SETI Star Travelers - 1 of 2


Larry Klaes (lklaes@bbn.com)
Wed, 28 Jul 1999 12:47:15 -0400


>>>>

<excerpt>Date: Wed, 28 Jul 1999 12:32:43 -0400

From: Larry Klaes

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To: lklaes@bbn.com

Subject: Star Travelers

http://www.foxnews.com/scitech/features/popsci/interstellar1.sml

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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

</fontfamily></bold><fontfamily><param>arial</param><color><param>6666,6666,6666</param><smaller>7.07
a.m. ET (1107 GMT) July 27, 1999</smaller></color></fontfamily>

<bold><fontfamily><param>arial</param><smaller>By Mariette
DiChristina</smaller></fontfamily></bold>
<<http://www.popsci.com>Popular Science

<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>

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.

<flushright>Photo

<<http://www.frassanito.com><fontfamily><param>arial</param><color><param>6666,6666,6666</param><smaller>Bob
Sauls/John Frassanito & Associates</smaller></color></fontfamily>

</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

</smaller></fontfamily>

If that sounds far out, it is, by nearly every measure you can think of
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."

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.

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.

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
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.)

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 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.

<flushright>Photo

<<http://www.frassanito.com><fontfamily><param>arial</param><color><param>6666,6666,6666</param><smaller>Bob
Sauls/John Frassanito & Associates</smaller></color></fontfamily>

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

</smaller></fontfamily>

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 times more massive than it was originally.

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.

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."

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.

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."

<flushright><<interstellar_beamcore.sml> Beam-core Engine System
Concept

</flushright>

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.

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.

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.

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.

<bold><fontfamily><param>arial</param><smaller>P A G E
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<bold><fontfamily><param>arial</param><smaller> | </smaller></fontfamily></bold> <<interstellar2.sml><bold><fontfamily><param>arial</param><smaller>2</smaller></fontfamily></bold>

     

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