Dawn first entered the belt (whose lower boundary may be defined as the greatest distance Mars gets from the sun (249,230,000 kilometers, or 154,864,000 miles) in June 2008. It remained within the belt for 40 days before its carefully planned orbital path brought it below the asteroid belt's lower boundary.
This time around, Dawn's flight path will remain above this hypothetical lower boundary for the rest of the mission and for the foreseeable future - Dawn will become the first human-made object to take up permanent residence in the asteroid belt.
The mission of the 1,098-kilogram (2,421-pound) Dawn spacecraft is to reconnoiter Vesta and Ceres, the asteroid belt's two most massive inhabitants -- the asteroid Vesta and dwarf planet Ceres. The goal of this eight-year, 4.9-billion-kilometer (3-billion-mile) mission is to answer basic questions about the formation of planets in our solar system. NASA's unmanned Dawn spacecraft will be the first ever to orbit two planetary bodies on a single voyage. Dawn is 619 days away from arrival at its first celestial objective, asteroid Vesta.
For more information on Dawn please visit: http://dawn.jpl.nasa.gov/