The Tech Behind Telescopes Like JWST and Hubble

Telescopes have revolutionized our understanding of the cosmos. From the earliest optical telescopes crafted by Galileo to the powerful space-based observatories like the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST), these instruments represent the pinnacle of human curiosity and engineering. But what exactly makes these marvels of modern science tick? What kind of technology powers our vision of the distant universe?

This article dives deep into the technological foundations of telescopes like Hubble and JWST, exploring how they work, what makes them different, and how they continue to reshape our understanding of space.

A Tale of Two Telescopes: Hubble and JWST

Before exploring the technology, it’s important to understand the basic distinctions between Hubble and JWST. Though both are space telescopes and serve complementary scientific roles, they differ significantly in design, purpose, and technological implementation.

Hubble: The Optical Workhorse

Launched in 1990 and orbiting about 547 kilometers above Earth, the Hubble Space Telescope observes in visible, ultraviolet (UV), and near-infrared light. It was designed to capture crisp, detailed images of celestial objects by getting above Earth’s atmosphere, which distorts and absorbs certain wavelengths of light.

JWST: The Infrared Giant

In contrast, the James Webb Space Telescope, launched in December 2021, is designed primarily for infrared observation. Located about 1.5 million kilometers from Earth at the second Lagrange point (L2), JWST can observe extremely faint and distant galaxies whose light has been redshifted into the infrared spectrum due to the expansion of the universe.

Mirror Technology: Seeing Through Giant Eyes

The most iconic components of both telescopes are their mirrors. These mirrors are not just glass—they are precision-engineered optical systems critical to the quality of the data they collect.

Hubble’s Primary Mirror

Hubble uses a single 2.4-meter diameter mirror made of ultra-low expansion glass, which ensures dimensional stability across a wide temperature range. The mirror is coated with a thin layer of aluminum and protected by a layer of magnesium fluoride to optimize reflection in the UV and visible spectrum.

However, the mirror's early history is infamous. After launch, it was discovered that the mirror had been ground to the wrong shape—off by just 2.2 microns—causing spherical aberration. NASA corrected this with a servicing mission in 1993, adding corrective optics known as COSTAR.

JWST’s Segmented Mirror

JWST’s primary mirror is an 18-segment hexagonal array, spanning a total of 6.5 meters in diameter—making it over 2.5 times larger than Hubble’s. Each segment is made from beryllium and coated with gold to enhance infrared reflectivity. Beryllium is chosen for its strength, lightness, and ability to perform well at cryogenic temperatures.

These segments can be adjusted individually with extreme precision using actuators, ensuring perfect alignment during space operation. This design allows JWST to be folded during launch and then deployed once in orbit—a feat never before attempted at such scale.

Detectors: The Digital Eyes of Space

While mirrors focus the light, detectors convert it into digital signals for scientific analysis.

Hubble’s CCDs

Hubble uses Charge-Coupled Devices (CCDs) to capture images and spectra in the UV, visible, and near-infrared bands. These are similar in principle to the sensors found in digital cameras but are far more sensitive and operate at extremely low temperatures to reduce electronic noise.

JWST’s Infrared Detectors

JWST employs Mercury-Cadmium-Telluride (HgCdTe) detectors optimized for infrared sensitivity. These detectors must be cooled to around -266°C (just 7 Kelvin above absolute zero) to prevent thermal noise from overwhelming the faint infrared signals.

To achieve this, JWST uses a cryocooler and its innovative sunshield system to maintain the instrument's low temperature. Without this cooling, the telescope itself would glow brightly in infrared, masking the signals from distant galaxies.

Instruments: The Scientific Toolkits

Both telescopes are equipped with an array of scientific instruments, each tailored for specific observational tasks.

Hubble’s Suite

Hubble’s five primary instruments include:

Wide Field Camera 3 (WFC3) – for imaging in UV, visible, and near-infrared.
Advanced Camera for Surveys (ACS) – optimized for visible light surveys.
Cosmic Origins Spectrograph (COS) – UV spectroscopy for studying interstellar and intergalactic matter.
Space Telescope Imaging Spectrograph (STIS) – combines imaging and spectroscopy across multiple wavelengths.
Fine Guidance Sensors (FGS) – help with accurate pointing.

JWST’s Arsenal

JWST features four main instruments:

Near Infrared Camera (NIRCam) – captures high-resolution images in near-infrared.
Near Infrared Spectrograph (NIRSpec) – capable of analyzing the spectra of over 100 objects simultaneously.
Mid-Infrared Instrument (MIRI) – observes mid-infrared light, revealing colder celestial bodies like dust clouds and distant galaxies.
Fine Guidance Sensor / Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS) – assists with precise pointing and exoplanet characterization.

Each of these instruments must operate under extreme environmental constraints, requiring radiation shielding, thermal stability, and precise optical alignment.

Pointing and Stability: Keeping the View Still

Capturing distant cosmic objects requires a telescope to remain incredibly stable and accurately pointed. A slight tremble can blur a photo or ruin a spectrum.

Hubble’s Gyroscopes and Reaction Wheels

Hubble uses gyroscopes and reaction wheels to orient and stabilize itself in space. These systems work in concert with star trackers and fine guidance sensors, allowing Hubble to maintain focus on a single star for hours or even days. Over the years, servicing missions have replaced or upgraded these components to extend Hubble’s operational life.

JWST’s Star Tracker and Control Systems

JWST also uses reaction wheels and a Fine Guidance Sensor to achieve extraordinary pointing accuracy—down to a few milli-arcseconds. Given the telescope’s massive mirror and remote location, achieving this level of precision required major advancements in control algorithms and spacecraft design.

Thermal Engineering: Battling the Heat (and Cold) of Space

Space is not uniformly cold. Sunlight, even from 1.5 million kilometers away, can heat spacecraft instruments beyond operational limits if not properly managed.

Hubble’s Thermal Protection

Hubble relies on insulation and radiators to manage heat. It operates in low Earth orbit, meaning it experiences rapid temperature swings as it orbits Earth every 90 minutes. Its systems are built to handle these fluctuations, which add mechanical and electronic strain.

JWST’s Sunshield Marvel

JWST’s thermal environment is even more complex. To protect its infrared instruments from heat, it uses a five-layer sunshield the size of a tennis court. Each layer, made from a special material called Kapton, reflects and disperses heat. The sun-facing side reaches temperatures of around 85°C, while the instrument side is chilled to -233°C. This contrast enables JWST to detect faint infrared signatures without interference.

Data Transmission: From Deep Space to Earth

Collecting data is only half the job—getting it back to Earth is another technical challenge.

Hubble’s Earth Proximity Advantage

Being in low Earth orbit, Hubble communicates with Earth multiple times per day using NASA’s Tracking and Data Relay Satellite System (TDRSS). Data is downlinked quickly and continuously updated.

JWST’s Long-Distance Link

JWST, parked at L2, uses the Deep Space Network (DSN) to send its data back to Earth. The signal, traveling 1.5 million kilometers, must be strong and precise. This requires high-gain antennas and carefully managed communication windows. Despite the distance, data transfer speeds remain impressive—up to 28.6 Mbps under optimal conditions.

Maintenance and Longevity: Then vs. Now

One of Hubble’s most celebrated features is its maintainability. It was designed for servicing missions by astronauts aboard the Space Shuttle, which allowed five such missions to upgrade and repair it. This extendable design greatly lengthened its useful life.

JWST, by contrast, is not serviceable due to its remote location. Its complex deployment sequence had to be executed perfectly, with over 300 single points of failure. As such, JWST had to be built with redundancy and utmost reliability. It’s expected to operate for at least a decade, possibly more with fuel conservation and minimal wear on its systems.

The Legacy and Future of Space Telescopes

Both Hubble and JWST have already transformed our view of the universe. Hubble brought us iconic images like the Pillars of Creation and deep field views of the early universe, while JWST is beginning to uncover even earlier galaxies and probe the atmospheres of exoplanets.

Technologically, they represent two generations of telescope design. Hubble was the culmination of 20th-century optical engineering, while JWST is a masterclass in 21st-century systems integration, cryogenics, and precision mechanics.

Looking forward, future telescopes like the Nancy Grace Roman Space Telescope and LUVOIR (Large UV Optical Infrared Surveyor) aim to continue this legacy, pushing further into unknown territory with even more advanced technology, broader spectral ranges, and wider fields of view.

Conclusion

The tech behind telescopes like JWST and Hubble is not just about seeing far into space—it’s about pushing the boundaries of what’s possible in physics, engineering, and human ingenuity. From segmented gold-coated mirrors and cryogenic detectors to sunshield deployments and data relay from deep space, these observatories are feats of innovation and perseverance.

As we continue to develop new instruments to explore the cosmos, each telescope builds upon the triumphs and lessons of its predecessors, guiding us further into the mysteries of the universe.