James Webb Space Telescope

James Webb Space Telescope

A rendering of the James Webb Space Telescope with its components fully deployed.
Names	Next Generation Space Telescope (NGST; 1996–2002)
Mission type	Astronomy
Operator	STScI (NASA)
COSPAR ID	2021-130A
SATCAT no.	50463
Website	Official website
Mission duration	10 years (planned) 2 years, 5 months, 14 days (elapsed)
Spacecraft properties
Manufacturer	Northrop Grumman Ball Aerospace L3Harris
Launch mass	6,161.4 kg (13,584 lb)
Dimensions	20.197 m × 14.162 m (66.26 ft × 46.46 ft), sunshield
Power	2 kW
Start of mission
Launch date	25 December 2021 (2021-12-25), 12:20 UTC
Rocket	Ariane 5 ECA (VA256)
Launch site	Centre Spatial Guyanais, ELA-3
Contractor	Arianespace
Orbital parameters
Reference system	Sun–Earth L2 orbit
Regime	Halo orbit
Periapsis altitude	250,000 km (160,000 mi)
Apoapsis altitude	832,000 km (517,000 mi)
Inclination	4.0560
Period	6 months
Main telescope
Type	Korsch telescope
Diameter	6.5 m (21 ft)
Focal length	131.4 m (431 ft)
Focal ratio	f/20.2
Collecting area	25.4 m2 (273 sq ft)
Wavelengths	0.6–28.3 μm (orange to mid-infrared)
Transponders
Band	S-band, telemetry, tracking, and control Ka-band, data acquisition
Bandwidth	S-band up: 16 kbit/s S-band down: 40 kbit/s Ka-band down: up to 28 Mbit/s
Instruments
FGS-NIRISS MIRI NIRCam NIRSpec
Elements
Integrated Science Instrument Module Optical Telescope Element Spacecraft (Bus and Sunshield)
James Webb Space Telescope mission logo

The James Webb Space Telescope (JWST) is a space telescope developed by NASA with contributions from the European Space Agency (ESA), and the Canadian Space Agency (CSA). The telescope is named after James E. Webb, who was the administrator of NASA from 1961 to 1968 and played an integral role in the Apollo program. It is intended to succeed the Hubble Space Telescope as NASA's flagship mission in astrophysics. JWST was launched 25 December 2021 on Ariane flight VA256. It is designed to provide improved infrared resolution and sensitivity over Hubble, and will enable a broad range of investigations across the fields of astronomy and cosmology, including observations of some of the most distant events and objects in the Universe such as the formation of the first galaxies, and allowing detailed atmospheric characterization of potentially habitable exoplanets.

JWST's primary mirror, the Optical Telescope Element, consists of 18 hexagonal mirror segments made of gold-plated beryllium which combine to create a 6.5 meter (21 ft 4 inch) diameter mirror – considerably larger than Hubble's 2.4 m (7.9 ft) mirror. Unlike Hubble, which observes in the near ultraviolet, visible, and near infrared (0.1–1.0 μm) spectra, JWST will observe in a lower frequency range, from long-wavelength visible light (red) through mid-infrared (0.6–28.3 μm). This will enable it to observe high-redshift objects that are too old and too distant for Hubble. The telescope must be kept very cold to observe in the infrared without interference, so it will be deployed in space near the Sun–Earth L₂ Lagrange point, about 1.5 million kilometers (930,000 mi) from Earth. A large sunshield made of silicon- and aluminum-coated Kapton will keep its mirror and instruments below 50 K (−223 °C; −370 °F).

The NASA Goddard Space Flight Center (GSFC) in Maryland managed the development and the Space Telescope Science Institute is operating JWST. The prime contractor was Northrop Grumman.

Development began in 1996 for a launch that was initially planned for 2007 with a US$500 million budget. There were many delays and cost overruns, including a major redesign in 2005, a ripped sunshield during a practice deployment, a recommendation from an independent review board, the COVID-19 pandemic, issues with the Ariane 5 rocket and the telescope itself, and communications issues between the telescope and the launch vehicle. Concerns among the involved scientists and engineers about the launch and deployment of the telescope have been well-described.

Construction was completed in late 2016, when an extensive testing phase began. JWST was launched 12:20 UTC 25 December 2021 by an Ariane 5 launch vehicle from Kourou, French Guiana and was released from the upper stage 27 minutes later. The telescope was confirmed to be receiving power, and as of December 2021 is traveling to its target destination.

Features

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light

The James Webb Space Telescope has a mass about half of Hubble Space Telescope's, but its primary mirror, a 6.5 m (21 ft)-diameter gold-coated beryllium reflector has a collecting area over six times as large, 25.4 m² (273 sq ft), using 18 hexagonal mirrors with 0.9 m² (9.7 sq ft) obscuration for the secondary support struts.

JWST 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. The design emphasizes the near to mid-infrared for three main reasons:

• high-redshift objects have their visible emissions shifted into the infrared
• cold objects such as debris disks and planets emit most strongly in the infrared
• this band is 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 (see figure of atmospheric absorption). 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)) thus the telescope itself radiates strongly in the infrared bands.

JWST will operate in a halo orbit around the Sun-Earth L₂ (Lagrange point), approximately 1,500,000 km (930,000 mi) beyond Earth's orbit around the Sun. By way of comparison, Hubble orbits 550 km (340 mi) above Earth's surface, and the Moon is roughly 400,000 km (250,000 mi) from Earth. This distance probably makes it impossible for a crewed mission to repair or upgrade the observatory in the future, as was done for Hubble. During the long JWST testing period, NASA officials referred to the idea of a servicing mission, but no plans were announced.

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 continuous orientation of its unique sunshield and equipment Bus toward the Sun, Earth and Moon to block their heat and light and to maintain communications. This arrangement will keep the temperature of the spacecraft below the 50 K (−223 °C; −370 °F) necessary for faint infrared observations.

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  Three-quarter view of the top
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  Bottom (Sun-facing side)
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  Prop blueprint of JWST

Sunshield protection

Main article: James Webb Space Telescope sunshield

Test unit of the sunshield stacked and expanded at the Northrop Grumman facility in California, 2014

To make observations in the infrared spectrum, JWST must be kept under 50 K (−223.2 °C; −369.7 °F); otherwise, infrared radiation from the telescope itself would overwhelm its instruments. It therefore uses a large sunshield to block 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 shielding maintains a stable temperature for the structures on the dark side, which is critical to maintaining precise alignment of the primary mirror segments in space.

The five-layer sunshield, each layer as thin as a human hair, is constructed from Kapton E, a commercially available polyimide film from DuPont, with membranes specially coated with aluminum on both sides and a layer of silicon doped aluminum on the Sun-facing side of the two hottest layers to reflect the Sun's heat back into space. Accidental tears of the delicate film structure during testing in 2018 were among the factors delaying the project.

The sunshield was designed to be folded twelve times so that it 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). The sunshield was hand-assembled at ManTech (NeXolve) in Huntsville, Alabama, before it was delivered to Northrop Grumman in Redondo Beach, California, for testing.

Because of the sunshield, JWST does not have an unlimited field of view at any given time. The telescope can see 40 percent of the sky from one position and can see all of the sky over a period of six months, the amount of time it takes to complete its halo orbit around L₂.

Optics

Main article: Optical Telescope Element

Engineers cleaning a test mirror with carbon dioxide snow, 2015

Main mirror assembled at Goddard Space Flight Center, May 2016

JWST'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 were built as a single large mirror, this would have been too large for existing launch vehicles. The mirror is therefore composed of 18 hexagonal segments which will unfold after the telescope is launched. Image plane wavefront sensing through phase retrieval will be used to position the mirror segments in the correct location using very precise micro-motors. Subsequent to this initial configuration, they will 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 will use 126 small motors to occasionally adjust the optics as there are few environmental disturbances of a telescope in space.

JWST'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. In addition, there is a fine steering mirror which can adjust its position many times per second to provide image stabilization.

Ball Aerospace & Technologies is the principal optical subcontractor for the JWST project, led by prime contractor Northrop Grumman Aerospace Systems, under a contract from the NASA Goddard Space Flight Center, in Greenbelt, Maryland. Eighteen primary mirror segments, secondary, tertiary and fine steering mirrors, plus flight spares have been fabricated and polished by Ball Aerospace & Technologies based on beryllium segment blanks manufactured by several companies including Axsys, Brush Wellman, and Tinsley Laboratories.

Scientific instruments

NIRCam model

NIRSpec model

MIRI 1:3 scale model

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 which will have a spectral coverage ranging from the edge of the visible (0.6 μm) through the near infrared (5 micrometers). There are 10 sensors each of 4 megapixels. NIRCam will also serve as the observatory's wavefront sensor, which is required for wavefront sensing and control activities. NIRCam was built by a team led by the University of Arizona, with principal investigator Marcia J. Rieke. The industrial partner is Lockheed-Martin's Advanced Technology Center in Palo Alto, California.
• NIRSpec (Near InfraRed Spectrograph) will also perform 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. The mechanisms and their optical elements were designed, integrated and tested by Carl Zeiss Optronics GmbH of Oberkochen, Germany, under contract from Astrium.
• MIRI (Mid-InfraRed Instrument) will measure 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, part of the Science and Technology Facilities Council (STFC)). MIRI features similar wheel mechanisms to NIRSpec which are also developed and built by Carl Zeiss Optronics GmbH under contract from the Max Planck Institute for Astronomy, Heidelberg, Germany. The completed Optical Bench Assembly of MIRI was delivered to Goddard Space Flight Center in mid-2012 for eventual integration into the ISIM. 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, National Research Council), 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 is also providing 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. Because the NIRISS is physically mounted together with the FGS, they are often referred to as a single unit; however, they 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.

The infrared detectors for the NIRCam, NIRSpec, FGS, and NIRISS modules are being provided by Teledyne Imaging Sensors (formerly Rockwell Scientific Company). The James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) and Command and Data Handling (ICDH) engineering team uses SpaceWire to send data between the science instruments and the data-handling equipment.

Spacecraft bus

Main article: Spacecraft bus (James Webb Space Telescope)

Diagram of the spacecraft bus. The solar panel is in green and the light purple panels are radiators.

The spacecraft bus is the primary support component of the James Webb Space Telescope which hosts 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 other two major elements of JWST are the Integrated Science Instrument Module (ISIM) and the Optical Telescope Element (OTE). Region 3 of ISIM is also inside the spacecraft bus; region 3 includes ISIM Command and Data Handling subsystem and the MIRI cryocooler. The spacecraft bus is connected to Optical Telescope Element via the Deployable Tower Assembly, which also connects to the sunshield. 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 masses 350 kg (770 lb), and must support the 6,200 kg (13,700 lb) space telescope. It is made primarily of graphite composite material. It was assembled in California, assembly was completed in 2015, and then it had to be integrated with the rest of the space telescope leading up to its 2021 launch. The spacecraft bus can rotate the telescope with a pointing precision of one arcsecond, and isolates vibration down to two milliarcseconds.

In the central computing, memory storage, and communications equipment, the processor and software direct data to and from the instruments, to the solid-state memory core, and to the radio system which can send data back to Earth and receive commands. The computer also controls the pointing of the spacecraft, taking in sensor data from the gyroscopes and star tracker, and sending commands to the reaction wheels or thrusters.

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 litres or 21.0 US gallons at launch).

Comparison with other telescopes

Comparison with Hubble primary mirror

Primary mirror size comparison between JWST and Hubble

The desire for a large infrared space telescope traces back decades. In the United States, the Space Infrared Telescope Facility (SIRTF, 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. Compared to ground telescopes, space observatories were free from atmospheric absorption of infrared light. Space observatories opened up a whole "new sky" for astronomers.

The tenuous atmosphere above the 400 km nominal flight altitude has no measurable absorption so that detectors operating at all wavelengths from 5 μm to 1000 μm can achieve high radiometric sensitivity.

— S. G. McCarthy and G. W. Autio, 1978.

However, infrared telescopes have a disadvantage: 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 spacecraft design, in particular by placing the telescope in a dewar with an extremely cold substance, such as liquid helium. This has meant most infrared telescopes have a lifespan limited by their coolant, as short as a few months, maybe a few years at most.

In some cases, it has been possible to maintain a temperature low enough through the design of the spacecraft to enable near-infrared observations without a supply of coolant, such as the extended missions of Spitzer Space Telescope and Wide-field Infrared Survey Explorer. 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 converted to a cryocooler that worked continuously. The James 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.

James Webb Space Telescope Official Poster

Selected space telescopes and instruments

Name	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
JWST	2021	0.6–28.5	6.5	Passive, and cryocooler (MIRI)

JWST's delays and cost increases can be compared to the Hubble Space Telescope. When Hubble formally started in 1972, it had an estimated development cost of US$300 million (or about US$1 billion in 2006 constant dollars), 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.

Of the other NASA observatories that were proposed around the same time, most have already been canceled or put on hold, including Terrestrial Planet Finder (2011), Space Interferometry Mission (2010), International X-ray Observatory (2011), MAXIM (Microarcsecond X-ray Imaging Mission), SAFIR (Single Aperture Far-Infrared Observatory), SUVO (Space Ultraviolet-Visible Observatory), and SPECS (Submillimeter Probe of the Evolution of Cosmic Structure).

History

Background

See also: James E. Webb § NASA, and James E. Webb § Legacy

Selected events

Year	Events
1996	NGST started
2002	named JWST, 8 to 6 m
2004	NEXUS cancelled
2007	ESA/NASA MOU
2010	MCDR passed
2011	Proposed cancel
2016	Final assembly completed
2021	Launch

Early development work for a Hubble successor between 1989 and 1994 led to the Hi-Z telescope concept, 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 disappointing performance of the Hubble Space Telescope in its first years played a significant role in the birth of the JWST. In 1993, NASA readied the Space Shuttle mission that would carry a replacement for HST's camera and a retrofit for its imaging spectrograph to compensate for the spherical aberration in its primary mirror. While the astronomical community eagerly awaited this mission, NASA cautioned that this extraordinary advance in working in space carried significant risk and that its successful completion was in no way guaranteed. Consequently, the Association of Universities for Research in Astronomy (AURA, the consortium managing the Space Telescope Science Institute) formed a committee of leading American astronomers to evaluate the effectiveness of the repair mission and to explore ideas for future space telescopes that would be needed if the repair mission fell short. The "HST & Beyond Committee," as it became known, had the good fortune to see the unqualified success of the Space Shuttle Servicing Mission 1 in December 1993 and the unprecedented public response to the stunning images that the HST delivered. The astronomy community, and NASA itself, were no less enthusiastic.

Emboldened by HST's success, and recognizing innovative work in Europe for future missions the 1996 report of the HST & Beyond Committee 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 own 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 to hundreds of degrees below 0 °C), and began the planning process for the future JWST.

Beginning in the 1960s, and at the beginning of each decade since, the National Academies organized the community of U.S. astronomers to think creatively about astronomical instruments and research for the subsequent decade, and to reach consensus on goals and priorities. A faithful supporter of these 'Decadal Surveys of Astronomy and Astrophysics', NASA has also been extraordinarily successful in developing programs and tools to accomplish Survey recommendations. So, even with the substantial support and excitement in the mid-1990s for NASA's beginning to work on a successor to the HST, the astronomical community regarded as essential a high prioritization by the 2000 Decadal Survey. Preparation for the Survey 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 the NGST concept matured, it amplified the importance of a mission 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. Late in the 1990s NASA created the 'Origins Subcommittee' to guide this effort and the 'Beyond Einstein Subcommittee' to oversee missions where the universe is a laboratory for fundamental astrophysics, for example, black holes and supernovae. As hoped, the NGST received the highest ranking in the 2000 Decadal Survey of Astronomy & Astrophysics, which allowed the project to proceed with the full endorsement of a community consensus.

The concept that would become JWST originated in 1996, as a proposal named Next Generation Space Telescope (NGST). In 2002, after further development of the design, it 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. JWST is a project of NASA, with international collaboration from the European Space Agency (ESA) and the Canadian Space Agency (CSA).

In the "faster, better, cheaper" era in the mid-1990s, NASA leaders pushed for a low-cost space telescope. The result was 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, 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 2003, NASA awarded TRW the US$824.8 million prime contract for JWST. 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.

Development

NASA's Goddard Space Flight Center in Greenbelt, Maryland, is leading the management of the observatory project. The project scientist for the James Webb Space Telescope is John C. Mather. Northrop Grumman Aerospace Systems serves as the primary contractor for the development and integration of the observatory. They are responsible for developing and building the spacecraft element, which includes both the satellite bus and sunshield. Ball Aerospace & Technologies has been subcontracted to develop and build the Optical Telescope Element (OTE). Northrop Grumman's Astro Aerospace business unit has been contracted to build the Deployable Tower Assembly (DTA) which connects the OTE to the spacecraft bus and the Mid Boom Assembly (MBA) which helps to deploy the large sunshields on orbit. Goddard Space Flight Center is also responsible for providing 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 wavelength 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. ESA is contributing about €300 million, including the launch. The Canadian Space Agency pledged $39 million Canadian in 2007 and in 2012 delivered its contributions in equipment to point the telescope and detect atmospheric conditions on distant planets.

Construction

A JWST mirror segment, 2010

Mirror segments undergoing cryogenic tests at the X-ray & Cryogenic Facility at Marshall Space Flight Center

The assembled telescope following environmental testing

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 successfully 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 JWST itself remained on schedule.

By 2011, the JWST project was in the final design and fabrication phase (Phase C). As is typical for a complex design that cannot be changed once launched, there are detailed reviews of every portion of design, construction, and proposed operation. New technological frontiers were pioneered by the project, and it passed its design reviews. In the 1990s it was unknown if a telescope so large and of such low mass was possible.

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

In March 2018, NASA delayed JWST's launch an additional year to May 2020 after the telescope's sunshield ripped during a practice deployment and the sunshield'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 also found JWST had 344 potential single-point failures. 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, JWST underwent final tests at a Northrop Grumman factory 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.

JWST has a history of major cost overruns and delays which have resulted in part from outside factors such as delays in deciding on a launch vehicle and adding extra funding for contingencies. By 2006, US$1 billion had been spent on developing JWST, with the budget at about US$4.5 billion at that time. A 2006 article in the journal Nature noted a study in 1984 by the Space Science Board, which estimated that a next generation infrared observatory would cost US$4 billion (about US$7 billion in 2006 dollars).

Then-planned launch and total budget

Year	Planned launch	Budget plan (billion USD)
1997	2007	0.5
1998	2007	1
1999	2007 to 2008	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
2013	2018	8.8
2017	2019	8.8
2018	2020	≥8.8
2019	March 2021	9.66
2021	Dec 2021	9.70

The telescope was originally estimated to cost US$1.6 billion, but the cost estimate grew throughout the early development and had reached about US$5 billion by the time the mission was formally confirmed for construction start in 2008. In summer 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 independent 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 JWST. US$3 billion had been spent and 75% of its hardware was in production. This budget proposal was approved by 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 issued a statement in support of JWST, as did Maryland US Senator Barbara Mikulski. A number of editorials supporting JWST appeared in the international press during 2011 as well. In November 2011, Congress reversed plans to cancel JWST and instead capped additional funding to complete the project at US$8 billion.

Some scientists have expressed concerns about growing costs and schedule delays for the Webb telescope, which competes for scant astronomy budgets and thus threatens funding for other space science programs. Because the runaway budget diverted funding from other research, a 2010 Nature article described JWST as "the telescope that ate astronomy."

A review of NASA budget records and status reports noted that JWST is plagued by many of the same problems that have affected other major NASA projects. Repairs and additional testing included underestimates of the telescope's cost that failed to budget for expected technical glitches and missed budget projections, thus extending the schedule and increasing costs further.

On 27 March 2018, NASA announced that JWST's launch would be pushed back to May 2020 or later, admitting that the project's costs might exceed US$8.8 billion. NASA committed to releasing a revised cost estimate after a new launch window was determined with the European Space Agency (ESA).

In February 2019, despite expressing criticism over cost growth, Congress increased the mission's cost cap by US$800 million.

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 will provide the Fine Guidance Sensor and the Near-Infrared Imager Slitless Spectrograph plus manpower to support operations.

Several thousand scientists, engineers, and technicians spanning 15 countries have contributed to JWST. A total of 258 companies, government agencies, and academic institutions are participating in the project; 142 from the United States, 104 from 12 European countries, and 12 from Canada.

Participating countries

• Austria
• Belgium
• Canada
• Czech Republic
• Denmark
• Finland
• France
• Germany
• Greece
• Ireland
• Italy
• Luxembourg
• Netherlands
• Norway
• Portugal
• Spain
• Sweden
• Switzerland
• United Kingdom
• United States

Public displays and outreach

Early full-scale model on display at NASA Goddard Space Flight Center (2005)

A large telescope model has been on display at various places since 2005: in the United States at Seattle, Washington; Colorado Springs, Colorado; Greenbelt, Maryland; Rochester, New York; New York City; and Orlando, Florida; and elsewhere at Paris, France; Dublin, Ireland; Montreal, Canada; Hatfield, United Kingdom; and Munich, Germany. The model was built by the main contractor, Northrop Grumman Aerospace Systems.

In May 2007, a full-scale model of the telescope was assembled for display at the Smithsonian Institution's National Air and Space Museum on the National Mall, Washington, D.C. The model was intended to give the viewing public a better understanding of the size, scale and complexity of the satellite, as well as pique the interest of viewers in science and astronomy in general. The model is significantly different from the telescope, as the model must withstand gravity and weather, so is constructed mainly of aluminum and steel measuring approximately 24 m × 12 m × 12 m (79 ft × 39 ft × 39 ft) and weighs 5,500 kg (12,100 lb).

The model was on display in New York City's Battery Park during the 2010 World Science Festival, where it served as the backdrop for a panel discussion featuring Nobel Prize laureate John C. Mather, astronaut John M. Grunsfeld and astronomer Heidi Hammel. In March 2013, the model was on display in Austin for SXSW 2013. Amber Straughn, the deputy project scientist for science communications, has been a spokesperson for the project at many SXSW events from 2013 onwards in addition to Comic Con, TEDx, and other public venues.

Controversy over name

In March 2021, an article in Scientific American urged NASA to reconsider the name of the telescope, based on Webb's alleged complicity during the Lavender Scare persecution of LGBTQ employees during the Harry S. Truman administration. In September 2021, NASA announced it had declined to rename the telescope. Former administrator Sean O'Keefe, who made the decision to name the telescope after administrator Webb, denounced discrimination against "talented professionals on the basis of their personal preferences," but stated that to suggest Webb should "be held accountable for that activity when there's no evidence to even hint [that he participated in it] is an injustice." However records do show that Webb planned and participated in meetings during which he handed over homophobic material. One member of NASA's Astrophysics Advisory Committee (APAC) resigned in response to this decision.

Mission

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 the formation and evolution of galaxies
• to understand the formation of stars and planetary systems
• 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, JWST's instruments will not measure visible or ultraviolet light like the Hubble Telescope, but will have a much greater capacity to perform infrared astronomy. JWST 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).

JWST 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.

Launch and mission length

Main article: Ariane flight VA256

The launch (designated Ariane flight VA256) took place as scheduled on 25 December 2021 on an Ariane 5 launch vehicle from the Guiana Space Centre in French Guiana. Upon successful launch, NASA administrator Bill Nelson called it "a great day for planet Earth." The observatory was attached to the Ariane 5 launch vehicle via a launch vehicle adapter ring which could be used by a future spacecraft to grapple the observatory to attempt to fix gross deployment problems. However, the telescope itself is not serviceable, and astronauts would not be able to perform tasks such as swapping instruments, as with the Hubble Telescope. The telescope was released from the upper stage 27 minutes 7 seconds after launch, beginning a 30-day orbit adjustment that will place the telescope at the L₂ Lagrange point. The flight includes three planned course corrections, because the observatory can recover from slight underthrust, but not from slight overthrust (the sunshield must remain between telescope and Sun, preventing turning around to slow down), therefore most of its flight will be at a slightly slower speed than the final speed for L₂ orbit.

The telescope's nominal mission time is five years, with a goal of ten years. The planned five-year science mission begins after a six-month commissioning phase. JWST needs to use propellant to maintain its halo orbit around L₂, which provides an upper limit to its designed lifetime, and it was designed to carry enough for ten years. An L₂ orbit is unstable, so it requires orbital station-keeping to prevent the telescope from drifting away from its orbital configuration. By December 29, four days after launch, mission control determined that JWST should have enough fuel to support "significantly more" than the expected ten-year lifetime in its halo orbit. The precision of the Ariane 5 launch and the first midcourse correction were credited with limiting the use of onboard fuel.

• 
  Ariane 5 and JWST at the ELA-3 launch pad
• 
  Ariane 5 containing JWST moments after lift-off
• 
  JWST as seen from the ESC-D Cryotechnic upper stage shortly after separation, approximately 29 minutes after launch. Part of the Earth with the Gulf of Aden can be seen in the background.

Orbit

JWST will not be exactly at the L₂ point, but circle around it in a halo orbit.

Two alternate Hubble Space Telescope views of the Carina Nebula, comparing ultraviolet and visible (top) and infrared (bottom) astronomy. Far more stars are visible in the latter.

JWST will orbit the Sun near the second Lagrange point (L₂) of the Earth-Sun 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 allow 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 will circle about the L₂ point in a halo orbit, which will be inclined with respect to the ecliptic, have a radius of approximately 800,000 km (500,000 mi), and take 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 in order to avoid pushing the JWST beyond the semi-stable L₂ point, a situation which would be unrecoverable. Randy Kimble, the Integration and Test Project Scientist for the James Webb Space Telescope, compared the precise station-keeping of the JWST 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."

Animation of James Webb Space Telescope trajectory

Top view

Side view

Side view from the Sun

Infrared astronomy

Infrared observations can see objects hidden in visible light, such as the HUDF-JD2 shown here.

JWST is the formal successor to the Hubble Space Telescope (HST), and since its primary emphasis is on infrared astronomy, it is also a successor to the Spitzer Space Telescope. JWST will far surpass both those telescopes, being able to see many more and much older stars and galaxies. Observing in the infrared spectrum is a key technique for achieving this, because of cosmological redshift, and because it better penetrates obscuring dust and gas. This allows observation of dimmer, cooler objects. Since water vapor and carbon dioxide in the Earth's atmosphere strongly absorbs most infrared, ground-based infrared astronomy is limited to narrow wavelength ranges where the atmosphere absorbs less strongly. Additionally, the atmosphere itself radiates in the infrared spectrum, often overwhelming light from the object being observed. This makes a space telescope preferable for infrared observation.

The more distant an object is, the younger it appears; its light has taken longer to reach human observers. Because the universe is expanding, as the light travels it becomes red-shifted, and objects at extreme distances are therefore easier to see if viewed in the infrared. JWST's infrared capabilities are expected to let it see back in time to the first galaxies forming just a few hundred million years after the Big Bang.

Infrared radiation can pass more freely through regions of cosmic dust that scatter visible light. Observations in infrared allow the study of objects and regions of space which would be obscured by gas and dust in the visible spectrum, such as the molecular clouds where stars are born, the circumstellar disks that give rise to planets, and the cores of active galaxies.

Relatively cool objects (temperatures less than several thousand degrees) emit their radiation primarily in the infrared, as described by Planck's law. As a result, most objects that are cooler than stars are better studied in the infrared. This includes the clouds of the interstellar medium, brown dwarfs, planets both in our own and other solar systems, comets, and Kuiper belt objects that will be observed with the Mid-Infrared Instrument (MIRI).

Some of the missions in infrared astronomy that impacted JWST development were Spitzer and the Wilkinson Microwave Anisotropy Probe (WMAP). Spitzer showed the importance of mid-infrared, which is helpful for tasks such as observing dust disks around stars. Also, the WMAP probe showed the universe was "lit up" at redshift 17, further underscoring the importance of the mid-infrared. Both these missions were launched in the early 2000s, in time to influence JWST development.

Ground support and operations

The Space Telescope Science Institute (STScI), in Baltimore, Maryland, on the Homewood Campus of Johns Hopkins University, was selected as the Science and Operations Center (S&OC) for JWST with an initial budget of US$162.2 million intended to support operations through the first year after launch. In this capacity, STScI will be responsible for the scientific operation of the telescope and delivery of data products to the astronomical community. Data will be transmitted from JWST to the ground via the NASA Deep Space Network, processed and calibrated at STScI, and then distributed online to astronomers worldwide. Similar to how Hubble is operated, anyone, anywhere in the world, will be allowed to submit proposals for observations. Each year several committees of astronomers will peer review the submitted proposals to select the projects to observe in the coming year. The authors of the chosen proposals will typically have one year of private access to the new observations, after which the data will become publicly available for download by anyone from the online archive at STScI.

The bandwidth and digital throughput of the satellite is designed to operate at 458 gigabits of data per day for the length of the mission. Most of the data processing on the telescope is done by conventional single-board computers. The conversion of the analog science data to digital form is performed by the custom-built SIDECAR ASIC (System for Image Digitization, Enhancement, Control And Retrieval Application Specific Integrated Circuit). NASA stated that the SIDECAR ASIC will include all the functions of a 9.1 kg (20 lb) instrument box in a 3 cm (1.2 in) package and consume only 11 milliwatts of power. Since this conversion must be done close to the detectors, on the cool side of the telescope, the low power use of this IC will be crucial for maintaining the low temperature required for optimal operation of JWST.

Transit and deployment

Starting 31 minutes after launch, and continuing for about 13 days, JWST began the process of deploying its solar array, antenna, sunshield, and mirrors. The electricity-generating solar panel deployed automatically on the day of launch, one and a half minutes after the telescope separated from the Ariane rocket second stage; this took place slightly sooner than expected because launch rotation was much closer to ideal than deployment plans had envisaged. The separation and solar panel extension were both visible in a live feed from a camera on the rocket. At 7:50 pm EST, about 12 hours after launch, the telescope's pair of primary rockets began firing for 65 minutes to make the first of three planned mid-course corrections. On day two, the high gain communication antenna also deployed automatically; all other deployments are manually commanded by mission controllers, allowing flexibility in case of unexpected events.

On December 27, at 60 hours after launch, Webb's rockets fired for nine minutes and 27 seconds to make the second of three mid-course corrections for the telescope to arrive at its L2 destination. On December 28, three days after launch, mission controllers began the multi-day deployment of Webb's all-important sunshield. Controllers sent commands that successfully lowered the forward and aft pallet structures, which contain the sunshield. This deployment precedes the actual unfolding and extension of the delicate shield membranes, which are pulled out of the pallets by telescoping beams in a subsequent step.

On December 29, controllers successfully extended the Deployable Tower Assembly, a pipe-like column, which moved apart the two main segments of the observatory, the telescope with its mirrors and scientific instruments, and the "bus" holding electronics and propulsion. The assembly lengthened 48 in (1,200 mm) in a process that lasted six and a half hours, including many preparatory commands. Deployment created the needed distance between the JWST segments to allow extreme cooling of the telescope and room for the sunshield to unfold. On December 30, controllers successfully completed two more steps in unpacking the observatory. First, commands deployed the aft "momentum flap", a device that provides balance against solar pressure on the sunshield, saving fuel by reducing the need for thruster firing to maintain Webb's orientation. Next, mission control released and rolled up covers that protect the sunshield, exposing it to space for the first time.

On December 31, the ground team extended the two telescoping "mid booms" from the left and right sides of the observatory, pulling the five sunshield membranes out of their folded stowage in the fore and aft pallets, which were lowered three days earlier. Deployment of the left side boom (in relation to pointing direction of the main mirror) was delayed when mission control did not initially receive confirmation that the sunshield cover had fully rolled up. After looking at extra data for confirmation, the team proceeded to extend the booms. The left side deployed in 3 hours and 19 minutes; the right side took 3 hours and 42 minutes. With that step, Webb's sunshield resembled its complete, kite-shaped form and extended to its full 47-foot width. Commands to separate and tension the membranes were to follow.

Nearly a month after launch, another trajectory correction will be initiated to place JWST into a halo orbit at around L2.

• Nominal deployment sequence
• 
  Planned deployment timeline
• Animation of JWST's orbit

Allocation of observation time

Atmospheric windows in the infrared: Much of this type of light is blocked when viewed from the Earth's surface. It would be like looking at a rainbow but only seeing one color.

JWST observing time will be allocated through a General Observers (GO) program, a Guaranteed Time Observations (GTO) program, and a Director's Discretionary Early Release Science (DD-ERS) program. The GTO program provides guaranteed observing time for scientists who developed hardware and software components for the observatory. The GO program provides all astronomers the opportunity to apply for observing time and will represent the bulk of the observing time. GO programs will be selected through peer review by a Time Allocation Committee (TAC), similar to the proposal review process used for the Hubble Space Telescope. JWST observing time is expected to be highly oversubscribed.

Early Release Science program

In November 2017, the Space Telescope Science Institute announced the selection of 13 Director's Discretionary Early Release Science (DD-ERS) programs, chosen through a competitive proposal process. The observations for these programs will be obtained during the first five months of JWST science operations after the end of the commissioning period. A total of 460 hours of observing time was awarded to these 13 programs, which span science topics including the Solar System, exoplanets, stars and star formation, nearby and distant galaxies, gravitational lenses, and quasars.

General Observer Program

Selection of Cycle 1 GO programs was announced on 30 March 2021. In the Cycle 1 proposal review, 266 proposals were approved, including "13 large and treasury" programs producing data for public access.

See also

• Attitude control
• James Webb Space Telescope timeline
• List of largest infrared telescopes
• List of largest optical reflecting telescopes
• List of space telescopes
• Nancy Grace Roman Space Telescope, planned launch no later than 2027
• New Worlds Mission (proposed occulter for the JWST)
• Physical cosmology
• Satellite bus
• Solar panels on spacecraft
• Spacecraft design
• Spacecraft thermal control

Further reading

• Jonathan P. Gardner; et al. (November 2006). "The James Webb Space Telescope". Space Science Reviews. 123 (4): 484–606. arXiv:astro-ph/0606175. Bibcode:2006SSRv..123..485G. doi:10.1007/s11214-006-8315-7. S2CID 118865272. The formal case for JWST science presented in 2006.
• Jason Kalirai (April 2018). "Scientific discovery with the James Webb Space Telescope". Contemporary Physics. 59 (3): 259–290. arXiv:1805.06941. Bibcode:2018ConPh..59..251K. doi:10.1080/00107514.2018.1467648. S2CID 85539627. A review of JWST capabilities and scientific opportunities.

External links

• Official NASA website / Official STScI website / Official French website
• JWST NASA – About page − Timeline details / Webb orbit / L2 / Communicating
• JWST NASA – *TRACKING* page − from Launch to L2 (second Lagrangian point)
• JWST Text – Most Critical Events – Launching and Deployment (December 2021)
• JWST Video (12:02): 1st Month – Launching and Deployment (animation; January 2017)
• JWST Video (08:06): 1st Month − Launching and Deployment (update; October 2021)
• JWST Video (31:22): Technical Engineering Details (December 2021)
• JWST Video (05:07): Successful Launch into Outer Space (December 25, 2021)
• JWST Video (02:43): Successful Detachment from Rocket (December 25, 2021)