Star Travelers - Part 1 of 2

Larry Klaes (
Wed, 28 Jul 1999 13:50:40 -0400


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<bold><fontfamily><param>helvetica</param><bigger>Star Travelers

</bigger>Craft Powered by Antimatter, Fusion and

Solar-Driven Sails Could Take Us to Interstellar Space=20

a.m. ET (1107 GMT) July 27, 1999</smaller></color></fontfamily>=20

<bold><fontfamily><param>arial</param><smaller>By Mariette
<underline><color><param>0000,0000,fefe</param>Popular Science

</color></underline><italic>Fox News and 'Popular Science' have merged
efforts to offer the best in science and technology news. Keep checking back over the coming weeks as we expand our combined coverage.</italic>=20

Robert Frisbee is huffing cheerily as he ambles downhill toward a nondescript building on NASA's Jet Propulsion Laboratory campus in Pasadena, California. The San Gabriel mountains form a stunning backdrop, and the sun has warmed the January air to spring-like temperatures, but Frisbee doesn't seem to notice any of it. Indeed, his mind is far away. In interstellar space, to be exact. Frisbee is talking about how we'll someday visit the stars with spacecraft.=20


Sauls/John Frassanito &

</flushright> <fontfamily><param>helvetica</param><smaller>Ramjet Fusion
Engine: In one interstellar engine concept, charged particles streaming out at one-third the speed of light would provide thrust for a fusion-powered spacecraft=20


If that sounds far out, it is, by nearly every measure you can think of =97 the tremendous distances between stars, mission trip times measured in decades, and required technological advances so dramatic that even some researchers refer to them as "miracles."=20

Nevertheless, there's no shortage of well-reasoned ideas about how to conquer the NASA centers, universities, research institutions, and companies are laying the groundwork for experiments that will advance the necessary technologies. And while depicting trips to other stars has long been a staple for science fiction writers, today it is the stuff of long-range strategic goals for NASA.=20

The NASA Origins program plans a series of progressively more capable telescopes, culminating in the imaging of Earth-like planets around the nearest 1,000 stars. Building on that, NASA Administrator Dan Goldin has said he wants the agency to launch interstellar missions in the next 25 years. To drive the necessary advances, "We have to set goals so tough they hurt," Goldin has said.=20

Even at this embryonic stage, it's already more than apparent that the task is as difficult as it could possibly be and still remain possible =97 scientists think. Start with the vast scale of the cosmos. Voyager I, launched September 5, 1977, illustrates the scope of the problem. After speeding along for more than 20 years, it is now 6.8 billion miles away from Earth traveling at nearly 51,000 mph. That's about 10 light-hours away. (A light-hour is the distance light travels in one hour at 186,000 miles per second.)=20

But the closest star to Earth is Proxima Centauri, which is 4.3 light-years, or 25 trillion miles, away. If Voyager were pointed in the right direction, Frisbee and JPL colleague Stephanie Leifer calculate that it would take some 74,000 years to make the trip. But interstellar missions must occur on a human time scale =97 preferably within an individual's lifetime. That means a maximum of 40 years for a "slow" mission, and a far more desirable 10 years for a fast one.=20


Sauls/John Frassanito &

</flushright> <fontfamily><param>helvetica</param><smaller>Beam-Core
Engine System=20


And then there's Einstein. A spacecraft that aims to cross vast distances at high speeds also must contend with the theory of special relativity. The theory mandates that as an object approaches the speed of light, its mass increases. To get to Proxima Centauri in, say 10 years, the craft would have to whiz along at nearly half light speed. At that velocity, it would become 1=BD times more massive than it was originally.=20

Frisbee, a chemist whose job it is to analyze such missions, puts it another way: "If you take a 1-ton spacecraft, such as Voyager, and bring it up to one-half the speed of light, it'll require one month's worth of all the energy produced today by humans." Even if it were possible to build a big enough fuel tank, conventional chemical rockets don't have the power, or energy density, to do the job.=20

One last thing: It's one kind of propulsion requirement to get up to speed and coast for a fly-by mission, as Voyager did to the outer planets in our solar system. But to stop to orbit or land at an interstellar target, the spacecraft has to expend energy to slow down. "From a propulsion point of view," says Frisbee, "we've immediately doubled the requirements."=20

So what's an interstellar mission planner to do? "When all is said and done, you're kind of stuck with fusion or antimatter [for an onboard engine]," says Frisbee. "Even fission doesn't have enough energy." The other chief option, he says, is to leave the engine at home. Solar-powered lasers parked in orbit around our sun, for instance, could push craft with thin sails across space. "Right now, based on our current level of ignorance, they're all equally impossible. . . or possible," says Frisbee.=20

Take antimatter, for instance. If antimatter comes in contact with regular matter, they annihilate; the mass of both is turned into energy. "The antimatter-matter reaction has the highest energy density we know of," says Stephanie Leifer of JPL. The reaction releases charged particles, which could be directed out the back of a spacecraft for thrust using magnetic "nozzles." The charged particles move very fast, approximately one-third the speed of light. However, says Leifer, "We don't know how to make nozzles big enough [for an antimatter engine]. It's not totally infeasible, but it's very tough."=20

Engine System Concept

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Add to that another big problem. A pure antimatter engine would need thousands of tons of antimatter, plus matter, on the order of the size of the Washington Monument. But today, mere nanograms of antimatter are made at special laboratories like Fermilab and CERN. "We'd probably have to have an infrastructure in space, to harvest the antimatter," speculates Leifer.=20

The effort might be defensible, since antimatter could be used for medical applications like imaging and destroying certain cancer tumors. But then there's another issue. Antimatter also can't contact matter, so it's been difficult to store more than a tiny amount in magnetic traps, which keep charged particles from hitting the matter containment walls and annihilating.=20

Enter physicist Gerald Smith and his team at Penn State. Smith suggests a way to vastly reduce the antimatter requirements. "We'll never have even a ton of antimatter, in my view," he says. "We think we can ignite with a microgram of antimatter, which we can foresee doing with the current technology." Ignite what? A fusion reaction.=20

His team is attacking the problem in several fronts. First, successful tests with a shoebox-size antimatter trap built at Penn State that could theoretically hold 100 million antiprotons, or positively charged particles of antimatter, have inspired researchers to build a larger one with the Marshall Space Flight Center in Huntsville, Alabama, to be finished this summer. Smith estimates it could hold 10,000 times as many antiprotons as the smaller trap. The trap will enable eventual tests with a planned antimatter plasma gun, which will be used to ignite the fusion reaction.=20

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