Meet JWST, NASA’s Optical Powerhouse

By Ibtisam AbbasiReviewed by Louis CastelAug 26 2025

The James Webb Space Telescope (JWST), arguably the most significant collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), is central to exploring the origins of the universe. Equipped with cutting-edge, highly efficient optical mirrors, JWST offers exceptional resolution. Its ability to observe over 100 objects at once sets it apart as a leading tool for the next generation of space exploration.

Image Credit: Vadim Sadovski/Shutterstock.com

What Makes JWST an Optical Powerhouse?

As the flagship mission of modern space exploration and the direct successor to the iconic Hubble Telescope, the James Webb Space Telescope (JWST) stands out as a first-of-its-kind technological achievement. It incorporates advanced optical innovations that go well beyond what Hubble was capable of, setting a new benchmark for space-based observation.

Next-Gen Optical and Science Equipment

JWST is a state-of-the-art infrared observatory equipped with a cryogenic aperture measuring 6.6 meters in diameter. This design enables highly efficient imaging and spectroscopic studies across both the near-infrared (NIR) range, from 0.6 to 5 μm, and the mid-infrared band, spanning 5 to 28 μm.

The observatory’s flight system is made up of three main components, with the centerpiece being the Integrated Science Instrument Module (ISIM). This module houses four key instruments: the Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI), and the Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS). Together, they form the scientific core of JWST, enabling a broad range of high-precision observations.¹

The Optical Telescope with Advanced Image Correction Technology

JWST’s optical telescope is engineered to deliver highly corrected images to the Integrated Science Instrument Module (ISIM). It features a 25 m² light-collecting area and uses a three-mirror anastigmatic (TMA) design, achieving a Strehl ratio of 0.86 at a wavelength of 2 μm, an indicator of its exceptional image quality.

This TMA configuration enables the telescope to capture sharp, high-resolution images across a wide field of view while correcting for spherical aberration and field curvature. With an effective f-number of 20, the system also includes an integrated Fine Steering Mirror (FSM), which ensures precise optical pointing and stable image acquisition throughout observations.

Advanced Mirrors and Actuating System

JWST’s primary mirror consists of 18 hexagonal beryllium (Be) segments mounted on a rigid composite backplane. Each segment measures 1.32 meters flat-to-flat and can be adjusted in six degrees of freedom (DOF) to ensure precise alignment. Beryllium was chosen for its low coefficient of thermal expansion within the telescope’s cryogenic operating range of 35–55K. When properly phased, the segments act as a single, high-quality mirror.

Each mirror segment features a controllable radius of curvature and is coated with a reflective gold layer via vapor deposition, ensuring high reflectivity across the 0.6 to 28.1 μm wavelength range. The 18 segments are divided into three types with distinct aspheric prescriptions, depending on their position. Thanks to the mirror’s six-fold symmetry, segments of the same type are interchangeable.

Six actuators, arranged in three bipods per segment and connected to the composite backplate, provide rigid-body motion. Designed to function at both cryogenic and ambient temperatures, these actuators enable both coarse and fine adjustments for optimal optical performance.²

Download the PDF of the article

Exploring the Universe through Spectroscopy

Spectroscopy has long been a cornerstone for experts and researchers working to decode the universe and study astrophysical phenomena. By applying quantum principles, scientists design spectrographs that analyze the way light splits and how specific wavelengths are absorbed or emitted. This technique helps determine the chemical composition of astronomical bodies and provides critical data on their pressure, temperature, and even the behavior of distant galaxies.⁴

The James Webb Space Telescope (JWST) uses spectroscopy to explore four key scientific themes. One of the most significant is the study of the universe’s earliest light, signaling the end of the cosmic “dark ages.” Between 100 to 400 million years after the Big Bang, the first stars and galaxies began to form. During this period, dark matter halos, representing the mass density of these early structures, started to grow.

These first stars were massive, ending their lives in powerful supernovae or collapsing directly into black holes. JWST can detect the faint light from these early cosmic events by analyzing Lyman-alpha dropouts at extremely high redshifts. Similar to the first stars, early galaxies emitted intense ultraviolet radiation, creating ionized bubbles in the intergalactic medium. Using its advanced spectroscopic instruments, particularly those in the Integrated Science Instrument Module (ISIM), JWST can observe the brightest redshift sources. This enables scientists to study the process of reionization and how it influenced the formation of galaxies.

JWST also excels in deep analysis of the H-alpha (Hα) emission line, allowing researchers to measure very low star formation rates—down to about one solar mass per year, at redshifts around z ~ 5. Additionally, it enables the measurement of galactic properties such as those described by the Tully-Fisher relation, even in dark galaxies at high redshifts. This provides valuable insights into the evolution of stars and galaxies and the complex relationship between visible matter and dark matter.

Another critical capability of JWST is capturing high-resolution images of silhouette circumstellar disks around young, low-mass celestial bodies. These observations offer essential clues about how planets form. Furthermore, JWST’s ability to analyze the composition and structure of protoplanetary disks around stars supports efforts to trace the sources of water and organic compounds—key ingredients in the search for the origins of life.⁵

Inside JWST: NIRSpec and Other Optical Instruments

Among the core instruments within the Integrated Science Instrument Module (ISIM), NIRSpec stands out as the first of its kind to offer multi-object spectroscopic capabilities. By dispersing light into a spectrum, NIRSpec reveals valuable information about the physical properties and chemical composition of celestial objects. It operates across a wavelength range of 0.6 to 5.3 μm, enabling both single-object analysis using fixed slits and powerful multi-object observations via a novel micro-shutter assembly.

This micro-shutter array (MSA) is an advanced grid of approximately 248,000 miniature shutters that can be individually opened or closed. This allows astronomers to selectively transmit or block light, making it possible to capture spectra from multiple targets simultaneously, significantly increasing efficiency in crowded fields of view.

Complementing NIRSpec is NIRCam, the primary imaging instrument for the near-infrared range. NIRCam is crucial for detecting light from some of the universe’s earliest galaxies and plays a key role in tracking the motion of exoplanets with high precision.⁷

In the mid-infrared range, JWST relies on the Mid-Infrared Instrument (MIRI) for both imaging and spectroscopic analysis. MIRI operates between 4.9 and 28.8 μm and includes nine broadband filters that support high-quality imaging at wavelengths from 5.6 to 25.5 μm. This makes it especially valuable for studying cooler cosmic objects, such as distant galaxies, dust clouds, and forming planetary systems.⁸

Finally, the FGS acts as a guiding sensor, locking onto the bright stars in deep space, allowing for capturing high-quality images. Its all-reflective design allows for wide-field grism spectroscopy, and parallel imaging in coordination with NIRCam.⁹

Optical Challenges

Aligning the 18 primary mirror segments of the James Webb Space Telescope (JWST) to achieve diffraction-limited performance at 2 μm is a complex and highly demanding task. The system had to be robust enough to account for both thermal variations and deployment-related imperfections.

To meet this challenge, engineers integrated a highly advanced Wavefront Sensing and Control Subsystem (WFS&C). This system enables precise alignment and orientation of the 18 individual mirror segments, ensuring they are phase-aligned to function as a single, unified optical surface. Through this wavefront matching, the telescope can deliver high-quality images with remarkable efficiency. In fact, the 6.6-meter diffraction-limited telescope achieves about 70% operational efficiency without any deformation of its optical structural components, thanks to the capabilities of the WFS&C.¹⁰

Thermal management is another critical aspect of JWST’s design. Operating at cryogenic temperatures, the telescope relies on carefully engineered thermal control elements to maintain the stability of its optical system. These components ensure that each subsystem remains within its optimal temperature range for peak performance. The use of specialized materials, advanced optical coatings, and a finely tuned structural design all contribute to minimizing the effects of thermal fluctuations, essentially “athermalizing” the entire telescope assembly for consistent, reliable operation in space.¹¹

What Does the Future Hold?

The engineering challenges behind the James Webb Space Telescope (JWST) have led to the development of lighter, more adaptable technologies, laying the groundwork for future missions like the Habitable Worlds Observatory (HWO).

Recently, JWST’s Mid-Infrared Instrument (MIRI) helped detect an exoplanet within the disk of a 6.4-million-year-old star, TWA 7. Based on the data, the planet’s mass is estimated at about 0.3 times that of Jupiter, showcasing JWST’s sensitivity in observing young planetary systems.

JWST’s technology is also shaping future projects like the Nancy Grace Roman Space Telescope, with its optical systems and testing protocols serving as templates. Some upcoming mission concepts even plan to use JWST in parallel with other instruments, highlighting its ongoing value in expanding our understanding of the universe.

Want more space-related optics? Learn about Anisotropic Cosmic Birefringence

Further Reading

1. National Aeronautics and Space Administration (NASA). Integrated Science Instrument Module (ISIM). James Webb Space Telescope Mission. [Online]. Available at: https://science.nasa.gov/mission/webb/integrated-science-instrument-module-isim/ [Accessed on: August 18, 2025].
2. McElwain, M. et. al. (2023). The James Webb Space Telescope Mission: Optical Telescope Element Design, Development, and Performance. Publications of the Astronomical Society of the Pacific. 135(1047). 058001. 1-34. Available at: https://doi.org/10.1088/1538-3873/acada0
3. Menzel, M. et. al. (2024). Lessons learned from systems engineering on the James Webb Space Telescope. Journal of Astronomical Telescopes, Instruments, and Systems. 10(1). 011208. Available at: https://doi.org/10.1117/1.JATIS.10.1.011208
4. Center for Astrophysics, Harvard and Smithsonian (2025). Spectroscopy. [Online]. Available at: https://www.cfa.harvard.edu/research/topic/spectroscopy [Accessed on: August 19, 2025].
5. Gardner, J. (2012). The James Webb Space Telescope: Extending the Science. Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave. Proceedings of the SPIE. 8442. 844228. 11. Available at: https://doi.org/10.1117/12.926551
6. National Aeronautics and Space Administration (NASA). (2025). Near InfraRed Spectrograph (NIRSpec). James Webb Space Telescope Mission. [Online]. Available at: https://science.nasa.gov/mission/webb/nirspec/ [Accessed on: August 21, 2025].
7. National Aeronautics and Space Administration (NASA). (2025). Near Infrared Camera (NIRCam). James Webb Space Telescope Mission. [Online]. Available at: https://science.nasa.gov/mission/webb/nircam/ [Accessed on: August 21, 2025].
8. National Aeronautics and Space Administration (NASA). (2025). Mid-Infrared Instrument (MIRI). James Webb Space Telescope Mission. [Online]. Available at: https://science.nasa.gov/mission/webb/mid-infrared-instrument-miri/ [Accessed on: August 21, 2025].
9. National Aeronautics and Space Administration (NASA). (2025). FGS/NIRISS. James Webb Space Telescope Mission. [Online]. Available at: https://science.nasa.gov/mission/webb/fine-guidance-sensor-near-infrared-imager-and-slitless-spectrograph-fgs-niriss/ [Accessed on: August 21, 2025].
10. Acton, D. et. al. (2012). Wavefront sensing and controls for the James Webb Space Telescope. In Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave. 8442. 877. SPIE. Available at: https://doi.org/10.1117/12.925015
11. Feinberg, L. et. al. (2024). James Webb Space Telescope optical stability lessons learned for future great observatories. Journal of Astronomical Telescopes, Instruments, and Systems. 10(1). 011204-011204. Available at: https://doi.org/10.1117/1.JATIS.10.1.011204
12. Arenberg, J. et. al. (2024). Special Section Guest Editorial: Lessons Learned from the James Webb Space Telescope Program. Journal of Astronomical Telescopes, Instruments, and Systems. 10(1). 011201. Available at: https://doi.org/10.1117/1.JATIS.10.1.011201
13. Goddard Engineering and Technology Directorate, NASA. (2025). Micro-Electro Mechanical Systems (MEMS) Capability. [Online]. Available at: https://etd.gsfc.nasa.gov/capabilities/capabilities-listing/micro-electro-mechanical-systems/ [Accessed on: August 22, 2025].
14. Lagrange, A. et al. (2025). Evidence for a sub-Jovian planet in the young TWA 7 disk. Nature. 642. 905–908. Available at: https://doi.org/10.1038/s41586-025-09150-4

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.