Hacker News Reader

Comment by tlb | Hacker News Reader

I worry that the necessary straightness of the tube will be difficult to achieve. The pads float 0.5 to 1.3 mm from the inside of the tube, so deviations from straightness on that scale will cause the pads to crash. Any contact at 760 mph would probably damage the pad, plugging the air holes.

View on HN

Isn't there some kind of inverse square law affecting the force between the walls and capsule? The closer you get to contact, the harder it pushes back?

It should be largely self-correcting.

If someone shot the tube with a medium sized gun, would the impact cause an internal defect on the order of 0.5mm?

The tubes for the passenger-only version would be 20 to 23 mm in thickness. I'm not sure what damage a medium-sized gun would do to steel that thick.

According to some quick youtube searching, armor-piercing rounds versus regular steel would create problems: http://youtu.be/q_zZd0NsYG4 .

Sure, so would high explosives directly on the tube. I am considering a situation that could conceivably be accidental because it is incredibly difficult to engineer something that can stand up to malice.

The bar to malice is important to consider. If the bar is "high explosives or shaped charges", then you are probably okay. If the bar is "a redneck who is bored with shooting stop-signs", then that might be a problem.

Bored people don't shoot guns at trains today. Why would they start?

Because there's no possibility that shooting at a train would result in a fireball a thousand yards high, whereas...

How thick are propane tanker cars?

Back of the bar napkin calculation with Barlow's formula, assuming 200psi (about what bbq tanks are at iirc?), somewhere around half an inch.

Because the tube isn't a train?

Are you sure? I imagine most trains these days are pretty tolerant of that, it could easily go unnoticed.

Bored people shoot track, put pennies on tracks, drop water balloons from freeway overpasses, put potatoes in car exhaust pipes, and on and on. Its important to consider the most random variable in the safety equation - bored people.

I'd say all these concerns warrant putting the damn thing underground.

Reply on news.ycombinator.com