On another site (we don't like to advertise), I came across a http://www.popsci.com/popsci/aviationspace/a3bfe2e6fb5c6110vgnvcm1000004eecbccdrcrd.html , in which scramjets are discussed. It's been making the rounds again, so you've quite likely seen it elsewhere. I thought I'd do a little looking into their claims, and here's what I came up with. Anybody care to fault my physics; I wouldn't be surprised if I mucked up somewhere:
I think it'll be a long time before we start seeing scramjets for consumer travel, and here's why -- it's just too fast. "In 2004, NASA's unmanned X-43A ... reached Mach 9.6, setting the world speed record for a jet-powered aircraft. It took only 10 seconds of scramjet power to get it up to that speed."
That's a hair over 32 gee, people. That *will* kill you, see http://www.thespacereview.com/article/410/1. OK, you say, that's not the sort of acceleration profile you'd use for a consumer flight. The great circle distance from JFK to Melbourne [Tullamarine Intl] is 10374 mi. If we assume uniform acceleration to the halfway point, then uniform deceleration from there, the case with the lowest required acceleration, then we need to cover 5,187 mi in 1 hour.
That's 7.6 gravity. It won't kill you, but it's certianly not comfortable. That's the lowest possible accleration to get from New York to Melbourne in two hours, and it assumes a pretty amazing engine -- one that can run continously for two hours, and one that can instantly cut from full thrust forward to full thrust reverse.
It's not going to be possible to get humans from NYC to Australia in two hours without some sort of major change in the way we think physics works -- inertial dampers or teleporters.
[ this is good ] for making me think.
Originally posted on theorbtwo.vox.com