Hacker News Reader

Comment by e2e8 | Hacker News Reader

I don't think that objection, by itself, invalidates the the video author's criticisms. According to Wikipedia, the hyperloop is intended to have a pressure of 100 Pa or 0.1 % of atmospheric pressure[1]. That is not much different from a prefect vacuum for the purposes of an approximate engineering calculation.

[1] https://en.wikipedia.org/wiki/Hyperloop

View on HN

That's like saying there's no difference between 99.9℅ the speed of light and going all the way there, from an engineer perspective. Turns out, one of these requires an infinite more expenditure of energy than the other. Similarly, if you're evacuating a tube by removing gave the gas at a time, 1/1000 is attainable. 0? Not so much.

I don't disagree but that is not issue here. The issue is that for the purposes of discussing the mechanics of the tube like strength, seals, safety etc. the small amount of air left in the tube should not throw off simple calculations by too much.

No, the air in the tube matters, at least in Musk's original design, which has the pod running on a very thin air cushion. In practice, most designs are maglev, for which a hard vacuum is best.

But that amount of air may not matter too much for the points discussed in the video which have to do with strength, seals, etc.

That, and AFAIR original design had a system to pull the air from the front to the back, thus lowering the drag while reducing the need for lower air pressure.

Reply on news.ycombinator.com