Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph

Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph (FGS-NIRISS) is an instrument for the planned James Webb Space Telescope that combines a Fine Guidance Sensor and a science instrument, a near-infrared imager and a spectrograph. The FGS/NIRISS is being built by the Canadian Space Agency as part of the international project to build a large infrared space telescope with the United States and various European states. FGS-NIRISS observes light from the wavelengths of 0.8 to 5.0 microns. The instrument has four different observing modes. Physically the FGS and NIRISS are combined, but optically they are separate with the FGS being used by the telescope to point it, whereas NIRISS is an independent science instrument. The spectroscopic mode is capable of doing exoplanet spectroscopy. The detector for NIRISS is a 2048 x 2048 pixel HgCdTe array, where each pixel is 18 microns on a side according to the STSCi. The field of view is 2.2' x 2.2' which gives a plate scale of about 0.065 arcsec/pixel.

The FGS helps the telescope aim and stay pointed at whatever it is commanded to look at. FGS helps provide data to the JWST Attitude Control System (ACS) and do this it is a big sky coverage and sensitivity, to give a high probability it can find a guide star.

NIRISS is designed for performing:

The aperture masking interfermotry mode uses a seven-hole aperture masking disc, and should allow the detection of exoplanets within certain ranges of light and types of stars.

The Engineering Test Unit of the FGS was delivered to NASA in 2010. The flight units were planned to be delivered later after the ETU, which enabled testing with other JWST hardware. The flight units of FGS/NIRISS were delivered to NASA in August 2012.

The FGS functionality supports JWST pointing at the desired targets. The FGS is designed to find pre-selected guide stars, which allows the telescope to precisely pointed at the desired target. The actual pointing of the telescope is handled by other segments, especially the systems in the Spacecraft Bus and the fine guidance mirror in the Optical Telescope Element

Previously, the Canadians were working on a tuneable image filter. This device was intended to allow a narrow filter band to be selected (as opposed to a fixed filter band). The TFI was cancelled into 2011 and work rolled-over into the NIRISS. The TFI would have a selectable filter band between 1.5 – 5 µm.

In July 2011 the Canadian Space Agency (CSA) reluctantly discontinued work on the Tunable Filter Imager (TFI) when it became clear that issues associated with the cryogenic operation of its Fabry-Perot etalon were unlikely to be resolved in time to meet the instrument's delivery schedule...

...
Wikipedia