Asteroid explorer Dawn lifts off

NASA launches the unmanned Dawn spacecraft, a vehicle designed to explore the two largest bodies in the asteroid belt between Mars and Jupiter. Dawn will also test a new charged ion propulsion system designed to improve on the performance of traditional chemical propellants (though its fine-tuning reaction control system will still use small engines powered by “rocket fuel”). Dawn is intended to visit and orbit the asteroid Vesta in 2011, which it will then depart after mapping to explore Ceres in 2015.