I have to wonder, would making the capsule the size of a small subway car completely destroy the economics of it?

https://en.wikipedia.org/wiki/Helios_Airways_Flight_522

https://en.wikipedia.org/wiki/1999_South_Dakota_Learjet_cras...

http://en.wikipedia.org/wiki/Armstrong_Limit

http://en.wikipedia.org/wiki/Time_of_useful_consciousness

Also look at the TUC (time of useful consciousness) that it´s below 5 secs when flying that high. That means that you have less than 5 secs to put your oxigen mask on before you lose conciousness, or behave with out knowing what is happening. Also due to the extreme low pressure, you´ll have a horrible a horrible stomach ache due to the expansion of the gases inside you. Your blood (or at least the corporal fluids exposed directly to the low pressure) will start boiling.

Not funny. Maybe one solution could be wearing some kind of pressure suit for this trips. But that is not going to be very convinient..

    At or above the Armstrong limit, exposed bodily liquids 
    such as saliva, tears, and the liquids wetting the alveoli 
    within the lungs — but not vascular blood (blood within the     
    circulatory system) — will boil away without a pressure suit

The Armstrong Limit is at 62,000 feet. Jetliners fly at below 45,000 feet.

http://www.google.be/url?sa=t&rct=j&q=&esrc=s&source=web&cd=...

You got to think that a decompression will happen. Something traveling that fast inside a tube is probable to develope vibrations and material fatigue if something is not working properly (like the compressor or a air cushion), also there can be small parts released from the front pod impacting on the next one.

It doesn´t need to be a huge crash, just a crack on the hull, it will decompress that small pod in seconds.

Also what will happen when of tens of pods traveling that fast, find that there is a sudden recompression of the tube? How fast are they going to stop due to the front overpressure (the compressor is relatively low powered)?. Is not going to be a gentle stop either.

I still think that it´s a great idea, and that there will be ways of solving those problems, but it´s going to be difficult and require lots of R&D.

It seems that detecting failures of this nature quickly would be the important thing. The fix looks to be relatively easy, though you would cause a major disruption to the whole Loop.

The passenger plus vehicle version of the Hyperloop will depart as often as the passenger only version, but will accommodate 3 vehicles in addition to the passengers. [p12]

The passenger plus vehicle version of the Hyperloop capsule has an increased frontal area of 43 ft2 (4.0 m2 ), not including any propulsion or suspension components. This accounts for enough width to fit a vehicle as large as the Tesla Model X. [p15]

Tubes would be bigger, and the system would cost more.

For the advantage of a short journey people will put up with it, especially if it can get you to the centre of the city rather than an airport on the outskirts.

Try LA to Sydney in coach.

Translation, it's going to cost more than $20.

Plus, with a car you'd have a 7-8 hour journey to look into.

And with an (equally cramped if not worse) plane you'll have more traval time than in this scheme, if you include waiting to depart, the lengthy procedures at the airport and getting to the airport in the first place.

It's a failure of the onboard steam tanks that scares me. ("The steam is stored onboard until reaching the station. Water and steam tanks are changed automatically at each stop")

I don't want to think about what the result of that would look like for the cleanup crew. Eeeewww.

They're just gonna have to send in a crew of astronauts to chisel the freeze-dried human stew off the inside of the tube.

The failure mode for composite overwrap pressure vessels is a slow leak, due to the overwrap containing the metal.

The current design has the passengers in an enclosed capsule in between the compressors and the batteries, with a pressurized air channel running right down the center isle.

Keeping the cabin cool will be a challenge. If that emergency braking is activated, it could get a little warm in there before they are rescued.

I think they may have to quickly repressurize the loop if a car ever gets stuck.

The pressure ratio for the compressors in the CFM56 engines in current model 737-800 models is 32.8:1, so somewhere in the neighborhood of 400-500 psi (will depend a lot on altitude).

Seriously, we've been building machinery to operate safely in this pressure and temperature range for a long time.

Engines do fail on passenger jetliners from time to time. There are numerous stories of planes landing safely after an engine catches fire. But the plane is travelling at a good speed through the atmosphere. How would things be different in a much smaller vehicle sitting stationary in a mild vacuum?

How would passengers escape a battery fire? (as has been seen multiple times on very modern jets)

If the tube had to be repressurized in an emergency, how long would the tube be out of service to be pumped back down again?

Is it worth building a three tube system for such a possibility?

The meta point: If you can't plan around a 30-minute window of no bathroom access, that biological restriction is a bigger concern than arriving at your destination quickly.

and if you go to the bathroom right before takeoff, you'll delay the flight.

The only thing I really dislike so far is the battery pack in the pod. I would have wanted to see something more elegant instead. And this way we halve the weight of the pod.

Perhaps the redundant vacuum pumps are spaced frequently enough that the power transfer problem would be easy, but I doubt it.

The problem with the images of the Hyperloop interior is that it looks very much unlike anything you currently find in trains. It looks more like the inside of a race car – with a belt and all – and it doesn’t look like you are supposed to get up and walk around. It doesn’t seem as though there is enough space for that. Maybe that’s just some designer having an unnecessary flight of fancy (but that doesn’t exactly inspire confidence in the design if it’s that badly though out), maybe that’s an inherent downside of the design. Either way, not good.

Smoothness is mostly due to track quality, and is a practical result of design for high-speed running.

At least in Germany WiFi sucks and is not available everywhere – and even if it is you have to be lucky and actually be in a train that supports it. In general seats are most definitely more comfortable in longer distance trains. Yeah, you can find a seat that’s less comfortable in a long distance train than in a regional train, sure, but that’s hardly the point, is it?!

And electrical outlets are getting more common, sure, but the vast majority of German regional trains does not have them and you can only be certain that there will one in a high speed train.

WiFi varies a lot from country to country — some places you're lucky to get it on any train, others it's becoming coming common on even regional trains; seats on a lot of the older ICE2 sets were really quite terrible prior to their recent refurbishment, and a lot of IC trains in Germany had far better seats; electrical outlets differ from place to place — the TGV Duplex will never have power outlets at all seats, for example, despite being a high speed train, as there simply isn't sufficient power spare to provide them, and as another example in the UK it depends far more on rolling stock age (or refurbishment date) than whether it's a long-distance train or not.

I've only had time to skim the full PDF, but there's something about experiencing 0.5g of acceleration - unsure if that is a constant or if that is simply right at the very beginning.

If you're going to experience 0.5g of acceleration over a prolonged period, letting passengers get up and move about is going to be a bad idea. It also doesn't look like there's enough roof to get about in that capsule. 0.5g doesn't sound like a lot until you think about it as 50% of your body weight tacked on, in a direction you're not used to having it tacked on. Pretty simple in a seat, much less simple trying to walk.

That's not how vectors work. It's only 11% extra weight. If its reasonably smooth, that's easy walking.

If the top speed is 700mph then you'd have 142 seconds of 0.5 g acceleration to get to top speed. How often you'd be accelerating or decelerating would depend on how many intermediate stations there are.