Like the end of a very long and eventful road trip, NASA's Dawn spacecraft has its main goal in sight. The space agency says that the unmanned probe has emerged from behind the Sun as it uses its ion propulsion to catch up with the dwarf planet Ceres in the asteroid belt and that mission control was able to re-establish contact. The craft has received instructions for executing a series of maneuvers that will take it on its final approach phase, which will end with it going into orbit around Ceres.
Dawn was launched on September 27, 2007 atop a Delta II rocket from Space Launch Complex 17B at Cape Canaveral Air Force Station, Florida. After making a flyby of Mars on February 4, 2009 in a slingshot maneuver, it went into orbit around the protoplanet Vesta on July 16, 2011, where it carried out a 14-month survey of the surface.
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The 1,240 kg (2,730 lb) spacecraft then used its ion thruster to send it on a three and a half year passage to Ceres. When it arrives in March 2015, it will mark the first visit to a dwarf planet by any spacecraft. By visiting Vesta and Ceres, Dawn will have visited the two most massive objects in the asteroid belt, with the Texas-sized Ceres the largest object in the asteroid belt between Mars and Jupiter and making up a third of the mass of the entire belt. In addition, Dawn set a new record by firing its ion engine for a total of about 5 years running time.
"Orbiting both Vesta and Ceres would be truly impossible with conventional propulsion," says Marc Rayman, Dawn's chief engineer and mission director at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "Thanks to ion propulsion, we're about to make history as the first spaceship ever to orbit two unexplored alien worlds."
The Dawn probe is 400,000 mi ( 640,000 km) from Ceres and closing in on it at 450 mph (725 km/h). JPL says that as Dawn approaches, it will return scientific data and the most detailed images ever taken of the dwarf planet.
The video below discusses Dawn's ion propulsion system.