Tuesday, July 27, 1999 Published at 15:15 GMT 16:15 UK
Tiny probe set for close encounter
The swift flyby will take place on Thursday
By BBC News Online Science Editor Dr David Whitehouse
After nine months of cruising through space using a new propulsion system, the Deep Space 1 (DS-1) spacecraft is set for a close encounter with a small asteroid.
The craft will come to within 14 kilometres (nine miles) of the rock, the closest approach made by a probe to any space body without actually landing on it.
The swift fly-by will take place on Thursday. Pictures and scans will be used to analyse the asteroid's chemical composition. Only four of the tens of thousands of asteroids that inhabit our Solar System have ever been visited by spaceprobes.
Very little is known about the target asteroid, a potato-shaped piece of rock discovered in 1992 and thought to be only about a mile in diameter.
Designated 1992 KD on its discovery, it has just been renamed Asteroid Braille following a competition organised by the Planetary Society. The name honours Louis Braille, the 19th-century French educator who developed the system of dot writing for blind people.
Deep Space 1 will fly past the tiny world at 56,000 kph (35,000 mph). The encounter will occur some 189 million kilometres (118 million miles) from Earth.
Deep Space 1 was launched on 24 October last year. It was designed to test 12 innovative technologies that could be used by future spacecraft. These include an autonomous navigation system that lets the spacecraft guide itself and a novel propulsion system, an ion engine that propels it through space by ejecting a stream of xenon atoms.
"This is a really challenging encounter and it may not work," said Dr Marc Rayman, DS-1's chief mission engineer at Nasa's Jet Propulsion Lab in California.
"We didn't build DS-1 to be an asteroid fly-by spacecraft. The focus of the spacecraft is testing technologies. This is a bonus."
DS-1's primary mission ends in September but there is a possibility that it could be extended. If it is, it could fly by a dying comet known as Wilson-Harrington in January 2001. It may then visit comet Borrelly, one of the most active comets to visit the inner Solar System regularly.