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Why Don't We Have Personal Jetpacks?

 Where's my jetpack? It's a question so synonymous with pop futurism that it's inspired a TV Trope, a book, and numerous annoyed letters to Popular Mechanics (sorry). The fact is there are working jetpacks. But one isn't coming to the mass market to handle your daily commute anytime soon.
The idea has actually existed since the 1920s, when science-fiction pulp magazines imagined jetpack-wearing heroes. (James Bond would don his famous jetpack in 1965's Thunderball.) Since the 1950s, government agencies and DIY nerds alike have been researching jetpacks in earnest, but the technology just hasn't made it off the ground, so to speak.
Generally, what we call jetpacks are technically rocket packs, because they work the way rocket engines do: by combing fuel, usually hydrogen, with an oxidizing agent. The chemical reaction produced by the fuel and oxidizer is highly exothermic, meaning it releases
copious heat energy. The resulting hot gas shoots downward to provide thrust.
A mass-marketed jetpack isn't feasible for a few reasons. For one thing, humans just aren't meant to fly. Being relatively squat and unwieldy creatures, we require a relatively large amount of force to lift into the air.

Other methods of airborne transport get around this issue by putting people in aerodynamic contraptions such as planes, or by mimicking more flight-friendly creatures, as a wing suit does. But a jetpack is meant to be something that straps to your back and carries you away. Creating that amount of lift with a rocket-propulsion system means burning a lot of fuel, so until recently even the best jetpacks could stay in the air for only about 30 seconds.

Ky Michaelson, a jetpack-building enthusiast known as The Rocketman, says the future is in actual jetpacks, such as the Martin Jetpack. The gasoline needed to power a jet turbine is 13 times lighter than the amount of hydrogen fuel needed to provide the same thrust, giving you more room for your fuel supply—you just have to deal with a jet engine strapped to your back.

Announced in 2010 and still in development, the Martin Jetpack aims to provide 30 minutes of air time. According to the Martin Jetpack website, the device is expected to cost $100,000 at the very least. That's a lot of dough for a method of transport that promises to be incredibly unsafe and extremely loud (Michaelson describes the sound of his rocket belts as being "like a fire extinguisher times a thousand, and very piercing"). The pack will probably include a parachute. But if both that and the engine failed, your descent would make helicopter crashes look positively swan-like.

So, no, you won't be going to work by jetpack next week. But that doesn't mean you can't have fun with today's tech. Just look at PopMech flying around with the water-powered JetLev

Read more: Why Don't We Have Personal Jetpacks? - Popular Mechanics