NASA asteroid probe launched from Florida

CAPE CANAVERAL, Fla. Sept 27 (Reuters) A pioneering spacecraft that could serve as a blueprint for future interplanetary transport blasted off aboard an unmanned Delta rocket today on a mission to explore two giant asteroids between Mars and Jupiter.

The probe, called Dawn, will be the first to travel to and orbit two different celestial bodies, a maneuver that previously would have required far too much fuel to be possible.

Instead of traditional chemical-burning rocket thrusters, Dawn is powered by a trio of solar-powered electric engines that ionize and expel xenon gas, emitting a glowing blue after-burn in the process.

The first step in Dawn's journey was as routine as it comes, with a beefed up Delta 2 rocket, built by United Launch Alliance, lifting off at 7:34 a m from Cape Canaveral Air Force Station in Florida.

Launch was delayed seven minutes to allow time for a boat that had strayed beneath the flight path to move. The Delta rocket, which was outfitted with nine strap-on motors for extra power, drops its spent boosters into the ocean.

The Coast Guard notifies mariners to steer clear of the area.

After reaching orbit around Earth, Dawn was to stretch out its solar wing panels to begin collecting energy to power its ion engines, which work by electrically charging xenon gas and passing it through a magnetic field.

The gas is expelled at about 89,000 miles per hour (143,231 kilometers per hour), which pushes the spacecraft forward in the opposite direction.

The pressure is very gentle, about equal to the force of a piece of notebook paper on the palm of a human hand, but builds up over time.

Dawn will take four days to speed up to 60 mph (97 kph), but within a year will be zipping along at more than 5,500 mph (8,851 kph). During that time it will use only about 15 gallons of fuel.

Dawn's targets are two of the largest objects in the asteroid belt, the rocky body Vesta, which is similar to Earth's moon, and the icy dwarf planet Ceres.

Although the objects are relatively close to each other, they formed under vastly different conditions.

Scientists are eager to compare the two worlds to learn more about the original materials and processes of the solar system's creation.

Dawn is expected to reach Vesta in four years and spend about six months in orbit before leaving orbit and continuing on to Ceres.

REUTERS SS KN1745