Closest Encounter

By LEON JAROFF

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 its own systems and navigated with the aid of an electronic brain reminiscent of HAL, the willful computer in the movie 2001: A Space Odyssey. "What was science fiction a year ago is now science fact," exulted Marc Rayman, the chief mission engineer.

Only one glitch occurred. As DS1 sped past Braille, its camera failed to track the asteroid properly, producing only six tiny and disappointing images shot from 8,700 miles away. But DS1's remote-sensing instruments downloaded streams of data that should reveal much about Braille's composition. Having consumed only 25 lbs. of its original 180 lbs. of xenon fuel, the spacecraft has enough left to intercept and investigate two comets, one burnt out, the other highly active. Appropriately enough, if NASA gives the go-ahead, DS1 would reach those comets in the year 2001.

--By Leon Jaroff