Not Such a Stretch to Reach for the Stars

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A starship without an engine?
CONCEPT An Icarus Interstellar design for an unmanned probe uses decades  of technological advances to build on a 1970s British project called Daedalus
It may seem a fantastical notion, but hardly more so than the idea of building a starship of any kind, especially with NASA’s future uncertain at best.

Yet here in Orlando, not far from the launching site of the space program’s most triumphant achievements, the government’s Defense Advanced Research Projects Agency, or Darpa, drew hundreds this month to a symposium on the 100-Year Starship Study, which is devoted to ideas for visiting the stars.

Participants — an eclectic mix of engineers, scientists, science fiction fans, students and dreamers — explored a mix of ideas, including how to organize and finance a century-long project; whether civilization would survive, because an engine to propel a starship could also be used for a weapon to obliterate the planet; and whether people need to go along for the trip. (Alternatively, machines could build humans at the destination, perhaps tweaked to live in non-Earth-like environs.)

“The space program, any space program, needs a dream,” said one participant, Joseph Breeden. “If there are no dreamers, we’ll never get anywhere.”

It was Dr. Breeden who offered the idea of an engineless starship.

A physicist by training, he had most recently devised equations that forecast to banks how much they were going to lose on their consumer loans.

From his doctoral thesis, Dr. Breeden remembered that in a chaotic gravitational dance, stars are sometimes ejected at high speeds. The same effect, he believes, could propel starships.

First, find an asteroid in an elliptical orbit that passes close to the Sun. Second, put a starship in orbit around the asteroid. If the asteroid could be captured into a new orbit that clings close to the Sun, the starship would be flung on an interstellar trajectory, perhaps up to a tenth of the speed of light.

“The chaotic dynamics of those two allow all the energy of one to be transferred to the other,” said Dr. Breeden, who came toting copies of a paper describing the technique. “It’s a unique type of gravity assist.”

Darpa, by design, pursues out-of-the-box projects without immediate military use. (In the 1960s and 1970s, for instance, the agency laid the groundwork for the Internet.)

AMBITIONS A 1967 test of a nuclear engine. NASA has revived such work.

David L. Neyland, the director of tactical technology at Darpa, who orchestrated the one-year starship study, noted that his agency was founded more than 50 years ago as a response to Sputnik, the Soviet Union’s cold war satellite coup.

And the research and development of technologies that could lead to a starship, he said, would likely create useful military spinoffs.

“At every step along the way in the space business, the Department of Defense has benefited,” Mr. Neyland said.

In the talks, speakers laid out challenges that, while herculean, did not seem out of the realm of the possible, even without resorting to exotic physics like “Star Trek” warp drives.

Still, the sheer distances are daunting. “The problem of the stars is larger than most people realize,” said James Benford, a physicist who organized sessions on starship propulsion.

Richard Obousy, president of Icarus Interstellar, an organization of volunteers that has already spent several years on starship designing, gave an analogy. If Earth were in Orlando and the closest star system, Alpha Centauri, were in Los Angeles, then NASA’s two Voyager spacecraft, the most distant manmade objects, have traveled just one mile.

Another way of looking at the challenge is that in 10,000 years, the speed of humans has jumped by a factor of about 10,000, from a stroll (2.6 m.p.h.) to the Apollo astronauts’ return from the Moon (26,000 m.p.h.). Reaching the nearest stars in reasonable time — decades, not centuries — would require a velocity jump of another factor of 10,000.

The first steps, however, are easy to imagine. Even in the 1950s, rocket scientists realized that the current engines — burning kerosene or hydrogen and spewing flames out the nozzle — are the rocket equivalent of gas guzzlers. They designed nuclear engines that use reactors to heat liquid hydrogen into a fast-moving stream of gas. NASA had such engines ready for a hypothetical manned mission to Mars to follow the Moon landings.

Today, the space agency has revived that work, beginning with studies on an ideal fuel for a space reactor, and new nuclear engines could be ready by the end of the decade.

As for radioactivity concerns, the reactors would not be started until they reached space. “Space is a wonderful place to use nuclear power, because it is already radioactive,” said Geoffrey Landis, a scientist at the NASA Glenn Research Center in Ohio (and a science fiction author).

More advanced nuclear engines could use reactors to generate electric fields that accelerated charged ions for the thrust. Then fusion engines — producing energy through the combining of hydrogen atoms — could finally be powerful enough for interstellar travel.

The British Interplanetary Society put together a concept for a fusion-powered starship in the 1970s called Daedalus, extrapolating from known physics and technology. Dr. Obousy’s group, Icarus Interstellar, is revisiting the Daedalus design to see if 30-some years of new technology can produce a better starship.

Written by physicsgg

October 19, 2011 at 10:20 am

Posted in SPACE

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