The James Webb Space Telescope (JWST) is a space telescope for infrared astronomy, and currently the largest optical telescope in space. It is developed by the U.S. National Aeronautics and Space Administration (NASA), in partnership with the European Space Agency (ESA) and the Canadian Space Agency (CSA). It was launched on 25 December 2021 on an Ariane 5 rocket from Kourou, French Guiana, and arrived at the halo orbit circling the Sun–Earth L2 Lagrange point in January 2022. The first image was released to the public on 11 July 2022. With its advantages in near to mid-infrared bands which are difficult to study with current ground-based and space telescopes, it can better observe high-redshift objects, colder objects, and objects obscured by dust clouds. The expected lifetime cost for the project of NASA is US$9.7 billion, with US$8.8 billion spent on the spacecraft design and development, and US$861 million planned to support five years of mission operations. Representatives from ESA and CSA stated their contributions to approximately €700 million and CA$200 million, respectively.
Its key goals includes:
- Searching for the light from earliest stars and galaxies after the Big Bang
- Studying the formation and evolution of galaxies
- Studying the formation of stars and planets
- Studying planetary systems and the origins of life

To study the infrared spectrum, the telescope needs to be kept under 50 K. It is equipped with a five-layer 14.162 m × 69.54 m sunshield and operates near the Sun–Earth L2, allowing the sunshield to block the radiation from the Sun, Earth, and Moon, which are always on the same side of it. Each layer of the sunshied is made of aluminum coated Kapton E film, with an extra layer of doped silicon on the Sun-facing side of the two hottest layers to reflect the radiation away into space. To fit it into the Ariane 5 rocket's payload fairing, the sunshield needs to be folded 12 times.
JWST's optical design is a three-mirror anastigmat. Its primary mirror is a 6.5 m-diameter gold-coated beryllium reflector composed of 18 hexagonal segments, which can fold up before launch and be adjusted with 10 nanometer accuracy with its 132 actuators. The secondary mirror in the front of JWST is 0.74 m in diameter. The diffraction spikes of the primary mirror segments and the spider supporting the secondary mirror contribute to most of the identical "six-spikes-plus-two-fainter-ones" in its photographs.
JWST has 4 science instruments within its Integrated Science Instrument Module (ISIM), including:
- Near Infrared Camera (NIRCam). An infrared imager with a spectral coverage from the edge of the visible (0.6 μm) through to the near infrared (5 μm). It is also used to align and focus the main mirror segments.
- Near Infrared Spectrograph (NIRSpec). It performs spectroscopy over the wavelength range of NIRCam with three different observing modes.
- Mid-Infrared Instrument (MIRI). It contains a mid-infrared camera and an imaging spectrometer. Its temperature is maintained under 6K by a helium gas mechanical cooler.
- Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS). The FGS is used to stabilize the line-of-sight of the observatory during science observations, and the NIRISS is for for astronomical imaging and spectroscopy in the 0.8 μm to 5 μm wavelength range.
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