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Comment by JoeAltmaier | Hacker News Reader

Hyperloop appears to be a niche solution to a specific transportation situation. It may work (be profitable/useful) for a time between specific destinations. Then the population situation (density, distribution) will change and it will become less profitable or even be discarded.

Its not clear that any current pair of cities currently fit the sweet spot for hyperloop. Even if some did, its not clear a hyperloop could be built in time, before the situation changes and they exit the sweet spot.

Execution and timing will be especially critical to a successful venture.

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Probably true, but at the same time, there's a build-it-and-they-will-come effect that accompanies major public transportation projects, for example the Metro light rail in Phoenix. By running it from the airport to the downtown convention center district and then uptown to Bethany Home Rd. on 19th Ave., they have provided some significant convenience and cachet to the downtown area that has been struggling for decades with revitalization. Millennials are parking themselves in trendy apartment buildings near the downtown and the light rail has contributed to that lifestyle.

Will it last? Time will tell, but the trend today is to increase usage. The biggest complaint about the light rail is that it doesn't go far enough, though there are plans afoot to extend it over time.

There's plans to extend it to Metro Center (at the time they made the plans, it made sense - today, not so much). It's also pretty much extended to downtown Mesa (stops somewhere near - maybe in front of? - the HeatSync Labs hackerspace...

There are also very real technical questions to be considered with holding a vacuum over that much pipe, especially when there's gonna be some seismic activity, potential for sabotage etc. I'm not sure that it really is economically viable unless there's some kind of incredibly durable and flexible material to be had which is as easy to use as concrete, about as cheap as concrete, but basically magical spiderwebs.

It's not a vacuum, it's a partial vacuum (1 millibar). Apparently that's supposed to make it much easier to achieve with pumps, even with leaks.

For it to be enough of the vacuum to yield real benefits in terms of The fluid dynamics of the air of the tunnel, it needs to be hard enough to be hard to achieve as in this case. It is easier to achieve than the kind of vacuum NASA might want to draw to test devices, or that somebody with a Watt balance might need, but honestly that only goes to show how horrendously difficult it is to pull that kind of vacuum

There are plenty of breakdowns of the specific numbers that were given in the proposal. If you know enough to contradict one of those assessments or have enough knowledge of the engineering and current technology required to assess the proposal as a whole, feel free to submit your own numbers or point to the assessment you believe best covers the reality of the situation.

Otherwise, definitive statements about small portions of a rather large and complicated proposal that don't provide evidence for their assertions aren't really worth reading. Sorry if that comes across as harsh (it's less directed at you, and more towards the situation as a whole), but this topic is so fraught with people making assertions based on rumors and assumptions rather than the actual data presented that there's a real problem wading through the misinformed to get to the useful information.

If you have those numbers to share, great, otherwise...

The original proposal is available.[1] It includes enough numbers to make estimates of the physics involved. If you want to see what's essentially two youtubers arguing over the physics involved, check this[2] out. It gets a little petty by the end, but there is copious physics and math demonstrated, which you can assess yourself (along with whether the assumptions they make are valid). They do, specifically, go over what would be required to achieve the level of partial vacuum specified, as well as what would be required to safely achieve controlled rapid pressurization in an emergency.

Or you can do a little googling. There's plenty of people that have jumped in with an assessment, and just about as many that have come after to refute some or all of their work.

1: http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf

2: https://www.youtube.com/playlist?list=PLSPi1JFx4_-Gz0Fm0qq2K...

I was wondering if there were updates about this myself. There's been lots of work talked about researching the fluid / heat & weight dynamics, but very little about maintaining the vacuum - which seems to me a more fundamental problem here...

I'm also interested to know what's the plan in case of a brutal rupture of the tunnel. A wall of air rushing through the pipe to meet a car traveling at supersonic speed doesn't sound very pleasant.

Maybe they just plan to make the pipe sturdy enough that it wouldn't be a practical concern?

Thicker pipe = $$$

It's worth noting that conventional railways tend to sacrifice a bit of speed (relative to what you could engineer them for) in favour of being flexible in terms of how much passenger capacity can be provided, supporting a mixture of local/express services, and so forth. So the 'sweet spot' for a conventional or high-speed rail line between two locations may tend to be larger.

When the first wave of criticism came after Musk presented his Hyperloop concept the argument I found the most compelling was that at those speeds if you change direction very fast or the lateral and vertical accelerations felt by the passenger quickly becomes uncomfortable or even unbearable.

That means that if you have some kind of obstacle on the way, such as a mountain, lake or even a city you can't easily swerve around to avoid it. You either have to anticipate your turn extremely early (huge turn radius) or you basically have to tunnel through it (extremely expensive).

For the same reason if you decide to pass over mountains you might have to start elevating the track well before you meet the slope because you can't brutally change your inclination from 0 to, say, 20 degrees brutally without inflicting a few gees to the passengers. So you'd basically build a ramp to smooth it up, which would also be quite expensive.

Has this been addressed?

I think his plan is to tunnel through: https://www.boringcompany.com/faq/

Also, what if landscapes shift due to tectonic plate movement?

I'm scared to fly as it is, but hurtling through the air at mach 1 there is far less chance of an obstacle than hurtling through a cramped vacuum tube at mach 1.

If the seal on the hyperloop is ever broken (anywhere along the loop), the tube will fill with air and the train/pod will naturally come to a stop due to air resistance.

I'm sure that it will but will it do so safely when traveling at the speed of sound?

If I jump from an airliner into the ocean I'll naturally come to a stop due to water resistance but I don't think I'm going to enjoy that very much.

This is a genuine question by the way, I really don't know what kind of deceleration to expect in this situation. It just seems like in this situation the train would behave a bit like a piston meeting the rushing wall of air head-on. I can't imagine that it would make for a particularly gentle stopping.

and then what do the people inside do?

Climb out and walk to the nearest escape hatch in the hyperloop tunel. Or perhaps sit just sit there for an hour or so and wait to be rescued. It's really not that different from a subway being derailed or a carnival ride breaking down.

What if it hits something, like:

An obstacle in the pipe

A misaligned tunnel wall due to shifting Earth

Other pods ahead of it

> An obstacle in the pipe

How is an obstacle going to get into a vacuum sealed pipe? Unless there are parts literally falling off of the pods, I can't really see this happening.

> A misaligned tunnel wall due to shifting Earth

This would most likely break the vacuum seal and be detected immediately.

> Other pods ahead of it

Seems easy to avoid. We don't typically hear about trains crashing into each other, so I don't see why we'd expect that to happen with pods.

I'm not familiar with the limitations of the system, and I know the point is speed, but couldn't they just slow down before traversing the obstacle?

I suppose, but you obviously decrease the average speed that way. It could be pretty significant too, if you want to reach bullet-train speed for your maneuvers you have to slow down to around ~300km/h from your 1000+km/h cruising speed.

That's a delta-v of at least 700km/h or about 200m/s. At a deceleration of 1g it'll take about 20 seconds, and an other 20 seconds to get back to speed after that. And 1g sounds like a lot for public transportation, especially for so long. Maybe they could rotate the seats to keep the acceleration downwards from the point of view of the passengers?

And obviously it'll take a lot of energy to re-accelerate the car, so you might want to store the braking energy to reuse it but I'm not sure if it's practical to store such a huge amount of energy so quickly.

I remember the throughput was also fairly low compared to high speed rail, and many of the savings came from questionable areas (running the tube through highway medians, stopping the hyperloop at the outskirts of the city instead of going into the city like rail does).

Agreed. I'm not sure how Hyperloop scales to population changes especially if it is below ground. Sounds like a very expensive infrastructure investment.

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