JWST: ESA, NASA, and CSA Cool Telescope - Part 2 - The Instruments
Image Credit: NASA's James Webb Space Telescope
As we mentioned in our previous post, JWST or Webb is NASA, ESA, and the Canadian Space Agency (CSA) telescope. You can also find out more about the mission’s scientific goals in the previous post.
JWST will carry four state-of-the-art science instruments with detectors that can record extremely faint signals: the mid-infrared camera and spectrograph (MIRI) developed by NASA and ESA, the near-infrared spectrograph (NIRSpec) developed by ESA with elements provided by NASA's Goddard Space Flight Center, the near-infrared camera (NIRCam) designed by NASA with components provided by the University of Arizona, and the combined fine guidance sensor and near-infrared imager and slitless spectrograph (FGS-NIRISS) developed by CSA. JWST also counts with innovative technologies, such as lightweight optics, deployable sun-shield, folding segmented mirror, improved detectors, cryogenic actuators & mirror control, and micro-shutters.
Image Credit: ESA
The Mid-Infrared Camera and Spectrograph (MIRI)
The MIRI is an essential tool for studying old and distant stellar clusters, areas of intense star formation hidden behind thick dust, the light that is emitted, reflected, and transmitted by exoplanets. It will also help understand hydrogen emission from extreme distances, the physics of protostars, Kuiper Belt objects, extrasolar planets, and faint comets. MIRI will produce mid-infrared images and spectra with a unique combination of sharpness and sensitivity, including coronographic mode, avoiding bias from Webb's light. MIRI infrared detectors will be colled to a very cold 7K. MIRI is a combined mid-IR camera (1.4' × 1.9') and spectrograph (R~3000) and was the first of the four instruments to be delivered to NASA in 2012. It has been integrated into the James Webb Space Telescope (JWST) payload module called the Integrated Science Instrument Module (ISIM).
The Near-infrared Spectrograph (NIRSpec)
The NIRSpec will simultaneously obtain spectra of more than 100 galaxies or stars and is sensitive over a wavelength range equal to the peak emission from the most distant galaxies. It will support JWST's four main science themes by providing low, medium, and high-resolution spectroscopic observations in the near-infrared. It will help understand the formation and chemical abundances of young distant galaxies by exploring the intergalactic medium's history, for example, the gaseous material that fills the vast volumes of space between the galaxies. To characterize the properties and compositions of atmospheres of extrasolar planets allows the determination of water presence. NIRSpec is a wide-field (3.5' × 3.5') multi-object near-IR spectrometer with spectral resolutions of R~100, R~1000, and R~2700, allowing scientists to study objects in covers of gas and dust.
The Near-Infrared Camera (NIRCam)
The NIRCam is mainly designed for detecting faint objects, essential for studying the first stars, star clusters, and galaxy cores formed after the Big Bang. Also, for the study of distant galaxies formation or merging processing, light distortion due to dark matter, and the discovery of supernovae in remote galaxies. NIRCam is a two-channel wide-field (2.2' × 4.4') with a large selection of filters, providing critical measurements for JWST's primary mirror segments' shape in-orbit adjustment.
The Combined Fine Guidance Sensor and Near-Infrared Imager and Slitless Spectrograph (FGS-NIRISS)
The NIRISS is a wide-field (2.2' × 2.2') imager with a spectroscopic observing mode optimized for exoplanets, designed to ease spectra recovery even when they overlap. It will also contribute to all of the mission's science themes. It will enable scientists to determine the composition of exoplanets' atmospheres, analyze distant galaxies, and examine objects that are very close together. To allow the stable pointing at the milli-arcsecond level required by JWST to achieve its scientific goals, JWST is also equipped with an FGS. The FGS will keep Webb on target, allowing it to determine its position, locate its celestial targets, track moving targets, remain steadily locked or pointed, with very high precision, on a specific celestial target.
Image Credit: NASA/Chris Gunn
The Mirrors
Webb is a three-mirror anastigmat telescope. The tertiary mirror removes resulting astigmatism and flattens the focal plane, allowing a broader view.
The golden mirror is 6.5 meters wide, making Webb the largest space-based telescope ever built. The mirror comprises 18 hexagonal gold-coated ultra-lightweight beryllium unfolded segments that can be adjusted individually to shape after launch. Each piece is 1.32 meters (4.3 feet) in diameter and weighs approximately 20 kilograms (46 pounds). Webb's secondary mirror is 0.74 meters in diameter.
The hexagonal shape allows a high filling factor (fit together without gaps) and six-fold symmetry. If the segments were circular, there would be gaps between them; however, a circular-like shape is wanted to focus the light into the most compact region on the detectors. And symmetry allows the use of only three different optical prescriptions for 18 segments.
The Sun-Shield and Radio Transmitter
Webb will have a deployable tennis court-sized (22 m × 12 m) sun-shield to protect the telescope from the Sun's heat and keep it in perpetual shadow, allowing the telescope and the instruments to cool to -233 °C. That is needed to prevent the instrument's infrared emission from disturbing the astronomical targets' signals.
JWST will also count with a high-frequency radio transmitter. Large radio antennas worldwide will receive Webb's transmitter signals and send them to the Webb Science and Operation Center (S&OC) at the Space Telescope Science Institute (STScI) in Baltimore, USA.
The team at the S&OC will handle the scientific operation of the observatory. Such as selecting, planning, and carrying out all science observations; near real-time flight operations like performing observations, uplinking and downlinking data, monitoring the observatory behavior; generating calibrated data, and archiving and distributing raw and calibrated data.
The telescope will be launched onboard Ariane V from the European Spaceport of Kourou, in French Guiana, in a folded position and will deploy once in space. It will take Webb about two weeks to fully unfold and two more weeks to travel to its destination.
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This article was written by Juliane Verissímo - Marketing Department of VisionSpace.