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" Strictly speaking, you could the say the business of jet packs is, indeed, taking off. The number of companies looking to sell them to private consumers has increased by as much as 33 percent in the last week alone. And since the going assumption is that all human beings would like to be able to fly\u2014not by plane or helicopter or oversize cannon, but strapped to a thunderous gadget with intuitive controls\u2014that&amp;#039;s good news. Then there&amp;#039;s the bad news. First, these jet packs aren&amp;#039;t what they seem: Jet-powered devices are in development (and models were tested as early as the &amp;#039;60s), but all models on the verge of availability are, in fact, jet-free and called, officially, rocket belts. Second, while last year there were two commercial rocket-belt manufacturers\u2014Mexico&amp;#039;s Tecnologia Aeroespacial Mexicana (TAM) and Colorado-based JetPack International\u2014there are now three: Thunderbolt Aerosystems, based in California, plans to start selling its ThunderPack TP-R2G2 rocket belt to customers this summer. Why is another entry in the fledgling human-flight business bad news? After all, three companies might be just enough to spur the kind of innovation that a healthy niche industry needs. Well, that&amp;#039;s the problem with so-called jet packs: everything. It isn&amp;#039;t simply a matter of technology in its infancy\u2014the eight-track paving the way for the cassette, or the Roomba for the domestic android. Rocket belts have been disappointing for decades, and although word of the sub-$100,000 ThunderPack has made the rounds online this past week, the hurdles have yet to be cleared. At best, today&amp;#039;s rocket belts are an excellent party trick, worthy of halftime stunts and air show demonstrations. At worst, they&amp;#039;re a marketing campaign for a product that no one&amp;#039;s actually supposed to buy. So here&amp;#039;s why it&amp;#039;s time to stop talking about rocket belts, for good, and get back to the business of making jet engines wearable.  Fly Weight On a full tank, the new ThunderPack TP R2-G2 weighs between 170 to 182 pounds, depending on the type of fuel used (the slightly heavier model adds kerosene to the standard hydrogen peroxide mixture). The models offered by TAM and JetPack International, which we detailed in depth here, are lighter\u2014but not by much, at around 139 pounds. Although rocket belts come with sturdy frames, they don&amp;#039;t include strength-boosting exoskeletons. Your back and legs are doing the heavy lifting, not only keeping you from buckling, but from topping over backwards like an overturned turtle. According to Thunderbolt president Carmelo Amarena, the ThunderPack is easier on pilots than the competition&amp;#039;s, since the weight sits on the hips instead of the shoulders. But what happens when you land while wearing a rocket belt? Apparently, knee injuries. JetPack&amp;#039;s resident pilot, Eric Scott, has suffered at least six of them, and Wendell Moore, one of the inventors of the original rocket belt, fractured his knee during a tethered test flight. Jet packs might prove slightly lighter than rocket belts, thanks to dramatically improved fuel efficiency, but the real advantage would be better controlled landings. Amarena believes that a jet-powered device would make relatively gradual turns, particularly during low-speed operations, such as takeoffs and landings. And when your landing gear is made of flesh and blood, coming in &amp;quot;hot&amp;quot; is to be avoided. Unfortunately, jet packs are going to be heavy. And if enough people buy them, someone is bound to lose control, and destroy his or her knees. But if tomorrow&amp;#039;s jet packs deliver on even a fraction of what these companies are promising, it might just be worth it.  Fuel Economy Across each of the rocket belts you&amp;#039;ll be able to buy this year, weight becomes largely a function of fuel\u2014the ThunderPack TP-R2G2, for example, requires from 98 to 102 pounds of it. In exchange, the pilot gets up to 75 seconds of flight. And that, surprisingly, is a breakthrough. JetPack International&amp;#039;s H202 can last 33 seconds, while TAM&amp;#039;s belt can only stay aloft for half a minute. That begs the big question: How far can you fly on 100 pounds of fuel? In theory, the TP-R2G2 can travel 3260 ft., which is over two-thirds of a mile. For an aircraft that&amp;#039;s paltry, but perfectly understandable. There&amp;#039;s nothing aerodynamic about a rocket belt, and nothing generating lift other than raw thrust. And for a rocket belt, this is an impressive potential range, easily surpassing the Hollywood stunts and Olympic stadium hops of decades past. But as practical applications begin to take shape, new problems inevitably tag along. A rocket rescue of trapped mountain climbers\u2014clearly the stuff of sci-fi legends\u2014would mean carrying an additional human, in turn requiring more thrust, more fuel and even more total weight to deal with during landings. As for military uses, there&amp;#039;s a reason DARPA never followed through on apparently successful tests. Whether you&amp;#039;re vaulting over a castle wall or flying headfirst into an open helicopter, a rocket-belt-enabled assault is essentially a challenge: Can you shoot me before I crash? Jet packs, however, could change everything. All three major players are planning to release systems with exponentially greater range than their current rocket belts. Last year, JetPack International founder Troy Widgery told Popular Mechanics that by the end of 2007, the company would release the T73, a jet-fuel-powered turbine belt capable of 19 minutes of flight. When we contacted him for an update on the $200,000 device, Widgery said, &amp;quot;We were trying to have it by the beginning of 2008, but it could be the middle now.&amp;quot;  TAM continues to work on its propane-burning jet belt, and is waiting for tests before announcing further details or a possible release schedule. Thunderbolt, in its recent press release, mentioned a followup model that could fly for as long as 35 minutes, with availability as early as this year. This is standard practice in the rocket-belt industry\u2014announce one product, but divert attention to the better one down the line. And between JetPack&amp;#039;s missed T73 deadline and Thunderbolt and TAM&amp;#039;s vague promises, are we getting any closer to a viable product? To their credit, the heads of all three companies are quick to acknowledge the relative uselessness of rocket belts. These are simply proof-of-concept designs on the way to the real prize\u2014something you can fly for minutes, not seconds. &amp;quot;The future is not really in building rocket-powered devices and expecting everyone to have one in their garage,&amp;quot; Thunderbolt&amp;#039;s Amarena says. &amp;quot;The rocket fuel is very finicky. You don&amp;#039;t want it sitting around under your bed.&amp;quot; Storing hydrogen peroxide and other oxidizers means dealing with your local fire marshal, and prohibitive costs, even for someone rich enough to buy a $100,000 rocket belt\u2014one half-minute ride could cost thousands.  Gallons of inexpensive kerosene, on the other hand, are already safely sitting in garages across the country. Amarena&amp;#039;s team has been working on a jet pack that would burn standard jet fuel, as well as kerosene or even diesel, since 1996. &amp;quot;The design is already finished,&amp;quot; he says. &amp;quot;What&amp;#039;s stopping us is funding.&amp;quot; Thunderbolt had secured seed money for its two rocket belts, but to cross the finish line, it might actually have to sell a few. And that&amp;#039;s the ultimate dilemma all three of these companies are facing: Why would anyone buy a rocket belt, knowing that they&amp;#039;re funding the birth of the first true jet packs?  The Bottom Line It&amp;#039;s a hard thing to do, bursting bubbles, but here goes: You&amp;#039;re as likely to fly a rocket belt as an F-22. In other words, at this moment, it&amp;#039;s physically possible to be a rocketeer. But this is a very select group, and despite years of promises, membership is still closed to the public. Both TAM and JetPack International include flight lessons in their respective $125,000 and $155,000 prices, but neither company has turned a single wealthy citizen into a proud rocket-belt owner. In an e-mail, TAM founder Juan Manuel Lozano wrote that although two companies in Asia were interested in buying some of his belts, Lozano &amp;quot;decided not to sell to them because they wanted an agreement with a lot of responsibility for me, and I didn&amp;#039;t wanted to be involved in a lawsuit.&amp;quot; Both JetPack International and Thunderbolt Aerosystems currently make money from air show demos, and Amarena says that since Thunderbolt announced its new belt last week, &amp;quot;We have identified at least four real, potential customers within the U.S., and one in Europe.&amp;quot; He plans to make it perfectly clear just how problematic rocket belts are: For example, while the Federal Aviation Administration doesn&amp;#039;t require certification for rocket-powered devices, pilots would be advised to fly no higher than 50 ft. to avoid disrupting air traffic. But barring any additional investment in the company, belt sales, however few, could be crucial toward producing an actual jet pack. So, to a certain extent, we&amp;#039;re left where we began, with a childhood fantasy that&amp;#039;s only as real as three companies would have us believe. But what&amp;#039;s become clear is that everyone, even the ones building the rocket belts that attract these occasional media frenzies, is waiting for his jet pack. And missed or missing deadline aside, no one is being intentionally deceived\u2014we&amp;#039;re deceiving ourselves. With a little patience, and a little funding, we could actually have the pleasure of grumbling over regulatory issues we never dreamed possible. Like being limited to specific kinds of air strips, because the jet strapped to your back is classified by the FAA as an ultralight. Or being required to wear a ballistic parachute, because Amarena&amp;#039;s Thunderjet design could reach altitudes as high as 10,000 feet (and, for the record, speeds of up to 160 mph, provided someone can solve wind-resistance issues). So while rocket belts continue to taunt our collective inner child, if you can wait another year, or two, or maybe 10, something truly impossible is barreling toward you like the proverbial bat out of hell. Or, possibly, like a guy strapped to a jet. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/flight/a2564/4247253/>