Fine Guidance Sensor / Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS) - NASA Science

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Quick Facts

FGS is a guider that locks on to bright stars in deep space to keep Webb on target creating sharp high quality images.

FGS is a guider that locks on to bright stars in deep space to keep Webb on target creating sharp high quality images.

FGS allows Webb to determine its position, locate its celestial targets, track moving targets and remain steadily locked or pointed with very high precision on a specific celestial target.

FGS allows Webb to determine its position, locate its celestial targets, track moving targets and remain steadily locked or pointed with very high precision on a specific celestial target.

FGS is so sensitive that it can detect a tiny angular displacement equivalent to the thickness of a human hair as seen from one kilometre away.

FGS is so sensitive that it can detect a tiny angular displacement equivalent to the thickness of a human hair as seen from one kilometre away.

NIRISS enables scientists to determine the composition of exoplanets' atmospheres, observe distant galaxies, and examine objects that are very close together.

NIRISS enables scientists to determine the composition of exoplanets' atmospheres, observe distant galaxies, and examine objects that are very close together.

FGS/NIRISS operates over a wavelength range of 0.6 to 5.0 microns

FGS/NIRISS operates over a wavelength range of 0.6 to 5.0 microns

Fine Guidance Sensor (FGS)
Near Infrared Imager and Slitless Spectrograph (NIRISS)

FGS

The Fine Guidance Sensor (FGS) is a "guider" that "locks on" to bright stars in deep space allowing Webb to point very precisely, so that it can obtain high-quality images.

NIRISS

The Near-Infrared Imager and Slitless Spectrograph (NIRISS) provides near-infrared imaging and spectroscopic capabilities. As the only instrument capable of aperture mask interferometry, NIRISS has the unique ability to capture images of bright objects at a resolution greater than the other imagers. The NIRISS is used to investigate the following science objectives: first light detection, exoplanet detection and characterization, and exoplanet transit spectroscopy.

Graphic titled “NIRISS, Near-Infrared Imager and Slitless Spectrograph” illustrating its components, wavelength range, field of view, imaging modes, and spectroscopy modes. Components section includes icons for camera, spectrographs, and aperture mask. Wavelength range highlighted for visible and near-infrared. Field of view shows a small portion of a spiral galaxy outlined with a white square. Imaging modes includes icons for standard and aperture mask interferometry. Spectroscopy modes includes icons for wide-field slitless and single-object slitless. Select View Description for more details.

FGS/NIRISS Instrument Infographic - described in the sections below in the same order as they appear in the graphic.

NASA, ESA, CSA, Andi James (STScI)

Techical Description

The JWST Near-Infrared Imager and Slitless Spectrograph (NIRISS) provides unique observational capabilities between 0.6 and 5 μm that complement those available with NIRCam and NIRSpec. Its efficient, all-reflective design enables low-resolution, wide-field grism spectroscopy; medium-resolution grism spectroscopy optimized for applications requiring extreme spectrophotometric stability; aperture masking interferometry; and parallel imaging through filters matched to those available with NIRCam.

Components

Camera: captures two-dimensional images of regions of space.
Spectrograph : spread light out into a spectrum so that the brightness of each individual wavelength can be measured.
Aperture mask : a metal plate with seven hexagonal holes that is placed in front of the detectors to increase the effective resolution of the telescope and capture more detailed images of extremely bright objects.

Wavelength

NIRISS is designed to capture light ranging in wavelength from 0.6 microns (visible red) to 5 microns (mid-infrared).

Fields of View

An instrument’s field of view is the amount of sky that it can observe at any given point in time. (The actual area that can be observed depends on the distance of the object being observed.) In this graphic, a Hubble Space Telescope image of the Whirlpool Galaxy (M51) is shown for scale. The image covers an area of 9.6 × 6.6 arcminutes. (The full Moon has a diameter of about 31 arcminutes across the sky.) NIRISS covers a field of view roughly 2.2 × 2.2 arcminutes.

Webb's guider (FGS) and four science instruments (NIRCam, NIRSpec, NIRISS, and MIRI) share the field of view of the Webb telescope optics, but they actually see different parts of the sky at any given observation. Credit: NASA

Imaging Modes

Standard: is the equivalent to basic digital photography and involves capturing pictures of a wide variety of objects and materials in space that emit or reflect infrared light.
Aperture Mask Interferometry (AMI): involves using an aperture mask to increase the effective resolution of the telescope and capture more detailed images. When the aperture mask is in place, only the light that passes through the holes makes it to the detectors—the rest is blocked. AMI simulates the effect of a telescope array, in which a number of telescopes work together to simulate the light-gathering ability of a single, much larger telescope. AMI is used to separate light of bright objects like stars that are close together in space or on the sky.

Spectroscopy Modes

Wide-field slitless Spectroscopy: involves capturing the overall spectrum of a wide field of view: a field of stars, part of a nearby galaxy, or many galaxies at once.
Single-Object Slitless Spectroscopy : involves capturing the spectrum of a single bright object like a star in a field of view.

FGS/NIRISS Development Gallery

Gallery of the development, testing and commissioning of the FGS/NIRISS in reverse chronological order.

The image below is a SLIDESHOW. Hover over the image to see the image title and controls. Click the image to go to a detail page with more info and the ability to download the image at various resolutions (click downward arrow in lower right corner).

A Lift for Webb's Fine Guidance Sensor

Video: FGS/NIRISS 3d Diagram Rotation

FGS engineering diagram"

FGS/NIRISS was built by the Canadian Space Agency.

FGS/NIRISS Development Team

NIRISS is a contribution of the Canadian Space Agency to the JWST project. Honeywell International designed and built the instrument in collaboration with a team lead by the Principal Investigator, René Doyon of the Université de Montréal. Additional technical support was provided by the National Research Council of Canada’s Herzberg Astronomy and Astrophysics Research Centre.

Webb Telescope's Fine Guidance Sensor Gets Lots of Guidance

The FGS/NIRISS at NASA Goddard before integration into the instrument module.

More on Webb's Instruments

In this illustration, the multilayered sunshield on NASA’s James Webb Space Telescope stretches out beneath the observatory’s honeycomb mirror

NIRCam

Near Infrared Camera

In this illustration, the multilayered sunshield on NASA’s James Webb Space Telescope stretches out beneath the observatory’s honeycomb mirror

MIRI

Mid-Infrared Camera

In this illustration, the multilayered sunshield on NASA’s James Webb Space Telescope stretches out beneath the observatory’s honeycomb mirror

NIRSpec

Near Infrared Spectrometer

In this illustration, the multilayered sunshield on NASA’s James Webb Space Telescope stretches out beneath the observatory’s honeycomb mirror

FGS/NIRISS

Fine Guidance Sensor / Near Infrared Imager and Slitless Spectrograph

In this illustration, the multilayered sunshield on NASA’s James Webb Space Telescope stretches out beneath the observatory’s honeycomb mirror

ISIM

Webb's Integrated Instrument Module ( contains all instruments)

In this illustration, the multilayered sunshield on NASA’s James Webb Space Telescope stretches out beneath the observatory’s honeycomb mirror

Webb Observatory

Observatory Overview Page