reach 4000 kph before you reach halfway to your destination, then the track experiences the reaction, and can't be built on piddly little concrete pylons. Similarly when changing direction: fast aircraft use a "half-rate" turn of 1.5 deg per second. For a 4000 kph train changing direction from N to NE, say, the turn will take 30s, and to limit the sideways acceleration to 0.5g, the radius of the turn is near enough 28.6 km (17.7 miles). Around the curve [1], that's about 28 miles of track that has to be braced to support a force equivalent to 122% of the weight of the train. See 'piddly pylons', supra.
I don't say that it can't be done. I just don't expect the engineering investment to be justified by the economics of the business case.
[1] I've simplified. In reality, you have to turn gradually into the curve, and gradually out again, along an 'Euler spiral'
Why would you limit yourself to only 0.1g? A passenger jet pulls a lot more than that during a full thrust takeoff (i.e. short runway) and people are fine with it. A fast sports car (Porsche, Corvette, i.e. kind of car us normal folks could afford, not one of the hypercar exotics) pulls around 1g in first gear.
So let's cut that 300km by 90% and accelerate at 1g. After all, you will be seated during this phase of the trip just like you are at the start/end of a flight. We humans are pretty used to dealing with 1g, given that we experience it all the time. Pretty sure no one would complain about 55 seconds of acceleration. The deceleration would be more of a problem, but the seats could swivel round so you face the other way. Or if not use a five point belt instead of a lap belt and deceleration at half a gee instead of a full gee to be nice.
The problem isn't the 1g of acceleration, it is the far faster deceleration that will occur if the tube is damaged. Same problem as hyperloop, you are just as dead either way.
Rear facing seats that recline during acceleration are a safer design. You accelerate as fast as people find comfortable. Once you stop accelerating the seat returns to the upright position to allow 1g deceleration at the destination or much much more deceleration in an emergency.
@nolveys ..... "I was in one of those on a hour flight" .....
Given that the acceleration and deceleration only take minutes, and after that you are at constant speed, and in a tube you can't see out of, how could you tell which way you are facing in a hyperloop to know that you were facing in an uncomfortable rear direction?
"much much more deceleration in an emergency"
Hitting the end of the tube will suffice. Has great deceleration.
Seriously how are you going to decelerate when the emergency (a breach in this case) is accelerating you?
Where is all that INCREASING energy going to go? Brakes convert it to heat. How do you cool the brakes so they dont melt you or whats left of the tube? Coolant? how do you cool the coolant? Cant use a heatsink can you as there is no atmosphere to sink it to. Cant sink it to the outside of the tube as you are not connected to it, thats the point of the hyperloop. How about a tank of liquid nitrogen? Well as you cool the brakes with that, the liquid nitrogen will warm up and annoyingly turn into a gas and expand. Where do you put all of that? You cant let it out into the tube as it will add to the acceleration you are already battling against.
Could they use the magnetic track to act as a brake? Ok, but same issue with heat, if it will be effective at all considering the very low efficiency (no friction on the track = great low energy acceleration but terrible braking performance).
Its clear that what is needed is Star Trek tech called "force fields" and inertial dampeners. Musk should be trying to find a way to eliminate inertia. Then much of this could be resolved. The force fields will be used to add structural integrity to the tube and vehicle, also they can be used to seal breaches!
Why isnt Musk building force fields and inertial dampeners?? This stuff has been in peoples dreams for years.
@DuncanLarge. ..... "Seriously how are you going to decelerate when the emergency (a breach in this case) is accelerating you?"
Easy: You bleed air into the tube anywhere there is a significant pressure differential between adjacent sections of tube, thus gently(ish) air breaking all the cars as the tube pressurizes up to atmospheric pressure. As long as there is air between the cars they aren't going to collide. The cars then limp to their destination or an emergency exit whilst playing relaxing music to the terrified occupants.
Please use this new google think to look up the basics of how these systems work. The whole principle is to avoid friction in all forms, be that breaks or propulsion or air resistance.
Both systems use electricity to generate velocity and regenerate said velocity back into electricity for breaking, it's a rather efficient way of propulsion. Friction braking is an utter wasteful exercise
Also, you can Radiate heat, you know just like stars manage to radiate heat across the vacuum of space.
@DuncanLarge
What the hell are you going on about?
You would only be accelerated if there was a breach behind the direction of travel.
Heat from braking? Conventional brakes would only work if the train was on rails... Remember, this is a maglev. It will be hovering and all braking and acceleration will be provided by magnetism. Any heat generated by these systems should easily be shunted outside of the tube.
I'm no engineer, but these things didn't take much time to consider...
"Could they use the magnetic track to act as a brake? "
Duh.....
Linear motors can be used for deceleration as well as acceleration. Kinetic energy returned to the electrical system can be reused elsewhere or dumped to trackside resistor packs.
It's no different to any other kind of electric rail system in that respect.
TFA:
> long-distance cargo and passenger routes at its top speed [of 4000 kph]
DougS:
> let's ... accelerate at 1 g.
OK. To reach 4x103 km s-1 accelerating at 9.8 m s-2 will take 113 seconds. That's nearly two minutes of unpleasantly high acceleration. (Civil airliners only have a thrust ratio high enough for about 0.3g).
Given that s = u.t + 1/2 . a . t2, I think distance travelled until full speed is reached is about 62.9 km. Thirty-nine miles of the toughest takeoff you ever had unless you've flown a jet off an aircraft carrier.
And another thing! At 4000 kph, a 70 ton train will have 8.64 x 1010 J of kinetic energy. Supplying that in 113 seconds will consume 763 MW, a significant chunk of the output of China's largest nuclear reactor. Those are going to be mighty big power cables, and the brakes are going to be pretty hot when the train pulls into the station. I'm all mathed out, and can't be bothered to work out whether 86 GJ is enough to melt a 70 ton train.
unpleasantly high acceleration? 1g? sitting down? nah. You hands might feel a bit heavy, and whilst it would be noticeable, you could put up with it all day, unless you're a particularly fragile little snowflake.
Have you ever experienced prolonged g? I have, in light aircraft, and I'm 6ft and the taller you are the more susceptible to high g you are too. For me 5-6g is where it really starts to get unpleasant. 3g is very typical on rollercoasters and doable for minutes at a time. fighter pilots can pull 12g for tens of seconds with a suit. The human body is fairly resiliant to it, particularly when your spine is perpendicular to the force (as it would be in a train.) Plenty on g-forces and human limits on wikipedia. I'll quote one - test subjects were able to complete simple cognitive and physical tasks at 6g for 10 minutes.
You could quite easily have a acceleration of 3g on a system like this - your passengers can realistically withstand that for 20 seconds at the start and end without much of an issue, provided they're harnessed. Plenty of people will think this is really scary and choose alternative options, yes, but they already do with aeroplanes too. It's a mach 3.2 train - I think passengers will probably expect a bit of an adrenaline rush. I would.
Only Jonathan Richards mentioned the tremendous amount of power needed for the acceleration, but I don't think anyone mentioned the nearly equally amounts of power generated by the deceleration (reduced by losses due to the minimal friction and heat).
Remember that the track is essentially a linear motor, which means for the time it's decelerating, it's essentially a linear *generator*. In order to keep running costs in terms of power down, that 86 GJ of generated electricity has got to go somewhere, somewhere preferably reusable for the next / return journey's acceleration.
"At 4000 kph, a 70 ton train will have 8.64 x 1010 J of kinetic energy."
1: Why would a pod weigh 70 tons?
2: Regenerative braking, not friction braking - the latter would be silly except in emergencies. Even modern rail trains hardly use their friction brakes except for very low speeds.
3: Distance is irrelevant to the passengers, what they care about is duration of the acceleration.
4: There are no windows, so front or rear facing is irrelevant. You use which is best for safety and if you have screens on the thing, make it look like they're facing forward - noone will complain that way.
"The problem isn't the 1g of acceleration, it is the far faster deceleration that will occur if the tube is damaged. Same problem as hyperloop, you are just as dead either way."
If a tube is punctured then even in full atmosphere the worst case deceleration is only going to be 2-3g for a very short period. The bigger problem will be people not restrained and things flying around the cabin - chinese are some of the worst fliers for taking their seatbelts off as soon as the light goes out and really don't care that the most heavily injured during turbulence are passengers not wearing seatbelts or the passengers that they land on.
If a tube is punctured then even in full atmosphere the worst case deceleration is only going to be 2-3g for a very short period.
You sure about that? I'm sure it is true for sub-sonic velocities, but we're talking about supersonic velocities here. The air that rushes in would be almost like a brick wall to the capsule. Perhaps I'm wrong, I'm not an aerodynamic engineer, or any sort of engineer, but the idea it would decelerate at 2 or 3g from mach 3 just seems wrong to me.
So?
It's 1200km from Beijing to Shanghai and takes more than 5 hours on the current 300km/h trains.
That's a small run compared to many of the distances in China. It's a _big_ country - only slightly smaller in square miles than the USA lower 48.
I can easily see the 300km/h(*) lines being used for shorthaul and tubes for longer runs. Even on short runs, it doesn't matter if the pods don't hit 1900km/h, they'll still be much faster than the trains for distances of 300km.
(*) Many of them have just had their speeds returned to 350km/h
With upwards of 200 million people moving en masse at chinese new year, many will happily pay a premium to not have to sit on a train or aircraft for 6-8 hours and the rest will be happier the trains are less crowded.
The interesting part of all this is not the tubes - they're relatively easy - but how to safely handle stub switching for routing and how to handle multiple pods in flight. Should they dynamically link up into a train or should they run with separation, etc?
If china's contemplating this and decides to act, then it will happen. This is a country which went from no fast rail to more high speed rail than the rest of the world combined in less than 20 years - and running at higher speeds too(**). Their specialist rail building equipment is mind boggling (look up the bridge building videos on youtube) and can teach more than a few lessons to infrastructure builders in the rest of the world.
The knock-on economic benefits of this kind of infrastructure are only just starting to make themselves obvious to outsiders, particularly when china's freight rail network has had a similar overhaul with far less fanfare.
(**) Yes, two crashes, yes lots of corruption discovered - but they've nailed that down and fixed the technology. European high speed rail has had just as deadly crashes.
No, the casualties will happen when there's a breach in the tube - whether caused by terrorism, faulty construction or just dodgy maintenance.
You missed the most obvious reason - earthquakes and loess subsidence. If it happens under a normal train people and goods stand a chance. If it happens under anything going at that speed there will be no survivors.
You can easily build a system like this in Scandinavia, large portions of Europe (except the South), etc. China - not so much (except a very short one for showing off).
Followed by uncomfortable emergency braking for the following cars (whether intentional via safety systems or from the loss of vacuum/power), depending upon their speed.
A tunnel breach could spell disaster for more than one car in that scenario, depending upon separation distances and velocity at that time..
People, get your systems engineering right.
Linear acceleration could be similar to an airliner on take-off; a bit uncomfortable but nothing worse, although as someone mentioned above, it'll take a loooong distance to accelerate to top speed.
Breaches of the tube will "only" be a problem if a) they occur within the emergency stopping distance of the capsule, and b) they include a breach of the rails, or misalignment of the two broken-apart tube sections. In all other cases, it'll be an emergency stop and ticket refund; but in that combination it'll be a disaster.
Quite another topic, however, is turn radius. By my quick BOTE check, in order to keep centrifugal acceleration to an acceptable level at speeds of 1100 m/s or so, you'd need a curve radius of several hundred kilometers - the exact value depending on what you consider "acceptable". That means we're essentially talking arrow-straight tubes; which even in China would place a fantastic burden on the poor civil engineers tasked with routing the system.
Breaches of the tube will "only" be a problem if a) they occur within the emergency stopping distance of the capsule, and b) they include a breach of the rails, or misalignment of the two broken-apart tube sections.
Or sudden re-pressurisation of the tunnel, so you are now hitting ground pressure at full speed, whereas you have been travelling in a near-vacuum.
"That means we're essentially talking arrow-straight tubes; which even in China would place a fantastic burden on the poor civil engineers tasked with routing the system."
On the upside, moving people, villages, even towns out of the way isn't such an insurmountable problem as it is in most other countries.
Something close to 90% of the upper levels of the Chinese government are engineers (http://siliconafrica.com/90-of-top-chinese-government-officials-are-scientists-engineers/).
This is what happens when a bunch of engineers get control of the treasury - they go nuts with infrastructure projects. Not that I'm objecting, this particular project looks pretty cool, and anything that embarrasses my current country of residence (the US) into upgrading its absolutely woeful infrastructure is also good.
All those promises for the Great Bowl of China ....
not spherical, frequency limited, and full aperture unavailable ... so make it a tourist site ...
Yeah, yeah, sure, engineers ....
"The entire county town stinks of this gas after nightfall, and there are some plainclothes people going around getting people out of their homes and beating them up," he said. "I think they're hired by the factory."
"http://www.rfa.org/english/news/china/leak-04142015103014.html
Yeah basically we waste just as much money on boondoggles in the US as China is now doing, but our boondoggles are all defense related.
The F35 being a prime example of throwing away a trillion dollars and getting nothing good in return - the whole idea was "the F22 is too expensive to buy as many as we want for modernization, so we'll design a new cheaper fighter and con our allies into buying it too". Unfortunately it is now more expensive than the F22 and performs worse. If we really wanted cheap we should have kept building F16s and F18s, the large majority of our combat load doesn't have stealth as a requirement.
Imagine if instead of F35s we were building high speed trains across the US, or repaving the interstate highway system to the specs Germany uses for the Autobahn, or giving people a tax cut that wouldn't increase the deficit for once...
Early in the Obama administration there was a plan for a very cost effective high speed transit system. I wonder what became of it.
From the cartoon mockup it looks like there are only six rows of seats in those pods so even at four rows it's 24 people per pod. That's an expensive trip and you'd need lots of pods to make it mass transit and I don't see it ever being able to handle even a tiny fraction of the new year holiday traffic. I'd think engineers and scientists could figure out those pods likely aren't feasible since there is little else to it other than a few rows of seats and it will certainly need some mechanicals on board such as HVAC which will require some sort of thermal store and longer trips will need some sort of air treatment or CO2 scrubber. Maybe even pump the cabin pressure down to save on O2.
Overall it looks more like a bunch of marketing folk got together to make a sales pitch video for non-engineers.
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This experiment is only relevant for a tube that is evacuated from one end. Engineers don't design things like that because it would be stupid. Instead the air is evacuated from many points along the length. In a catastrophic failure scenario you let the air back in gradually so you have nice springy air cushioning between the cars.
Instead of using an impervious glass tube the video needs to be remade with a tube that is made porous at the moment of failure. The ball bearing can be brought to a stop at any point along the tube depending on how fast you let the air in.
... same as hyperloop.
Even assume passengers were in a huge multi-segment train of say 1,000 people. How many minutes do you need between each train to ensure safety? From the above calculations it seems like 5 minutes absolute minimum. So your total capacity on a multi-trillion-dollar system is 12,000 people per hour, in each direction if you have a pair of tunnels.
To increase this you have the multiply up the number of tunnel pairs you are prepared to build, at roughly N times the cost.
For fun, compare the cost of building a regular rail network (where you basically just flatten the ground and lie some concrete and metal on it), with the cost of building a high vacuum tunnel system with integrated linear motors.
Yet, 12K people per hour is far more than you generally can get out of flying between A and B.
I do think it is very expensive but hey, the capital expenditure might stop or slow down the Chinese take over of the rest of the world(by buying everything in sight) so not all bad eh?
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Is designed to highlight the impracticality of physical bodies. We will be allowed to discuss it until "budgets" intervene then we will be offered the option to fully virtualising our existence, dropping the existing heavy meat sack for a much better alternative that us mere humans are incapable of currently conceiving (in all senses).
Once we have sold our souls to the devil signed up we will no longer need to be restricted by the laws of the physical universe, we will have to pay a monthly subscription to retain virtual existence etc. but that's all in the small print...
Anyway back to the gee whiz moving bodies thing.
Taking first-hand experience of the current Maglev train Shanghai runs to the airport, that accelerates to 217mph (350km/hr) in around 2 minutes, so keeping that linear level of acceleration means 6 minutes to ~660mph, 11 minutes to over 1000mph. Note also, that train didn't require fancy leaning seats, suits and it was still comfortable to move around.
The other flipside that has to be accounted for in China - it's a seriously big country (5200km/3200miles east to west, and similar north to south). So even if you started at top speed and ended at same, that's still 3 HOURS east to west. So anything that gives solutions to move people big distances at high speed is fair game over there.
I remember Eric really well.
He did about the best Royal Institution Christmas lectures "The Engineer through the Looking Glass" - it was that, and Attenborough the year before started me on the downward spiral into science.
EDIT: A short excerpt
Why? The wastrels of Parliament are already promising to throw hundreds of billions of quid at HS2, HS3, Crossrail 2, Hinkley Point (and a range of other hoped for nuclear power plants), supporting £16bn a year on housebuilding, not to mention about £15bn on smart meters, several tens of billions on roads, a billion on the Northern Line extension etc etc.
In the period 2016-2021, there's about £300bn of UK infrastructure investment planned, see the House of Commons Library briefing paper 6594, dated 2 March 2017 - the punchline table is bottom of page 15. Even if you wanted to do more, the country doesn't have the capacity to do any more, and there's a question mark over the capability to deliver that £300bn.
"The upside of Crossrail is that it is likely to be at close to full capacity during rush hours almost immediately."
The downside is that they only bored 2 tunnels, meaning that if anything goes wrong in one (or maintenance is needed), everything stops.
They looked into this 100 years ago and came to the same conclusion as Elon and China will.
It cant work, can kill people and if they do manage to get it working it will be a total PITA to keep it working with round the clock "red alert" style, to the second maintenance and the ever present fear of entering the hyperloop on foot and coming out in several bits flying faster than a bullet simply because the sun warmed up the tube too much that day or some annoyed guy in the middle of nowhere shoots his gun at the tube for target practice.
I assume that Elon and China will build all the little huts/small villages across the entire route that will house all the "red alert" fix it now or people will die within the next 60 seconds maintenance staff? I mean you simply cant leave any square centimetre of the tube unlatched, unmonitored.
This is as crazy an idea as building an intercity railway with tracks made out of wood with trains intending to run over it at 100 MP/h.
Here Elon and China. Have this for free. It may work much better, if at all, in a triangular tube grown out of a single diamond crystal. But I bet nobody will be able to afford to ride it.
So, its in a near or partial vacuum, what happens when that is lost? Are we having airlocks at regular intervals dividing the 'track' up into sections, and then how do we stop the thing inside that section from 4000km/h without doing a Colonel John Paul Stapp on them. Oh and if you can avoid that , where is all that energy going to go? It will be given up as heat so we will then cook the passengers. Great idea all.
The aim is to send a train through as near a vaccum as can be maintained.
So how do passengers embark? How do they exit? How do they breath?
Okay, embark and exit are basically the same: Probably something akin to how the space shuttle connects to the ISS. However, you have to supply air for the passengers to breath. All this will set limits on how many passangers can travel in each car, and what the turn around time is per train. Different options come with different risks and costs and I doubt the trains will be able to carry enough people to make the system viable economically. So to me this sounds like a white elephant: Something to brag about publically, but lament the expense of privately.
And all that is before we even consider the risks of vandalism/terrorism and the dread human error...
So how do passengers embark? How do they exit? How do they breath?
Not that I believe that this will be feasible but these 3 challenges at least are fairly easy to answer I think.
Embark/disembark
This would have to happen at atmospheric pressure and the car would then move through an airlock to join/leave the depressurised tunnel.
If the tube is a close fit for the cars then you would be unable to board/exit whilst in the system (the doors would open inwards but the clearance would be minimal for crawling out - assuming that there was an egress point you were aiming for.
How do they breathe
Compressed Air carried onboard. You have an issue of what happens if the cabin depressurises enroute, and I don't think that drop-down oxygen masks will cut it here.....
Maybe they would wear pressure suits anyway as a safety precaution (the mind boggles though given that most people would probably be unable to put a lifejacket on quickly). The pressure suits would have to be worn at all times since a sudden depressurisation would not leave time to put helmets/gloves on.
This means that::
* Passenger comfort - how do you go to the toilet during the journey if pressurised.....
* If you get stuck mid-tunnel then after recovering from your deceleration you have to rely on stored air supplies OR require that section of track at least to be repressurised whilst you await rescue - if you can't get out
Your points are ones I had thought of - but there are problems.
1) You're talking about passing the whole train through an airlock. This will take time meaning you need to carry more air for the passengers. The alternative is to use a docking tube and keep the train in the depressurised tunnel, but here you'd want to seal off that section of tunnel as a precaution. This would be faster on turn around, but you'd still need airlocks to allow trains to be replaced for maintenance.
2) Yes, compressed air would have to be pumped into tanks, or they would need swappable tanks of air. Even a half hour journey will require a supply and to keep the train size down, you'd need to replenish that supply at each stop - or at designated points.
This is the point, though: it's the logistics of how to run the system if someone went ahead and built it. Added to this, as you say, is passenger comfort, and how to deal with the inevitable system failure, but it's all cost and that cost won't be decreasing any time soon.
"So how do passengers embark? How do they exit? How do they breath?"
Embarkation etc was done by atmospheric railways 150 years ago. The tubes aren't a hard vacuum, so if you have an airlock section that leaks some air into the transportation system it will be sucked out quickly anyway.
Paradoxically, the safest way to handle leaks is to have controlled ones with associated vacuum pumps - possibly as many as one per tube section. That way when the power goes off, pressure rises slowly in an entire section instead of rushing in at one end and the combined effort of the pumps can handle any major leaks smaller than a full breach.
Apologies.
Basically there is a newish highway that runs from Thaialnd somewhere down near BKK I think and then runs up through Burma / Myanmar into Northern India. It's very long, but totally avoids the Indian Ocean, fast transport even just shoving containers of goods along that route could be bit of a game changer.
China's also been exploring a high speed rail network and/or the possibility of rebuilding the Burmese rail system to get access to deepwater facilities at Yangon as part of its new Silk Roads plan.
Given that they're also pushing at least 2 standard gauge lines across central Asia into Europe to avoid the expense, delays and complexity of gauge changes at each edge of the Russian rail network as well as a trans-India proposal via Mandalay, this is clearly a play for better access to Africa and the Middle East.
The knock on effects of a burmese line are interesting. It would open up western China to international commerce in a way that it's never seen before and possibly help move the economic centre of mass away from the coastal strip.
Why are they trying? Apart from the obvious (less shipping distance/faster shipping), there's a major bottleneck with access between the Indian Ocean and the South China Sea due to shallow waters and a bunch of reefs. SE Asia was dry land right down to the tip of what's now the Indonesian archipelago during the last ice age and the continental shelf is shallow enough that there are only a few navigable channels into the Indian ocean. That recent US navy collision near Singapore was more down to traffic density than bad seamanship.
There's also the issue of carbon emissions - China can't afford to have sea level rise more than a couple of metres or they'll have to rehouse at least 100 million people, so they're working on everything to get emissions down. This is why they have so many energy research projects running. Their point of view is that they can't afford not to explore every possibility.
Trains can be electrified and run on renewables or nuclear power. Ships can't (nuclear shipping is a non-starter even if it was a molten salt reactor) and nor can aircraft (which is ironic, as LFTRs are a direct result of the US's attempts at trying.)
I'm pretty sure that once the chinese get LFTRs working and commercially viable, they'll be selling them to all comers - and developing countries in particular. The potential there for increased carbon emissions outstrips any savings we can make in the developed world, therefore doing so makes sense on a "stability of the global ecosystem" point of view.
Getting back to tubes. If China wants to do it and if it's technically feasible, then it will probably happen. Things like the Shanghai maglev might get built as prestige projects(*) but something the size of a tubeway network will need serious consideration of the financials.
(*) If you don't want to spend the money on the maglev there's a metro station at the airport. Think of it as Shanghai's version of the Heathrow Express.
Just why is nuclear shipping a non-starter? I would think you'd end up with huge long-term savings in shipping costs since you can haul more (not just more power, but also less wasted space to house fuel) for longer. Plus whoever solves the problem of a damn-safe compact reactor can also sell the idea to rural communities, islands, and so on in the name of electrical independence.
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