To acquire science data at Vesta and Ceres, Dawn carries three instrument systems. In addition, an experiment to measure gravity will be accomplished with existing spacecraft and ground systems.
The Framing Camera
is designed to acquire detailed optical images for scientific purposes as well as for navigation in the vicinities of Vesta and Ceres. Dawn carries two identical and physically separate cameras for redundancy, each with its own optics, electronics and structure. Each camera is equipped with an f/7.9 refractive optical system with a focal length of 150mm and can use 7 color filters, provided mainly to help study minerals on Vesta's surface. In addition to detecting the visible light humans see, the cameras register near-infrared energy. Each camera includes 8 gigabits of internal data storage. The Max Planck Institute for Solar System Research, Germany, was responsible for the cameras' design and fabrication, in cooperation with the Institute for Planetary Research of the German Aerospace Center and the Institute for Computer and Communication Network Engineering of the Technical University of Braunschweig.
Image top: Artist concept fo Dawn camera. Image credit: Max Planck Institute for Solar System Research
The elemental composition of both Vesta and Ceres will be measured with the Gamma Ray and Neutron Detector
. This instrument uses a total of 21 sensors with a very wide field of view to measure the energy from gamma rays and neutrons that either bounce off or are emitted by a celestial body. Gamma rays are a form of light, while neutrons are particles that normally reside in the nuclei of atoms. Together, gamma rays and neutrons reveal many of the important atomic constituents of the celestial body's surface down to a depth of one meter (three feet). Gamma rays and neutrons emanating from the surface of Vesta and Ceres will tell us much about the elemental composition of each. Many scientists believe that Ceres may be rich in water; if that is the case, the signature of the water may be contained in this instrument's data. Unlike the other instruments aboard Dawn, the detector has no internal data storage. The instrument was developed by Los Alamos National Laboratory, Los Alamos, N.M.
The surface mineralogy of both Vesta and Ceres will be measured by the Visible and Infrared Mapping Spectrometer
. The instrument is a modification of a similar spectrometer flying on both the European Space Agency's Rosetta and Venus Express missions. It also draws significant heritage from the visible and infrared mapping spectrometer on NASA's Cassini spacecraft. Each picture the instrument takes records the light intensity at more than 400 wavelength ranges in every pixel. When scientists compare its observations with laboratory measurements of minerals, they can determine what minerals are on the surfaces of Vesta and Ceres. The instrument has 6 gigabits of internal memory, which may be operated as 3 gigabits of redundant data storage. The spectrometer is provided by the Italian Space Agency, and was designed and built at Galileo Avionica, in collaboration with Italy's National Institute for Astrophysics.
Dawn will make another set of scientific measurements at Vesta and Ceres using the spacecrafts radio transmitter and sensitive antennas on Earth. Monitoring signals from Dawn, scientists can detect subtle variations in the gravity fields of the two space objects. These variations will point to how mass is distributed in each body, in turn providing clues about the interior structure of Vesta and Ceres.