Dawn

Dawn (spacecraft)

Dawn is a space probe launched by NASA on September 27, 2007, to study the two most massive objects of the asteroid belt – the protoplanet Vesta and the dwarf planet Ceres. Currently en route to Ceres and scheduled and expected to arrive in February 2015, Dawn was the first spacecraft to visit Vesta, entering orbit on July 16, 2011. Should its mission succeed, it will also be the first spacecraft to visit Ceres and to orbit two separate extraterrestrial bodies.
The mission is managed by NASA's Jet Propulsion Laboratory, though European partners from the Netherlands, Italy and Germany contributed major components. It is the first NASA exploratory mission to use ion propulsion to enter orbits; previous multi-target missions using conventional drives, such as the Voyager program, were restricted to flybys.
NASA's Jet Propulsion Laboratory provided overall planning and management of the mission, the flight system and scientific payload development, and provided the Ion Propulsion System. Orbital Sciences Corporation provided the spacecraft, which constituted the company's first interplanetary mission. The Max Planck Institute for Solar System Research and the German Aerospace Center (DLR) provided the framing cameras, the Italian Space Agency provided the mapping spectrometer, and the Los Alamos National Laboratory provided the gamma ray and neutron spectrometer.[4]
Framing camera (FC) — The framing camera uses 20 mm aperture, f/7.5 refractive optical system with a focal length of 150 mm.A frame-transfer charge-coupled device (CCD), a Thomson TH7888A, at the focal plane has 1024 × 1024 sensitive 93-μrad pixels, yielding a 5.5° x 5.5° field of view. An 8-position filter wheel permits panchromatic (clear filter) and spectrally selective imaging (7 narrow band filters). The broadest filter allows imaging from about 400 to 1050 nm. In addition, the framing camera will acquire images for optical navigation in the vicinities of Vesta and Ceres. The FC computer is a custom radiation-hardened Xilinx system with a LEON2 core and 8 GiB of memory. The camera will offer resolutions of 17 m/pixel for Vesta and 66 m/pixel for Ceres.Because the framing camera is vital for both science and navigation, the payload has two identical and physically separate cameras (FC1 & FC2) for redundancy, each with its own optics, electronics, and structure.
Visual and infrared spectrometer (VIR) — This instrument is a modification of the visible and infrared thermal-imaging spectrometer used on the Rosetta and Venus Express spacecraft. It also draws its heritage from the Saturn orbiter Cassini's visible and infrared mapping spectrometer. The spectrometer's VIR spectral frames are 256 (spatial) × 432 (spectral), and the slit length is 64 mrad. The mapping spectrometer incorporates two channels, both fed by a single grating. A CCD yields frames from 0.25 to 1.0 μm, while an array of HgCdTe photodiodes cooled to about 70K spans the spectrum from 0.95 to 5.0 μm.
Gamma Ray and Neutron Detector (GRaND) — This instrument is based on similar instruments flown on the Lunar Prospector and Mars Odyssey space missions. It will be used to measure the abundances of the major rock-forming elements (oxygen, magnesium, aluminium, silicon, calcium, titanium, and iron) on Vesta and Ceres, as well as potassium, thorium, uranium, and water (inferred from hydrogen content).