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Comment: Re:Iron Man's Suit Defies Physics -- Mostly (Score 2, Interesting) 279

by John Carmack (#23266718) Attached to: The Science of Iron Man
Hydrogen peroxide powered rocket packs fly for around 30 seconds, because they have a specific impulse of around 125, meaning that one pound of propellant can make 125 pound-seconds of thrust, meaning that it takes about two pounds of propellant for every second you are in the air. Mass ratios are low for anything strapped to a human, so the exponential nature of the rocket equation can be safely ignored.

A pretty hot (both literally and figuratively) bipropellant rocket could manage about twice the specific impulse, and you could carry somewhat heavier tanks, but two minutes of flight on a rocket pack is probably about the upper limit with conventional propellants.

However, an actual jet pack that used atmospheric oxygen could have an Isp ten times higher, allowing theoretical flights of fifteen minutes or so. Here, it really is a matter of technical development, since jet engines have thrust to weight ratios too low to make it practical. There is movement on this technical front, but it will still take a while.

John Carmack

Comment: Re:VMWare (Score 1) 962

by agent oranje (#13296151) Attached to: Mac OS X Running on Non-Apple Hardware
You'd have to be a masochist to run Final Cut Pro on Rosetta.

It won't run on Rosetta, as FCP requires a G4, I do believe. For that matter, parts of Apple's pro video line require a G5. So, unfortunately for Mac users like me, it will prove necessary to buy a new version of Final Cut Studio when the P4 PowerMacs come out - which adds like $1200 onto the upgrade price.

Why yes, I am still bitter that my old software isn't going to work. If Apple doesn't make this switch worth while, it's back to Linux for me!

Refreshed by a brief blackout, I got to my feet and went next door. -- Martin Amis, _Money_

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