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Exploring the smallest terrestrial planet: Dawn at Vesta
The Dawn mission is designed to map Vesta and
Ceres from polar orbit for close to one year each. The
ion-propelled Dawn spacecraft is illustrated in Figure
1. Dawn carries a framing camera with clear and
color filters, a visible and infrared mapping
spectrometer, a gamma ray and neutron spectrometer,
and obtains radiometric data on the gravity field. The
camera obtains stereo imagery from which a global
shape and topography model are derived. The
mapping spectrometer determines the mineral
composition of the surface and the gamma and
neutron spectrometer determines the elemental
composition. As Dawn approaches Vesta, as
illustrated in Figure 2, it measures the rotational
characteristics of the body to determine the
orientation of the rotation axis. This in turn
determines when solar illumination reaches the north
pole and when mapping can be completed. As shown
in Figure 3, there are three science orbits: Survey at a
radial distance of 3000 km and a period of 69 hr;
high-altitude mapping at a radial distance of 950 km
and a period of 12.3 hr; and low-altitude mapping at
a radius of 465 km and a period of 4 hours. Vesta is
the ultimate source of the HED meteorites from
which much has been learned about their parent body.
By the time of this presentation we will have
surveyed the region around Vesta for moons,
determined a much more accurate mass and rotation
axis for Vesta, and have preliminary information on
surface features and composition from the survey
orbit