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This should give you an indication of the size of the Dawn spacecraft as scientists prepared it for launch.
Here is the Dawn spacecraft with its ion propulsion system installed.
The ion propulsion system goes through a test on Earth. Dawn has three 30-centimeter-diameter (12-inch) ion thrust units. It produces an electrical charge to accelerate ions from xenon fuel that will be 10 times faster than chemical fuel.
The spacecraft uses only 10 ounces of fuel per day and would accelerate on an Earth highway from 0 to 60 miles per hour in 4 days. But without gravity in space, its got speed to burn.