For the third time in two days, NASA postponed the launch of its asteroid-bound Dawn probe Saturday, with liftoff now slated for no earlier than September.
The new delay for Dawn comes after its planned Monday liftoff was moved to July 15 earlier Saturday, but now clears the spacecraft?s Cape Canaveral Air Force Station launch site for the August flight of NASA?s Mars Phoenix lander.
NASA spokesperson George Diller said mission managers opted for the new launch target because of limited liftoff opportunities in July and the need to prepare for the planned Aug. 3 Phoenix flight.
?A September launch for Dawn maintains all of the science mission goals that a July launch would have performed,? Diller said in an update from NASA?s Kennedy Space Center in Cape Canaveral.
The $449 million Dawn mission will be the first to launch a probe to both Vesta and Ceres, the two largest space rocks in the solar system, in the Asteroid Belt between the orbits of Mars and Jupiter.
The eight-year mission is slated to carry Dawn first to Vesta in October 2011, where it will orbit the bright, dense space rock. After a detailed mapping mission, Dawn is slated to move on to spherical Ceres - which is also considered a dwarf planet - by February 2015.
NASA initially had until July 19 to launch Dawn before standing down to allow preparations for Phoenix?s August launch.
Dawn?s mission has weathered a series of delays over the last week. Plans for a Friday launch were reset to Sunday after nearby storms prevented fueling of the spacecraft?s Delta 2 rocket. Mechanical issues with a telemetry relay aircraft and the unavailability of a tracking ship delayed the planned launch from Sunday to Monday, and ultimately to July 15.
Dawn also survived an initial cancellation in March 2006, before NASA revived the science mission a few weeks later.
NASA has until about Oct. 20 to launch Dawn, after which the Vesta and Ceres begin to move away from each other in their respective orbits, the mission?s principal investigator Chris Russell has said. They two space rocks will be near each other again in about 15 years, he added.
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