Near-infrared spectrometer on the Infrared Telescope in Space

The Near-Infrared Spectrometer (NIRS) is a grating spectrometer with two 12 element InSb linear arrays, and is one of the four focal-plane instruments of the Infrared Telescope in Space (IRTS) mission, which will be launched in early 1995. The NIRS was designed to measure the absolute sky brightness with coarse spectral resolution; searching for extragalactic background light is the primary purpose of our observations. The wavelength coverage of the NIRS ranges from 1.4 to 4.0 microns with a spectral resolution of 0.12 microns. The field of view is 8 sq arcmin. The NIRS has been calibrated and tested with the flight IRTS telescope in the laboratory. The response and noise were found to be as expected from the design values. After integrating all of the focal-plane instruments with the telescope into the flight cryostat, NIRS shows good performance and will be able to achieve a high sensitivity in orbit.