Image: Artist’s impression of the James Webb Space Telescope pillars

The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. Its high-resolution and high-sensitivity instruments allow it to view objects too old, distant, or faint for the Hubble Space Telescope. This enables investigations across many fields of astronomy and cosmology, such as observation of the first stars and the formation of the first galaxies, and detailed atmospheric characterization of potentially habitable exoplanets.

The Webb was launched on 25 December 2021 on an Ariane 5 rocket from Kourou, French Guiana. In January 2022 it arrived at its destination, a solar orbit near the Sun–Earth L₂ Lagrange point, about 1.5 million kilometers (930,000 mi) from Earth. The telescope’s first image was released to the public on 11 July 2022.

The U.S. National Aeronautics and Space Administration (NASA) led Webb’s design and development and partnered with two main agencies: the European Space Agency (ESA) and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center (GSFC) in Maryland managed telescope development, while the Space Telescope Science Institute in Baltimore on the Homewood Campus of Johns Hopkins University operates Webb. The primary contractor for the project was Northrop Grumman.

The telescope is named after James E. Webb, who was the administrator of NASA from 1961 to 1968 during the Mercury, Gemini, and Apollo programs.

Webb’s primary mirror consists of 18 hexagonal mirror segments made of gold-plated beryllium, which together create a 6.5-meter-diameter (21 ft) mirror, compared with Hubble’s 2.4 m (7 ft 10 in). This gives Webb a light-collecting area of about 25 square meters, about six times that of Hubble. Unlike Hubble, which observes in the near ultraviolet and visible (0.1 to 0.8 μm), and near-infrared (0.8–2.5 μm) spectra, Webb observes a lower frequency range, from long-wavelength visible light (red) through mid-infrared (0.6–28.3 μm). The telescope must be kept extremely cold, below 50 K (−223 °C; −370 °F), so that the infrared light emitted by the telescope itself does not interfere with the collected light. Its five-layer sun shield protects it from warming by the Sun, Earth, and Moon.

Initial designs for the telescope, then named the Next Generation Space Telescope, began in 1996. Two concept studies were commissioned in 1999, for a potential launch in 2007 and a US$1 billion budget. The program was plagued with enormous cost overruns and delays. A major redesign was accomplished in 2005, with construction completed in 2016, followed by years of exhaustive testing, at a total cost of US$10 billion.

Features

The mass of the James Webb Space Telescope is about half that of the Hubble Space Telescope. Webb has a 6.5 m (21 ft)-diameter gold-coated beryllium primary mirror made up of 18 separate hexagonal mirrors. The mirror has a polished area of 26.3 m² (283 sq ft), of which 0.9 m² (9.7 sq ft) is obscured by the secondary support struts, giving a total collecting area of 25.4 m² (273 sq ft). This is over six times larger than the collecting area of Hubble’s 2.4 m (7.9 ft) diameter mirror, which has a collecting area of 4.0 m² (43 sq ft). The mirror has a gold coating to provide infrared reflectivity and this is covered by a thin layer of glass for durability.

Webb is designed primarily for near-infrared astronomy, but can also see orange and red visible light, as well as the mid-infrared region, depending on the instrument being used. It can detect objects up to 100 times fainter than Hubble can, and objects much earlier in the history of the universe, back to redshift z≈20 (about 180 million years cosmic time after the Big Bang). For comparison, the earliest stars are thought to have formed between z≈30 and z≈20 (100–180 million years cosmic time), and the first galaxies may have formed around redshift z≈15 (about 270 million years cosmic time). Hubble is unable to see further back than very early reionization at about z≈11.1 (galaxy GN-z11, 400 million years cosmic time).

The design emphasizes the near to mid-infrared for several reasons:

• high-redshift (very early and distant) objects have their visible emissions shifted into the infrared, and therefore their light can be observed only via infrared astronomy;
• infrared light passes more easily through dust clouds than visible light;
• colder objects such as debris disks and planets emit most strongly in the infrared;
• these infrared bands are difficult to study from the ground or by existing space telescopes such as Hubble.

Ground-based telescopes must look through Earth’s atmosphere, which is opaque in many infrared bands. Even where the atmosphere is transparent, many of the target chemical compounds, such as water, carbon dioxide, and methane, also exist in the Earth’s atmosphere, vastly complicating analysis. Existing space telescopes such as Hubble cannot study these bands since their mirrors are insufficiently cool (the Hubble mirror is maintained at about 15 °C [288 K; 59 °F]) which means that the telescope itself radiates strongly in the relevant infrared bands.

Webb can also observe objects in the Solar System at an angle of more than 85° from the Sun and has an apparent angular rate of motion of less than 0.03 arc seconds per second. This includes Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, their satellites, comets, asteroids, and minor planets at or beyond the orbit of Mars. Webb has the near-IR and mid-IR sensitivity to be able to observe virtually all known Kuiper Belt Objects. In addition, it can observe opportunistic and unplanned targets within 48 hours of a decision to do so, such as supernovae and gamma-ray bursts.

Location and orbit

Webb operates in a halo orbit, circling a point in space known as the Sun–Earth L₂ Lagrange point, approximately 1,500,000 km (930,000 mi) beyond Earth’s orbit around the Sun. Its actual position varies between about 250,000 and 832,000 km (155,000–517,000 mi) from L₂ as it orbits, keeping it out of both Earth and Moon’s shadow. By way of comparison, Hubble orbits 550 km (340 mi) above the Earth’s surface, and the Moon is roughly 400,000 km (250,000 mi) from Earth. Objects near this Sun–Earth L₂ point can orbit the Sun in synchrony with the Earth, allowing the telescope to remain at a roughly constant distance with the continuous orientation of its sun shield and equipment bus toward the Sun, Earth, and Moon. Combined with its wide shadow-avoiding orbit, the telescope can simultaneously block incoming heat and light from all three of these bodies and avoid even the smallest changes of temperature from Earth and Moon shadows that would affect the structure, yet still maintain uninterrupted solar power and Earth communications on its sun-facing side. This arrangement keeps the temperature of the spacecraft constant and below the 50 K (−223 °C; −370 °F) necessary for faint infrared observations.

Sunshield protection

To make observations in the infrared spectrum, Webb must be kept under 50 K (−223.2 °C; −369.7 °F); otherwise, infrared radiation from the telescope itself would overwhelm its instruments. Its large sun-shield blocks light and heat from the Sun, Earth, and Moon, and its position near the Sun–Earth L₂ keeps all three bodies on the same side of the spacecraft at all times. Its halo orbit around the L₂ point avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield and solar arrays. The resulting stable temperature for the structures on the dark side is critical to maintaining precise alignment of the primary mirror segments.

The five-layer sun-shield, each layer as thin as a human hair, is made of Kapton E film, coated with aluminum on both sides and a layer of doped silicon on the Sun-facing side of the two hottest layers to reflect the Sun’s heat into space. Accidental tears of the delicate film structure during deployment testing in 2018 led to further delays in the telescope deployment.

The sun shield was designed to be folded twelve times so that it would fit within the Ariane 5 rocket’s payload fairing, which is 4.57 m (15.0 ft) in diameter, and 16.19 m (53.1 ft) long. The shield’s fully deployed dimensions were planned as 14.162 m × 21.197 m (46.46 ft × 69.54 ft).

Keeping within the shadow of the sun shield limits the field of regard, Webb, at any given time. The telescope can see 40 percent of the sky from any one position but can see all of the sky over six months.

Optics

Webb’s primary mirror is a 6.5 m (21 ft)-diameter gold-coated beryllium reflector with a collecting area of 25.4 m² (273 sq ft). If it had been designed as a single, large mirror, it would have been too large for existing launch vehicles. The mirror is therefore composed of 18 hexagonal segments (a technique pioneered by Guido Horn d’Arturo), which unfolded after the telescope was launched. Image plane wavefront sensing through phase retrieval is used to position the mirror segments in the correct location using precise actuators. After this initial configuration, they only need occasional updates every few days to retain optimal focus. This is unlike terrestrial telescopes, for example, the Keck telescopes, which continually adjust their mirror segments using active optics to overcome the effects of gravitational and wind loading. The Webb telescope uses 132 small actuation motors to position and adjust the optics. The actuators can position the mirror with 10 nanometer accuracy.

Webb’s optical design is a three-mirror anastigmat, which makes use of curved secondary and tertiary mirrors to deliver images that are free from optical aberrations over a wide field. The secondary mirror is 0.74 m (2.4 ft) in diameter. In addition, there is a fine steering mirror that can adjust its position many times per second to provide image stabilization. Photographs taken by Webb have six spikes plus two fainter ones due to the spider supporting the secondary mirror.

Scientific instruments

 

The Integrated Science Instrument Module (ISIM) is a framework that provides electrical power, computing resources, cooling capability as well as structural stability to the Webb telescope. It is made with bonded graphite-epoxy composite attached to the underside of Webb’s telescope structure. The ISIM holds the four science instruments and a guide camera.

• NIRCam (Near Infrared Camera) is an infrared imager that has spectral coverage ranging from the edge of the visible (0.6 μm) through to the near-infrared (5 μm). There are 10 sensors each of 4 megapixels. NIRCam serves as the observatory’s wavefront sensor, which is required for wavefront sensing and control activities, used to align and focus the main mirror segments. NIRCam was built by a team led by the University of Arizona, with principal investigator Marcia J. Rieke.

• NIRSpec (Near Infrared Spectrograph) performs spectroscopy over the same wavelength range. It was built by the European Space Agency at ESTEC in Noordwijk, Netherlands. The leading development team includes members from Airbus Defence and Space, Ottobrunn and Friedrichshafen, Germany, and the Goddard Space Flight Center; with Pierre Ferruit (École normale supérieure de Lyon) as NIRSpec project scientist. The NIRSpec design provides three observing modes: a low-resolution mode using a prism, an R~1000 multi-object mode, and an R~2700 integral field unit or long-slit spectroscopy mode. Switching of the modes is done by operating a wavelength preselection mechanism called the Filter Wheel Assembly, and selecting a corresponding dispersive element (prism or grating) using the Grating Wheel Assembly mechanism. Both mechanisms are based on the successful ISOPHOT wheel mechanisms of the Infrared Space Observatory. The multi-object mode relies on a complex micro-shutter mechanism to allow for simultaneous observations of hundreds of individual objects anywhere in NIRSpec’s field of view. There are two sensors, each of 4 megapixels.

• MIRI (Mid-Infrared Instrument) measures the mid-to-long-infrared wavelength range from 5 to 27 μm. It contains both a mid-infrared camera and an imaging spectrometer. MIRI was developed as a collaboration between NASA and a consortium of European countries and is led by George Rieke (University of Arizona) and Gillian Wright (UK Astronomy Technology Centre, Edinburgh, Scotland). The temperature of the MIRI must not exceed 6 K (−267 °C; −449 °F): a helium gas mechanical cooler sited on the warm side of the environmental shield provides this cooling.

 

• FGS/NIRISS (Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph), led by the Canadian Space Agency under project scientist John Hutchings (Herzberg Astronomy and Astrophysics Research Centre), is used to stabilize the line-of-sight of the observatory during science observations. Measurements by the FGS are used both to control the overall orientation of the spacecraft and to drive the fine steering mirror for image stabilization. The Canadian Space Agency also provided a Near Infrared Imager and Slitless Spectrograph (NIRISS) module for astronomical imaging and spectroscopy in the 0.8 to 5 μm wavelength range, led by principal investigator René Doyon at the Université de Montréal. Although they are often referred to together as a unit, the NIRISS and FGS serve entirely different purposes, with one being a scientific instrument and the other being a part of the observatory’s support infrastructure.

NIRCam and MIRI feature starlight-blocking coronagraphs for observation of faint targets such as extrasolar planets and circumstellar disks very close to bright stars.

Spacecraft bus

The spacecraft bus is the primary support component of the James Webb Space Telescope, hosting a multitude of computing, communication, electric power, propulsion, and structural parts. Along with the sunshield, it forms the spacecraft element of the space telescope. The spacecraft bus is on the Sun-facing “warm” side of the sunshield and operates at a temperature of about 300 K (27 °C; 80 °F).

The structure of the spacecraft bus has a mass of 350 kg (770 lb), and must support the 6,200 kg (13,700 lb) space telescope. It is made primarily of graphite composite material. The assembly was completed in California in 2015. It was integrated with the rest of the space telescope leading to its 2021 launch. The spacecraft bus can rotate the telescope with a pointing precision of one arcsecond and isolates vibration to two milliarcseconds.

Webb has two pairs of rocket engines (one pair for redundancy) to make course corrections on the way to L₂ and for station keeping – maintaining the correct position in the halo orbit. Eight smaller thrusters are used for attitude control – the correct pointing of the spacecraft. The engines use hydrazine fuel (159 liters or 42 U.S. gallons at launch) and dinitrogen tetroxide as oxidizer (79.5 liters or 21.0 U.S. gallons at launch).

Servicing

Webb is not intended to be serviced in space. A crewed mission to repair or upgrade the observatory, as was done for Hubble, would not be possible, and according to NASA Associate Administrator Thomas Zurbuchen, despite best efforts, an uncrewed remote mission was found to be beyond available technology at the time Webb was designed. During the long Webb testing period, NASA officials referred to the idea of a servicing mission, but no plans were announced. Since the successful launch, NASA has stated that nevertheless limited accommodation was made to facilitate future servicing missions. These accommodations included precise guidance markers in the form of crosses on the surface of Webb, for use by remote servicing missions, as well as refillable fuel tanks, removable heat protectors, and accessible attachment points.

Software

Ilana Dashevsky and Vicki Balzano write that Webb uses a modified version of JavaScript, called Nombas ScriptEase 5.00e, for its operations; it follows the ECMAScript standard and “allows for a modular design flow, where onboard scripts call lower-level scripts that are defined as functions”. “The JWST science operations will be driven by ASCII (instead of binary command blocks) on-board scripts, written in a customized version of JavaScript. The script interpreter is run by the flight software, which is written in the programming language C++. The flight software operates the spacecraft and the science instruments.”

Comparison with other telescopes

The desire for a large infrared space telescope traces back decades. In the United States, the Space Infrared Telescope Facility (later called the Spitzer Space Telescope) was planned while the Space Shuttle was in development, and the potential for infrared astronomy was acknowledged at that time. Unlike ground telescopes, space observatories are free from atmospheric absorption of infrared light. Space observatories opened a “new sky” for astronomers.

However, there is a challenge involved in the design of infrared telescopes: they need to stay extremely cold, and the longer the wavelength of infrared, the colder they need to be. If not, the background heat of the device itself overwhelms the detectors, making it effectively blind. This can be overcome by careful design. One method is to put the key instruments in a dewar with an extremely cold substance, such as liquid helium. The coolant will slowly vaporize, limiting the lifetime of the instrument from as short as a few months to a few years at most.

It is also possible to maintain a low temperature by designing the spacecraft to enable near-infrared observations without a supply of coolant, as with the extended missions of the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer, which operated at reduced capacity after coolant depletion. Another example is Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument, which started out using a block of nitrogen ice that depleted after a couple of years but was then replaced during the STS-109 servicing mission with a cryocooler that worked continuously. The Webb Space Telescope is designed to cool itself without a dewar, using a combination of sunshields and radiators, with the mid-infrared instrument using an additional cryocooler.

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 delays and cost increases have been compared to those of its predecessor, the Hubble Space Telescope. When Hubble formally started in 1972, it had an estimated development cost of US$300 million (equivalent to $2,098,807,000 in 2022), but by the time it was sent into orbit in 1990, the cost was about four times that. In addition, new instruments and servicing missions increased the cost to at least US$9 billion by 2006 (equivalent to $13,064,708,000 in 2022).

Development history

Background (development to 2003)

Major Milestones

Year	Milestone
1996	Next Generation Space Telescope project first proposed (mirror size: 8 m)
2001	NEXUS Space Telescope, a precursor to the Next Generation Space Telescope, cancelled
2002	Proposed project renamed James Webb Space Telescope, (mirror size reduced to 6 m)
2003	Northrop Grumman awarded contract to build telescope
2007	Memorandum of Understanding signed between NASA and ESA
2010	Mission Critical Design Review (MCDR) passed
2011	Proposed cancellation
2016	Final assembly completed
25 December 2021	Launch

Discussions of a Hubble follow-on started in the 1980s, but serious planning began in the early 1990s. The Hi-Z telescope concept was developed between 1989 and 1994: a fully baffled 4 m (13 ft) aperture infrared telescope that would recede to an orbit at 3 Astronomical unit (AU). This distant orbit would have benefited from reduced light noise from zodiacal dust. Other early plans called for a NEXUS precursor telescope mission.

Correcting the flawed optics of the Hubble Space Telescope (HST) in its first years played a significant role in the birth of Webb. In 1993, NASA conducted STS-61, the Space Shuttle mission that replaced HST’s camera and installed a retrofit for its imaging spectrograph to compensate for the spherical aberration in its primary mirror.

The HST & Beyond Committee was formed in 1994 “to study possible missions and programs for optical-ultraviolet astronomy in space for the first decades of the 21st century.” Emboldened by HST’s success, its 1996 report explored the concept of a larger and much colder, infrared-sensitive telescope that could reach back in cosmic time to the birth of the first galaxies. This high-priority science goal was beyond the HST’s capability because, as a warm telescope, it is blinded by infrared emission from its optical system. In addition to recommendations to extend the HST mission to 2005 and to develop technologies for finding planets around other stars, NASA embraced the chief recommendation of HST & Beyond for a large, cold space telescope (radiatively cooled far below 0 °C), and began the planning process for the future Webb telescope.

Preparation for the 2000 Astronomy and Astrophysics Decadal Survey (a literature review produced by the United States National Research Council that includes identifying research priorities and making recommendations for the upcoming decade) included further development of the scientific program for what became known as the Next Generation Space Telescope and advancements in relevant technologies by NASA. As it matured, studying the birth of galaxies in the young universe, and searching for planets around other stars – the prime goals coalesced as “Origins” by HST & Beyond became prominent.

As hoped, the NGST received the highest ranking in the 2000 Decadal Survey.

An administrator of NASA, Dan Goldin, coined the phrase “faster, better, cheaper”, and opted for the next big paradigm shift for astronomy, namely, breaking the barrier of a single mirror. That meant going from “eliminate moving parts” to “learn to live with moving parts” (i.e. segmented optics). To reduce mass density tenfold, silicon carbide with a very thin layer of glass on top was first looked at, but beryllium was selected at the end.

The mid-1990s era of “faster, better, cheaper” produced the NGST concept, with an 8 m (26 ft) aperture to be flown to L₂, roughly estimated to cost US$500 million. In 1997, NASA worked with the Goddard Space Flight Center, Ball Aerospace & Technologies, and TRW to conduct technical requirement and cost studies of the three different concepts, and in 1999 selected Lockheed Martin and TRW for preliminary concept studies. Launch was at that time planned for 2007, but the launch date was pushed back many times (see table further down).

In 2002, the project was renamed after NASA’s second administrator (1961–1968), James E. Webb (1906–1992).Webb led the agency during the Apollo program and established scientific research as a core NASA activity.

In 2003, NASA awarded TRW the US$824.8 million prime contract for Webb. The design called for a de-scoped 6.1 m (20 ft) primary mirror and a launch date of 2010. Later that year, TRW was acquired by Northrop Grumman in a hostile bid and became Northrop Grumman Space Technology.

Early development and replanning (2003–2007)

Development was managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with John C. Mather as its project scientist. The primary contractor was Northrop Grumman Aerospace Systems, responsible for developing and building the spacecraft element, which included the satellite bus, sun shield, Deployable Tower Assembly (DTA) which connects the Optical Telescope Element to the spacecraft bus, and the Mid Boom Assembly (MBA) which helps to deploy the large sun shields on orbit, while Ball Aerospace & Technologies was subcontracted to develop and build the OTE itself, and the Integrated Science Instrument Module (ISIM).

Cost growth revealed in spring 2005 led to an August 2005 re-planning. The primary technical outcomes of the re-planning were significant changes in the integration and test plans, a 22-month launch delay (from 2011 to 2013), and elimination of system-level testing for observatory modes at wavelengths shorter than 1.7 μm. Other major features of the observatory were unchanged. Following the re-planning, the project was independently reviewed in April 2006.

In the 2005 re-plan, the life-cycle cost of the project was estimated at US$4.5 billion. This comprised approximately US$3.5 billion for design, development, launch and commissioning, and approximately US$1.0 billion for ten years of operations. The ESA agreed in 2004 to contributing about €300 million, including the launch. The Canadian Space Agency pledged CA$39 million in 2007 and in 2012 delivered its contributions in equipment to point the telescope and detect atmospheric conditions on distant planets.

Detailed design and construction (2007–2021)

In January 2007, nine of the ten technology development items in the project successfully passed a Non-Advocate Review. These technologies were deemed sufficiently mature to retire significant risks in the project. The remaining technology development item (the MIRI cryocooler) completed its technology maturation milestone in April 2007. This technology review represented the beginning step in the process that ultimately moved the project into its detailed design phase (Phase C). By May 2007, costs were still on target. In March 2008, the project completed its Preliminary Design Review (PDR). In April 2008, the project passed the Non-Advocate Review. Other passed reviews include the Integrated Science Instrument Module review in March 2009, the Optical Telescope Element review completed in October 2009, and the Sunshield review completed in January 2010.

In April 2010, the telescope passed the technical portion of its Mission Critical Design Review (MCDR). Passing the MCDR signified the integrated observatory can meet all science and engineering requirements for its mission. The MCDR encompassed all previous design reviews. The project schedule underwent review during the months following the MCDR, in a process called the Independent Comprehensive Review Panel, which led to a re-plan of the mission aiming for a 2015 launch, but as late as 2018. By 2010, cost over-runs were impacting other projects, though Webb itself remained on schedule.

By 2011, the Webb project was in the final design and fabrication phase (Phase C).

Assembly of the hexagonal segments of the primary mirror, which was done via a robotic arm, began in November 2015 and was completed on 3 February 2016. The secondary mirror was installed on 3 March 2016. The final construction of the Webb telescope was completed in November 2016, after which extensive testing procedures began.

In March 2018, NASA delayed Webb’s launch an additional 2 years to May 2020 after the telescope’s sunshield ripped during a practice deployment and the sun-shield’s cables did not sufficiently tighten. In June 2018, NASA delayed the launch by an additional 10 months to March 2021, based on the assessment of the independent review board convened after the failed March 2018 test deployment. The review identified that Webb’s launch and deployment had 344 potential single-point failures – tasks that had no alternative or means of recovery if unsuccessful, and therefore had to succeed for the telescope to work. In August 2019, the mechanical integration of the telescope was completed, something that was scheduled to be done 12 years before in 2007.

After construction was completed, Webb underwent final tests at Northrop Grumman’s historic Space Park in Redondo Beach, California. A ship carrying the telescope left California on 26 September 2021, passed through the Panama Canal, and arrived in French Guiana on 12 October 2021.

Cost and schedule issues

NASA’s lifetime cost for the project is expected to be US$9.7 billion, of which US$8.8 billion was spent on spacecraft design and development and US$861 million is planned to support five years of mission operations. Representatives from ESA and CSA stated their project contributions amount to approximately €700 million and CA$200 million, respectively.

A study in 1984 by the Space Science Board estimated that building a next-generation infrared observatory in orbit would cost US$4 billion (US$7B in 2006 dollars, or $10B in 2020 dollars). While this came close to the final cost of Webb, the first NASA design considered in the late 1990s was more modest, aiming for a $1 billion price tag over 10 years of construction. Over time this design expanded, added funding for contingencies, and had scheduling delays.

Progression of estimates for schedule and cost, along with major milestones

Year	Planned launch	Budget plan (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 to 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 2008, when the project entered preliminary design review and was formally confirmed for construction, over US$1 billion had already been spent on developing the telescope, and the total budget was estimated at US$5 billion (equivalent to $7.49 billion in 2022). In the summer of 2010, the mission passed its Critical Design Review (CDR) with excellent grades on all technical matters, but schedule and cost slips at that time prompted Maryland U.S. Senator Barbara Mikulski to call for an external review of the project. The Independent Comprehensive Review Panel (ICRP) chaired by J. Casani (JPL) found that the earliest possible launch date was in late 2015 at an extra cost of US$1.5 billion (for a total of US$6.5 billion). They also pointed out that this would have required extra funding in FY2011 and FY2012 and that any later launch date would lead to a higher total cost.

On 6 July 2011, the United States House of Representatives Appropriations Committee on Commerce, Justice, and Science moved to cancel the James Webb project by proposing an FY2012 budget that removed US$1.9 billion from NASA’s overall budget, of which roughly one quarter was for Webb. US$3 billion had been spent and 75% of its hardware was in production. This budget proposal was approved by a subcommittee vote the following day. The committee charged that the project was “billions of dollars over budget and plagued by poor management”.  In response, the American Astronomical Society stated support of Webb, as did Senator Mikulski. Several editorials supporting Webb appeared in the international press during 2011 as well. In November 2011, Congress reversed plans to cancel Webb and instead capped additional funding to complete the project at US$8 billion.

While similar issues had affected other major NASA projects such as the Hubble telescope, some scientists expressed concerns about growing costs and schedule delays for the Webb telescope, worrying that its budget might be competing with those of other space science programs. A 2010 Nature article described Webb as “the telescope that ate astronomy”. NASA continued to defend the budget and timeline of the program to Congress.

In 2018, Gregory L. Robinson was appointed as the new director of the Webb program. Robinson was credited with raising the program’s schedule efficiency (how many measures were completed on time) from 50% to 95%. For his role in improving the performance of the Webb program, Robinsons’s supervisor, Thomas Zurbuchen, called him “the most effective leader of a mission I have ever seen in the history of NASA.” In July 2022, after Webb’s commissioning process was complete and it began transmitting its first data, Robinson retired following a 33-year career at NASA.

On 27 March 2018, NASA pushed back the launch to May 2020 or later, with a final cost estimate to come after a new launch window was determined with the European Space Agency (ESA). In 2019, its mission cost cap was increased by US$800 million. After launch windows were paused in 2020 due to the COVID-19 pandemic, Webb was launched at the end of 2021, with a total budget of just under US$10 billion.

Partnership

NASA, ESA, and CSA have collaborated on the telescope since 1996. ESA’s participation in construction and launch was approved by its members in 2003 and an agreement was signed between ESA and NASA in 2007. In exchange for full partnership, representation, and access to the observatory for its astronomers, ESA is providing the NIRSpec instrument, the Optical Bench Assembly of the MIRI instrument, an Ariane 5 ECA launcher, and manpower to support operations. The CSA provided the Fine Guidance Sensor the Near-Infrared Imager Slitless Spectrograph and manpower to support operations.

Several thousand scientists, engineers, and technicians spanning 15 countries have contributed to the build, test, and integration of Webb. A total of 258 companies, government agencies, and academic institutions participated in the pre-launch project; 142 from the United States, 104 from 12 European countries (including 21 from the U.K., 16 from France, 12 from Germany, and 7 international), and 12 from Canada. Other countries as NASA partners, such as Australia, were involved in the post-launch operation.

Participating countries:

Naming concerns

In 2002, NASA administrator (2001–2004) Sean O’Keefe decided to name the telescope after James E. Webb, the administrator of NASA from 1961 to 1968 during the Mercury, Gemini, and much of the Apollo programs.

In 2015, concerns were raised around Webb’s possible role in the lavender scare, the mid-20th-century persecution by the U.S. government targeting homosexuals in federal employment. In 2022, NASA released a report of an investigation, based on an examination of more than 50,000 documents. The report found “no available evidence directly links Webb to any actions or follow-up related to the firing of individuals for their sexual orientation”, either in his time in the State Department or at NASA.

Mission goals

The James Webb Space Telescope has four key goals:

• to search for light from the first stars and galaxies that formed in the universe after the Big Bang
• to study galaxy formation and evolution
• to understand star formation and planet formation
• to study planetary systems and the origins of life

These goals can be accomplished more effectively by observation in near-infrared light rather than light in the visible part of the spectrum. For this reason, Webb’s instruments will not measure visible or ultraviolet light like the Hubble Telescope, but will have a much greater capacity to perform infrared astronomy. Webb will be sensitive to a range of wavelengths from 0.6 to 28 μm (corresponding respectively to orange light and deep infrared radiation at about 100 K or −173 °C).

Webb may be used to gather information on the dimming light of star KIC 8462852, which was discovered in 2015, and has some abnormal light-curve properties.

Additionally, it will be able to tell if an exoplanet has methane in its atmosphere, allowing astronomers to determine whether or not the methane is a biosignature.

Orbit design

Webb orbits the Sun near the second Lagrange point (L₂) of the Sun–Earth system, which is 1,500,000 km (930,000 mi) farther from the Sun than the Earth’s orbit, and about four times farther than the Moon’s orbit. Normally an object circling the Sun farther out than Earth would take longer than one year to complete its orbit. But near the L₂ point, the combined gravitational pull of the Earth and the Sun allows a spacecraft to orbit the Sun in the same time that it takes the Earth. Staying close to Earth allows data rates to be much faster for a given size of antenna.

The telescope circles about the Sun–Earth L₂ point in a halo orbit, which is inclined concerning the ecliptic, has a radius varying between about 250,000 km (160,000 mi) and 832,000 km (517,000 mi) and takes about half a year to complete. Since L₂ is just an equilibrium point with no gravitational pull, a halo orbit is not an orbit in the usual sense: the spacecraft is actually in orbit around the Sun, and the halo orbit can be thought of as controlled drifting to remain in the vicinity of the L₂ point. This requires some station-keeping: around 2.5 m/s per year from the total ∆v budget of 93 m/s. Two sets of thrusters constitute the observatory’s propulsion system. Because the thrusters are located solely on the Sun-facing side of the observatory, all station-keeping operations are designed to slightly undershoot the required amount of thrust to avoid pushing Webb beyond the semi-stable L₂ point, a situation that would be unrecoverable. Randy Kimble, the Integration and Test Project Scientist for the James Webb Space Telescope, compared the precise station-keeping of Webb to “Sisyphus […] rolling this rock up the gentle slope near the top of the hill – we never want it to roll over the crest and get away from him”.