SpaceX Is Building a Hyperloop Test Track

Jason Koebler reports that SpaceX is building a small-scale version of Elon Musk's hyperloop transport tube system, which can move cargo and people at speeds over 700 mph. The test track will be approximately one mile long, and its inner diameter will be between four and five feet. But while SpaceX is building the track, it's not going into full development mode. Instead, the company is turning it into a competition. Other organizations will be invited to build pods — the containers that move through the tubes — and test them inside the track. They say the competition will be geared toward university students and independent engineering teams. SpaceX expects the testing to happen next June, and they've published a document with details on the competition. They add, "The knowledge gained here will continue to be open-sourced."

Comments

Reasons why I don't like Musk's hyper loop

[OzPeter]

1. All the diagrams give the impression that it will be like people flying through tubes as in Futurama. Instead you will be sealed inside a metallic "bullet", that runs in a metallic tube - no windows for you (sort of like James Bond in The Living Daylights). It's a pity if you have any sort of claustrophobia.

2. While the device doesn't run in a complete vacuum, it runs in an atmosphere that is low to the point of being unbreathable. But the device doesn't contain any onboard air supply - instead it relies on the driving compressor/fan assembly to compress the air to a human sustainable amount. So if the device loses power for any reason (electrical, mechanical, computational) then you better be able to hold your breath for a long long time.

3. There was no indication that the loop itself was anything more than a single tube. Thus there is no capability to bypass any section. So if a device fails, all devices that are already in transit and behind it are screwed (see 2 above).

Re:Reasons why I don't like Musk's hyper loop

[OzPeter]

That's a tough one.

Maybe over a span of fifteen minutes or so?

So do you want to fill the whole pipe up at once? Or are you going to break it into airtight sections with pressure proof doors at each end? Because each set of doors you insert into the system will cost money in maintenance and testing and will have to be available 100% of the time.

Now lets do some basic math. Suppose that you let the air in at 1/3 the speed of sound in order to protect equipment and people. Assume no friction and that the air travels down the pipe as a plug. So the maximum distance between doors is constrained by the time it takes the air to traverse that distance. 15 minutes is 900 seconds. At 100m/s the air will travel a maximum of 90000 metres.

So in a perfect world you have to have emergency self sealing doors located every 90km along the pipe. So lets round that down to 50 miles. GIven 400 miles between LA and SFO, that means you need 8 sets of emergency doors. But there is the chance that a capsule could stop on a door, or a door could fail. So you need at least to double the number of doors in order to stay within your safety limit. So that's 16 sets. Plus we ignored friction, so lets add another 4 to round it up to 20 sets of doors.

So that's 20 sets of mechanical devices that need regular maintenance and weekly (if not more) testing - and that testing has to be done when the hyper loop is not in use - because if a door does not fully retract after testing then the capsule is screwed. They also need high availability power supplies to operate the doors, and pumps to pump each individual section back down to its working pressure, and a staff of people to service them (probably another 5 to 10 people on payroll based up and down the hyper loop just to do that on a sustainable basis).

So we have just added a shitload more money to the operating costs of the hyper loop.

Re:To head off the Hyperloop misconceptions...

[Rei]

On the front of how the concept can be significantly improved upon, here's one: pumping is a very small fraction of the total costs. You could significantly increase the pumping and not have a significant impact on the costs. If you increase the pumping by, say, an additional 4x and inject water vapor, then you will achieve an 80% water vapor atmosphere (water does not condense at such low pressures). This offers a ~40% increase in the speed of sound and thus the maximum speed of the vehicle and reduces its resistance at a given speed.

One can take it further and inject hydrogen instead of water vapor. Most of the downsides that immediately come to mind don't actually turn out to be problems in practice - at such low pressures it's not flammable even if mixed with air, such low pressures aren't an embrittlement risk, the quantity of hydrogen needed is trivially small and thus costs little and poses little ozone hazard, etc. It's basically still "nearly a vaccuum", just with trace hydrogen rather than trace air. Pure hydrogen allows a maximum velocity nearly 4x that of the standard Hyperloop approach.

(Helium is another option, though not quite as good as hydrogen and more expensive. Also, if one wants to go faster and with less resistance than hydrogen, then there's only two options: 1) hot hydrogen, and 2) hard vacuum with maglev (aka, not hyperloop))

Let's be honest about the purpose of the hyperloop

[Bruce Perens]

Although the hyperloop is possible and might even be practical someday, let's please be honest about the reason it was created. Elon Musk just wanted to kill the California high-speed rail.

That might have been OK if there was a hope that we could actually replace it practically with a hyperloop. But given the history of bleeding-edge rail - ride any maglevs lately? We haven't even had much success with monorails outside of theme parks and Las Vegas - we don't really have any working system to replace high-speed rail. Hyperloop should really be called "Pipes that carry People" and we need decades of work on it before considering intercity lines.