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The idea of soaring through the sky with nothing more than a suitcase-sized rocket strapped to one's back has captured the public's imagination since rocket packs (read The Trouble with Rocket Packs) were first introduced shortly after World War II. And when James Bond strapped one on over his tux in Thunderball, its fascination only grew. Yet, with the exception of the occasional demonstration at a Pro Bowl game, parade or convention, the rocket pack has remained mostly grounded, a vision of the future that never quite materialized. They are loud (about 160 decibels—enough to rupture an eardrum), require quite a bit of skill to fly, and can only stay aloft for about 30 seconds—hardly enough time for even Bond to vanquish any threat posed by SPECTRE.

That has led many interested in personal flight to look at the jet pack, a technology with a similarly checkered past but with the potential to extend that flight duration thanks to improved fuel economy (thanks to an air-breathing jet turbine rather than a rocket pack's hydrogen peroxide gas, which is quickly depleted). And engineers may be getting somewhere.

In January, Thunderbolt Aerosystems, Inc., a Mountain View, Calif., maker of both rocket and jet packs, unveiled plans to develop by the middle of 2009 a jet-powered device called THUNDERJET, which the company claims will be able to stay in the air for up to 35 minutes. If successful, THUNDERJET could be a candidate for a host of defense, commercial and personal purposes, says Thunderbolt founder Carmelo Amarena, including support for military missions, disaster relief efforts and border patrol. "My goal is not to replicate the original rocket belt," he adds, but rather to develop a jet pack that makes personal flight available to the masses.

THUNDERJET will debut only after Thunderbolt releases two new versions of its rocket pack this year—one next month capable of up to 50 seconds of flight and one in early August that will pack even more fuel, allowing a pilot to fly for as long as 75 seconds. Although these rocket pack improvements are laudable, they barely double the capability of rocket technology developed 40 years ago, making the production of working jet pack a much more coveted prize.

Thunderbolt is not alone in its quest to deliver a jet pack. Troy Widgery's goal since founding Jet Pack International about four years ago in Denver has been to build a unit that flies under the power of a single jet-turbine engine and can keep a pilot airborne for up to seven minutes. Sticking points have been improving fuel efficiency, getting sufficient thrust out of the pack's turbine to lift both pack and pilot, and developing an engine that responds quickly to the flyer's hand controls, because turbines typically have more of a lag time than rockets. "[The jet pack] will be as fast at top speed and look very similar to [a] rocket pack," Widgery says, adding that he hopes to have a working model by the end of the year.

If these companies can come up with a turbine small enough to wear yet powerful enough to lift a person off the ground, they will improve the technology by a large measure and may finally give the jet pack the efficiency and reliability needed to be embraced by the mainstream in ways rocket-pack technology never has.

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