The Dawn Mission

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The Dawn Mission

The Dawn Mission launched a spacecraft on a trajectory to Vesta and Ceres in September 2007 (Figure 29). The Dawn spacecraft (Figure 30) will carry three science instruments whose data will be used in combination to characterize these bodies. These instruments consist of a visible camera, a visible and infrared mapping spectrometer, and a gamma ray and neutron spectrometer (Figure 30). In addition to these instruments, radiometric and optical navigation data will provide data relating to the gravity field and thus bulk properties and internal structure of the two bodies.

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Figure 29: The interplanetary trajectory of the Dawn spacecraft (from Russell et al., 2007 and The Dawn Mission webpage.)

Dawn received a gravity assist from Mars in February 2009. After departing from Mars, the Dawn spacecraft will settle back into cruise for another orbit around the Sun during which it will gradually spiral outward into the asteroid belt between Mars and Jupiter. Upon arrival at Vesta in August 2011, Dawn will conduct a survey of the region around the asteroid for any possible natural satellites, dust and debris. It will then use ion propulsion to brake itself into a polar mapping orbit around Vesta. The spacecraft will follow a series of circular near-polar orbits allowing it to study nearly the entire surface of the asteroid. These different orbits will be varied in altitude (200 km to 2500 km) and orientation relative to the sun to achieve the best positioning for the various observations planned. Dawn will spend up to nine months at the asteroid. In addition to many new images of the surface of Vesta, it is anticipated that the gamma ray detector instrument - GRaND - will provide elemental data for the surface of the asteroid that will help make links to the meteorite collection and to understanding the origin of the various rock types on Vesta. For example, K/Th ratios will provide information about the material that grew to form the asteroids and may be useful in determining how the composition of the solar nebula changed with heliocentric distance. The abundance of rock-forming elements, such as Fe and Ti, provides information about how igneous rocks form. The large impact basin at the south pole of Vesta provides an opportunity to determine the composition of the interior of this planet, providing additional constraints on structure and thermal evolution.

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Figure 30: The Dawn spacecraft showing the full extent of the 20 m tip to tip solar array. Bottom: close up views of the back and front of the main spacecraft showing the various instruments and hardware (from Russell et al., 2007 and The Dawn Mission webpage.)

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