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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
Software

+ - Avoid using Vista, keep XP and wait for Windows 7

Submitted by
reube
reube writes "Vista.Blorge reports that while Operating System changes and upgrades are a major hassle for enterprises, no one says that enterprises necessarily have to go through the hassle of adopting every changes and upgrades. Avoiding some upgrades may be a better option for enterprises. The report attempts to answer three important questions such (1) Is it worth moving to Vista? (2) Is Windows XP worth holding on? and (3) Is Windows 7 worth waiting for? It also articulates and presents arguments that it is better for enterprises to stay using Windows XP and wait for the coming Windows 7 than upgrade to Vista."

"If you want to eat hippopatomus, you've got to pay the freight." -- attributed to an IBM guy, about why IBM software uses so much memory

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