NASA is beginning the final preparations for next Wednesday's launch of the Dawn probe, aboard a Delta II rocket. The Dawn probe, costing over US$250 million, will visit the dwarf planet Ceres and the asteroid Vesta. The launch was originally planned for mid-June, however due to a damaged crate, shipping delays, and a damaged solar panel, NASA chose to delay it until now. Last week the spacecraft was delivered to the launch pad, and engineers performed tests to ensure that it is ready for launch. Today, the payload fairings were installed, and the probe is ready for its launch next week onto its 5 billion kilometer (3.2 billion mile) mission.
As the Delta II launches, three stages of rockets will propel the probe towards its first target. With the help of ion thrusters, it will reach Mars in mid-2009. Using Mars' gravity, the probe will speed up and proceed towards the first asteroid, Vesta, in late 2011. After orbiting for seven months, it will leave Vesta in mid-2012, and arrive at Ceres in 2015. After making scans of Ceres, it will enter an orbit around Ceres that will ensure that it does not impact the asteroid for half a century. This is required due to the United Nations' “Outer Space Treaty”, which states that “harmful contamination” of these asteroids must be avoided.
The targets of this mission, Ceres and Vesta, couldn't be less alike. Ceres (diameter 975 km, 600 miles) is larger than Vesta (578 km, 350 miles). This makes Ceres approximately the size of Texas. NASA believes Ceres could contain water beneath its outer crust because, like Earth, its inner layers are heavier than the outer layers, and Ceres' outer layer is lighter than water. Vesta, on the other hand, is the size of Arizona, and has a surface of volcanic rock, which astronomers believe came from its hot inner layers. Vesta also has a large crater – almost 500 km (300 miles) across – on its southern pole. The collision that caused this likely blasted enough rock into space to fill a container 160 by 160 by 80 km (100 by 100 by 50 miles).
The probe will make several observations of these asteroids: it will compare the makeup, shape, size, and densities, analyze craters, and determine mass, gravity, rotation. To determine the makeup, the probe carries a mapping spectrometer, and tools to map emissions of neutrons and gamma rays. Using this information, NASA can compare the formation of these bodies to learn more about our solar system, for example, to test a theory which states that a number of stony meteorites may be debris from Vesta.
There's one more piece of equipment aboard the probe: A small silicon chip containing the names of 350,000 people who submitted their names to the “Send Your Name to the Asteroid Belt” campaign. After next week's launch, the spacecraft will deploy its solar panels and undergo two months of testing before it begins the cruise to Mars.

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NASA prepares to launch mission to nearby asteroids