James Webb Space Telescope

James Webb Space Telescope
Company type	Space observatory
Industry	Astronomy, Space science
Founded	1996; 30 years ago
Founder	NASA, ESA, CSA
Headquarters	Greenbelt, Maryland, United States
Area served	Space-based astronomical observations
Key people	NASA Goddard Space Flight Center (development), Space Telescope Science Institute (operations), Northrop Grumman (main contractor)
Products	Infrared space telescope
Website	www.jwst.nasa.gov

The James Webb Space Telescope (JWST) is an observatory operating in space, specifically engineered for infrared astronomical observations. As the most sizable telescope deployed beyond Earth’s atmosphere, it boasts instruments with exceptional resolution and sensitivity, allowing it to detect celestial bodies that are extremely old, remote, or faint—objects beyond the reach of the Hubble Space Telescope. This advanced capability facilitates investigations in both astronomy and cosmology, including the examination of the universe’s earliest stars, the formation of primordial galaxies, and the detailed study of atmospheres surrounding potentially habitable exoplanets.

Despite having a mirror diameter approximately 2.7 times greater than that of Hubble, JWST attains similar optical resolution by focusing on the infrared wavelength range. Because infrared wavelengths are longer, a larger collecting surface is necessary to maintain comparable resolution.

The telescope was launched on 25 December 2021 aboard an Ariane 5 rocket from French Guiana. By January 2022, JWST had arrived at its operational position near the Sun–Earth L₂ Lagrange point, situated roughly 1.5 million kilometers from Earth. The inaugural public release of its images occurred on 11 July 2022.

Development of JWST was spearheaded by NASA in collaboration with the European Space Agency (ESA) and Canadian Space Agency (CSA). The project’s development was overseen by NASA’s Goddard Space Flight Center, while ongoing operations are managed by the Space Telescope Science Institute. Northrop Grumman acted as the main contractor responsible for construction.

The telescope is named in honor of James E. Webb, NASA administrator from 1961 to 1968. Its primary mirror is composed of 18 hexagonal segments made from beryllium and coated with gold, together forming a 6.5-meter diameter reflective surface—approximately six times the light-collecting capacity of Hubble’s mirror. Unlike Hubble, which covers ultraviolet to near-infrared wavelengths (0.1 to 2.5 micrometers), JWST observes from visible red light through mid-infrared wavelengths (0.6 to 28.5 micrometers). To minimize interference from its own infrared emissions, JWST operates at temperatures below 50 kelvin, achieved through a five-layer sunshield that blocks heat from the Sun, Earth, and Moon.

Initial conceptual work began in 1996 under the name Next Generation Space Telescope with an initial target launch date set for 2007 and a budget around $1 billion. The program encountered substantial delays and budget increases, leading to a significant redesign in 2005. Construction was completed in 2016 followed by comprehensive testing phases. The overall expenditure escalated to roughly $10 billion.

Features

The James Webb Space Telescope (JWST) weighs about half as much as the Hubble Space Telescope but incorporates a primary mirror made of gold-coated beryllium consisting of 18 hexagonal segments. The polished surface area measures , with portions obscured by secondary support structures, resulting in a light-collecting area of —more than six times that of Hubble’s mirror diameter and collecting surface area combined. The gold layer improves infrared reflectivity and is shielded by a thin glass coating for protection.

Primarily optimized for near-infrared astronomy, JWST also captures orange and red visible light along with mid-infrared wavelengths depending on its suite of instruments. It can detect objects up to 100 times fainter than what Hubble can observe and probe cosmic epochs reaching as far back as redshift z≈20—approximately 180 million years after the Big Bang. This extends well beyond Hubble’s observational limit near z≈11.1 (about 400 million years after cosmic origin).

JWST focuses on near- to mid-infrared bands because emissions from high-redshift sources shift into these wavelengths; infrared radiation penetrates cosmic dust more effectively; cooler objects such as planetary debris disks emit primarily in infrared; and these spectral regions are difficult to explore from Earth or previous space telescopes.

Terrestrial observatories contend with atmospheric opacity across many infrared bands due to molecules like water vapor and methane that absorb these wavelengths. Earlier space telescopes like Hubble have mirrors warm enough (~) to generate significant infrared noise themselves, limiting their sensitivity in these ranges.

Webb routinely tracks Solar System bodies moving at speeds up to 75 milliarcseconds per second (mas/s), with higher velocity tracking available upon request. This capability enables observation of planets from Mars through Pluto, their moons, comets, asteroids, and nearly all known Kuiper Belt Objects. Additionally, JWST can respond within 48 hours to transient phenomena such as supernovae and gamma-ray bursts.

Location and orbit

The Webb telescope follows a halo orbit around the Sun–Earth L₂ Lagrange point, situated approximately beyond Earth's path. Its orbit oscillates within about of L₂, preventing it from entering the shadow zones cast by Earth and the Moon. By comparison, Hubble orbits at an altitude of above Earth, while the Moon lies at a distance of . This orbital arrangement enables Webb to consistently maintain its sunshield and equipment bus oriented toward the Sun, Earth, and Moon. Such positioning effectively blocks heat and light from these bodies, ensuring stable temperatures below , which is crucial for sensitive infrared measurements, while also providing continuous solar power and communication with Earth.

Sunshield protection

To perform infrared astronomy effectively, Webb must keep its temperature under to avoid interference from its own heat emissions. Its expansive five-layer sunshield serves to block light and thermal radiation from the Sun, Earth, and Moon—all aligned on one side due to its L₂ halo orbit. This thermal stability is essential for the accurate alignment of the primary mirror segments.

Each sunshield layer consists of thin Kapton E film coated with aluminum; the two outermost layers further incorporate doped silicon coatings to reflect solar heat efficiently. The sunshield offers an extraordinary sun protection factor (SPF) of 1,000,000, vastly surpassing typical sunscreen levels. Designed to fold twelve times to fit inside the Ariane 5 rocket’s payload fairing with a diameter of , it unfolds in space to a full size of .

During deployment testing in 2018, accidental tears occurred, causing delays; however, these issues were resolved prior to launch. The sunshield’s shadow restricts Webb’s instantaneous field of regard to about 40% of the sky, yet it can scan the entire celestial sphere over a six-month period.

Optics

Webb's primary mirror features a diameter gold-coated beryllium reflector with a collecting surface area. To comply with launch vehicle constraints, it is composed of 18 hexagonal segments that unfolded once in space—a concept originally developed by Guido Horn d'Arturo. Precise positioning of these mirror segments is achieved through image plane wavefront sensing via phase retrieval techniques using 132 small actuators. These actuators require only occasional adjustments to sustain focus, unlike ground-based telescopes such as the W. M. Keck Observatory, which continuously modify their mirrors to counter gravitational and wind disturbances. The actuators can position segments with an accuracy within 10 nanometers.

The telescope’s optical design is a three-mirror anastigmat, incorporating curved secondary (diameter ) and tertiary mirrors that produce wide-field images free from aberrations. A fine steering mirror enables rapid image stabilization. The hexagonal shape of the primary mirror segments generates distinctive diffraction spikes—six prominent with two fainter—visible in point source imagery.

Scientific instruments

The Integrated Science Instrument Module (ISIM) supplies electrical power, computing resources, cooling systems, and mechanical support for Webb’s instruments. Constructed from bonded graphite-epoxy composite material, ISIM houses four scientific instruments along with a guide camera.

NIRCam (Near Infrared Camera) functions as an infrared imager spanning wavelengths from 0.6 to 5 μm, equipped with ten sensors each containing 4 megapixels. It also operates as the observatory's wavefront sensor for mirror alignment and focusing tasks. The University of Arizona led NIRCam’s development under principal investigator Marcia J. Rieke.
NIRSpec (Near Infrared Spectrograph), developed by the European Space Agency (ESA) at ESTEC in the Netherlands with significant contributions from Airbus Defence and Space and NASA's Goddard Space Flight Center, covers the same wavelength range as NIRCam. It offers three observation modes: a low-resolution prism mode, R~1000 multi-object spectroscopy utilizing a micro-shutter array, and R~2700 integral field or long-slit spectroscopy. Mode changes are managed by Filter Wheel and Grating Wheel assemblies based on mechanisms proven by ISOPHOT technology.
MIRI operates across mid-to-long infrared wavelengths between 5 and 27 μm, combining both a mid-infrared camera and spectrometer in one instrument. Developed through collaboration between NASA and European partners under leadership from George Rieke (University of Arizona) and Gillian Wright (UK Astronomy Technology Centre), MIRI functions at temperatures below 6 K using a helium gas mechanical cooler located on the warm side of the environmental shield.
FGS/NIRISS, overseen by the Canadian Space Agency (CSA) with project scientist John Hutchings (Herzberg Astronomy and Astrophysics Research Centre), is responsible for stabilizing Webb’s line-of-sight during observations. The FGS manages spacecraft orientation and fine steering mirror corrections. CSA also supplied NIRISS for imaging and slitless spectroscopy covering wavelengths from 0.8 to 5 μm under leadership by René Doyon at the Université de Montréal. While often grouped together, FGS serves as a support instrument whereas NIRISS performs scientific imaging roles.

Both NIRCam and MIRI are equipped with coronagraphs that block starlight, enabling detection of faint objects such as exoplanets and circumstellar disks near bright stars.

Spacecraft bus

The JWST's main support structure, known as the spacecraft bus, contains vital systems such as computing, communications, power supply, propulsion, and the spacecraft’s framework. Together with the sunshield, it constitutes the spacecraft portion of the space telescope. Located on the sunshield's Sun-facing "warm" side, this component functions at an approximate temperature of .

Weighing , the bus provides support for the telescope and is primarily built from graphite composite materials. Its assembly was finalized in California in 2015 before being integrated with the telescope ahead of its 2021 launch. The bus allows the telescope to rotate with a pointing accuracy of one arcsecond and offers vibration damping down to two milliarcseconds.

Propulsion includes two sets of rocket engines—one set serving as redundancy—to perform trajectory corrections during transit to L₂ and maintain station keeping. Additionally, eight smaller thrusters handle attitude control for fine pointing adjustments. The propulsion system uses hydrazine fuel (at launch) alongside dinitrogen tetroxide oxidizer (at launch).

Servicing

Webb was not engineered for servicing in orbit. Unlike the Hubble Space Telescope, crewed repair or upgrade missions are not possible, and during its design phase NASA concluded that uncrewed remote servicing missions were beyond current technological capabilities. Although servicing was considered during testing phases, no definitive plans were established. After launch, NASA confirmed that Webb includes limited features to facilitate potential future servicing efforts remotely, such as precise guidance markers, refillable propellant tanks, removable heat shields, and accessible attachment points.

Software

The telescope operates on a customized version of JavaScript, specifically Nombas ScriptEase 5.00e, which complies with the ECMAScript standard and supports a modular architecture where onboard scripts call lower-level functions. The flight software, developed in C++, runs the script interpreter and governs both the spacecraft systems and its scientific instruments.

Comparison with other telescopes

The quest to build large infrared space telescopes has a long history, beginning with early initiatives like the Space Infrared Telescope Facility (later renamed the Spitzer Space Telescope) developed alongside the Space Shuttle program. Unlike ground-based observatories, space-based telescopes avoid atmospheric interference that absorbs infrared radiation, enabling new observational capabilities.

Infrared observatories must maintain extremely low temperatures to prevent their own thermal emissions from overwhelming sensitive detectors. Conventional designs rely on cryogenic dewars filled with coolants such as liquid helium, which restrict mission durations to months or a few years. Alternatively, some missions achieve cooling without expendable resources, demonstrated by extended operations of Spitzer and the Wide-field Infrared Survey Explorer. Webb employs sunshields and radiators for passive cooling while using a cryocooler specifically for its mid-infrared instrument.

Selected space telescopes and instruments
Name	Launch year	Wavelength (μm)	Aperture (m)	Cooling
Spacelab Infrared Telescope (IRT)	1985	1.7–118	0.15	Helium
Infrared Space Observatory (ISO)	1995	2.5–240	0.60	Helium
Hubble Space Telescope Imaging Spectrograph (STIS)	1997	0.115–1.03	2.4	Passive
Hubble Near Infrared Camera and Multi-Object Spectrometer (NICMOS)	1997	0.8–2.4	2.4	Nitrogen, later cryocooler
Spitzer Space Telescope	2003	3–180	0.85	Helium
Hubble Wide Field Camera 3 (WFC3)	2009	0.2–1.7	2.4	Passive and thermo-electric
Herschel Space Observatory	2009	55–672	3.5	Helium
James Webb Space Telescope	2021	0.6–28.5	6.5	Passive and cryocooler (MIRI)

Webb's development experienced delays and budget increases reminiscent of those encountered by its predecessor, the Hubble Space Telescope. Initially projected to cost US$300 million in 1972, Hubble's expenses quadrupled by its launch in 1990, with total costs—including servicing missions—reaching at least US$9 billion by 2006.

Background (development to 2003)

Key milestones
Year	Event
1996	Initial proposal of the Next Generation Space Telescope project (mirror diameter: 8 m)
2001	Cancellation of the NEXUS Space Telescope, a forerunner to the Next Generation Space Telescope
2002	Project renamed James Webb Space Telescope, with mirror size reduced to 6 m
2003	Contract awarded to Northrop Grumman for telescope construction
2007	Memorandum of Understanding signed between NASA and ESA
2010	Successful completion of Mission Critical Design Review (MCDR)
2011	Consideration of project cancellation
2016	Completion of final assembly
25 Dec 2021	Launch

Planning for a successor to the Hubble Space Telescope began in earnest during the early 1990s. The Hi-Z telescope concept, developed between 1989 and 1994, envisioned a fully baffled infrared telescope with a large aperture operating at approximately 3 AU from the Sun to minimize zodiacal dust interference. Early initiatives also included the NEXUS mission as a precursor.

The need to address Hubble’s optical flaws in the early 1990s played a significant role in shaping the Webb telescope. The 1994 report from the HST & Beyond Committee advocated for a larger, colder infrared observatory capable of exploring early galaxies—surpassing Hubble’s warm telescope limitations—and recommended extending HST operations through 2005. NASA embraced this direction and began formal planning for what would evolve into the Webb telescope.

Refinements to NGST’s scientific objectives were made during preparations for the 2000 Astronomy and Astrophysics Decadal Survey, focusing on galaxy formation studies and exoplanet detection. NGST was designated as the highest priority mission in this survey.

NASA Administrator Dan Goldin promoted "faster, better, cheaper" methodologies and steered development toward segmented mirror designs to lower mass density. Ultimately, beryllium was chosen over silicon carbide for mirror fabrication.

In the mid-1990s, NGST concepts featured an aperture planned for L2 orbit with an estimated budget of US$500 million. By 1997, NASA partnered with Goddard Space Flight Center, Ball Aerospace, and TRW for technical assessments; Lockheed Martin and TRW were selected in 1999 to conduct preliminary design work. The initial launch was scheduled for 2007 but encountered multiple postponements.

In 2002, the project adopted the name James Webb Space Telescope in honor of James E. Webb, NASA’s second administrator who strongly supported scientific advancement during his leadership.

NASA awarded TRW a prime contract valued at US$824.8 million in 2003 for constructing Webb with a reduced primary mirror size and an anticipated launch in 2010. Later that year, Northrop Grumman acquired TRW, establishing Northrop Grumman Space Technology as the main contractor.

Early development and replanning (2003–2007)

NASA’s Goddard Space Flight Center led development efforts with John C. Mather serving as project scientist. Northrop Grumman Aerospace Systems acted as the principal contractor responsible for spacecraft components including the satellite bus, sunshield, Deployable Tower Assembly (DTA), and Mid Boom Assembly (MBA) used in sunshield deployment. Ball Aerospace & Technologies was subcontracted to deliver the Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM).

A cost increase identified in spring 2005 prompted a comprehensive replanning in August that year, resulting in significant modifications such as a revised integration and testing schedule, a launch delay of approximately 22 months (shifting from 2011 to 2013), and elimination of system-level testing below wavelengths of 1.7 μm. Other observatory specifications remained intact. An independent review followed in April 2006.

The replan in 2005 projected total lifecycle costs around US$4.5 billion: approximately US$3.5 billion allocated to design, development, launch, and commissioning phases, plus US$1 billion earmarked for ten years of operational expenses. ESA committed about €300 million in 2004, which included launch services. The Canadian Space Agency contributed CA$39 million in 2007, supplying critical hardware by 2012 that enabled precise telescope pointing and atmospheric characterization capabilities for exoplanet studies.

Detailed design and construction (2007–2021)

At the start of 2007, nine out of ten essential technology advancements successfully cleared a Non-Advocate Review, significantly reducing project risks and allowing progression into the detailed design phase (Phase C). The last remaining technology, the MIRI cryocooler, reached maturity by April 2007. By May that year, the project remained within its budget targets. The initiative successfully passed several critical evaluations including the Preliminary Design Review in March 2008, a Non-Advocate Review in April 2008, the Integrated Science Instrument Module review in March 2009, the Optical Telescope Element review in October 2009, and the Sunshield review in January 2010.

In April 2010, the telescope cleared its Mission Critical Design Review (MCDR), verifying compliance with all scientific and engineering mission requirements. Subsequently, an Independent Comprehensive Review Panel recommended re-planning the mission with a targeted launch date in 2015, which was later extended to as late as 2018. Despite cost overruns affecting other projects by 2010, Webb maintained its schedule.

By 2011, the project advanced into final design and manufacturing stages. Assembly of the primary mirror's hexagonal segments using a robotic arm commenced in November 2015 and concluded by February 2016; installation of the secondary mirror followed in March 2016. Final construction wrapped up in November 2016, succeeded by rigorous testing phases.

In March 2018, NASA postponed launch by two years to May 2020 due to issues with sunshield deployment; an additional delay to March 2021 was announced in June 2018 after an independent review uncovered 344 potential single-point failures—critical steps lacking recovery options—demanding flawless execution. Mechanical integration was completed in August 2019, marking a twelve-year delay from the original schedule.

Following assembly, comprehensive testing took place at Northrop Grumman's Space Park facility in California. The telescope departed California on 26 September 2021, transited through the Panama Canal, and arrived in French Guiana on 12 October 2021 in preparation for its December launch.

Cost and schedule issues

As of September 2022, NASA’s total expenditure for the project is projected to reach US$9.7 billion, with US$8.8 billion allocated to spacecraft design and development and US$861 million designated for five years of mission operations. Contributions from ESA and CSA are approximately €700 million and CA$200 million respectively.

Initial projections from the late 1990s estimated a $1 billion budget over a decade; however, significant design changes led to increased costs and delays. A Space Science Board study from 1984 had anticipated that a next-generation infrared observatory would cost around US$4 billion (equivalent to $10 billion in 2020 dollars).

Evolution of schedule and budget estimates alongside key milestones
Year	Planned launch	Budget estimate (billion USD)
1998	2007	1
2000	2009	1.8
2002	2010	2.5
2003	2011	2.5
2005	2013	3
2006	2014	4.5
2008: Preliminary Design Review
2008	2014	5.1
2010: Critical Design Review
2010	2015–2016	6.5
2011	2018	8.7
2017	2019	8.8
2018	2020	≥8.8
2019	March 2021	9.66
2021	Dec 2021	9.70

By the time of the Preliminary Design Review in 2008, expenditures exceeded US$1 billion with total budget expectations around US$5 billion (approximately $6.5 billion adjusted for inflation). After successfully passing the Critical Design Review in mid-2010, escalating schedule delays and cost overruns prompted Senator Barbara Mikulski to commission an external Independent Comprehensive Review Panel (ICRP). This panel forecasted a launch no earlier than late 2015 with an additional US$1.5 billion cost increase, raising total estimates to US$6.5 billion while warning that further postponements would inflate expenses.

In July of 2011, the House appropriations committee proposed terminating the project by cutting US$1.9 billion from NASA’s budget—about one-quarter of Webb’s funding—even though US$3 billion had already been invested and most hardware was under production. The committee cited mismanagement and budget excesses as causes for concern; however, support from the American Astronomical Society and Senator Mikulski played a pivotal role in sustaining funding. By November, Congress reversed cancellation plans and limited additional funding to US$8 billion.

The challenges with cost overruns and scheduling reflected difficulties encountered by other NASA missions such as Hubble, raising apprehensions about Webb’s influence on overall space science budgets. NASA consistently defended both the program’s financial plan and timeline amidst skepticism.

In 2018, Gregory L. Robinson assumed leadership as Webb program director and is credited with improving schedule adherence from roughly half completion to over ninety-five percent efficiency. His tenure received commendations from NASA leadership before his retirement in July 2022 following Webb’s commissioning.

NASA postponed launch dates multiple times—the final target set for late December of 2021—with corresponding increases in mission expenses. Early in 2019, the mission’s cost cap rose by US$800 million. Although COVID-19 pandemic disruptions impacted timelines, they did not prevent eventual launch.

No single cause accounted for rising costs; future large-scale telescope projects will need rigorous control over five critical factors:

System complexity management
Oversight of critical paths and administrative overhead
Verification process challenges
Programmatic constraints
Strategies emphasizing early integration and testing

Collaborative Effort

Since 1996, NASA, ESA, and CSA have worked together on the telescope project. ESA's participation in its assembly and launch received approval in 2003, followed by a formal agreement with NASA in 2007. In return for full partnership status and access for its scientific community, ESA contributed the NIRSpec instrument, the Optical Bench Assembly of the MIRI instrument, an Ariane 5 ECA launch vehicle, and ongoing operational assistance. The CSA provided the Fine Guidance Sensor, the Near-Infrared Imager Slitless Spectrograph, along with personnel support for mission operations.

The construction, testing, and integration phases engaged thousands of professionals—including scientists, engineers, and technicians—from 15 different nations. Prior to launch, the project involved 258 organizations: 142 based in the United States; 104 across 12 European countries (notably 21 from the United Kingdom, 16 from France, and 12 from Germany); and 12 from Canada. Additional contributors such as Australia have been involved in activities following launch.

Participating nations:

Controversy Over Naming

In 2002, then NASA administrator (2001–2004) Sean O'Keefe designated the telescope in honor of James E. Webb, who led NASA from 1961 to 1968 during landmark programs including Project Mercury, Project Gemini, and the Apollo programs.

Concerns arose in 2015 regarding Webb’s alleged involvement in the lavender scare, a mid-20th-century U.S. government initiative that targeted homosexual federal employees. In response, NASA conducted an extensive review in 2022, examining more than 50,000 documents. The investigation concluded there was "no available evidence directly links Webb to any actions or follow-up related to the firing of individuals for their sexual orientation" during his periods at the State Department or NASA. Despite opposition within parts of the community, NASA has chosen to retain the telescope’s name.

Scientific Objectives

The James Webb Space Telescope is designed to fulfill four key scientific aims:

capturing light emitted by the earliest stars and galaxies formed after the Big Bang
exploring processes involved in galaxy formation and evolution
investigating mechanisms of star formation and planet formation
examining planetary systems and probing questions about the origins of life

These objectives are optimally pursued through near-infrared observations rather than visible wavelengths. Unlike the Hubble Space Telescope, Webb’s suite of instruments specializes in infrared astronomy, spanning wavelengths from 0.6 to 28 μm (ranging from orange light through deep infrared).

Webb is capable of studying unusual dimming events such as those exhibited by star KIC 8462852, known for its irregular light fluctuations. Additionally, it can detect methane within exoplanet atmospheres—a potential biosignature—which is critical for evaluating their habitability.

Orbital Configuration

The telescope maintains an orbit around the Sun near the second Lagrange point () within the Sun–Earth system, situated approximately beyond Earth’s orbit—about four times farther out than the Moon. Positioned near , where gravitational forces from Earth and the Sun balance out, Webb completes a solar orbit every year synchronized with Earth’s period. This proximity facilitates more efficient data transmission.

Webb travels along a halo orbit around , inclined relative to the ecliptic, with an orbital radius ranging between and , completing a full cycle roughly every six months. Since represents a gravitational equilibrium point without net pull, Webb effectively orbits the Sun while maintaining its relative position near by controlled gradual drifting.

To maintain station-keeping requires about annually from a total ∆v budget of , utilizing two sets of thrusters mounted on the Sun-facing side. To prevent drifting beyond acceptable limits, thrust application is intentionally kept slightly below maximum—a delicate maneuver described by Integration and Test Project Scientist Randy Kimble as akin to "rolling a rock up a gentle slope without letting it roll over the crest."

Infrared astronomy

The James Webb Space Telescope (JWST) follows in the footsteps of the Hubble Space Telescope (HST) and the Spitzer Space Telescope, with a primary emphasis on infrared astronomy. It is designed to outperform its predecessors by detecting a greater number of stars and galaxies, including those from earlier cosmic epochs. Observing in the infrared spectrum is essential because of the cosmological redshift phenomenon and its capacity to penetrate obscuring dust and gas, allowing examination of fainter and cooler celestial bodies. Since Earth's atmosphere absorbs much of the infrared radiation and generates infrared background noise, ground-based infrared observations are confined to limited wavelength ranges, making a space-based observatory indispensable for comprehensive study.

Due to the universe's expansion, light emitted by distant objects shifts toward longer wavelengths, making infrared detection crucial for investigating extremely remote and youthful galaxies. Webb’s infrared instruments are tailored to capture galaxies that emerged within a few hundred million years following the Big Bang.

Infrared wavelengths can traverse cosmic dust clouds that scatter visible light, enabling detailed analysis of star-forming molecular clouds, planet-forming circumstellar disks, and energetic galactic nuclei. Objects with temperatures below several thousand kelvins predominantly emit radiation in the infrared range; thus, Webb is optimally suited to study the interstellar medium, brown dwarfs, planets both inside and beyond our solar system, comets, and Kuiper belt objects using its Mid-Infrared Instrument (MIRI).

Pioneering missions that influenced Webb’s development include the Spitzer Space Telescope and the Wilkinson Microwave Anisotropy Probe (WMAP). Spitzer underscored the significance of mid-infrared observations for phenomena such as circumstellar dust disks, while WMAP detected early universe signals at redshift 17, highlighting mid-infrared’s pivotal role. Both missions launched in the early 2000s and helped shape Webb’s scientific objectives and design.

Ground support and operations

The Space Telescope Science Institute (STScI), situated on the Homewood Campus of Johns Hopkins University in Baltimore, Maryland, was designated in 2003 as Webb’s Science and Operations Center (S&OC). An initial budget of US$162.2 million was allocated to support operations through the first year post-launch. STScI manages scientific operations for the telescope and is responsible for delivering data products to researchers worldwide. Data from Webb is relayed via the NASA Deep Space Network, then processed and calibrated at STScI before being made accessible online to astronomers globally. Mirroring Hubble’s operational model, observation proposals can be submitted by scientists worldwide; these proposals undergo annual peer review to determine selection. Researchers granted observing time generally have exclusive access for one year before their data becomes publicly available through STScI’s online archive.

Webb’s communication system supports a data transmission capacity of 458 gigabits daily (maintaining an average rate of 5.42 Mbps). The majority of onboard data processing utilizes standard single-board computers. Instrument analog signals are converted to digital form by a specialized SIDECAR ASIC (System for Image Digitization, Enhancement, Control And Retrieval Application Specific Integrated Circuit). NASA emphasizes that this ASIC consolidates all functions of a 9.1 kg instrument box into a compact 3 cm device while consuming only 11 milliwatts of power—an essential factor for preserving the telescope’s cryogenic operating conditions.

For temporary scientific data storage, Webb carries a 68 GB solid-state drive (SSD). Over its anticipated 10-year mission lifespan, this capacity is projected to reduce to approximately 60 GB due to radiation exposure and read/write wear effects.

Micrometeoroid impacts

Between 23 and 25 May 2022, the C3 segment of the primary mirror was struck by a micrometeoroid approximately the size of a large dust particle, marking the fifth and most significant impact since launch, as reported on 8 June 2022. Engineers addressed the damage by adjusting a mirror actuator to compensate for the strike. Despite this event, NASA confirmed that all observing modes of the JWST were fully operational and ready for scientific use by 10 July 2022. Typically, Webb encounters micrometeoroid impacts about once or twice monthly, with only the May 2022 collision causing appreciable harm. In response to this incident, mission teams revised observation protocols to mitigate future risks by steering clear of "micrometeoroid avoidance zones" along the telescope's orbital path.

Launch

The telescope was successfully launched as planned on 25 December 2021 at 12:20 UTC aboard an Ariane 5 rocket (flight VA256) from the Guiana Space Centre in French Guiana. Immediately after separation from the upper stage—27 minutes post-liftoff—the observatory began receiving power and entered a two-week deployment phase while traveling toward its target orbit. Its trajectory involved a 30-day maneuver to reach a Lissajous orbit around the L2 Lagrange point.

The launch velocity was slightly below what was required for the final orbit, intentionally slowing Webb during transit to enable precise insertion into L2 on 24 January 2022. Three scheduled trajectory corrections were executed to fine-tune its path, avoiding excessive thrust that could jeopardize delicate instruments or disrupt sunshield alignment.

Since the L2 orbit is inherently unstable, periodic station-keeping maneuvers using onboard fuel are necessary. The Ariane 5’s accurate launch and initial adjustments preserved sufficient propellant for an expected mission duration of ten years, with potential extension up to about two decades. Space.com characterized the launch as "flawless."

Transit and structural deployment

Following a flawless launch, Webb detached from its rocket’s upper stage 27 minutes after liftoff. Starting approximately 31 minutes later and continuing over nearly two weeks, Webb deployed critical components including its solar array, antenna, sunshield, and mirrors. Control commands predominantly originated from the Space Telescope Science Institute in Baltimore, Maryland, except for the initial automatic unfolding of solar panels and antenna deployment. The mission design allowed ground teams flexibility to modify deployment sequences if necessary.

At 7:50 p.m. EST on launch day (25 December), roughly twelve hours after liftoff, Webb’s primary propulsion system fired for 65 minutes in its first of three mid-course adjustments. On the following day, the high-gain communication antenna automatically deployed.

At about 60 hours post-launch on 27 December, Webb executed its second mid-course correction with a nine-minute and twenty-seven-second rocket burn en route to L2. The multi-day deployment of the sunshield commenced on 28 December. By 30 December, an aft "momentum flap" was extended to counterbalance solar pressure on the sunshield and reduce fuel consumption by limiting thruster use.

On 31 December, two telescoping mid booms were extended from either side of the observatory; deployment durations were three hours nineteen minutes for the left boom and three hours forty-two minutes for the right boom. Membrane separation and tensioning operations were successfully completed between 3 and 4 January. The secondary mirror was deployed and secured within approximately 1.5 millimeters tolerance on 5 January.

The final major structural deployment involved unfolding the primary mirror wings—each consisting of three segments folded for launch. NASA deployed and locked the port-side wing on 7 January, followed by the starboard wing on 8 January, completing all major structural deployments.

On 24 January 2022 at 2:00 p.m. EST—nearly one month after launch—Webb performed its third and final trajectory correction to enter its designated halo orbit around the Sun–Earth L2 point.

The MIRI instrument supports four observation modes: imaging, low-resolution spectroscopy, medium-resolution spectroscopy (MRS), and coronagraphic imaging. On August 24, NASA reported increased friction in a mechanism supporting MRS—a grating wheel responsible for selecting wavelength ranges—during preparation for an observation.

Commissioning and testing

Beginning on 12 January 2022, the process of aligning the mirrors commenced while the telescope was still en route. Over approximately ten days, both the primary mirror segments and the secondary mirror were gradually shifted from their secured launch configurations. Each of the 132 actuator motors, engineered to perform minute adjustments in increments as small as 10 nanometers, executed over 1.2 million movements (totaling 12.5 mm) during this initial positioning phase.

Achieving mirror alignment necessitated placing all 18 primary segments along with the secondary mirror within a tolerance of 50 nanometers. To illustrate this degree of precision, NASA compared it to scaling the primary mirror to the size of the United States, where each segment would be comparable to Texas and aligned within roughly 1.5 inches.

This intricate alignment procedure was segmented into seven distinct stages, all of which were rigorously practiced using a one-sixth scale model. After cooling the instruments to 120 K, NIRCam targeted the seventh-magnitude star HD 84406 located in Ursa Major. To assess the initial orientation of each primary mirror segment, NIRCam captured 1560 images. At first, misaligned segments produced eighteen blurred star images. These were identified and matched to their corresponding segments during "Segment Image Identification," then corrected for significant focusing errors through phase retrieval in "Segment Alignment," and finally combined precisely into a single image during "Image Stacking."

Further refinement achieved a functional accuracy of 50 nanometers by employing dispersed fringe sensing techniques that compared images from pairs of mirror segments ("Coarse Phasing") and introduced deliberate defocusing to detect remaining errors ("Fine Phasing"). These procedures were iterated three times and are planned for regular verification throughout operations. Following these steps, alignment was successful at one specific point within NIRCam’s field of view. The process then extended across all instruments ("Telescope Alignment Over Instrument Fields of View"), culminating in final fine phasing and image quality assessments ("Iterate Alignment for Final Correction"). At this stage, the mirror segments were fully synchronized to produce sharply focused images.

NASA announced on 3 February 2022 that NIRCam had detected the telescope’s first photons, signifying a critical milestone. By 11 February, phase one alignment was nearing completion with every primary mirror segment locating and imaging HD 84406; this phase concluded on 18 February, followed by phases two and three about a week later. Although the segments began operating collectively after these stages, achieving complete coherence as a unified mirror depended on finishing all seven phases. Meanwhile, numerous other commissioning and calibration activities for various instruments advanced simultaneously.

Allocation of observation time

Observation time on Webb is distributed through multiple programs: General Observers (GO), Guaranteed Time Observations (GTO), Director’s Discretionary Early Release Science (DD-ERS), calibration efforts, and Director’s Discretionary Time (DDT). The GTO program allocates guaranteed time to scientists involved in developing Webb’s hardware and software components, whereas the GO program—awarded via peer review by a Time Allocation Committee—provides the majority of observing time to the wider astronomical community. The DDT program is reserved for urgent observations requiring immediate attention.

Early Release Science program

In November 2017, the Space Telescope Science Institute awarded 13 Director's Discretionary Early Release Science (DD-ERS) programs following a competitive selection process. These Early Release Observations (ERO) took place within the initial five months of Webb’s science operations after commissioning. Collectively, these programs received 460 hours of observation time, addressing crucial subjects such as the Solar System, exoplanets, star formation, galaxies, gravitational lensing, and quasars. Out of this allocation, the 13 ERS initiatives utilized 242.8 hours of telescope time, not including overhead or slew durations.

Early Release Science programs
Name	Principal Investigator	Category	Observation time (hours)
Radiative Feedback from Massive Stars as Traced by Multiband Imaging and Spectroscopic Mosaics	Olivier Berné	Stellar Physics	8.3
IceAge: Chemical Evolution of Ices during Star Formation	Melissa McClure	Stellar Physics	13.4
Through the Looking GLASS: A JWST Exploration of Galaxy Formation and Evolution from Cosmic Dawn to Present Day	Tommaso Treu	Galaxies and the IGM	24.3
A JWST Study of the Starburst-AGN Connection in Merging LIRGs	Lee Armus	Galaxies and the IGM	8.7
The Resolved Stellar Populations Early Release Science Program	Daniel Weisz	Stellar Populations	20.3
Q-3D: Imaging Spectroscopy of Quasar Hosts with JWST Analyzed with a Powerful New PSF Decomposition and Spectral Analysis Package	Dominika Wylezalek	Massive Black Holes and their Galaxies	17.4
The Cosmic Evolution Early Release Science (CEERS) Survey	Steven Finkelstein	Galaxies and the IGM	36.6
Establishing Extreme Dynamic Range with JWST: Decoding Smoke Signals in the Glare of a Wolf-Rayet Binary	Ryan Lau	Stellar Physics	6.5
TEMPLATES: Targeting Extremely Magnified Panchromatic Lensed Arcs and Their Extended Star Formation	Jane Rigby	Galaxies and the IGM	26.0
Nuclear Dynamics of a Nearby Seyfert with NIRSpec Integral Field Spectroscopy	Misty Bentz	Massive Black Holes and their Galaxies	1.5
The Transiting Exoplanet Community Early Release Science Program	Natalie Batalha	Planets and Planet Formation	52.1
ERS observations of the Jovian System as a Demonstration of JWST's Capabilities for Solar System Science	Imke de Pater	Solar System	9.3
High Contrast Imaging of Exoplanets and Exoplanetary Systems with JWST	Sasha Hinkley	Planets and Planet Formation	18.4

General Observer Program

During GO Cycle 1, a total of 6,000 observation hours were allocated, while proposals totaling 24,500 hours were submitted by 1,173 applicants. On 30 March 2021, approval was granted to 266 programs, which included 13 major and treasury initiatives that offered public access to their data. The announcement for Cycle 2 of the GO program took place on 10 May 2023. Webb's observations are planned on a weekly basis, with the Space Telescope Science Institute releasing the schedule every Monday. By Cycle 4, the demand intensified dramatically, with 2,377 proposals requesting approximately 78,000 hours—about nine times the available observing time—underscoring the telescope’s significant popularity within the astronomy community.

Scientific results

Following completion of its commissioning phase, JWST commenced full scientific operations on 11 July 2022. Most experimental data remain under proprietary control for one year prior to public dissemination. Observations made by JWST have substantially enhanced understanding in areas such as exoplanet characterization, investigations into the universe’s initial billion years, and other critical astrophysical subjects. Comparing Webb’s deep-field imagery with that of Hubble reveals its superior ability to uncover cosmic features previously beyond detection.

First full-color images

The official launch of Webb’s general science operations occurred with the release of its first full-color images and spectroscopic data on 12 July 2022. The inaugural image, titled Webb's First Deep Field, was unveiled by U.S. President Joe Biden on 11 July 2022. Notable early releases comprised:

Carina Nebula – star-forming region NGC 3324, also known as the "Cosmic Cliffs".
WASP-96b – atmospheric study revealing water signatures around a giant gas exoplanet located 1,120 light-years away.
Southern Ring Nebula – structures of gas and dust emitted by an aging star approximately 2,500 light-years distant.
Stephan's Quintet – a group of five galaxies exhibiting colliding gas and dust that trigger new star formation; the four central galaxies lie about 290 million light-years away.
SMACS J0723.3-7327 – a galaxy cluster at redshift 0.39 demonstrating gravitational lensing effects; includes three primordial galaxies dating back roughly 13.1 billion years.

On 14 July 2022, NASA showcased JWST infrared images capturing Jupiter and its environment, emphasizing the telescope’s capabilities for solar system exploration.

A simultaneous preprint authored by scientists from NASA, ESA, and CSA confirmed that JWST’s scientific performance surpassed expectations. Its instruments acquired exoplanet spectra with precision exceeding 1000 parts per million per data point and successfully tracked objects moving at velocities more than twice the required minimum. The telescope also secured spectra from hundreds of stars near the Milky Way’s Galactic Center. Additional observation targets included:

Moving bodies: Jupiter's rings and moons such as Europa, Thebe, Metis, along with asteroids including 2516 Roman, 216 Kleopatra, and 4015 Wilson-Harrington.
Exoplanets: Jupiter-sized HAT-P-14b observed using NIRCam grism time-series, NIRISS SOSS mode, and NIRSpec BOTS mode.
NIRISS aperture masking interferometry (AMI): identification of a low-mass companion star, AB Doradus C, at a separation of 0.3 arcseconds—marking the first demonstration of AMI from space.
MIRI low-resolution spectroscopy: investigation of hot super-Earth L 168-9 b, orbiting a luminous red dwarf star.

Early luminous galaxies

Within just a fortnight following the release of Webb's initial images, multiple preprints emerged highlighting a variety of highly luminous galaxies at extreme redshifts, dating between 235 and 280 million years after the Big Bang—significantly earlier than any previously identified. On 17 August 2022, NASA unveiled an extensive mosaic composed of 690 frames captured by Webb's NIRCam, revealing numerous primordial galaxies. Some objects, such as CEERS-93316, were initially assigned a photometric redshift of z=16.7 (corresponding to roughly 235.8 million years after the Big Bang), but subsequent spectroscopic measurements revised this estimate to about z=4.91.

In September 2022, the concept of primordial black holes was introduced as a potential explanation for the existence of these unexpectedly massive early galaxies. By May 2024, JWST discovered the most distant galaxy known to date, JADES-GS-z14-0, observed at redshift 14.32, approximately 290 million years post-Big Bang. This galaxy is part of the JWST Advanced Deep Extragalactic Survey (JADES) and exhibits luminosity and mass far exceeding expectations for its era. Comprehensive investigations using JWST's NIRSpec and MIRI instruments revealed its substantial size and dust content, posing challenges to current theories on the formation of early galaxies.

Additional significant findings and analyses

In June 2023, organic molecules were identified in the SPT0418-47 galaxy located 12 billion light-years away.

NASA celebrated Webb’s inaugural year on 12 July 2023 by releasing an image showcasing a star-forming region within the Rho Ophiuchi cloud complex, situated roughly 390 light-years from Earth.

During December 2023, NASA published holiday-themed imagery from JWST, including visuals of the Christmas Tree Galaxy Cluster.

By May 2024, JWST detected the most remote black hole merger recorded so far within the galaxy system ZS7, which took place about 740 million years after the Big Bang. This discovery suggests that black holes underwent rapid growth via mergers in the Universe’s early stages.

External links

Official NASA / STScI / ESA / French portals
JWST NASA – Tracking from Launch to Final Calibration
JWST NASA – Overview: Timeline, orbit details, L2 location, communications
Key Milestones for JWST Launch and Deployment (2021)
JWST Video (31:22): Engineering Highlights (2021)
JWST Video (12:02): First Month – Launch and Deployment Animation (2017)
JWST Video (8:06): First Month Update (2021)
JWST Video (3:00): Second Month Mirror Alignment (Feb 2022)
Live coverage of JWST Mission Control deployment events (2022):