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"Science fiction is a literature of ideas, hunches, and dreams." So writes Paul Gilster near the end of a deliciously speculative book that may convert science fiction readers to nonfiction. Gilster, the technology columnist of the News & Observer in North Carolina, takes readers on leaps of imagination beyond the probable, past the unlikely, skirting the unbelievable, through the land of supposed impossibility, into the future where, one way or another, humanity will be pursuing Centauri Dreams, or, as the subtitle states, Imagining and Planning Interstellar Exploration.
An avid science-fiction reader himself, Gilster knows that the genre works best at the limits of technological plausibility or, at its most extreme, in the regime of non-impossibility. Consider, for example, faster-than-light travel. No self-respecting scientist claims that "Star Trek" warp drives are plausible extensions of today's technology. But mathematical loopholes in physicists' best theories of space-time are easily transformed to wormholes that persist long enough for a spacecraft to squeeze through.
In Gilster's extensive research, he encountered scientists who are willing to discuss that not quite impossible dream, though they spend most of their time working toward feasible but very challenging concepts that will enable the completion of a mission to a nearby star, perhaps in the Alpha Centauri system, within the working lifetime of a scientist. Each idea under discussion is likely to run aground on a technological snag not yet discovered, but, writes Gilster, enough concepts are in play that it is reasonable to expect such a mission to be launched within a century. "The field is top heavy with ideas, alive with the loopy challenge of pushing a spacecraft to a sizable percentage of the speed of light."
The schemes are, of course, audacious. In one, a system of lasers and a combiner orbit near the Sun. The lasers provide both energy and an illuminated pathway to the target star, with the help of a giant Fresnel lens, one-third the diameter of the Moon, orbiting between somewhere between Saturn and Uranus.
Another, called Starwisp, is an ultralight mesh with microprocessors at each intersection. This remarkable space sail "would be accelerated at 115 times earth gravity by a 10-billion-watt microwave beam, reaching one-fifth the speed of light within days of launch." It would arrive at its destination in 21 years.
Besides describing a number of technologies to reach the stars, Gilster also discusses the issues of communication between the spacecraft and Earth, the need for self-maintenance en route, and the requirement for on-board decision-making software once the probe reaches its objective. Most readers will find rough spots with either the technical detail or the need to stretch their disbelief beyond the breaking point. But they will plow ahead nonetheless, for, as Gilster notes, "Whether or not we achieve interstellar travel, we seem to be hardwired to need the imagining of it."
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