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In the late 1940s the rocket pack—over the years also called the "rocket belt," "jump belt" and "jet vest"—became more than a comic book concept when engineers at the U.S. military's Redstone Arsenal in Huntsville, Ala., began experimenting with rockets that could be used to carry a person into the air and allow him or her to land safely again using their feet as landing gear. In 1952 inventor Thomas Moore, strapped tightly to his cylindrical backpack, hovered in the air for just a few seconds at Redstone, but it was enough to launch a series of campaigns to develop the technology that would bring personal flight to life.

These high-flying hopes were soon tempered by a number of limitations, most importantly the inability to keep a pilot in the air long enough to do anything militarily significant before running out of fuel. When the Redstone team's funding ran out, the next step fell to Bell Aerosystems in Niagara Falls, N.Y.

The U.S. Army in 1959 contracted Bell to develop what they referred to as a 120-pound "small rocket lift device" that a pilot could strap on and control using motorcycle-type rotating grips for the throttle and yaw. Bell demonstrated its Rocket Belt in April 1961, when pilot Harold Graham flew seven to 10 miles (11 to 16 kilometers) per hour for 13 seconds over a distance of 112 feet (34 meters) at Fort Bragg, N.C. At the military's prompting, Bell also developed plans for a jet-powered pack that would be superior to the Rocket Belt in range and speed, flying as fast as 100 mph (160 kph).

According to a 1968 company report to the military, Bell's jet pack (read Will the Personal Jet Pack Ever Get off the Ground?) would be used for "light mobility systems missions" that involved armed and visual reconnaissance as well as aerial fire troop support and messenger services. The jet pack Bell showed the Pentagon that year, however, failed to get their approval. "It was turbine engine and was fairly heavy," says Carmelo Amarena, founder of Mountain View, Calif., rocket- and jet-pack maker Thunderbolt Aerosystems, Inc. "The military thought that it was too bulky, so they didn't go for it."

The Rocket Belt didn't fare much better. "Bell couldn't develop a long-duration flying device that was really practical," says William Higgins, a radiation physicist at the Energy Department's Fermi National Accelerator Laboratory in Batavia, Ill., and a rocket pack enthusiast. Bell's engineers were also unsuccessful in quieting down the engine's noise, which meant they were not well suited for reconnaissance, Amarena says, adding, "The military didn't want their GIs to become target practice for the enemy."

Most rocket packs consist of two cylinders containing liquid hydrogen peroxide and one containing highly pressurized nitrogen gas, which forces the hydrogen peroxide into a gas generator, where it reacts violently with a catalyst made of silver to produce a stream of steam superheated to 1,370 degrees Fahrenheit (743 degrees Celsius). This hot gas vents out through two nozzles, one on each side of the pack, giving it an upward thrust.

Hydrogen peroxide is a good choice because it does not produce byproducts toxic to the pilot, says Dan Schlund,managing director of Dallas-based Powerhouse Productions, Inc., which for the past three decades has staged rocket-pack exhibitions with its Rocketbelt device in more than 35 countries. "Nothing over the years has proven to be better than hydrogen peroxide," he adds.

Today's rocket packs are flown by highly trained professionals who bob through the air at upward of 35 mph (55 kph). "As soon as you open that throttle, you pop off the ground," says Schlund, who flies under the moniker "Rocketman" and is a Screen Actors Guild–affiliated stuntman who has performed in live shows, movies (most recently this year's Stop-Loss) and TV shows, including Walker, Texas Ranger. "It almost feels like you're going up on a cable." To control the ascent, the pilot (who must weigh no more than about 175 pounds, or 80 kilograms) keeps himself or herself upright using the right hand for the throttle and the left to control the yaw, which moves flyer side to side. "It's pretty much like a dance," he adds. To descend, the pilot backs off on the throttle. Although Powerhouse's Rocketbelt can stay in the air for 30 seconds, pilots are instructed to keep their flight times to less than 28 seconds.

Still, it is unlikely that hydrogen peroxide–powered rocket packs will ever be able to stay aloft for more than a minute, Schlund acknowledges, because larger tank sizes create additional weigh that mitigate the additional fuel. Powerhouse's rocket pack carries seven gallons (26.5 liters) of fuel, weighs 165 pounds (75 kilograms) with full tanks, and generates 800 horsepower.

The rocket pack has proved to be good at one thing: gathering crowds of people to watch a human fly. Interest in jet pack technology says a lot about what people imagine for the future, "including the fact that we're often wrong," says Nick Sagan, son of the late scientist Carl Sagan, who writes about the failed promises of rocket packs—and several other devices—in You Call This the Future?, a book published this month by the Chicago Review Press that he co-authored by Mark Frary and Andy Walker. "I think that's a shame because there's something really exciting about the possibility of going wherever you want with your jet pack. It's the ultimate expression of control over our dominion."

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