What is it?: "a robotic spacecraft being sent by NASA on a space exploration mission to the two most massive members of the asteroid belt: the asteroid Vesta and the dwarf planet Ceres. Dawn is scheduled to explore Vesta between 2011 and 2012, and Ceres in 2015. It will be the first spacecraft to visit either body."
"Dawn is innovative in that it will be the first spacecraft to enter into orbit around a celestial body, study it, and then re-embark under powered flight to proceed to a second target. All previous multi-target study missions—such as the Voyager program—have involved rapid planetary flybys."
"Mission controllers have compared the Dawn mission with that of the fictional space voyages depicted on Star Trek. Dawn project system engineer Marc Rayman says, "Dawn is like the first real interplanetary spaceship! Many spacecraft have gathered data at multiple bodies, but Dawn will be the first to go somewhere, go into orbit, and be able to linger there, and then travel to another body and do the same thing." To do this, Dawn is powered by an ion plasma propulsion engine."
"Dawn will rely on the controlled venting of its plasma thrust to continuously accelerate toward Vesta. On its way, the spacecraft's ion engine will speed it up to about 24,600 miles per hour (11 kilometers per second), far more than any spacecraft has ever achieved."
Dawn launched onboard a Delta 7925H rocket from Cape Canaveral, Fl on September 27, 2007. Its mission duration is expected to be 8 years and it is currently 1 year and 5 months into its mission. On February 17th, 2009 it flew by Mars during a successful gravity assist.
Current location of Dawn
"The mission's goal is to characterize the conditions and processes of the solar system's earliest epoch by investigating in detail two of the largest protoplanets remaining intact since their formation. Ceres and Vesta have many contrasting characteristics that are thought to have resulted from them forming in two different regions of the early solar system; Ceres is theorized to have experienced a "cool and wet" formation that may have left it with subsurface water, and Vesta is theorized to have experienced a "hot and dry" formation that resulted in a differentiated interior and surface volcanism."
Sources:
Wikipedia
Scientific American
3.16.2009
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