The goal of the Dawn mission is to characterize the conditions and processes of the solar system's earliest history by investigating Vesta and Ceres in detail. Both protoplanets remain fundamentally intact since their formation, though each followed a very different evolutionary path. Vesta is dry and rocky while Ceres has a thick ice mantle and may even have an ocean beneath its icy crust.
"Dawn is the first spacecraft to orbit two planetary bodies in a single mission," said Joe Makowski, Orbital ATK's Dawn Phase E Program Manager. "This is the world's first chance to get an up-close look at two bodies which evolved very differently, but date back to the formation of the solar system. Obtaining detailed images and compositional data provides clues on planet formation, and that is exciting."
In July 2011, Dawn arrived at Vesta and spent over a year orbiting and mapping the giant asteroid with multiple cameras and spectrometers. While it orbited Vesta, Dawn returned spectacular, detailed images of the protoplanet. Data revealed that Vesta is an old, rocky body, heavily cratered with only trace amounts of water. Dawn returned more than 30,000 images and other measurements about the asteroid.
Dawn departed Vesta in September 2012, setting its sights on Ceres, the largest body between Mars and Jupiter in the main asteroid belt. Originally described as a planet, then an asteroid, Ceres was reclassified as a dwarf planet in 2006.
The spacecraft recently returned the sharpest images ever seen of Ceres, higher in resolution than those taken by the Keck ground observatory and the Hubble Space Telescope. Once Dawn orbits Ceres – which is scheduled to begin on March 6, 2015 – its cameras will begin returning images more than 800 times the resolution of Hubble.
"Ceres could be up to 27 percent water, a volume equivalent to the fresh water on Earth. It's mostly in ice form, but there may also be a subsurface ocean," Makowski said. "Dawn's exploration of Vesta and Ceres will allow scientists to compare the formation processes of two very different bodies."
One of Dawn's most unique features is its ion propulsion system, provided by JPL and integrated with the spacecraft platform by Orbital. In an ion propulsion engine, an electrical charge is applied to xenon gas, with charged metal grids accelerating the xenon particles out of the thruster. These particles push back on the thruster as they exit, creating a reaction force that propels the spacecraft. Dawn has now completed five years of accumulated thrust time, far more than any other spacecraft. This application of the world's most efficient space propulsion technology is revolutionizing solar system exploration and made Dawn's historic exploration of two planetary bodies possible.
"The interest and enthusiasm I see throughout the company for the Dawn mission is remarkable," Makowski said. "Everyone wants to know how Dawn, Orbital's first planetary mission, is doing. There is both pride in a job well done, and a confidence that the Orbital ATK team can deliver on big, future challenges."
Dawn is the work of the following mission partners: CalTech, JPL, Orbital ATK, the Max Planck Institute for Solar System Research/German space agency (MPS/DLR) and the Italian space agency/National Institute for Astrophysics (ASI/INAF). The Space Systems Group designed and built the spacecraft at the company's Dulles, Va. satellite manufacturing facility. It measures 65 feet in length and its dry mass is 1,631 pounds.
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