NISP instrument

The Euclid Mission's Near-Infrared Spectrometer and Photometer (NISP) instrument. NISP splits infrared light coming from these galaxies to derive key data, including their speed of outward expansion – measuring their ‘red shift’, on the same principle as a police radar gun. 

The NISP Instrument has two channels: a near-infrared photometer (NISP-P) and a near-infrared slitless spectrometer (NISP-S). The two channels have common optics, focal plane, electronics and support structure. Two wheel mechanisms are used to switch between the different channels: (1) a filter wheel mechanism contains the three near-infrared photometry filters, a cold shutter and an open position and (2) a 'grism' - combination of grating and prism - wheel with four grisms and an open position. To operate in the photometric mode, the grism wheel is rotated to the open position and the filter wheel is rotated to the required filter; to operate in spectroscopic mode the filter wheel is rotated to the open position and the grism wheel to a grism position. The optics consist of a corrector lens at the start of the instrument and a three lens camera after the grism/filter position that focuses light onto the focal plane.