JWST: Near Infrared Camera (NIRCam)

The Near Infrared Camera (NIRCam) is James Webb's primary imager that will cover the infrared wavelength range of 0.6 to 5 microns. NIRCam will detect the light from the earliest stars and galaxies in the process of formation, the population of stars in nearby galaxies, as well as young stars in the Milky Way and Kuiper Belt objects.  NIRCam is equipped with coronagraphs, instruments that allow astronomers to take pictures of very faint objects around a central bright object, like stellar systems. NIRCam's coronagraphs work by blocking a brighter object's light, making it possible to view the dimmer object nearby - just like shielding the sun from your eyes with an upraised hand can allow you to focus on the view in front of you. With the coronagraphs, astronomers hope to determine the characteristics of planets orbiting nearby stars.

NIRCAM Alignment selfie
Photo: NASA

NIRCam wavelength range

In addition to imaging with a wide range of narrow, medium, and broad filters, NIRCam also offers wide-field slitless (grism) spectroscopy and coronagraphic imaging modes, as well as time-series and grism time-series observing modes for high-accuracy photometric monitoring and spectrophotometric monitoring, respectively. NIRCam also obtains wavefront sensing measurements critical for periodic alignment and phasing of the segments of JWST's primary mirror.

NIRCam was built by a team at the University of Arizona and Lockheed Martin’s Advanced Technology Center, led by Principal Investigator Marcia Rieke from the University of Arizona.

NIRCam imaging covers the two adjacent fields of a total area of 9.7 arcmin². Long and short wavelengths are observed simultaneously. Because of the changing size of the PSF, the short wavelengths use four detectors in each module while the long wavelengths are covered by one detector.

NIRCam being installed into the instrument module
Photo: NASA

JWST Team Photo with Completed Flight Instrument module
Photo: NASA

The NIRCam has ten mercury-cadmium-telluride (HgCdTe) detector arrays. These are analogous to charge-coupled devices(CCD) found in ordinary digital cameras. The NIRCam is a science instrument but also an Optical Telescope Element wavefront sensor, which provides something similar to instant LASIK vision correction.

NIRCam Engineering Diagram
Photo credit: NASA

The James Webb Space Telescope has an 18-segment, approximately 6.5meter diameter primary mirror, which is so large it has to fold to fit into the launch vehicle. After launch, the telescope will deploy on its way out to its final orbit. Wavefront sensing and control is a technical term used to describe the subsystem that is required to sense and correct any errors in the telescope's optics. This is especially necessary because all 18 segments have to work together as a single giant mirror.

Ball Aerospace engineered a scaled telescope testbed to develop and demonstrate this technology. An image of the testbed telescope is shown on the right. In each of the 9 distinct alignment processes, the algorithms needed to align the deployed 18-mirrored telescope into a high-performance single-mirrored telescope were designed and demonstrated on the testbed.

Fully functional, 1/6th scale model of the JWST mirror in its optics testbed used to develop wavefront sensing and control.
Photo credit: NASA

Another view of the 1/6th scale model of the JWST mirror in the optics testbed.
Photo credit: NASA