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This is the story of NASA's Voyager probes, two spacecraft launched in 1977, and their extraordinary Grand Tour to the outer planets and beyond -- only better, because the author also deftly weaves in the story of the Western world's love affair with great voyages of discovery.

Societies explore for a laundry list of reasons: to find new goods to market, new territories to claim, new converts to the state religion, for pure knowledge, and sometimes just to answer the siren call of adventure. The 1600s marked the first great age of discovery, with Portugal and Spain fighting for primacy in sea trade. In the 18th century, England and France competed to circumnavigate the globe and be the first to measure an arc of the meridian.

The roots of the Voyager mission arose from the cold war, particularly Russia's launch of Sputnik, when "a new era of planetary exploration achieved escape velocity." Like earlier ocean-going rivalries, space launches could also be "a form of saber rattling," an extraordinarily visible challenge to competitors, and one the U.S. was happy to undertake.

By the 60s, the U.S. space program had taken formal shape. Research programs were defined and directed by three charismatic individuals. First was rocketry pioneer Werner von Braun, who blithely promised human settlements in space within a few decades. Meanwhile physicist James Van Allen (he of "Van Allen Belt" fame) saw space as a shiny "new laboratory for science" just waiting for researchers to move in. Finally, there was William Pickering, then-director of the Jet Propulsion Laboratory, whose focus was on pure exploration and discovery.

The roots of the Voyager mission were set in 1961, when mathematics grad student Michael Minovitch discovered the gravitational "slingshot effect" that would speed spacecraft along much faster than current rocket engines. The consequent discovery of a "once-in-176-years" planetary alignment coming up in the early 80s that would allow a probe to travel to Mars, Jupiter, Saturn, Uranus and Neptune within its operational lifetime made for an "irresistible" opportunity too good to ignore.

Until then, NASA's focus -- like the Russian space program -- had been on manned missions. But Voyager promised something for everyone. Stephen J. Pyne quotes JPL's Bruce Murray: "The scientific harvest was stupendous, the engineering challenge magnificent, the potential cultural impact great and enduring, and its value as cold war propaganda was immeasurable... Here was a space spectacular that America was especially equipped to win."

Like previous 'ages of discovery' before, the fact that the decision to go was made, didn't stop intramural quibbling over the proposed Mars-to-Neptune mission and its expanding budget. Questions came from scientists of "little" science, who were concerned that this "Big Science" project would consume the bulk of available research funding. In addition, astronomers wanted to make sure there would be something left over for the Space Telescope, another big multi-year program. Besides, they complained, Big Science already had the Viking lander, destined for Mars.

To save the program, JPL scaled back, focusing on paired close-up visits of Jupiter and Saturn. To save money and time, they also decided to based the Voyager platform on earlier Mariner probe technology.

As with previous "great ages" of exploration, the Voyager journey would take years, even decades. Sailors -- and scientists longing to study new realms -- had been accustomed to long trips. On the HMS Beagle, Darwin shared a tiny aft cabin with a sailor, somehow finding room to work, sketch and think in the same space where he slept. With Voyager, for the first time, the vessel would carry nothing but working scientific equipment.

And that long journey would need periodic support from the ground. Every planetary encounter -- years apart -- brought new data, and especially new photographs, which excited the public imagination as much as the breadfruit and tropical birds, chocolate and hot peppers returned in earlier ages. But for the dry spells between encounters, Voyager's own dedicated bard, astronomer Carl Sagan, was there to cast the mission in heroic mode, giving the probes personality and their mission the splendid gleam of a quest.

Voyager saw moons no one had suspected, and fascinating things about those moons -- volcanoes, vast chilly oceans, and weird geology. It uncovered the secrets of Saturn's rings and found more rings around Jupiter, Uranus and Neptune as well. And even now, working long past their expected lifetime, both probes continue to explore and observe as they journey through the heliosheath, the region between our solar system and interstellar space.

Together this tiny "flotilla" of space explorers has done "things no one predicted, found scenes no one expected, and promises to outlive its inventors." Pyne, an Arizona State University professor specializing in how people and nature interact, tells their story -- and the stories of the grand expeditions before them -- with skill and style.

Charlene's sixth grade teacher told her she would burn her eyes out before she was 30 if she kept reading and writing so much. Fortunately he was wrong. Her work has also appeared in Aboriginal SF, Amazing Stories, Dark Regions, MZB's Fantasy Magazine, and other genre magazines.