Six out of 18 mirrors of the James Webb Space Telescope being subjected to temperature dipping test
|Operator||"NASA / "ESA / "CSA / "STScI|
|Mission duration||5 years (design)
10 years (goal)
|Launch mass||6,500 kg (14,300 lb)|
|Dimensions||20.197 m × 14.162 m (66.26 ft × 46.46 ft) (sunshield)|
|Start of mission|
|Launch date||May 2020|
|Launch site||"Kourou "ELA-3|
|Reference system||"Sun–Earth L2|
|"Periapsis||374,000 km (232,000 mi)|
|"Apoapsis||1,500,000 km (930,000 mi)|
|Diameter||6.5 m (21 ft)|
|Focal length||131.4 m (431 ft)|
|Collecting area||25 m2 (270 sq ft)|
|Wavelengths||from 0.6 "µm ("orange)
to 28.5 µm (mid-"infrared)
|Band||"S-band (TT&C support)
"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
James Webb Space Telescope insignia
The James Webb Space Telescope (JWST) is a "space telescope developed in collaboration between "NASA, the "European Space Agency and the "Canadian Space Agency. In contrast to the "Hubble Space Telescope, which has a 2.4-meter (7.9 ft) mirror, the JWST "primary mirror is composed of 18 hexagonal mirror segments for a combined mirror size of 6.5-meter-diameter (21 ft 4 in). The telescope will be deployed in space near the Earth–Sun "L2 "Lagrangian point, and a large "sunshield will keep JWST's "mirror and four science instruments below 50 K (−220 °C; −370 °F).
The James Webb Space Telescope will offer unprecedented resolution and sensitivity from the long-wavelength (orange to red) visible light through the "mid-infrared (0.6 to 27 "μm) range. JWST's capabilities will enable a broad range of investigations across the fields of "astronomy and "cosmology. One particular goal involves observing some of the most distant events and objects in the "universe, such as the "formation of the first galaxies. These types of targets are beyond the reach of current ground and space-based instruments. Some other goals include understanding the "formation of stars and "planets, and "direct imaging of "exoplanets and "novas.
In gestation since 1996, the JWST is one of NASA's "Large Strategic Science Missions. The telescope is named after "James E. Webb, who was the second administrator of NASA and played an integral role in the "Apollo program. NASA has described JWST as the scientific successor to the "Hubble Space Telescope, but not a replacement, because the capabilities are not identical. The JWST idea arose from a desire in the late 1980s and 1990s to see high "redshift objects, older and farther away than previous instruments could assess. The result was a decision to extend the life of Hubble until the "Next Generation Space Telescope" (as it was then called) could go online and to investigate designs that would enable it to obtain images deeper into the infrared than Hubble, and beyond the capabilities of earlier space observatories such as the "Infrared Space Observatory and the "Spitzer Space Telescope.
In December 2016, NASA announced that the JWST had passed major milestones, including completion of its primary mirror and integration of science instruments with the payload module, and had begun undergoing acoustic and extreme vibration testing to simulate launch conditions. In March 2018, NASA delayed the JWST's launch an additional year after the telescope's sunshield ripped during a practice deployment and the sunshield's cables did not sufficiently tighten. The JWST is currently scheduled to launch in May 2020.
The JWST originated in 1996 as the Next Generation Space Telescope (NGST). In 2002 it was renamed after NASA's second administrator (1961–1968) "James E. Webb (1906–1992), noted for playing a key role in the "Apollo program and establishing scientific research as a core NASA activity. The JWST is a project of the "National Aeronautics and Space Administration, the "United States "space agency, with international collaboration from the European Space Agency and the Canadian Space Agency.
The telescope has an expected mass about half of "Hubble Space Telescope's, but its "primary mirror (a 6.5 meter diameter "gold-coated "beryllium reflector) will have a collecting area about five times as large (25 m2 or 270 sq ft vs. 4.5 m2 or 48 sq ft). The JWST is oriented toward "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, and this band is difficult to study from the ground or by existing space telescopes such as Hubble. Ground based telescopes must look through the atmosphere, which is opaque in many infrared bands (see figure of atmospheric transmission). 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 not cool enough (the Hubble mirror is maintained at about 15 degrees C) and hence the telescope itself radiates strongly in the IR bands.
The JWST will operate near the Earth-Sun "L2 (Lagrange) point, approximately 930,000 mi (1,500,000 km) beyond Earth's orbit. By way of comparison, Hubble orbits 340 miles (550 km) above Earth's surface, and the Moon is roughly 250,000 miles (400,000 km) from Earth. This distance makes post-launch repair or upgrade of the JWST hardware virtually impossible. Objects near this point can orbit the Sun in synchrony with the Earth, allowing the telescope to remain at a roughly constant distance and use a single sunshield to block heat and light from the Sun and Earth. This will keep the temperature of the spacecraft below 50 K (−220 °C; −370 °F), necessary for infrared observations. The prime contractor is "Northrop Grumman.
To make observations in the infrared spectrum, the JWST must be kept very cold (under 50 K (−220 °C; −370 °F)), otherwise infrared radiation from the telescope itself would overwhelm its instruments. Therefore, it uses a large "sunshield to block light and heat from the Sun, Earth, and Moon, and its position near the Earth–Sun "L2 point keeps all three bodies on the same side of the spacecraft at all times. Its halo orbit around "L2 avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield and solar arrays. The sunshield is made of "polyimide film, and has membranes coated with "aluminum on one side and "silicon on the other.
The sunshield is designed to be folded twelve times so it will fit within the "Ariane 5 rocket's 4.57 m (5 yards) × 16.19 m (17.7 yards) shroud. Once deployed at the L2 point, it will unfold to 21.197 m (23.18 yards) × 14.162 m (15.55 yards). The sunshield was hand-assembled at Man Tech (NeXolve) in "Huntsville, Alabama before it was delivered to "Northrop Grumman in "Redondo Beach, California, USA for testing.
JWST's "primary mirror is a 6.5-meter-diameter gold-coated "beryllium reflector with a collecting area of 25 m2. This is too large for existing launch vehicles, so the mirror is 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 like the "Keck which continually adjust their mirror segments using "active optics to overcome the effects of gravitational and wind loading, and is made possible because of the lack of 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 of "optical aberrations over a wide field. In addition, there is a fast steering mirror, which can adjust its position many times per second to provide "image stabilization.
"Ball Aerospace & Technologies Corp. 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 based on beryllium segment blanks manufactured by several companies including Axsys, Brush Wellman, and Tinsley Laboratories.
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.
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.
The Spacecraft Bus is the primary support component of the James Webb Space Telescope, that hosts a multitude of computing, communication, propulsion, and structural parts, bringing the different parts of the telescope together. Along with the "Sunshield, it forms the Spacecraft Element of the space telescope. The other two major elements of the 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 structure of the Spacecraft Bus must support the 6.5 ton space telescope, while it itself weighs 350 kg (about 772 lb). It is made primarily of graphite composite material. It was assembled in California by 2015, and after that it had to be integrated with the rest of the space telescope leading up to its planned 2020 launch. The bus can provide pointing of one-arcsecond and isolates vibration down to two (2) "milliarcseconds.
The Spacecraft Bus is on the Sun-facing "warm" side and operates at a temperature of about 300 K. Everything on the Sun facing side must be able to handle the thermal conditions of JWST's halo orbit, which has one side in continuous sunlight and the other in shade by the spacecraft sunshield.
Another important aspect of the Spacecraft Bus is 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 and moment of the spacecraft, taking in sensor data from the gyroscopes and "star tracker, and sending the necessary commands to the reaction wheels or thrusters depending.
Launch is planned May 2020 on an "Ariane 5 rocket. The observatory attaches to the Ariane 5 rocket 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. Its nominal mission time is five years, with a goal of ten years. JWST needs to use propellant to maintain its halo orbit around L2, which provides an upper limit to its designed lifetime, and it is being designed to carry enough for ten years. The planned five year science mission begins after a 6-month commissioning phase. An L2 orbit is only meta-stable so it requires "orbital station-keeping or an object will drift away from this orbital configuration.
The desire for a large infrared space telescope traces back decades; in the United States the Shuttle Infrared Telescope Facility 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; this would be 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 & 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. 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 and "NEOWISE. Another example is Hubble's 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 sunshield and radiators with the mid-infrared instrument using an additional cryocooler.
The telescope'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 $300 million (or about $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 $9 billion by 2006.
In contrast to other proposed observatories, most of which 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 the SPECS (Submillimeter Probe of the Evolution of Cosmic Structure), the JWST is the last big NASA astrophysics mission of its generation to be built.
|Selected space telescopes and instruments|
|Human eye||—||0.39–0.75 μm||0.007 m||N/A|
|"IRT||1985||1.7-118 μm||0.15 m||Helium|
|"ISO||1995||2.5-240 μm||0.60 m||Helium|
|Hubble "STIS||1997||0.115–1.03 μm||2.4 m||Passive|
|Hubble "NICMOS||1997||0.8-2.4 μm||2.4 m||Nitrogen, later cryo-cooler|
|"Spitzer||2003||3–180 μm||0.85 m||Helium|
|Hubble "WFC3||2009||0.2–1.7 μm||2.4 m||Passive + Thermo-electric |
|"Herschel||2009||55–672 μm||3.5 m||Helium|
|JWST||Planned||0.6–28.5 μm||6.5 m||Passive + Cryo-cooler (MIRI)|
|2002||named JWST, 8 to 6 m|
Early development work for a Hubble successor between 1989 and 1994 led to the Hi-Z telescope concept, a fully baffled[Note 1] 4-meter aperture infrared telescope that would recede to an orbit at 3 "AU. This distant orbit would have benefited from reduced light noise from "zodiacal dust. Other early plans called for a NEXUS precursor telescope mission.
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-meter aperture and located at L2, estimated to cost $500 million. In 1997, NASA worked with the "Goddard Space Flight Center, "Ball Aerospace, and "TRW to conduct technical requirement and cost studies, and in 1999 selected "Lockheed Martin and TRW for preliminary design concepts.
Launch was initially planned for 2007, but the launch date was subsequently pushed back many times (see table further down).
In 2002, NASA awarded the $824.8 million prime contract for the NGST, now renamed the James Webb Space Telescope, to TRW. The design called for a descoped 6.1-meter (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.
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 "spacecraft bus and sunshield. "Ball Aerospace 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). A "solar panel converts sunlight into electrical power that recharges batteries needed to operate the other subsystems, as well as the science instruments, but heat from these operations must be dissipated for optimal instrument performance at 50 K (−220 °C; −370 °F).
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 micrometers. Other major features of the observatory were unchanged. Following the re-planning, the project was independently reviewed in April 2006. The review concluded the project was technically sound, but that funding phasing at NASA needed to be changed. NASA re-phased its JWST budgets accordingly.
In the 2005 re-plan, the life-cycle cost of the project was estimated at about "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, and the Canadian Space Agency about $39M Canadian.
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 project, 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 have been pioneered by the project, and it has passed its design reviews. In the 1990s it was unknown if a telescope so large and 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 in February 2016. Final construction of the Webb telescope was completed in November 2016, after which extensive testing procedures began. In March 2018, NASA delayed the 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.
|1999||2007 to 2008||1|
|2010||2015 to 2016||6.5|
The JWST has a history of major cost overruns and delays which have resulted from outside factors such as delays in deciding on a launch vehicle and adding extra funding for contingencies. By 2006, $1 billion had been spent on developing JWST, with the budget at about $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 $4 billion (about $7 billion in 2006 dollars). Because the runaway budget diverted funding from other research, the science journal "Nature described the James Webb as "the telescope that ate astronomy" in 2010. In June 2011, it was reported that the Webb telescope would cost at least four times more than originally proposed, and launch at least seven years late. Initial budget estimates were that the observatory would cost $1.6 billion and launch in 2011.
The telescope was originally estimated to cost $1.6bn but the cost estimate grew throughout the early development reaching about $5bn by the time the mission was formally confirmed for construction start in 2008. In summer 2010, the mission passed its Critical Design Review with excellent grades on all technical matters, but schedule and cost slips at that time prompted Maryland US 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 $1.5bn (for a total of $6.5bn). 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 $1.9bn from NASA's overall budget, of which roughly one quarter was for JWST. $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". However, in November 2011, Congress reversed plans to cancel the JWST and instead capped additional funding to complete the project at $8 billion. Termination of the JWST project as proposed by the House appropriation committee also would have imperiled funding to other missions, such as the "Wide-Field Infrared Survey Telescope.
The "American Astronomical Society issued a statement in support of JWST in 2011, as did Maryland US Senator "Barbara Mikulski. A number of editorials supporting JWST appeared in the international press during 2011 as well.
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. A review of NASA budget records and status reports noted that the 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, missed budget projections, and evaluation of components to estimate extreme launch conditions, thus extending the schedule and increasing costs further.
One of the reasons why the cost grew so much is that it is difficult to forecast the cost of development, and in general budget predictability improved when initial development milestones were achieved. By the mid-2010s, the U.S. contribution was still expected to cost $8.8 billion. With the U.S. and international funding combined, the overall cost not including extended operations is projected to be over $10 billion when completed. On 27 March 2018, NASA officials announced that JWST's launch would be pushed back to May 2020 or later, and admitted that the project's costs might exceed the $8.8 billion price tag. In the March 27 press release announcing the latest delay, NASA said that it will release a revised cost estimate after a new launch window is determined in cooperation with the "ESA. If this cost estimate exceeds the $8 billion cap Congress put in place in 2011, as is considered likely, NASA will have to have the mission re-authorized by the legislature.
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.
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; "Manhattan, New York; and "Orlando, Florida; and elsewhere at "Paris, France; "Dublin, Ireland; "Montreal, "Quebec, "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 24×12×12 m (79×39×39 ft) and weighs 5.5 tonnes (12,000 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, Texas for "SXSW 2013.
The JWST's primary scientific mission 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 and 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 the 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. The JWST will be sensitive to a range of wavelengths from 0.6 (orange light) to 28 "micrometers (deep infrared radiation at about 100 K (−170 °C; −280 °F)).
The JWST will be located near the second "Lagrange point ("L2) of the Earth-Sun system, which is 1,500,000 kilometers (930,000 mi) from Earth, directly opposite to the Sun. 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 it takes the Earth. 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 kilometers (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 2–4 m/s per year from the total budget of 150 m/s. Two sets of thrusters constitute the observatory's propulsion system.
JWST is the formal successor to the "Hubble Space Telescope (HST), and since its primary emphasis is on infrared observation, 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 is a key technique for achieving this, because it better penetrates obscuring dust and gas, allows observation of dim cooler objects, and because of "cosmological redshift. 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, often overwhelming light from the object being observed. This makes space the ideal position 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 these objects 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 radiation in the visible spectrum. 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) requiring an additional cry-cooler.
Some of the missions in infrared astronomy that impacted JWST development were Spitzer and also the "WMAP probe. Spitzer showed the importance of mid-infrared, such as in its 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 launched in the early 2000s, in time to influence JWST development. On JWST the mid-infrared science instrument is MIRI, and it required an additional cry-cooler.
The "Space Telescope Science Institute (STScI), located 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 $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 NASA's "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.
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 kg (20 lb) instrument box in a 3 cm 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 the JWST.
JWST after-launch deployment planned timeline
JWST observing time will be allocated through a Director's Discretionary Early Release Science (DD-ERS) Program, a Guaranteed Time Observations (GTO) Program, and a General Observers (GO) 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. 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, meaning that the number of submitted GO proposals will be much larger than the number that can be approved in any observing cycle.
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.
Fig. 1. Cooler Architecture Overview
The Observatory is the space-based portion of the James Webb Space Telescope system and is comprised of three elements, the Integrated Science Instrument Module (ISIM), the Optical Telescope Element (OTE), which includes the mirrors and backplane, and the Spacecraft Element, which includes the spacecraft bus and the sunshield