Friday, October 23, 1998 Published at 15:58 GMT 16:58 UK
A new force in space exploration
Artist's impression of the Deep Space 1 ion drive
By Science Editor David Whitehouse
A new force is being unleased in space with the launch of Deep Space One.
Deep Space One is no ordinary spacecraft. When it gets into space it will ignite a revolutionary form of propulsion that some scientists say is the key to exploring the solar system.
They call it the 'ion drive' and when engaged it leaves a ghostly blue trail behind the spacecraft.
The trail is composed of ions - electrically charged particles - that stream from the ion engine providing about the same force as a piece of paper resting on your hand.
Conventional chemical rockets are far more powerful but also far more short lived, burning for seconds or minutes.
The ion drive provides a gentle force that can be sustained and is ultimately far more efficient than a conventional rocket.
The concept has been known for decades, and in the past Nasa conducted a few trials, but Deep Space One is the most significant test yet.
The probe's ultimate power source is the Sun. Electricity is generated by its solar panels which is then used to bombard a block of the element xenon causing ions to be given off.
These ions are then sucked out of the spacecraft and pushed away providing the small but persistent force. This way Deep Space One will eventually reach a speed of about 10,000mph.
But the ion drive is not the only new technology that the spacecraft will be testing. It will try out an automated navigation system that requires little contact with the Earth.
The 'AutoNav' system will face a severe test in July next year when it will steer the spacecraft during a flyby of an asteroid at a distance of just three miles.
If all goes well DS1 will in subsequent years be directed to pass close to a burned-out comet and then an active one.
Nasa's eventual aim is to use the knowledge gained in operating Deep Space One to construct fleets of spacecraft that can explore the solar system.
The next probe is this series, Deep Space Two, is set for launch in January.