Click image for larger TIF file: 883K
Click image for larger TIF file: 883K
The NEAR Infrared Spectrometer (NIS) measures the spectrum of reflected sunlight over the wavelength range of 0.8 to 2.6 microns, in 64 wavelength channels. These measurements allow inference of asteroid mineralogy, principally the composition of minerals containing iron. Incoming light is dispersed into a spectrum by a very finely grooved reflective "grating." This spectrum falls onto two separate linear -array detectors, one composed of germanium (Ge) and the other composed of indium-gallium arsenide (InGaAs). The Ge detectors measures 0.8-1.5 micron (800-1500 nanometer) light, and the InGaAs array measures 1.5-2.6 micron (1500-2600 nanometer) light. A three-position slit mechanism allows two fields of view: 13.3 x 13.3 mrad (0.76° x 0.76°) and 6.63 x 13.3 mrad (0.38° x 0.76°). These provide spot sizes of 0.65 x 1.3 km or 1.3 x 1.3 km from a 100-km distance. The entrance slit can also be closed altogether for background measurements. A scan mirror allows NIS's field of view also to be scanned over 2.44 radians (140°) in 6.98 mrad (0.4°) increments. Mirror scanning combined with spacecraft motion will be used to build up two-dimensional spectral images. NIS carries a diffusely reflecting gold plaque, that can reflect sunlight into the spectrometer for inflight calibration by correctly positioning the spacecraft and the scan mirror. Sensor Systems Group (SSG) supplied the NIS optics and mechanisms.
MSI NIS NLR XGRS MAG RS
