Astronomy Picture of the Day

Explanation: Space travel entered the age of the ion drive Saturday with the launch of Deep Space 1, a NASA mission designed primarily to test new technologies. Deep Space 1 is bound for asteroid 1992 KD in July 1999. Although the ion drive on Deep Space 1 provides acceleration much smaller than we feel toward Earth, it will gradually give the spacecraft the speed it needs to travel across our Solar System. The propulsion drive works by ionizing Xenon atoms with power provided by large panels that collect sunlight. As these ions are expelled by a strong electric field out the back, the spacecraft slowly gains speed. Pictured above, hot blue ions emerge from a prototype drive that was successfully tested last year at JPL.