Jet pack

Jet pack, rocket belt, rocket pack and similar names are used for various types of devices, usually worn on the back, that are propelled by jets of escaping gases (or in some cases liquid) to let a single user propel him or herself into the air or fly.

The concept emerged from science fiction in the 1960s and became popular as the technology became a reality. The most common use of the jet pack has been in extra-vehicular activities for astronauts. Despite decades of advancement in the technology, many obstacles remain in the way of use of the jetpack in the military or as a means of personal transport, including the challenges of Earth's atmosphere, Earth's gravity, low energy density of available fuels, and the human body not being naturally adapted to fly. To compensate for the limitations of the human body, the jet pack must accommodate for all factors of flight such as lift and stabilization.

The first jet pack was developed in 1919 by the Russian inventor Aleksandr Fyodorovich Andreyev. The project was well regarded by Nikolai Rynin and technology historians Yu. V. Biryukov and S. V. Golotyuk. Later it was issued a patent but apparently was not built or tested. It was oxygen-and-methane-powered (likeliest a rocket) with wings each roughly 1 m (3 feet) long.

A hydrogen peroxide-powered engine is based on the decomposition reaction of hydrogen peroxide. Nearly pure (90% in the Bell Rocket Belt) hydrogen peroxide is used. Pure hydrogen peroxide is relatively stable, but in contact with a catalyst (for example, silver) it decomposes into a mixture of superheated steam and oxygen in less than 1/10 millisecond, increasing in volume 5,000 times: 2 H₂O₂ → 2 H₂O + O₂. The reaction is exothermic, i.e., accompanied by the liberation of much heat (about 2,500 kJ/kg [5,800 BTU/lb]), forming in this case a steam-gas mixture at 740 °C [1,360 °F]. This hot gas is used exclusively as the reaction mass and is fed directly to one or more jet nozzles.

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