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

Ever since Doom days I always looked forward to new ID tech, and was always amazed not by ID games but by their groundbreaking game engines and prospects of other game developers using those engines to make awesome games. Looking at the first screenshots of ID next tech is a letdown for me. I understand these are very first shots, but to me it looks like it was built around Doom3 engine and I cant help but notice the plastic feel of the demonstration. For the first time I can remember there is a better looking engine in development (Crytek 2.0, [Crysis]) at the time of the announcement of new ID tech. Granted it might still be too early to tell but so far the engine does not look revolutionary to me. It looks more like an evolutionary step from Doom 3 engine. I am assuming that the limitations stem from the fact that the engine is designed to run on everything under the sun and 360, mac and ps3 is what limits its potential. Ensuring the engine would run smooth on consoles like PS3 and 360 limits the engine from using far more powerful hardware PC has to offer over consoles. This tech demo makes me glad there are developers like Crytek out there.