Some 117 million miles from Earth last week, a small, unmanned ship named Deep Space 1 swooped to within 10 miles of newly named asteroid Braille. The dramatic encounter marked by far the closest approach ever to an asteroid by a spacecraft and helped validate new and previously untried systems for unmanned spaceflight.
For 1800 hours during its roundabout nine-month, 500-million-mile journey to Braille, the little craft was accelerated by a futuristic ion-propulsion engine that provided gentle but continuous thrust. And for much of its mission the ship operated somewhat independently of its controllers at the Jet Propulsion Laboratory. It diagnosed...
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