NASA's Voyager spacecraft zoomed by our solar system's planets decades ago and are now traveling through interstellar space, ultimate destination unknown. Yet the final transmissions from the two deep space craft loom increasingly closer. Voyager 1 and Voyager 2, both launched in 1977, were built to last five years. They've now beamed back cosmic information for over 46 years, a feat made possible by a hardy spacecraft and a clever group of NASA engineers. The Voyagers' nuclear power supply (Plutonium-238), however, is running low. To preserve fuel, NASA turned off the probes' cameras and half of their science instruments. Now at 15 and 12 billion miles away, Voyagers 1 and 2 still beam back unprecedented information about their far-off environs, where no other human spacecraft has ventured before. They're returning data about the radiation in interstellar space and how far the sun's protective bubble of energy and particles extends into the cosmos. "The science data that the Voyagers