Comment Re:It's almost like the Concord verses the 747 aga (Score 1) 157
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Ok, let's look at an emergency scenario where a capsule (not the tube) undergoes rapid depressurization. To save the passengers, the ambient pressure in the entire tube must quickly (within a few seconds) be brought up to levels at which oxygen masks will function; about 20kPa. This can be done by flooding the tube with air evenly along its length; no tube destruction required. The question is whether a 20kPa tube atmosphere would impose problematic aerobraking forces on the capsules. At 700mph, you'd probably be ok. But at 1500mph, you'd immediately be exceeding the ambient speed of sound, which would be very bad.... Long story short: if your capsule suddenly depressurizes at 1500 mph, you're dead. But at 700 mph, you might still be ok. The risks and complexities associated with hypersonic tube travel seem to outweigh the benefits, at least for now. Subsonic is good enough, really.
Interesting, and necessary, scenario. But I think the "few seconds" constraint is extreme. At 800 mph the vehicle stops in 30s at 1g, and I suspect 3g (space shuttle launch) is not that intolerable in an emergency; its certainly not fatal. Unconsciousness takes about 15s. There have been vacuum chamber accidents where people have recovered after exposure to vacuum for 30s (i.e. yes, Bowman with no helmet could have beat HAL in 2001).
