Images taken during approach, flyby, and orbit of Eros will detect surface features as small as 3 meters. The 7-color capability of the instrument will complement the near-infrared and X-ray/Gamma-ray spectrometers in extrapolating variations in surface composition down to these small spatial scales.
MSI data will be critical to understanding the surface processes,
composition and compositional variation, and geologic history of Eros.
Mass: Camera head 5.05 k, Electronics, 4.5 kg
Brightnesses are encoded to 12 bits instead of the 8 bits used for similar previous imagers, providing 16 times the brightness resolution of such systems. The Si CCD is sensitive to the wavelength range of 400-1100 nm (visible and short-wavelength near-infrared light). A filter wheel has seven spectral filters designed primarily to discriminate iron-containing silicate minerals, and one broadband filter for low-light imaging and optical navigation.
The DPU contains software that controls the instrument and supports automatic exposure time control, acquisition of image sequences, and a three-tiered compression system offering several modes of lossless compression and seven lookup tables for converting the data from 12 to 8 bits.
The main science objectives for NEAR are to determine Eros's surface morphology and the processes that affect its surface, its internal structure, and its composition and relationship to meteorites. MSI is critical to accomplishing each of these goals.
MSI will image the surface at several spatial resolutions, as high as 3-5 meters. These high-resolution images, unprecedented from an orbiting spacecraft, will reveal the distribution and thickness of the asteroid's fragmental surface layer or "regolith," the history of impacts by fragments of other asteroids and comets that is recorded in craters, the character and locations of fractures of the asteroid's body, and the processes that affect the surface layer.
MSI images will also be used to determine the size, shape, and volume of Eros. Unlike previous targets of orbiting spacecraft, Eros's mass and density are unknown. The mass will be measured by radio tracking of the spacecraft as it approaches Eros; shape will be measured from MSI imagery during approach and flyby of the asteroid, as well as by NEAR's laser altimeter. The mass and shape measurements will provide the asteroid's density and density structure, which are necessary both for conducting the later orbital phase of the mission and for evaluating Eros's internal structure.
MSI's seven spectral filters are specifically chosen to distinguish between the spectra of sunlight reflected by the major iron-containing mineral constituents of Eros's surface. MSI has 70 times the spatial resolution of the near-infrared spectrograph, so color imagery from MSI will be used to extrapolate compositional information down to the spatial scale of meters. Correlation of the compositional variations with specific surface features such as fractures or craters will allow discrete rock units to be mapped, and will provide a window into the internal geologic structure exposed by craters.
On approach to Eros, MSI will also carry out a satellite search.
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