A jet pack, rocket belt, or rocket pack is a device worn on the back which uses jets of gas or liquid to propel the wearer through the air. The concept has been present in science fiction for almost a century and became widespread in the 1960s. Real jet packs have been developed using a variety of mechanisms, but their uses are much more limited than their fictional counterparts because of the challenges of the Earth's atmosphere, gravity, the low energy density of utilisable fuels, and the human body not being suited to flight, and they are principally used for stunts. A practical use for the jet pack has been in extra-vehicular activities for astronauts because of the apparent weightlessness and lack of friction-creating atmosphere in orbit. The term jet suit is used for a system incorpo