The Dawn mission was launched en route to Vesta and Ceres on 27 September 2007. These are the most massive objects in the Main Asteroid Belt, and the last of the larger 'unknown' bodies of the inner Solar System. Ceres, with a diameter of about 950 kilometres, is the largest known object in the Main Asteroid Belt, and in 2006 was classified – together with Pluto – as a dwarf planet.
Dawn carries a German camera system whose development and construction was coordinated by the Max Planck Institute of Solar System Research (MPS), in cooperation with the DLR Institute of Planetary Research. This camera is not only used for mapping and investigating the asteroids, but is also essential for the spacecraft’s navigation.
In February 2009, Dawn flew by Mars, gaining additional momentum for its journey to the Main Asteroid Belt. As the spacecraft approached Vesta, the camera was already scanning the surroundings for dust and possible small moons. The actual exploration of Vesta's surface began on 15 July 2011, when Dawn entered its orbit at an altitude of 16,000 kilometres. Dawn will investigate the second largest object in the asteroid belt for one year. In this time, the spacecraft will lower its orbit gradually by means of several braking manoeuvres.
Three consecutive observation phases
During the first observation phase, Dawn flew 2420 kilometres above Vesta's surface in an orbit with a period of 68 hours. At this level, images of the whole asteroid could be obtained and a spectral analysis carried out. An initial three-dimensional model of Vesta was generated from these individual images. The spectral analysis will provide information about the mineralogical composition of the asteroid's topmost layer.
In the second phase, Dawn began to orbit the asteroid in 12 hours at an altitude of 670 kilometres, from where it acquired high-resolution images to analyse geological formations in detail.
During phase three, the spacecraft descended to 180 kilometres above Vesta's surface. In this orbit, it takes Dawn a mere four hours to orbit the asteroid. In this phase, priority is being given to the measurements obtained with the Gamma Ray and Neutron Detector (GRaND). The purpose of the data acquired is to provide detailed information about the composition of the surface.
En route to Ceres in July 2012
In July 2012, after exploring Vesta, Dawn will set course for Ceres, which is farther away from the Sun. Following an outward spiral, Dawn will complete three quarters of an orbit around the Sun in about three years, reaching the largest and heaviest object in the Main Asteroid Belt in February 2015.
The exploration of Ceres will also be divided into three phases. Dawn will approach the surface of the dwarf planet down to an altitude of 690 kilometres. Subsequently, the probe is intended to orbit Ceres for at least 50 years, remaining on a stable orbit, as if in a type of 'quarantine'. In this way the planetary researchers want to prevent any terrestrial microbes that might be adhering to the probe from reaching the surface of Ceres if it crashes. If traces of primitive life were to be discovered there in future, they should not be the result of an import from Earth.
Dawn is the ninth mission in NASA's Discovery programme, which is distinguished by cost-efficient programmes with a comparatively low budget of about 500 million US dollars. The mission is coordinated by NASA’s Jet Propulsion Laboratory (JPL), which is also a department of the California Institute of Technology in Pasadena. The University of California in Los Angeles is responsible for the scientific part of the mission. The camera system on board the spacecraft was developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, in collaboration with the Institute of Planetary Research at the German Aerospace Center (DLR) in Berlin and the Institute for Data Technology and Communication Networks in Braunschweig. The camera project is financially supported by the Max Planck Society, DLR and NASA/JPL.