What makes small interferometers useful? Like NIRISS on JWST

What makes small interferometers useful? Like NIRISS on JWST

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NIRISS is an instrument on the James Webb Space Telescope. It has a "non-redundant aperture mask" which obviously covers most of the area of the sensor. It seems to be advantageous for high contrast imaging (like finding an exoplanet next to a star) and an alternative to coronagraphs. But however does that work? Why is it good to cover most of a sensor?

I have associated interferometers with creating as large as possible baselines for higher resolution, like the Very Large Baseline Array and the Spectr-R radio space telescope which gives up to a 390,000 km long baseline. So what is the magic with sacrificing sensor area to turn a single small telescope into an interferometer? Aren't all photons welcome? Would such an instrument do as well with a correspondingly smaller main mirror (maybe in separate fragments)?

A supplemental answer to probably someone's answer:

Why this can indeed be called interferometry:

Once one thinks in terms of physical optics (e.g. $ ext{exp}(j(omega t - mathbf{k} cdot mathbf{r} ))$ ) instead of ray optics, imaging is always an interference problem, and the math behind correlating signals from an array of radio telescopes to produce an image is not so much different than the math behind calculating an intensity pattern at the focal plane of an optical telescope.

From the Aperture Mask Interferometry section on page 5 of the JWST Pocket Guide (see below) you can see that they have no problem using terms like "interferometry" and "non-redundant baselines" as one would when laying out a sparse pattern of dish antennas in an array. See for example a Google Maps image of the Meerkat Array Core below, which has already produced images with only 16 sites occupied with active dishes.

While the mask shown in the question is a pupil mask, the pupil plane is conjugate to the telescope's aperture. So it's very similar to having seven large hexagonal holes in front of the JWST, or just using seven of the telescopes primary mirror's hexagonal mirror elements (with additional masking, these hexagons to not cover the full size of the individual elements, as shown in the illustration).

An important distinction though is that these seven small apertures are of the same order in size as their separation, while in a large radio telescope array, the spacing between receivers is usually somewhere between much larger and much much larger than the aperture of individual elements. So the analogy breaks down at this point.

What Aperture Masking Interferometry is for:

The purpose of using the mask is to enhance the system's resolution by narrowing the central peak of the point spread function compared to what you would get from the full aperture.

By loosing contrast in the full field due to diffraction artifacts, as well as loosing ~90% of the transmitted intensity, you can enhance contrast near the center of the field by narrowing the central diffractive peak, in this case in the range of 70 to 400 milli-arc seconds, according to the JAM Team's (JWST Aperture Masking Team) slides linked below.

From the first link:

Light admitted by 7 apertures in an otherwise opaque pupil mask interfere to produce an interferogram on the detector. This interfogram has a sharper core than is provided by normal "direct" imaging. The advantage is significant: while the ability to separate closely spaced objects with normal imaging is given by the familiar Rayleigh criterion (separation δθ=1.22λ/Dδθ=1.22λ/D , where λ is the wavelength of light and D is the diameter of the telescope), interferometry can resolve objects as close as δθ=0.5λ/Dδθ=0.5λ/D (the Michelson criterion). AMI allows planetary or stellar companions that are up to ~9 magnitudes fainter than their host star and separated by 70-400 mas to be detected and characterized. AMI can also be used to reconstruct high-resolution maps of extended sources, such as active galactic nuclei.

You can read more about it in:

  • JWST's NIRISS Aperture Masking Interferometry
  • ArXiv NIRISS aperture masking interferometry: an overview of science opportunities
  • The JAM Team's: Non-Redundant Aperture Masking Interferometry (AMI) and Segment Phasing with JWST-NIRISS

Below: MeerKAT array core from Google Maps at (30.7136109S, 21.4399576E).

The reason you would want to cover most of your aperture is so you can point directly at a huge light source (i.e. a star), but ignore most of the light coming from it. This makes it easier to directly detect faint features around the source that would ordinarily be washed out by the light from the source itself (i.e. planets and the like). I believe this is what LocalFluff was getting at with "advanced coronagraphy," and I don't believe it has anything to do with interferometery.

Brown Dwarfs & Rogue Planets as JWST Targets

About 1,000 light years away in the constellation Perseus, the stellar nursery designated NGC 1333 is emerging as a priority target for astronomers planning to use the James Webb Space Telescope. Brown dwarfs come into play in the planned work, as do the free-floating ‘rogue’ planets we discussed recently. For NGC 1333 is a compact, relatively nearby target, positioned at the edge of a star-forming molecular cloud. It’s packed with hundreds of young stars, many of them hidden from view by dust, a venue in which to observe star formation in action.

Hoping to learn more about very low mass objects, Aleks Scholz (University of St Andrews, UK) lays out plans for using JWST to chart the distinctions between objects that emerge out of gravitational collapse of gas and dust clouds, and objects that grow through accretion inside a circumstellar disk. Says Scholz:

“The least massive brown dwarfs identified so far are only five to 10 times heftier than the planet Jupiter. We don’t yet know whether even lower mass objects form in stellar nurseries. With Webb, we expect to identify cluster members as puny as Jupiter for the first time ever. Their numbers relative to heftier brown dwarfs and stars will shed light on their origins and also give us important clues about the star formation process more broadly.”

Image: Scientists will use Webb to search the nearby stellar nursery NGC 1333 for its smallest, faintest residents. It is an ideal place to look for very dim, free-floating objects, including those with planetary masses. Credit: NASA/JPL-Caltech/R. A. Gutermuth (Harvard-Smithsonian CfA).

Flying aboard JWST is an instrument called the Near Infrared Imager and Slitless Spectrograph (NIRISS), which Scholz and colleagues will use to analyze the temperature and composition of low-mass objects like these. It is the absorption signature of a particular object, especially water and methane molecules, that will be critical for the work. The advantage of the NIRISS instrument is that it can provide simultaneous spectrographic data on dozens of objects, shortening and simplifying the observational task. One of Scholz’ team, Ray Jayawardhana (Cornell University) has been involved in JWST instrumentation since 2004, and was active in the design and development of NIRISS.

Unable to sustain hydrogen fusion, a brown dwarf may have a mass between 1% and 8% that of the Sun. Most light emitted by these objects is in the infrared, and the already tricky targets are at the top of the size range in this study. Investigating free-floating planets takes us to another level, and even with that in mind, the distinction between a brown dwarf and a giant planet can be blurry. Koraljka Muzic (University of Lisbon), also on Scholz’ team, explains:

“There are some objects with masses below the 10-Jupiter mark freely floating through the cluster. As they don’t orbit any particular star, we may call them brown dwarfs, or planetary-mass objects, since we don’t know better. On the other hand, some massive giant planets may have fusion reactions. And some brown dwarfs may form in a disk.”

Looking through Scholz’ publication list, I noticed a recent paper (“Size and structures of disks around very low mass stars in the Taurus star-forming region” — citation below) that notes the challenge to planet formation models posed by the structure of disks around such stars.

In particular, several giant planets have been found around brown dwarfs, leaving open the question of whether they formed as binary companions or as planets. If the latter, models of planetesimal accretion are hard pressed to explain the process in this environment. The movement of dust presents a problem:

Different physical processes lead to collisions of particles and their potential growth, such as Brownian motion, turbulence, dust settling, and radial drift… All of these processes have a direct or indirect dependency on the properties of the hosting star, such as the temperature and mass. For instance, from theoretical calculations, settling and radial drift are expected to be more efficient in disks around VLMS [Very Low Mass Stars] and BDs [Brown Dwarfs], with BD disks being 15–20% flatter and with radial drift velocities being twice as high or even more in these disks compared to T-Tauri disks…. With radial drift being a more pronounced problem in disks around BDs and VLMS, it is still unknown how this barrier of planet formation is overcome in these environments where the disks are more compact, colder, and have a lower mass.

The paper on the Taurus star-forming region draws on data from ALMA (Atacama Large Millimeter/submillimeter Array), and notes the problems that we can hope JWST will alleviate:

Detection rate of substructures: millimeter dust substructures were directly detected in only 50% of the targets in our sample. Our results suggest that the detection of substructures in disks around VLMS is limited by angular resolution and sensitivity, since the dust radial extent is very small and these disks are also very faint. Deep, high angular resolution observations over a non-brightness biased sample of VLMS should confirm the ubiquity of substructures in these disks.

This is going to be an exciting area of research. As the paper points out, for every ten stars that form in our galaxy, somewhere between two and five brown dwarfs also form, and we already know that low-mass M-dwarfs account for as much as 75 percent of the Milky Way’s stars. When massive objects form around or near brown dwarfs, we are challenged to adjust our models of interactions within the disk and re-consider models of gravitational collapse. Interesting brown dwarf issues await JWST if we can just get it into operation.

The Scholz paper cited above is “Size and structures of disks around very low mass stars in the Taurus star-forming region,” Astronomy & Astrophysics Vol. 645, A139 (January 2021). Abstract.

Wow…. There sure is a lot riding on the JWST from exoplanet atmospheres to first light, the first galaxies. Fingers crossed the eventual launch goes smooth and it’s mission can be completed. Too distant to service like the Hubble.

And thanks Paul, you’ve been very profligate the last month or so posting quite a number of very interesting and well written articles, I’ve been a fan for about 10 years.

I enjoy the reader’s well thought out and sometimes provocative comments almost as much as the article itself, although I don’t often chime in (you all are WAY outta my league, lol).

And often, there are so many comments it gets difficult to track them and follow the thread.

Would it be possible to add some sorting tool, normally disabled…. that would allow the gentle reader to see latest comments (top of the page, for example)?

(PS, I may have posted this already, my Fred Flintstone lap top crashed just as I hit send, sorry).

Great to have you here, Deanna, and please feel free to join the discussion any time. Thank you for the kind words. Re comment sorting: It’s always an issue, and I’d like to find the right kind of tool for this. Still looking…

It’s hard to imagine just how interesting these objects are, their escape velocities are similar to our sun. Living around one would prove as dangerous as around stars with their powerful magnetic fields which could be tapped I would think by an intelligent species.


Beginning in Spring 2021, STScI will be hosting JWebbinars to teach the JWST community about tools and methods to analyze data from the James Webb Space Telescope. Each JWebbinar will provide virtual, hands-on instruction on common data analysis methods for JWST observations. All tutorials will be recorded and resources will be made available to the community online at a later date.

JWebbinar topics will include:

  • Overview of data analysis tools and data products
  • The JWST pipeline for imaging
  • The JWST pipeline for spectroscopy
  • Analyzing IFUs and spectral cubes
  • Analyzing MIRI photometry
  • Analyzing time series spectroscopy

Previous user training workshops are archived an available for proposers to review, too. These are not as up-to-date as the JWebbinar series.


Webb&rsquos unprecedented scientific power is a function of both the size of its primary mirror and the extreme sensitivity and precision of its four scientific instruments:

  • Mid-Infrared Instrument (MIRI)
  • Near-Infrared Camera (NIRCam)
  • Near-Infrared Spectrograph (NIRSpec)
  • Near-Infrared Imager and Slitless Spectrograph/Fine Guidance Sensor (NIRISS/FGS)

All scientific journal articles and many press releases will refer to specific instruments, instrument components, or observing modes used for observations with Webb.

This section provides some clarity on the function of each component, observing mode, and instrument, and the types of observations they are designed for.


Unlike simple backyard telescopes, which focus light from space directly into the eye, research telescopes include scientific instruments that record light precisely. Scientific instruments are crucial elements in both ground- and space-based telescopes, and are designed to optimize observations for scientific use.

During an observation with Webb, infrared light travelling from the target object or region of space is intercepted by the primary mirror, reflected onto the smaller secondary mirror, and then focused into the Integrated Science Instrument Module (ISIM). Mirrors then direct the light into one or more of the four scientific instruments, which may focus, filter, block, or disperse the light before it is recorded.

Each of Webb&rsquos four instruments is like a Swiss army knife of more specialized components, with multiple ways of observing (observing modes). Although some instruments are more suitable than others for observing specific types of objects, all four can be used for investigations of the wide variety of objects that make up the universe, including planets, stars, nebulae, and galaxies.


Each of Webb&rsquos four instruments includes a set of components that are common in research telescopes, along with components that are more specialized.

Common Components

Cameras capture two-dimensional images of regions of space. NIRCam and NIRISS capture images in the near-infrared, while MIRI captures mid-infrared images. NIRSpec is the only instrument without a camera.

Spectrographs spread light out into a spectrum so that the brightness of each individual wavelength can be measured. Webb has a number of different types of spectrographs, each designed for a slightly different purpose. All four of Webb&rsquos instruments have spectrographs.

Coronagraphs are opaque disks used to block the bright light of stars in order to detect the much fainter light of planets and debris disks orbiting the star. NIRCam and MIRI have coronagraphs.

Filters are thin sheets of specialized materials designed to transmit a certain range of wavelengths of light and block all others. Webb&rsquos filters are similar to light filters on handheld cameras, and are used in conjunction with cameras, coronagraphs, and spectrographs. All four instruments include numerous filters, including broad-band filters, which transmit a wide range of wavelengths narrow-band filters, which transmit a very narrow range of wavelengths and clear filters, which transmit all wavelengths collected by the telescope.

Detectors absorb light and convert it into electrical charges so that the information carried in the light (brightness, wavelength, and position) can be stored as digital data before being converted into radio signals and transmitted to Earth. Detectors are arranged in arrays, and are equivalent to the CCDs in a digital camera or the film in an analog camera. All four instruments have at least two detectors. NIRSpec, NIRISS, and NIRCam detectors are sensitive to near-infrared light (0.6 &ndash 4.9 µm). MIRI detectors are sensitive to mid-infrared light (4.9 &ndash 28.8 microns).

Specialized Components

Webb&rsquos microshutter array (MSA) is a grid of 248,000 tiny doors that can be opened and closed to transmit or block light in order to capture spectra of 100 individual objects or points in space at the same time (multi-object spectroscopy). NIRSpec is the only instrument with an MSA, and Webb is the only space telescope with an MSA.

The integral field unit (IFU) is a combination of camera and spectrograph used to capture and map spectra across a field of view in order to understand variation over space. NIRSpec and MIRI have IFUs.

Webb&rsquos aperture mask is a metal plate with seven hexagonal holes that is placed in front of the detectors to increase the effective resolution of the telescope and capture more detailed images of extremely bright objects (aperture mask interferometry). NIRISS is the only instrument with an aperture mask.


When astronomers plan observations with Webb, they choose not only their target of interest, but also the various observing modes required to address specific scientific questions. Observing modes on Webb are similar to modes on a digital camera. Different observing modes involve different combinations of components. Astronomers commonly observe the same target using more than one mode.

There are two broad groups of observation modes: imaging and spectroscopy.

Imaging with Webb

Imaging is equivalent to digital photography. Imaging is used to detect objects in a large field of view map the spatial relationship between various objects and materials in space and investigate the shape and structure of individual objects.

During imaging, infrared light from space is passed through filters onto an array of detectors. The detectors measure the intensity (brightness) of infrared light at thousands of points (pixels) across the field of view.

Imaging Modes

Webb has four imaging modes. All imaging modes employ filters and detectors, as well as cameras.

Standard Imaging is the equivalent to basic digital photography and involves capturing pictures of a wide variety of objects and materials in space that emit or reflect infrared light. (NIRCam, NIRISS, and MIRI)

Coronagraphic Imaging (sometimes called high-contrast imaging) involves using a coronagraph to block the light of a star in order to reveal the much dimmer light of nearby objects, such as exoplanets and debris disks. (NIRCam and MIRI)

Aperture Mask Interferometry (AMI) involves using an aperture mask to increase the effective resolution of the telescope and capture more detailed images. When the aperture mask is in place, only the light that passes through the holes makes it to the detectors&mdashthe rest is blocked. AMI simulates the effect of a telescope array, in which a number of telescopes work together to simulate the light gathering ability of a single, much larger telescope. AMI is used to separate light of bright objects like stars that are close together in space or on the sky. (NIRISS)

Time-Series Imaging involves capturing a series of images at regular intervals in order to measure changes over time. Time series is sort of like burst mode on a camera, and can be used to track changes in the brightness of a star or can be combined with coronagraphic imaging to track the motion of a planet. (MIRI and NIRCam)

The James Webb Space Telescope&rsquos Near Infrared Spectrograph (NIRSpec) has a microshutter array that can capture hundreds of colorful spectra at the same time.

Spectroscopy with Webb

Spectroscopy involves spreading light out into a spectrum in order to analyze the intensity (or brightness) of individual colors, or wavelengths. Differences in brightness with wavelength, and the presence or absence of specific wavelengths, provides information about temperature, composition, density, motion, and distance.

During a spectroscopic observation, light from space is directed through a spectrograph, which spreads the light out into its component wavelengths. The light then strikes the detectors, which measure the intensity (brightness) of each individual wavelength of light. Spectral data are typically plotted on a graph of intensity vs. wavelength.

Spectroscopy Modes

Webb has six spectroscopy modes. All spectroscopy modes involve filters and detectors as well as spectrographs.

Wide-Field Slitless Spectroscopy involves capturing the overall spectrum of a wide field of view &ndash a field of stars, part of a nearby galaxy, or many galaxies at once. (NIRCam and NIRISS)

Single-Object Slitless Spectroscopy involves capturing the spectrum of a single bright object like a star in a field of view. (MIRI and NIRISS)

Slit Spectroscopy provides the ability to capture the spectrum of a single object&mdasha single star, a single exoplanet, or a single distant galaxy&mdashin a wide field of view. Single slit spectroscopy is also used to analyze the spectrum of a small area of an object that is large in the field of view, such as a galaxy or planet. (NIRSpec and MIRI)

Multi-Object Spectroscopy involves using a microshutter array to capture individual spectra of up to 100 objects or locations in space at one time. Multi-object spectroscopy is important for efficiency, in particular when observing very distant and dim targets, such as ancient galaxies, which require hundreds of hours of observation time. (NIRSpec)

Integral Field Unit Spectroscopy (IFU) involves a combination of imaging and spectroscopy. During an IFU observation, the instrument captures an image of the field of view along with individual spectra of each pixel in the field of view. IFU observations allow astronomers to investigate how properties&mdashsuch as composition, temperature, and motion&mdashvary between different objects such as stars in a crowded star field, or from place to place over a large region of space such as a galaxy or nebula. (NIRSpec and MIRI)

Time-Series Spectroscopy involves capturing the spectrum of an object or region of space at regular intervals in order to observe how the spectrum changes over time. Time series spectroscopy is used to study planets as they transit their stars. (NIRCam, NIRSpec, and MIRI)


Wavelength Range

Webb is designed to capture light ranging in wavelength from 0.6 microns (visible red) to 28.8 microns (mid-infrared). Each instrument, however, covers only part of the full range, and each observing mode may cover an even smaller portion of the instrument&rsquos range. The wavelength coverage determines which specific scientific questions can be answered.

The near-infrared instruments (NIRCam, NIRSpec, and NIRISS) cover 0.6-5 microns, while the Mid-Infrared Instrument (MIRI) covers 4.9-28.8 microns.

Field of View

An instrument&rsquos field of view is the amount of sky that it can observe at any given point in time. Each instrument has a field of view that is unique in area, shape, and orientation. In some cases, different observing modes within an instrument cover fields of view of different sizes and shapes.


In general, resolution&mdashthe size of the smallest details that can be resolved in an image (spatial resolution), or the degree with which wavelengths of light can be differentiated in a spectrum (spectral resolution)&mdashis a function of the size of Webb&rsquos primary mirror and the wavelength of light (longer wavelengths have lower resolution). However, the actual resolution of an image or spectrum varies with observing mode and instrument. Researchers rely on this information to ensure that observations will yield data of sufficient resolution.


Each of Webb&rsquos four instruments is designed to study a wide range of objects and phenomena in space, including planets, stars, galaxies, gas clouds, debris disks, black holes, and dark matter.

What makes each instrument unique is its specific combination of components, observing modes, wavelength range, field of view, and resolution.

While some investigations are conducted with a single instrument and observing mode, most rely on a combination of instruments and/or observing modes.

Mid-Infrared Instrument (MIRI)

COMPONENTS: Camera, Coronagraphs, Spectrographs, Integral Field Unit

WAVELENGTH RANGE: 4.9 µm &ndash 28.8 µm (mid-infrared, which is unique to MIRI)

IMAGING MODES: Standard Imaging, Coronographic Imaging, Time-Series Imaging

SPECTROSCOPY MODES: Single-Object Slitless Spectroscopy, Slit Spectroscopy, Integral Field Unit Spectroscopy, Time-Series Spectroscopy

RESOLUTION: Medium-resolution imaging Low- and medium-resolution spectroscopy

MIRI provides imaging and spectroscopy capabilities in the mid-infrared. As the only mid-infrared instrument, astronomers rely on MIRI to study cooler objects like debris disks, which emit most of their light in the mid-infrared, and extremely distant galaxies whose light has been shifted into the mid-infrared over time.

MIRI was developed through a collaboration between the European Consortium (EC) and the Jet Propulsion Laboratory (JPL).

Near-Infrared Camera (NIRCam)

WAVELENGTH RANGE: 0.6 µm &ndash 5 µm (red to near-infrared)

DETECTORS: Mercury cadmium telluride

IMAGING MODES: Standard Imaging, Coronagraphic Imaging, Time-Series Imaging

SPECTROSCOPY MODES: Wide-Field Slitless Spectroscopy, Time-Series Spectroscopy

RESOLUTION: High-resolution imaging and spectroscopy

NIRCam is Webb&rsquos primary near-infrared imager, providing high-resolution imaging and spectroscopy for a wide variety of investigations. Because NIRCam is the only near-infrared instrument with coronagraphic and time-series imaging capabilities, it is crucial for many exoplanet studies.

In addition to imaging and spectroscopy, NIRCam is also part of Webb&rsquos wavefront sensing and control system, which detects and corrects for slight irregularities in the shape of the primary mirror or misalignment between mirror segments, giving the telescope the ability to focus clearly on objects near and far.

NIRCam was built by a team at the University of Arizona and Lockheed Martin&rsquos Advanced Technology Center.

Near-Infrared Spectrograph (NIRSpec)

COMPONENTS: Spectrographs, Integral Field Unit, Microshutter Array (Unique to NIRSpec)

WAVELENGTH RANGE: 0.6 µm &ndash 5 µm (red to near-infrared)

IMAGING MODES: N/A (with the exception of images collected during Integral Field Unit Spectroscopy)

SPECTROSCOPY MODES: Slit Spectroscopy, Multi-Object Spectroscopy (Unique to NIRSpec), Integral Field Unit Spectroscopy, Time-Series Spectroscopy

RESOLUTION: Low-, Medium-, and High-resolution spectroscopy

NIRSpec is one of Webb&rsquos versatile tools for near-infrared spectroscopy. In addition to standard single-slit spectroscopy to gather spectra of specific objects, NIRSpec also has an integral field unit to investigate spatial variations in spectra and a microshutter array to capture individual spectra of dozens of objects at once. This highly efficient design is part of what makes Webb ideal for studying extremely distant, faint galaxies.

NIRSpec was built for the European Space Agency by Airbus Industries with the microshutter array (MSA) and detector sub-systems fabricated by NASA.

Near-Infrared Imager and Slitless Spectrograph (NIRISS)/Fine Guidance Sensor (FGS)

COMPONENTS: Camera, Spectrographs, Aperture Mask

WAVELENGTH RANGE: 0.6 µm &ndash 5 µm (red to near-infrared)

DETECTORS: Mercury cadmium telluride

IMAGING MODES: Standard Imaging, Aperture Mask Interferometry (Unique to NIRISS)

SPECTROSCOPY MODES: Wide-Field Slitless Spectroscopy, Single-Slit Spectroscopy

RESOLUTION: High-resolution imaging Low- and Medium-resolution spectroscopy

NIRISS provides near-infrared imaging and spectroscopic capabilities. As the only instrument capable of aperture mask interferometry, NIRISS has the unique ability to capture images of bright objects at a resolution greater than the other imagers.

Housed in the same assembly as NIRISS is Webb&rsquos Fine Guidance Sensor (FGS). The FGS is a camera system designed to make sure Webb is stable and pointing in exactly the right direction throughout the observation. The FGS detects and identifies guide stars and ensures that Webb is locked onto those stars for the entire observation.

NIRISS is a contribution of the Canadian Space Agency. Honeywell International designed and built the instrument in collaboration with a team at the Université de Montréal. Additional technical support was provided by the National Research Council of Canada&rsquos Herzberg Astronomy and Astrophysics Research Centre.

Webb's Instruments

Webb's versatile instruments will work across a wide range of visible-red through mid-infrared colors. Each instrument is uniquely designed to look at particular details. In addition to filters that isolate particular color ranges, the instruments contain a variety of special tools designed to maximize the scientific knowledge gleaned from every observation.

Webb will have a total of four science instruments: the Near-Infrared Camera, Near-Infrared Spectrograph, Mid-Infrared Instrument, and the Fine Guidance Sensor/Near-Infrared Imager and Slitless Spectrograph. Webb's instruments are housed in the Integrated Science Instrument Module, a structure that functions as the heart of the Webb Telescope.


Webb's Near Infrared Camera (NIRCam) will help scientists answer questions about the early phases of star and galaxy formation. It will yield data about the shapes and colors of faraway, young galaxies, allowing astronomers to determine how galaxies change over time. In addition, NIRCam will help astronomers to determine the ages of stars in nearby galaxies.

Astronomers plan to use NIRCam to create an ultra-deep survey of the distant universe &mdash similar to the famous Hubble deep fields, but in infrared &mdash designed to find some of the most distant objects in space. NIRCam will take a series of pictures using filters that pick up different wavelengths, and use the changes in brightness it detects between these images to estimate the redshifts of the distant galaxies. Redshifting is the stretching of light toward longer wavelengths that occurs as light travels through the expanding universe, and can be used to gauge distance. These NIRCam observations will probe 13 billion years into the universe's past, and reveal more information about the characteristics of the first objects to appear in the universe.

NIRCam is equipped with coronagraphs, instruments that allow astronomers to take pictures of very faint objects around a central bright object, such as a star. NIRCam's coronagraphs work by blocking a brighter object's light, making it possible to view the dimmer object nearby &mdash just like shielding the sun from your eyes with an upraised hand can allow you to focus on the view in front of you. Using coronagraphs, astronomers hope to determine the characteristics of planets orbiting nearby stars.

NIRCam also will help ensure the perfect alignment and shape of Webb's primary mirror segments. NIRCam is equipped with special optics that can capture the image of a single, bright star and deliberately place it out of focus, spreading out its light. Astronomers then analyze that out-of-focus image, looking for patterns that are consistent with all the mirrors being in alignment, or indicative of a problem.

NIRCam will be Webb's primary imager at wavelengths 0.6-5 microns.

NIRCam is being built by the University of Arizona and Lockheed Martin. For more information, visit NASA's NIRCam page.


The Near-Infrared Spectrograph (NIRSpec) is the Webb telescope's primary spectrograph, unraveling the light of faint objects and their components. A spectrograph is an instrument that spreads light into its various wavelengths, allowing them to be analyzed. This helps scientists determine which elements the object contains, the velocity of various parts of the object, and its redshift.

NIRSpec will be used to measure accurate redshifts to distant galaxies and to measure their chemical evolution. NIRSpec will also study how gas and dust clump together to form new stars and planets.

A unique capability of NIRSpec will be its ability to study the light of more than 100 objects at once. This is made possible by the Micro Shutter Assembly (MSA). The MSA consist of arrays of thousands and thousands of tiny shutters that can be opened in the pattern of objects on the sky, allowing only the light from objects of interest into the instrument. This will allow NIRSpec to perform a spectroscopic survey of many distant galaxies at a variety of ages. The observations can reveal the star formation rate in each galaxy. They will also help measure the chemistry of galaxies, and study how stars change with a galaxy's age, answering questions like: what kinds of stars are forming in these galaxies, when does star formation stop, and what causes it to stop. With this information, scientists can determine how galaxies over time take on the properties we see in them today.

NIRSpec will be the Webb's primary spectrograph at wavelengths 0.6-5 microns.

NIRSpec is being built by the European Space Agency, with the detectors and multi-shutter array provided by Goddard Space Flight Center/NASA. For more information, visit NASA's NIRSpec page.


MIRI's sensitive camera and spectrograph will be able to see far away in time and space, back to a time when galaxies were young. MIRI is the only instrument on Webb that can see objects like these early galaxies, which appear in long mid-infrared wavelengths.

Because the universe is expanding, the light from stars similar to our Sun in these galaxies has been redshifted to mid-infrared wavelengths. MIRI will be able to detect these.

MIRI will play a large role in Webb's mission to understand faraway galaxy formation and evolution, the physical process of star formation, and the creation of the heavier chemical elements, such as carbon, oxygen, and iron. But even more excitingly, MIRI will be used to study the origins of the building blocks of life. In the cold regions where stars are forming, gas and dust are present. Both leave fingerprints in the spectra of forming stars, revealing how that gas and dust interacted to create stars. These materials are also the building blocks of the planetary systems being created around the young stars. These observations will reveal the origin of water and organic materials in young planetary systems.

MIRI is also equipped with a complex coronagraph, which blocks the glare of nearby bright objects to allow clear observations of faint objects.

MIRI will operate in the 5- to 28-micron wavelength range.

MIRI was built by the MIRI Consortium, a group that consists of scientists and engineers from European countries, a team from the Jet Propulsion Lab in California, and scientists from several U.S. institutions. For more information, visit NASA's MIRI page.

FINE GUIDANCE SENSORS/Near-Infrared Imager and Slitless Spectrograph (FGS/NIRISS)

Two instruments &mdash the Fine Guidance Sensor (FGS) and the Near-Infrared Imager and Slitless Spectrograph (NIRISS) &mdash are packaged together, but have separate purposes. The FGS is the guide camera for the observatory, which helps point the telescope, while NIRISS is a specialized science instrument.

Like NIRSpec, NIRISS is a spectrograph, designed to break light apart into separate wavelengths for analysis. NIRISS will be able to take extremely precise spectra of bright objects, capturing more light than NIRSpec. NIRISS will also be used to detect faint objects, like planets, that are very near their parent stars. Since it doesn&rsquot use a coronograph, it will use a special masking technique to capture objects that have very close proximities. And like NIRCam, NIRISS can make its observations through a variety of specially selected filters.

NIRISS will tackle a diverse range of science topics. It will discover distant galaxies in the universe and make detailed maps of crowded regions such as the centers of galaxies where quasars reside. Observations with NIRISS will examine the atmospheric makeup of potentially habitable, Earth-like planets found around nearby low-mass stars. Differences between spectra obtained from the star and planet, or the star only (when the planet is behind the star) will reveal the makeup and structure of the planet&rsquos atmosphere. Observations like these can determine whether the planet&rsquos atmosphere contains the organic molecules required to support life.

Balancing Act

The FGS helps point the telescope in two ways. First, at the start of an observation, it takes pictures to identify where the telescope is pointing. Then, it finds a &ldquoguide star&rdquo that is close to the field of view containing the object to be studied. As long as the guide star stays in exactly the same position in the field of the FGS, the telescope will point at the target of scientific interest, which can be examined by one of the science instruments.

The telescope tends to wander by small amounts, since it is orbiting in space and affected by solar radiation, its own moving parts, the sloshing of its propellant, and other forces. To track these changes, the FGS measures the position of the guide star 16 times per second and relays these measurements to the onboard computer. When the computer detects small drifts, it orders the telescope to correct itself in order to keep its positioning relative to the guide star.

The FGS and NIRISS are provided by the Canadian Space Agency. For more information, visit NASA's FGS/NIRISS page.

Canada’s Role

The Webb Telescope is set to be the most important space telescope of the next decade. As a collaborating member of the mission, Canada has a unique opportunity to highlight its technical and scientific expertise in space astronomy through its instrument contributions to the mission and continued support to scientists from Canadian institutions working on the Webb team.

In exchange for its contributions, Canada receives a guaranteed share of Webb’s observing time, ensuring immediate scientific discoveries for Canadian scientists.


Canada’s contributions to the Webb Telescope, the Fine Guidance Sensor (FGS) and the Near-Infrared Imager and Slitless Spectrograph (NIRISS), was delivered in a single unit to NASA’s Goddard Space Flight Center in 2012. Credit: NASA.

Canada contributed both the Fine Guidance Sensor (FGS) and the Near-Infrared Imager and Slitless Spectrograph(NIRISS) instrument to the Webb telescope. Both components have been packaged together into a single unit the size of a washing machine that weighs about 150 kilograms.

Fine Guidance Sensor

When a telescope wants to take clear images, it needs to point towards the object it is studying and carefully track it in the sky. Webb will move into position for observations using a system of gyroscopes, but it will also need to know where to look.

The Canadian-made Fine Guidance Sensor is an infrared camera that will act as Webb’s eyes. To get clear and detailed pictures of the Universe, Webb will use the FGS to lock on a star position with very high precision.

The FGS and Webb’s system of gyroscopes will work together with the final optical piece in Webb called the fine steering mirror (FSM) to stabilise the light beam coming from deep space objects. With input from the FGS, the FSM can tip and tilt tiny amounts very quickly to correct for a jittery lightbeam without having to move the entire telescope. All scientific observations taken by Webb will involve the use of the FGS.

Near-Infrared Imager and Slitless Spectrograph

Canada’s Near-Infrared Imager and Slitless Spectrograph will photograph and gather spectra from many types of celestial objects. A spectrum shows exactly how bright an object is at many different wavelengths, or colours. This gives detailed information on the characteristics of the observed object. NIRISS uses an infrared camera sensitive to infrared light between 0.6 and 5.0 microns. Once it has captured the infrared light of an object, the light can be broken up into a spectrum using a tool called a grism which is similar to the prisms used to break up sunlight into a rainbow.

NIRISS will also have another mode that will allow it to take an image and spectra simultaneously using a technique called interferometry which allows scientists to examine objects that are very close together.

NIRISS and all the other scientific instruments will be turned on when they are needed for specific science programs. Commands to do this will be sent from the Webb Science and Operation Center at the Space Telescope Science Institute in Baltimore, USA.

NIRISS will be able to study the atmospheres of exoplanets and determine their composition, observe distant galaxies and examine objects that are very close together in the sky.


Part of the Canadian JWST Team at a meeting at Honeywell in Kanata, Ontario in 2019.

The Webb science project in Canada is led by:

  • Principal Investigator: Prof. René Doyon, Université de Montréal
  • Project Scientist: Dr. Chris Willott, NRC-Herzberg Astronomy & Astrophysics

Researchers from a number of other universities and institutes also make up the Canadian Webb science team:

  • NRC-Herzberg Astronomy & Astrophysics
  • Saint-Mary’s University
  • Université de Montréal
  • University of Toronto
  • York University
  • Cornell University
  • Space Telescope Science Institute
  • University of Michigan
  • University of Rochester

Instrument Team

Funding for the Canadian portion of the Webb mission is provided by the Canadian Space Agency. The FGS/NIRISS unit was built, tested and maintained by Honeywell. Scientists from a number of other institutes have also worked on the Canadian instrument and guidance sensor:


Canadian scientists will be some of the first to use data taken by the Webb Telescope to make new discoveries about the Universe.

Thanks to the CSA’s important contribution to the mission, Canada will have guaranteed access to approximately 5% of Webb’s observing time reserved for programs selected through a competitive process for the General Observations (GO) program. These science programs will be chosen on a yearly basis while Webb is operational.

Canada’s contribution of the NIRISS scientific instrument and the Fine Guidance Sensor has also secured 450 hours of Webb time through the Guaranteed Time Observations (GTO) program during the first few years of the mission.

Finally, one Canadian-led science programs has been selected for the competitive Early Release Science (ERS) program which will have priority time during Webb’s first year of observing.

Guaranteed Time Observations (GTO) Programs

In exchange for the Canadian instrument contributions, the Canadian Webb science team have been allotted 450 hours of guaranteed observing time on the Canadian NIRISS instrument and Webb’s other instruments.

Seven small programs tackling subjects such as rogue planets, brown dwarfs and exoplanets will account for 47 of these hours. The remaining 403 hours will be split between two main programs. Click here for a full list of the Canadian GTO programs.

CANUCS: CAnadian NIRISS Unbiased Cluster Survey

Dr. Chris Willott, JWST Project Scientist, presents the CANUCS program. Credit: RASC Victoria.

Lead : Dr. Chris Willott, NRC-Herzberg
Program time : 199 hours
Instruments used: NIRISS, NIRCam, NIRSpec
Goal : Study some of the first galaxies ever formed understand the evolution of dwarf galaxies across time

The CANUCS program will observe very early galaxies using a technique called gravitational lensing. Massive groups of galaxies called clusters can warp and magnify light from very early galaxies, making them easier to observe.

Large masses such as galaxy clusters can deform spacetime. They act like a gravitational lens that deforms the light emitted by background galaxies. The background galaxies can also be magnified, making them easier to observe. Credit: NASA/ESA/L. Calçada.

The NIRISS instrument will collect images and spectra from these galaxies at different periods of the Universe’s history. This will help scientists better understand how galaxies evolved over time.

Webb’s large mirror will be especially useful to observe very small galaxies called dwarf galaxies. The CANUCS program will also help us better understand dark matter and star formation in very large galaxy clusters.

NEAT: NIRISS Exploration of the Atmospheric diversity of Transiting exoplanets

Prof. David Lafrenière, a member of the JWST Science Team, is leading the NEAT science program. Credit: Luc Turbide/Université de Montréal.

Lead : Prof. David Lafrenière, Université de Montréal
Program time : 204 hours
Instrument used: NIRISS
Goal : Observe and study the atmospheres of exoplanets, including their composition and temperature

The NEAT program will study exoplanets, planets that orbit stars other than the Sun. Exoplanets are often detected when they pass, or transit, in front of their parent star and dim its light.

While the exoplanet itself blocks the star’s light, some of the starlight passes through the exoplanet’s atmosphere. The NIRISS instrument will collect the spectra of this starlight which will show signatures of certain molecules found in the exoplanets’ atmospheres. This method is called transit spectroscopy.

When starlight passes through a planet’s atmosphere, certain parts of the light are absorbed by the atmosphere’s elements. By studying the starlight with these absorption lines, scientists can determine the composition of the planet’s atmosphere. Credit: Christine Daniloff/MIT, Julien de Wit.

Some of the NEAT program’s targets are rocky planets like Earth. The NEAT team hopes to make the very first detection of an atmosphere on such a planet. This could give us clues on whether or not these planets are habitable.

Early Release Science (ERS) Programs

To quickly make the most of Webb’s full science potential, a part of Webb’s first five months of operations has been dedicated to special Early Release Science (ERS) programs.

The proposed ERS programs went through a competitive process before being chosen based on their scientific merit and benefit for the global astronomical community.

One of the 13 chosen ERS programs is led by a Canadian astronomer.

Radiative Feedback from Massive Stars as Traced by Multiband Imaging and Spectroscopic Mosaics

Prof. Els Peeters leads one of 13 ERS programs on Webb during its first year. Credit: Western University.

Lead: Prof. Els Peeters, Western University
Program time: 28 hours
Instruments used: NIRCam, NIRSpec, MIRI
Goal: Study the interaction between light emitted by very massive stars and their surrounding environment and how this affects the material between stars called the interstellar medium (ISM)

The space between stars is often filled with gas and dust that can be heated by the light produced by these stars. This heating can be so intense that the gas and dust’s chemistry will change and the molecules will break down — or dissociate. These regions are called Photodissociation Regions (PDRs).

The Great Nebula in Orion is a region of space where stars are being formed from clouds of dust. The bar visible in the lower left quarter of the image is Orion’s Bar, a photodissociation region (PDR), where starlight is heating up and changing the nearby gas. Credit: NASA/C. O’Dell/S. Wong.

One well known example of a PDR is Orion’s Bar, which is part of Orion’s Nebula located in the Orion constellation.

A large part of the infrared light in galaxies is produced by these PDRs. Studying the chemical and physical processes happening in these regions will allow scientists to better understand how stars interact with their environment.

JWST (James Webb Space Telescope)

JWST is an orbiting optical observatory and a key element in NASA's Origins Program, optimized for observations in the infrared region of the electromagnetic spectrum. It is considered the successor mission of HST (Hubble Space Telescope) while operating over a different spectral range. At the NIR and MWIR wavelengths, it benefits from operating at intrinsically lower backgrounds than any comparably sized telescope on the ground. JWST, previously known as NGST (Next Generation Space Telescope), will be the premier space facility for astronomers in the decade following its launch. The overall objectives are to study the first stars and galaxies after the big bang. Major science goals (themes) of the mission are to find answers to the following questions: 1) 2)

&bull What is the shape of the Universe?

&bull How do stars and planetary systems form and interact?

&bull How did the Universe built up its present chemical/elemental composition?

&bull What is the nature of dark matter?

The radiation from the very distant objects to be observed is practically all in the infrared region. Many of the early events happened when the Universe was between 1 million and 1 billion years old, a period that is not known to earthlings (the dark ages of the Universe). To accomplish the goals of the science themes, the main JWST design requirement calls for the detection of objects up to 400 times fainter than those observable by current ground-based or spaceborne observatories.

Historical background: Large next-generation projects with high-performance observation requirements take about two decades (and more) from first studies to launch. Initial planning for the new mission started in 1989 (visions, conceptual studies). The goal was to have a successor mission for HST ready for launch well before 2010.

In the mid-1990s, a telescope design with an 8 m aperture was considered. The challenge was to come up with a lower cost for the large telescope than for previous much smaller space telescopes. This involved conceptual studies by industry. In 1996, a committee report was written, based on these studies: &ldquoNext Generation Space Telescope, Visiting a Time When Galaxies Were Young.&rdquo This report established also a roadmap to NGST activities, defining the new building blocks and to search for enabling technologies and concepts - in particular in the fields of large-aperture lightweight mirrors that are actively controlled, of advanced detector designs, of suitable cooling techniques for all critical components, and of precision metrology to achieve the goal of measuring ultra precise stellar positions.

A broad range of talent on a national and international level and from many institutions, academia and industry was directly involved in the NGST detailed definition phase (Phase A) including simulations and feasibility studies. In 1997, an ad hoc Science Working Group was formed which came up with thematic science goals and developed a so-called &ldquoDesign Reference Mission&rdquo (DRM), representing a hypothetical suite of key science observing programs [stating the expected physical properties (number density and brightness), the desired observation modes (wavelength band, spectral resolution, number of revisits), and a minimum operational life of 2.5 years to complete the mission] for NGST - which provided a yardstick for technology testing. DRM was and is the primary tool against which any JWST architectures are being measured. The shear complexity of the project and the performance requirements demanded a technology development and validation strategy to address and demonstrate a critical path to a workable design of the mission. 3) 4) 5) 6)

In 2000/1, the NGST project experienced a rescoping of the telescope size (from 8 m aperture to 6.5 m) to keep projected costs in bounds. There were also some technology maturity uncertainties.

The project started in 2002 with a Mission Definition Review. NASA began to realize that the critical technologies had reached a level of sufficient maturity to justify a go-ahead with the next phase of the project.

In September 2002, NASA renamed NGST to JWST (James Webb Space Telescope) in honor of James E. Webb (1906-1992), NASA's second administrator during the Apollo Program of the 1960s (1961-1968). At the same time in Sept. 2002, NASA awarded the prime contract of the JWST observatory development (spacecraft, telescope, integration and testing) to Northrop Grumman Space Technology (formerly TRW) of Redondo Beach, CA.

In the fall of 2003 ICR(Initial Confirmation Review) was given, starting the Phase B of the JWST project. The C/D Phase started in 2008.

The CDR (Critical Design Review) of the JWST (James Webb Space Telescope) is planned for December 2013 (Ref. 29).

Project partners: NASA leads an international partnership in the joint JWST mission that includes ESA (European Space Agency) and CSA (Canadian Space Agency). Both agencies (ESA, CSA) collaborated in the JWST project already at an early planning stage (1996). Aside from instrument contributions, ESA will also launch the JWST spacecraft on an Ariane 5 launcher as agreed to with NASA. NASA/GSFC is managing the JWST project, while STScI (Space Telescope Science Institute) of Baltimore, MD, is responsible for JWST science and mission operations, as well as ground station development (STScI is the same organization that is operating the Hubble Space Telescope). A formal JWST and LISA (Laser Interferometer Space Antenna) cooperation agreement between NASA and ESA was signed on June 18, 2007 at the International Paris Air Show at Le Bourget, France. 7) 8) 9) 10) 11)

A most interesting and valuable side effect of the technology development effort for JWST is that these new technologies will also be available to many other space projects (astronomy, space science, Earth observation, etc.) providing potentially a quantum step in observation performance.

The JWST mission concept is an ambitious and most challenging development program, requiring a lot of innovative technology introduction as well as conceptual breakthroughs on various levels to meet the proposed observational performances. The objectives of the science themes can only be met by a combination of a large-aperture telescope in space (6.5 m &phi ), a very low detection temperature to eliminate noise, and an ideal observing environment (elimination of stray light).

The observatory will be shielded from the sun and Earth by a large deployable sunshade, the entire telescope assembly will be passively cooled to about 37 K, giving JWST exceptional performance in the near-infrared and mid-infrared wavebands. The baseline wavelength range for the instrumentation is 0.6 - 28 µm, and the telescope will be diffraction-limited above 2 µm. The sensitivity of the telescope will be limited only by the natural zodiacal background, and should exceed that of ground-based and other space-based observatories by factors of 10 to 100,000, depending on the wavelength and type of observation. The JWST observatory will have a 5 year design life (with a goal of 10 years of operations) and will not be serviceable by astronauts (as is Hubble). The total mass of JWST at launch is estimated to be 6,500 kg.

Like Hubble, the JWST will be used by a broad astronomical community to observe targets ranging from objects within our Solar System to the most remote galaxies seen during their formation in the early universe.

Major enabling technologies are:

&bull Large deployable and lightweight beryllium mirrors (a folding 6.5 meter mirror made up of 18 individual segments, adjustable by cryogenic actuators). To fit inside the launch vehicle, the large space telescope prime mirror must be folded in sections for launch, then unfolded (deployed) precisely into place after launch, making it the first segmented optical system deployed in space.

&bull Deployment of large structures. Once in space, the multilayer sunshield that was folded over the optics during launch will deploy to its full size and keep the telescope shadowed from the sun.

&bull Introduction of MEMS technology to the microshutter system of the NIRSpec instrument. The programmable microshutters to allow object selection for the spectrograph.

Overview of payload instruments:

&bull NIRCam (Near-Infrared Camera), funded by NASA with the University of Arizona as prime contractor. CSA is participating in the development of the NIRCam instrument.

&bull NIRSpec (Near-Infrared multi-object Spectrograph), funded by ESA with EADS Astrium GmbH as prime contractor (the detector arrays and a micro-shutter are supplied by NASA/GSFC)

&bull MIRI (Mid-Infrared Camera-Spectrograph) a joint instrument of JPL and ESA. The instrument (about 50%) is being provided by ESA member states, coordinated but not funded by ESA.

&bull FGS (Fine Guidance Sensor) with TFI (Tunable Filter Imager), funded by CSA (Canadian Space Agency)

Figure 1: Photometric performance of JWST instruments as compared to those of current observatories (image credit: STScI)

Legend to Figure 1: Plotted is the faintest flux for a point source that can be detected at 10 sigma in a 104 s integration. The fluxes are given in Janskies as well as AB magnitudes. 12)

Figure 2: Comparison of JWST light gathering power vs spectral range with Hubble and Spitzer telescopes (image credit: STScI) 13)

Launch: The launch of the NASA/ESA/CSA James Webb Space Telescope (Webb) on an Ariane 5 rocket from Europe&rsquos Spaceport in French Guiana is now planned for November 2021. 14)

- American and European officials acknowledged June 1 that the launch of the James Webb Space Telescope will likely slip from the end of October to at least mid-November because of delays linked to the Ariane 5.

- At an ESA briefing about the space telescope, representatives of the agency and Arianespace said they were finalizing reviews to correct a payload fairing problem found on two Ariane 5 launches last year that had grounded the rocket since August. Arianespace described the issue last month as &ldquoa less than fully nominal separation of the fairing&rdquo on those two launches.

- &ldquoThe origin of the problem has been found. Corrective actions have been taken,&rdquo Daniel de Chambure, acting head of Ariane 5 adaptations and future missions at ESA, said. &ldquoThe qualification review has started, so we should be able to confirm all that within a few days or weeks.&rdquo

- He did not elaborate on the problem or those corrective actions, beyond stating that the problem took place during separation of the payload fairing. Industry sources said in May that, on the two launches, the separation system imparted vibrations on the payload above acceptable limits, but did not damage the payloads.

- The issue is not linked to a modification to the payload fairing required for JWST. Arianespace has been testing new vents on the fairing designed to reduce the pressure differential once the fairing is separated and thus reduce the loads on the spacecraft. &ldquoThe issue of the modification of the venting system and the fairing anomaly are different,&rdquo de Chambure said.

- The Ariane 5 is scheduled to make its next launch, the first since the August 2020 launch that had the payload fairing anomaly, in the second half of July, said Beatriz Romero, JWST project manager at Arianespace. That launch will be the first of two commercial Ariane 5 launches before the JWST launch.

- At a May 11 media event, Greg Robinson, program director for JWST at NASA Headquarters, said that the JWST launch would take place about four months after the first of the two commercial Ariane 5 launches ahead of it. That would push the launch, currently scheduled for no earlier than Oct. 31, to at least the middle of November.

- At the ESA briefing, Thomas Zurbuchen, NASA associate administrator for science, offered a similar schedule. Asked if a mid-November launch was likely, based on 10-week launch processing schedule that begins with JWST&rsquos shipment from California to the launch site in French Guiana in late August, he said that timeframe is &ldquoapproximately correct.&rdquo

- &ldquoWe want to be sure that we launch exactly when we&rsquore ready, not a day earlier,&rdquo he said. &ldquoThat is, when the spacecraft is ready and when the rocket and the fairing and everything is ready.&rdquo

NASA is targeting Oct. 31, 2021, for the launch of the agency&rsquos James Webb Space Telescope from French Guiana, due to impacts from the ongoing coronavirus (COVID-19) pandemic, as well as technical challenges. 15)

This decision is based on a recently completed schedule risk assessment of the remaining integration and test activities prior to launch. Previously, Webb was targeted to launch in March 2021.

&bull NASA&rsquos James Webb Space Telescope currently is undergoing final integration and test phases that will require more time to ensure a successful mission. After an independent assessment of remaining tasks for the highly complex space observatory, Webb&rsquos previously revised 2019 launch window now is targeted for approximately May 2020.

- &ldquoWebb is the highest priority project for the agency&rsquos Science Mission Directorate, and the largest international space science project in U.S. history. All the observatory&rsquos flight hardware is now complete, however, the issues brought to light with the spacecraft element are prompting us to take the necessary steps to refocus our efforts on the completion of this ambitious and complex observatory,&rdquo said acting NASA Administrator Robert Lightfoot.

- Testing the hardware on the observatory&rsquos telescope element and spacecraft element demonstrate that these systems individually meet their requirements. However, recent findings from the project&rsquos Standing Review Board (SRB) indicate more time is needed to test and integrate these components together and then perform environmental testing at Northrop Grumman Aerospace Systems in Redondo Beach, California, the project&rsquos observatory contractor.

- NASA is establishing an external Independent Review Board (IRB), chaired by Thomas Young, a highly respected NASA and industry veteran who is often called on to chair advisory committees and analyze organizational and technical issues. The IRB findings, which will complement the SRB data, are expected to bolster confidence in NASA&rsquos approach to completing the final integration and test phase of the mission, the launch campaign, commissioning, as well as the entire deployment sequence. Both boards&rsquo findings and recommendations, as well as the project&rsquos input, will be considered by NASA as it defines a more specific launch time frame. NASA will then provide its assessment in a report to Congress this summer.

- NASA will work with its partner, ESA (European Space Agency), on a new launch readiness date for the Ariane 5 vehicle that will launch Webb into space. Once a new launch readiness date is determined, NASA will provide a cost estimate that may exceed the projected $8 billion development cost to complete the final phase of testing and prepare for launch. Additional steps to address project challenges include increasing NASA engineering oversight, personnel changes, and new management reporting structures.

- This is a pivotal year for Webb when the 6.5-meter telescope and science payload element will be joined with the spacecraft element to form the complete observatory. The spacecraft element consists of the tennis-court-sized sunshield, designed by Northrop Grumman, and the spacecraft bus, which houses the flight avionics, power system, and solar panels. Because of Webb&rsquos large size, engineers had to design components that fold origami-style into the Ariane 5 rocket&rsquos fairing configuration.

- Webb has already completed an extensive range of tests to ensure it will safely reach its orbit at nearly one million miles from Earth and perform its science mission. As with all NASA projects, rigorous testing takes time, increasing the likelihood of mission success.

- &ldquoConsidering the investment NASA and our international partners have made, we want to proceed systematically through these last tests, with the additional time necessary, to be ready for a May 2020 launch,&rdquo said Thomas Zurbuchen, associate administrator for NASA&rsquos Science Mission Directorate.

- After the successful test performance of Webb&rsquos telescope and science payload in 2017 at NASA&rsquos Johnson Space Flight Center in Houston, the telescope element was delivered to Northrop Grumman earlier this year. Both halves of the 13,500-pound observatory now are together in the same facility for the first time.

- The spacecraft element will next undergo environmental testing, subjecting it to the vibrational, acoustic and thermal environments it will experience during its launch and operations. These tests will take a few months to complete. Engineers then will integrate and test the fully assembled observatory and verify all components work together properly.

- Webb is an international project led by NASA with its partners, ESA and the Canadian Space Agency. ESA is providing the Ariane 5 as part of its scientific collaboration with NASA.

- The James Webb Space Telescope will be the world&rsquos premier infrared space observatory and the biggest astronomical space science telescope ever built, complementing the scientific discoveries of NASA&rsquos Hubble Space Telescope and other science missions. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

Table 1: NASA statement of Release 18-019 of 27 March 2018 regarding the new launch target of May 2020 for JWST

Figure 3: James Webb Space Telescope Launch and Deployment (video credit: NASA, Northrop Grumman) 16)

&bull April 6, 2018: NASA has assembled members of an external Independent Review Board for the agency&rsquos James Webb Space Telescope. The board will evaluate a wide range of factors influencing Webb&rsquos mission success and reinforce the agency&rsquos approach to completing the final integration and testing phase, launch campaign, and commissioning for NASA&rsquos next flagship space science observatory.

- &ldquoWe are exploring every aspect of Webb&rsquos final testing and integration to ensure a successful mission, delivering on its scientific promise,&rdquo said Thomas Zurbuchen, Associate Administrator for NASA&rsquos Science Mission Directorate. &ldquoThis board&rsquos input will provide a higher level of confidence in the estimated time needed to successfully complete the highly complex tasks ahead before NASA defines a specific launch time frame.&rdquo

- The board, convened by NASA&rsquos Science Mission Directorate, includes individuals with extensive experience in program and project management, schedule and cost management, systems engineering, and the integration and testing of large and complex space systems, including systems with science instrumentation, unique flight hardware, and science objectives similar to Webb.

- The Independent Review Board review process will take approximately eight weeks. Once the review concludes, the board members will deliver a presentation and final report to NASA outlining their findings and recommendations, which are expected to complement recent data input from Webb&rsquos Standing Review Board. NASA will review those findings and then provide its assessment in a report to Congress at the end of June. Northrop Grumman Aerospace Systems, the project&rsquos observatory contractor, will proceed with the remaining integration and testing phase prior to launch.

The board consists of the following notable leaders in the space science community:

Mr. Thomas Young, NASA/Lockheed Martin in Bethesda, Maryland &ndash Retired (Chair)

Dr. William Ballhaus, Aerospace Corporation in El Segundo, California- Retired

Mr. Steve Battel, Battel Engineering, Inc. in Scottsdale, Arizona

Mr. Orlando Figueroa, NASA Headquarters and Goddard Space Flight Center in Greenbelt, Maryland &ndash Retired

Dr. Fiona Harrison, Caltech University in Pasadena, California

Ms. Michele King, NASA Office of Chief Financial Officer/Strategic Investments Division in Washington, DC

Mr. Paul McConnaughey, NASA/Marshall Space Flight Center/Webb Standing Review Board (Chair) in Huntsville, Alabama

Ms. Dorothy Perkins, NASA Goddard Space Flight Center in Greenbelt, Maryland - Retired

Mr. Pete Theisinger, Jet Propulsion Laboratory in Pasadena, California

Dr. Maria Zuber, Massachusetts Institute of Technology in Cambridge, Massachusetts

Table 2: Independent Review Board of JWST 17)

&bull Dec. 17, 2015: The next great space observatory took a step closer this week when ESA signed the contract with Arianespace that will see the James Webb Space Telescope launched on an Ariane 5 rocket from Europe&rsquos Spaceport in Kourou in October 2018. The contract includes a cleaner fairing and integration facility to avoid contaminating the sensitive telescope optics. 18)

- With a 6.5 m diameter telescope, the observatory must be launched folded up inside Ariane&rsquos fairing. The 6.6 ton craft will begin unfolding shortly after launch, once en route to its operating position some 1.5 million km from Earth on the anti-sunward side.

The orbit of JWST has been selected to be at L2. The spacecraft will be in a Lissajous (or halo) orbit about the Lagrangian point L2. In the Sun‐Earth system the L2 point is on the rotating Sun-Earth axis about the same distance away as L1 (1.5 million km, representing 1/100 the distance from Earth to the Sun) but at the opposite side of the Earth. The L1 location is inside the Earth orbit while the L2 location is outside the Earth orbit.

The halo orbit of JWST is in a plane slightly out of the ecliptic plane. This orbit avoids Earth and moon eclipses of the sun. The halo orbit period is about 6 months. Nominal station keeping maneuvers will be performed every half orbit (i.e. in intervals of about 3 months).

Figure 4: Locations of the five Lagrangian points in the Sun-Earth system

The L2 location is considered to offer the most advantageous viewing for astronomical targets (looking toward the universe) due to nearly constant lighting conditions (minimum of stray light). Another advantage of the L2 location is that it offers a stable thermal environment. The telescope is kept in perpetual shadow by looking into the deep space direction. The deep space provides a 2.7 K black body radiation. This ideal heat sink is being used to provide the passive cooling for the payload to a temperature range of about 37 K, shielded from sunlight (entering the spacecraft from the opposite direction) by a five-layer sunshield [passive cooling is the most elegant and economical method available to obtain the required operating temperatures for infrared detection].

Figure 5: Overview of JWST trajectory to L2 (image credit: NASA)

Figure 6: Artist's rendering of the JWST observatory (image credit: NASA)

JWST deployment sequence:

During the transfer orbit to L2 different elements of the JWST will be deployed and commissioning will start. The observatory has five deployment stages involving the following elements: 19)

1) Deployment of spacecraft appendages (solar arrays, high gain antenna)

2) Deployment of the sunshield (unfolding 2 days after launch)

4) Deployment of the secondary mirror (positioned on a tripod structure)

5) Deployment of the primary mirror wings

The deployment of the solar arrays and the high gain antenna is scheduled for the first day to provide the capabilities of onboard power generation and a spacecraft communications link. The unfolding of the sunshield will occur two days after launch, while the timeline for secondary and primary mirror deployment is foreseen after four days. &ldquoFirst light&rdquo will occur about 28 days after launch, initiating wavefront sensing and control activities to align the mirror segments. Instrument checkout will start 37 days after launch, well before the final L2 orbit insertion is obtained after 106 days. This is being followed by full commissioning procedures expected to last until about 6 months after launch. 20)

Figure 7: Deployment sequence of the OTE (image credit: NASA, STScI)

The Observatory architecture is comprised of three elements: OTE (Optical Telescope Element), ISIM (Integrated Science Instrument Module), and the spacecraft (bus and sunshield). A key aspect of the JWST architecture is the use of semi-rigid primary mirror segments mounted on a very stable and rigid backplane composite structure. The architecture is referred to as &ldquosemi-rigid&rdquo because it has a modest amount of flexibility that allows for on-orbit compensation of segment-to-segment radius of curvature variations. 21) 22) 23) 24) 25) 26) 27) 28) 29)

Figure 8: The three elements of the JWST flight segment (image credit: NASA) 30)

Figure 9: The JWST spacecraft, reflecting the addition of the trim flap and the new solar panel array (image credit: NASA)

(Optical Telescope Element)

- TMA (Three Mirror Anastigmatic) design, f/20, 25 m 2 collecting area
- Fine steering mirror (FSM) with line-of-sight (LOS) stabilization < 7.3 marcsec (or mas)
- Four separate deployments
- Semi-rigid hexagonal mirror segments and graphite composite backplane structure

- Superior image quality over the ISIM FOV, provides science resolution and sensitivity
- Excellent pointing control and stability in conjunction with the spacecraft attitude control
- Simple, reliable and robust deployment
- Allows ground verification of the OTE, provides stable optical performance over temperature

- Primary mirror deploys in two steps (2-chord fold)
- Composed of 18 semi-rigid hexagonal segments, each with set-and-monitor wavefront control actuators
- Mirror segment material is Beryllium

- Highly reliable deployment
- All segments are mechanically near-identical, achieving efficiencies in manufacturing, assembly and testing
- Known material properties with demonstrated optical performance over temperature

- Tripod configuration for support structure
- Deployment using a single redundant actuator
- Semi-rigid optic with 6 degrees of freedom (DoF) alignment

- Provides rigidity, minimizes obscuration and scattered light into the field of view
- Low risk, high margin (torque margin > 32 times the friction load)
- Permits reliable and accurate telescope alignment

Reduces stray light and houses the tertiary mirror and the FSM

- Simple semi-kinematic mount 8 m 2 of thermal radiators, and 19.9 m 3 volume.
- Contains all science instruments (SI) and FGS

- Provides a simple interface for the ISIM to decouple ISIM development from the OTE
- Allows for parallel development and early testing

- Integral 1 Hz passive vibration isolators
- Thermally isolates the OTE from the spacecraft

- Reduces S/C dynamic noise onto OTE/ISIM
- Achieves small mirror temperature gradients

- 5 layer &ldquoV&rdquo groove radiator design reduces solar energy to a few 10's of mW
- Folded about OTE during launch
- Sized (

19.4 m x 11.4 m) and shaped to limit solar radiation induced momentum buildup

- Provides a stable thermal environment for passively cooling the OTE and the ISIM
- Reliable deployment, protects OTE during launch
- Reduces the time and fuel for momentum unloading, increases operational efficiency

- Chandra-based attitude control subsystem
- Two-axis gimbaled high gain Earth-pointing antenna (omni-directional), Ka- and S-band
- 471 Gbit solid state recorder
- Propellant for >11 years

- Flight-proven low noise dynamic environment that minimizes line-of-sight jitter
- Contingency operations and link margin
- Store > 2 days of science & engineering data
- Extended operation capability

Table 3: Overview of key design features and benefits of the Observatory

Choose what science your satellite will be used to study, and then decide what wavelengths, instruments, and optics will help you learn the most about the science you've chosen. After you launch your satellite, you'll see what it looks like, and learn what real mission has data similar to the one you created. You'll discover a large range of astronomical missions, dating from the 1980s to today.


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Playing Hints:

As you make your choices, consider what science topics and wavelengths may be complementary. The number of options you will be allowed to be choose will be limited so you'll have to try to make the best decisions you can based on the parameters of the level you are playing. Sometimes there will be options that are grayed out and unavailable to choose. This because they may not be scientifically or technologically viable choices.

You can change what you have chosen at any time up to launch by using the back and forward buttons, and clicking on an icon will either select or deselect it. Be careful with your choices - if you try to combine too many uncomplimentary things, your satellite might end up a mess! You might want to start with a smaller mission on Level 1 and work your way up to the larger missions of Level 3. Good luck!


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Lee Feinberg talks about the top 3 things that Webb can do that Hubble cannot and more.

Paul Geithner (Webb Deputy Project Manager, Technical) provides answers to questions about the kind of freezing temperatures the Webb telescope will endure in space. (General Public)

The Webb telescope is a showcase for new technologies. Recently Paul Geithner provided a closer look at the technologies on the observatory. (General Public)

Paul Geithner provides insight on why the Webb telescope focuses on the infrared. (General Public)

Paul Geithner discusses progress, plans and next steps in building the Webb Telescope. (General Public)

Dr. John Mather (Nobel Laureate and Webb Senior Project Scientist) answering questions on Reddit. (General Public)

Dr. John Mather captured on Twitter during our first Tweet Chat. (General Public)

Dr. John Mather captured on Twitter during our second Tweet Chat. (General Public)

Dr. Mark Clampin (Webb Observatory Project Scientist) answers questions about Webb and exoplanets.

During SXSW 2014, we held a tweet-chat with some of the scientists on the"First Signs: Finding Life on Other Planets" panel.

Women with diverse jobs on the James Webb Space Telescope answered questions about the female experience working on a NASA flagship mission in the TwoXChromosomes subreddit.

During the USA Science & Engineering Festival in April 2014 and focused on STEM (Science, Technology, Engineering, Math) topics.

MIT's Dr. Sara Seager answered questions about exoplanets, the search for life, and the next technologies (like Webb!)

Technical FAQ on a variety of mission issues, aspects and capabilities. ( For the science/technical community.)

Webb and its Science Programs

Webb is the James Webb Space Telescope, sometimes called Webb, a facility-class space observatory operating in the visible, near and mid infrared. Webb's 6.6-meter diameter primary mirror has a 25-square-meter collecting area formed from eighteen hexagonal segments, and will be diffraction limited at 2 microns. It is a joint project of NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA). The telescope will be an infrared-optimized general-observer facility with four science instruments: a near-IR camera (0.6-5 microns) from the University of Arizona a near-IR spectrograph (1-5 microns) from ESA a near-IR imager and slitless spectrograph (0.7 &ndash 4.8 microns) from CSA and a mid-IR camera/spectrograph (5-28.5 microns) provided by the Jet Propulsion Laboratory, ESA and a nationally funded consortium of European institutes. In addition, CSA is providing the Fine Guidance Sensor. Webb is projected to launch in 2021 on an Ariane 5 ECA rocket to an orbit around the second Sun-Earth Lagrange point.

For more information, see the Project website. A detailed description of the science and implementation for Webb has been published (Gardner et al. 2006, Space Science Reviews, 123, 485 available without subscription Additional discussions of Webb science are in a series of science white papers.

We send out a Webb email newsletter several times a year (sign upon our For Scientists page) and hold Webb Town Hall meetings at the winter meetings of the American Astronomical Society.

There is a lot of information about Webb on the STScI website, and articles about Webb in the STScI newsletter.

If your institution would like to have a colloquium talk about Webb, or if you would like a talk about Webb at a conference you are organizing, please contact the Webb science team at: [email protected] We are also available for public talks.

Webb is named after James E. Webb (1906 &ndash 1992), NASA's second administrator. Webb is best known for leading Apollo, a series of lunar exploration programs that landed the first humans on the Moon. However, he also initiated a vigorous space science program that was responsible for more than 75 launches during his tenure, including America's first interplanetary explorers. For more information, see:, or Webb's official NASA biography at:

Webb Science

Topics in four areas of modern astronomy are being used to craft the engineering design of Webb: First Light and Reionization The Assembly of Galaxies The Birth of Stars and Protoplanetary Systems and Planetary Systems and the Origin of Life. In addition, Webb's instrument suite will have wide applicability across a broad range of scientific issues. For a detailed description of Webb science see Gardner et al. 2006, SSRv, 123, 485:
( Additional discussions of Webb science are in a series of science white papers, available from:
( Most of Webb's time will be allocated through a full peer-reviewed general observing program, similar to those of the Hubble and Spitzer Space Telescopes.

Theorists predict that the first stars formed through molecular hydrogen cooling at redshifts 20 8 solar masses and cooling by atomic hydrogen became efficient. These first galaxies had about 10 6 solar luminosities in stars, which corresponds to 1.4 nJy, or AB=31. Webb can detect these first galaxies with an ultra-deep field of about 100 hours per filter. The first galaxies then reionized the local inter-galactic medium, in a process that concluded by z=6. Using near-infrared spectroscopy of the bright z>7 quasars, galaxies or gamma-ray bursts, Webb will detect the Gunn-Peterson trough and patchy absorption that indicates the process of reionization.

Galaxy assembly is a process of hierarchical merging, during which the dark matter, gas, stars, metals, morphological structures and active nuclei build up to form the Hubble Sequence that we see today. Webb will conduct deep-wide surveys of galaxies in the rest-frame optical and near infrared over the redshift range 1 -->

Webb Observations

Webb possesses a combination of large aperture, diffraction-limited image quality, and infrared sensitivity over a broad wavelength range hitherto not available from ground- or space-based facilities. Webb has a larger collecting area than Hubble and its capabilities extend to longer wavelengths in the infrared. Webb is also much larger than Spitzer, providing greater sensitivity and finer angular resolution at wavelengths shorter than 28.5 microns. With multi-object and integral field spectroscopy, Webb's instruments provide capability that Hubble and Spitzer don't have. Its capabilities will let us understand the full population of galaxies at redshifts from 6 to 10 (for example to determine why we are finding early galaxies that are brighter and older than some theoretical predictions) and to detect the first galaxies to form as early as redshift 15. Webb is also needed to explore the assembly of galaxies and their nuclear black holes and how they are inter-related through processes such as feedback. It will trace the earliest stages of stellar evolution, penetrating the dense cold cloud cores where stars are born. It will obtain spectra to reveal the conditions in protoplanetary disks and to search for biologically important molecules, and will map the evolution of planetary systems by imaging debris disks and by studying exoplanets through coronagraphic imaging and transit spectroscopy.

Webb is designed to be complementary to existing and future ground-based facilities, making observations that are not possible from the ground, regardless of ground-based telescope aperture. The Astronomy and Astrophysics Advisory Committee, which evaluates ground- and space-based programs by NASA, NSF, and the Department of Energy, commissioned an extensive report on the complementary natures of Webb and a 30-meter ground-based telescope (available at Between 1 and 2.5 microns, Webb's strengths are complementary to those of the next-generation 30-meter aperture telescopes. Webb's wavelength coverage extends to 28.5 microns beyond about 2.5 microns, where ground-based sensitivity is severely limited by thermal emission from the atmosphere, Webb's sensitivity advantage will be immense.

The policies for Webb observers will be very similar to those of the other Great Observatories, with more than 80% of the observing time available to those submitting general observing (GO) proposals. An additional 10% of the time is Director's Discretionary Time, while the remaining 10% of the first five years is Guaranteed Time. The current expectation is that GO programs will start in the first year of the mission with a Cycle 1 call for proposals nominally being issued one year before launch. Cycle 1 is expected to include a mix of small, medium and large GO programs. Guaranteed time observers will complete their programs in the first three years of the mission. During the first year of operation there will be an Early Release Science (ERS) program that uses the Director's Discretionary time. The ERS programs will be competitively selected and ensure open access to representative datasets in support of the preparation of Cycle 2 proposals, and will engage a broad cross-section of the astronomical community in familiarizing themselves with JWST data and scientific capabilities. No specific decision has been taken regarding Legacy, Treasury or Key programs involving non-proprietary datasets. It is expected that the community will have the opportunity to comment on these ideas through a community workshop and/or a User Committee and that any initiative will be properly advertised and open to the astronomical community. NASA is planning for all Webb data to be public one year after the data are first available to the observer, similar to the policies for the Hubble Space Telescope, and that Education/Public Outreach efforts will also be similar to those for Hubble. Astronomers throughout the world will be able to request data from the Webb archive through the Internet. The public will also be able to view many of Webb's pictures through press release and image release archives on the Internet.

Webb will have a mission lifetime of not less than 5-1/2 years after launch, with the goal of having a lifetime greater than 10 years. The lifetime is limited by the amount of fuel used for maintaining the orbit, and by the testing and redundancy that ensures that everything on the spacecraft will work (mission assurance). Webb will carry fuel for a 10-year lifetime (with margin) the project will do mission assurance testing to guarantee 5 years of scientific operations starting at the end of the commissioning period 6 months after launch.

Webb's Budget

The full-scale model was built and is supported entirely with Northrop Grumman internal funds.

Webb's Instruments

The Near-Infrared Camera (NIRCam) provides filter imaging in the 0.6 to 5.0 micron range. With a dichroic splitting the light at 2.4 microns, NIRCam provides simultaneous imaging of a 2.2 by 4.4 arcmin 2 field of view in two filters. The short wavelength channel contains eight 2048 by 2048 pixel detectors with 32 milliarcsec pixels, and the long wavelength channel contains two 2048 by 2048 pixel HgCdTe detectors with 65 milliarcsec pixels. NIRCam contains 7 broad-band filters, 12 medium-band filters, several narrow-band filters and long wavelength slitless grisms. It contains the weak lenses and other hardware that will be used for wavefront sensing for the telescope. NIRCam contains a coronagraphic capability. NIRCam broad-band imaging will reach 11.4 nJy (AB=28.8) point-source detection at 2.0 microns, 10 sigma in 10,000 seconds.

The Near-Infrared spectrograph (NIRSpec) provides three different spectroscopic capabilities over the 0.6-5.0 micron domain. In its multi-object spectroscopy (MOS) mode, spectra of more than 100 sources can be obtained over a field of view of 9 square-arc-minutes. The selection of the spectroscopic targets for the MOS mode is performed using a state-of-the-art micro-electro-mechanical system (MEMS) that contains a total of more than 250,000 individually addressable micro-shutters. Micro-shutters will be opened at the location of the selected spectroscopic targets, each of them creating a small aperture of approximately 200 by 450 milli-arc-seconds on the sky.

NIRSpec also provides an Integral Field Unit (IFU) mode for spatially resolved spectroscopy of individual objects. Thanks to the use of an image-slicer, the IFU mode allows to obtain 900 spectra per exposure covering a 3 by 3 arc-seconds field of view with a spatial sampling of 100 milli-arc-seconds. Last but not least, a SLIT mode is available that will allow users to perform high-contrast spectroscopy using one of the 5 available slits. One of these slits is in fact a square 1.6-arc-second aperture introduced specially for the observation of extra-solar planet transits.

Three different spectral resolving power ranges will be available. Two series of 3 gratings will yield spectral resolving powers of R

2700 in 4 spectral bands covering the 0.7-5.0-micron domain. A prism will yield spectral resolving powers between 30 and 270 in a single spectral band covering the complete 0.6-5.0-micron domain.

The NIRSpec sensitivity in MOS mode will be 132 nJy (AB=26.1) in the continuum at 3 micron and at R

1000, the line sensitivity will reach 1.8 10 -18 erg s -1 cm -2 at 2 microns. These values are for a signal to noise of 10 and a series of 10 exposures of 1000s each.

The Near-Infrared Imager and Slitless Spectrograph provides three unique scientific capabilities over a field of view of 2.2 by 2.2 arcmin 2 . It conducts R

150 slitless spectroscopy at 0.8 to 2.25 microns optimized for Lyman alpha emission-line galaxy surveys. It conducts defocused R

700 slitless spectroscopy at 0.7 to 2.5 microns optimized for exoplanet transit spectroscopy of bright host stars. It uses a 7-aperture non-redundant mask to provide sparse-aperture interferometric imaging at 3.8, 4.3 and 4.8 microns, optimized for studying exoplanets. The NIRISS dectector is a single 2048 by 2048 pixel detector array with 65 milliarcsec pixels. NIRISS R

150 slitless spectroscopy will reach 5.5 x 10 -18 ergs s -1 cm -2 line sensitivity at 1.4 microns, 10 sigma in 10,000 seconds.

The Mid-Infrared Instrument (MIRI) provides imaging and spectroscopy over the wavelength range 5 to 28.5 micron. The imaging module provides broad-band imaging, coronagraphy and low-resolution slit spectroscopy. It has a 1024 by 1024 pixel detector array with 110 milliarcsec pixels. The coronagraphy is done with quarter-phase mask coronagraphs at 10.65, 11.4 and 15.5 microns, and a Lyot stop optimized for 23 microns. The low-resolution slit operates over 5 to 10 microns with R

100. MIRI uses an image slicer and dichroics to provide imaging spectroscopy over four simultaneous concentric fields of view ranging from 3 to 7 arcsec on a side. The spectral resolution ranges from R

2400 to 3600. MIRI spectroscopy uses two 1024 by 1024 Si:As arrays with plate scales between 200 to 470 milliarcsec. MIRI imaging sensitivity is 700 nJy (AB=24.3) at 10.0 microns and 8.7 &muJy (AB=21.6) at 21.0 microns. MIRI spectroscopic line sensitivity is 1.0 × 10 -17 erg s -1 cm -2 at 9.2 microns and 5.6 × 10 -17 erg s -1 cm -2 at 22.5 microns. These are 10 sigma in 10,000 seconds.

Webb's Technology

For status info, including recent milestones and what's next, view this section of our website.

Webb uses Teledyne HAWAII-2RG detector arrays for the NIRCam, NIRSpec, and FGS/NIRISS. Both NIRSpec and FGS use 5 micron cutoff detectors. NIRCam's short wavelength channels use 2.5 micron cutoff detectors, while NIRCam's long wavelength channels use 5 micron cutoff detectors identical to those in NIRSpec and FGS. For approximate calculations, the system-level read noise of all 3 near-infrared instruments is about 20 e- rms per correlated double sample, dark current is about 0.01 e-/s/pixel, and the QE is 70% from 0.6-1 microns and 80% from 1 micron to 5 microns. The different instruments use different readout modes with different numbers of non-destructive samples to meet their requirements. For a typical 1000 second long science integration, the total detector system noise is about 10 electrons rms for NIRCam and 6 electrons rms for NIRSpec and NIRISS. This performance is sufficient to achieve the sensitivity listed below.

The MIRI detectors build on the heritage from the Infrared Array Camera (IRAC) on Spitzer, but with significant performance enhancements such as the 1024 by 1024 pixel format, a lower read noise, and modifications in the detector prescription for better performance in the 5 to 10 micron range. Excellent detector arrays have been produced at Raytheon Vision Systems (RVS) which meet the instrument requirements for sensitivity. They have been further characterized at JPL and have been integrated into the MIRI Optical System the flight instrument has completed performance tests at the Rutherford Appleton Laboratory and is being prepared for delivery to Goddard for integration into the ISIM. For approximate sensitivity calculations, see

The instrument sensitivities are given in the following table:

Click to view high rez image

Sensitivity is defined to be the brightness of a point source detected at 10 &sigma in 10,000 s. Longer or shorter exposures are expected to scale approximately as the square root of the exposure time. Targets at the North Ecliptic Pole are assumed. The sensitivities in this table are subject to change. Prototype exposure time calculators are available at the Space Telescope Science Institute website.

Webb requires several new technologies, but these have been validated by testing and external review many years prior to launch. The program has a seven-year integration and test (I&T) plan to validate the flight hardware in an incremental and thorough way. The Project has purposely phased the contingency funding to ensure it fully covers this I&T phase, where most of the risk is, and to help resolve any problems that crop up during I&T. The deployments involved in Webb are being provided by Northrop Grumman, the world's leader in satellite deployments. NG has built satellites with more difficult and complex deployments, including 640 deployments with more than 2000 elements, with no mission failures. The Project follows NASA standard management requirements in which passage through each development stage is gated by independent expert review. The Project is managed by Goddard Space Flight Center whose mission success record exceeds that of any civil space sector organization (government or private).

The Webb thermal concept is rooted in the experience with Spitzer. The performance of that mission demonstrates the accuracy of the thermal models that were used to predict its operating temperature through the same kind of radiative cooling being used with Webb. The Spitzer outer shell &ndash which is analogous to the cold part of Webb &ndash is running at exactly the temperature (35 K) predicted by its thermal models. An extensive program of iterative testing and modeling with full-size components &ndash "pathfinders" will verify the Webb models. Pathfinders of increasing fidelity are constructed, along with tests of smaller assemblies (electrical harness, multi-layer insulation, radiator coatings). The pathfinders are compared with detailed thermal models so that scientists and engineers can be confident that the "bootstrapping"process results in a good physical understanding of the hardware. This understanding is verified by thermal vacuum testing. Because no single thermal-vacuum test can simulate realistic operational conditions for a fully integrated Webb observatory, a series of tests will verify performance of individual assemblies (instrument module, sunshield, spacecraft bus). These are followed by a comprehensive thermal test that involves the complete telescope and instrument module. Temperature data gathered during these tests are used to fine-tune thermal models to make them more representative of flight hardware. Independent thermal models are developed by NASA and the prime contractor team to mitigate risk. Finally, the Project uses external reviewers with relevant experience to assess the Webb thermal design and testing approach.

Because Webb, like virtually every satellite ever constructed, will not be serviceable it employs an extensive seven year integration and test program to exercise the system and uncover any issues prior to launch so they might be remedied. Unlike Hubble, which orbits roughly 350 miles above the surface of Earth and was therefore accessible by the Space Shuttle, Webb will orbit the second Lagrange point (L2), which is roughly 1,000,000 miles from Earth. There is currently no servicing capability that can be used for missions orbiting L2, and therefore the Webb mission design does not rely upon a servicing option.

The gyroscopes on HST and Chandra are mechanical devices dependent on bearings for their function, and they face problems typical of such designs. Webb has adopted a different gyroscope technology. The "Hemispherical Resonator Gyroscope" (HRG) uses a quartz hemisphere vibrating at its resonant frequency to sense the inertial rate. The hemisphere is made to resonate in a vacuum, and the hemisphere's rate of motion is sensed by the interaction between the hemisphere and separate sensing electrodes on the HRG housing. The result is an extremely reliable package with no flexible leads and no bearings. The internal HRG operating environment is a vacuum, thus once the gyroscope is in space any housing leaks would actually improve performance. The HRG eliminates the bearing wear-out failure mode, leaving only random failure and radiation susceptibility of the electronics (which all such devices share, and which can be mitigated by screening and shielding). Stress analyses of HRGs show this design has a "mean time before failure" of 10 million hours. As of June 2011, this type of device had accumulated more than 18 million hours of continuous operation in space on more than 125 spacecraft without a single failure.

The Webb primary mirror is made of 18 segments and stretches 6.6 meters from tip to tip (we round to 6.5m when discussing with the general public). Its area of slightly more than 25 square meters and its diffraction-limited resolution are approximately equivalent to a 6.0 meter conventional round mirror. At 2 microns, the FWHM of the image will be about 70 milli-arcsec.

The 18 hexagonal segments are arranged in a large hexagon, with the central segment removed to allow the light to reach the instruments. Each segment is 1.32 m, measured flat to flat. Beginning with a geometric area of 1.50 m 2 after cryogenic shrinking and edge removal, the average projected segment area is 1.46 m 2 . With obscuration by the secondary mirror support system of no more than 0.86 m 2 , the total polished area equals 25.37 m 2 , and vignetting by the pupil stops is minimized so that it meets the >25 m 2 requirement for the total unobscured collecting area for the telescope. The outer diameter, measured along the mirror, point to point on the larger hexagon, but flat to flat on the individual segments, is 5 times the 1.32 m segment size, or 6.6 m (see figure). The minimum diameter from inside point to inside point is 5.50 m. The maximum diameter from outside point to outside point is 6.64 m. The average distance between the segments is about 7 mm, a distance that is adjustable on-orbit. The 25 m 2 is equivalent to a filled circle of diameter 5.64 m. The telescope has an effective f/# of 20 and an effective focal length of 131.4 m, corresponding to an effective diameter of 6.57 m. The secondary mirror is circular, 0.74 m in diameter and has a convex aspheric prescription. There are three different primary mirror segment prescriptions, with 6 flight segments and 1 spare segment of each prescription. The telescope is a three-mirror anastigmat, so it has primary, secondary and tertiary mirrors, a fine steering mirror, and each instrument has one or more pick-off mirrors.

The Webb primary mirror consists of 18 hexagonal segments with three different prescriptions.

Hubble has a 2.4 m diameter round primary mirror. For the Advanced Camera for Surveys (ACS) and the Space Telescope Imaging Spectrograph (STIS), the central obscuration by the secondary is 0.33r, where r is the 1.2 m radius. Wide Field - Planetary Camera 2 (WFPC2) had a larger internal obscuration, which was oversized to ensure alignment, ranging between 0.39r and 0.43r. Using the 0.33r obscuration, the area of Hubble's mirror is &pi (1.2 2 ) (1-0.33 2 ) = 4.0 m 2 . Therefore, the ratio between the 25.0 m 2 Webb mirror and the Hubble mirror is 6.25.

JWST will employ Rockwell Collins Deutschland GBMH (Formerly Teldix) reaction wheels. These wheels have heritage traceable to the Teldix wheels flown on NASA's Chandra, EOS Aqua and Aura Missions.

Webb Integration and Testing

Webb will be tested incrementally during its construction, starting with individual mirrors and instruments (including cameras and spectrometers) and building up to the full observatory. Webb's mirrors and the telescope structure are first each tested individually, including optical testing of the mirrors and alignment testing of the structure inside a cold thermal-vacuum chamber. The mirrors are then installed on the telescope structure in a clean room at Goddard Space Flight Center (GSFC). In parallel to the telescope assembly and alignment, the instruments are being built and tested, again first individually, and then as part of an integrated instrument assembly. The integrated instrument assembly will be tested in a thermal-vacuum chamber at GSFC using an optical simulator of the telescope. This testing makes sure the instruments are properly aligned relative to each other and also provides an independent check of the individual tests. After both the telescope and the integrated instrument module are successfully assembled, the integrated instrument module will be installed onto the telescope, and the combined system will be sent to Johnson Space Flight Center (JSC) where it will be optically tested in JSC's largest vacuum chamber, which is being retrofitted for deep cryogenic operation. The process includes testing the 18 primary mirror segments acting as a single primary mirror, and testing the end-to-end system. The final system test will assure that the combined telescope and instruments are focused and aligned properly, and that the alignment, once in space, will be within the range of the actively controlled optics. In general, the individual optical tests of instruments and mirrors are the most accurate. The final system tests provide a cost-effective check that no major problem has occurred during assembly. In addition, independent optical checks of earlier tests will be made as the full system is assembled, providing confidence that there are no major problems.

The most expensive tests of a large space telescope are the final system tests. The Hubble Space Telescope did not have a final system test &ndash which could have caught the problem in the fabrication of the Hubble primary mirror &ndash because it was deemed too complex and expensive. Unlike Hubble, Webb is not designed for servicing thus Webb must be done right. The challenge has been to design a test strategy that assures success but is also affordable. The Webb test plan emphasizes incremental testing, accompanied by independent checks at each level of assembly to minimize the uncertainties left for the final system test. The plan does include a final system test, and this test makes use of the Webb active optics. This final test will assure that Webb can be aligned on-orbit, making the test cost effective yet retaining adequate redundancy and accuracy to detect any problems.

The overall Webb Project testing strategy will test all individual components as early as possible in the project schedule after they have been manufactured, so that time is available to fix or replace them if needed without costly schedule impacts. More complex systems, such as science instruments and operational systems, will get tested later in the Project schedule: early enough that fixes can be implemented if needed without major schedule impacts, but late enough in the project that necessary design effort and analyses have adequate time to complete. All critical Webb components and systems will be independently verified at the lowest possible level of assembly. In this approach, subtle manufacturing errors or system performance flaws have the best chance of surfacing early and unambiguously, which will minimize the risk of large and costly schedule impacts later in the project.

Many lessons were learned from building UV, optical, infrared and X-ray missions like Hubble, Spitzer and Chandra, including a key aspect of the Webb strategy: early independent tests of key optical parameters, with the highest performance tests performed at the lowest levels of assembly. The strategy also includes a full-up system test of the final assembly to catch significant errors anywhere in the optical chain. The lessons learned from earlier cryogenic telescopes have directly led to a more robust cold-testing strategy, including early testing. The Webb test program will also employ specific techniques that have been shown to be effective in earlier programs, such as the precision photogrammetry used in WMAP testing (already applied with excellent results to ISIM structure cryo-testing) and the auto-collimation optical testing approach utilized by Spitzer.

Webb and NASA Programmatic Issues

NASA is the lead partner in Webb, with significant contributions from the European Space Agency (ESA) and the Canadian Space Agency (CSA). Northrop Grumman is the main NASA industrial contractor, responsible for building the optical telescope, spacecraft bus, and sunshield, and for preparing the observatory for launch. NGAS is leading a team including two major sub-contractors: Ball Aerospace and Harris (formerly ITT-Exelis). The three principal beryllium mirror subcontractors to Ball Aerospace are Coherant (formerly Tinsley Laboratories), General Dynamics Global Imaging Technologies (formerly Axsys Technologies), and Materion (formerly Brush Wellman Inc.) The instrument complement is provided as follows:

  • The Mid-Infrared Instrument (MIRI) is provided by a consortium of European countries and the European Space Agency (ESA) and the NASA Jet Propulsion Laboratory (JPL) with detectors from Raytheon Vision Systems.
  • The Near-Infrared Spectrograph (NIRSpec) is provided by ESA.
  • The Near-Infrared Camera (NIRCam) is built by the University of Arizona working with Lockheed-Martin.
  • The Near-Infrared Imager and Slitless Spectrograph (NIRISS) are provided by the Canadian Space Agency (CSA).
  • All of the near-infrared detectors are supplied by Teledyne Technologies, Inc.

The launch vehicle and launch services are provided by ESA. The Science and Operations Center will be at the Space Telescope Science Institute (STScI).

The Webb project has partners or contractors in 27 states and the District of Columbia. In addition, in a program with the Girl Scouts of the USA, Webb has Education and Public Outreach activities in 41 states, the District of Columbia, Guam and a US Air Force Base in Japan.

Fourteen countries are providing hardware components to build the James Webb Space Telescope: Austria, Belgium, Canada, Denmark, France, Germany, Ireland, Italy, the Netherlands, Spain, Sweden, Switzerland, the United Kingdom and the United States of America. In addition: Finland, Greece, Luxembourg, Norway, Poland, Portugal, The Czech Republic and Romania are members of the European Space Agency and are also contributing to the success of Webb. The launch of Webb will take place in French Guiana, an overseas department of France located in South America. After launch, scientists from around the world will use the telescope for astronomical investigations.

Science goals and their associated measurement requirements ultimately define mission sizes. For some science questions the appropriate mission size is large, for others smaller missions will suffice. The 2000 decadal survey defined a number of scientific challenges some of which required technically ambitious missions. Webb was the top-ranked priority in the 2000 Decadal Survey. It addresses science that cannot be done by any other means. The balance between big and small missions is the result of prioritization in the Decadal Survey and NASA's implementation strategy. Historical publication and citation rates of the Great Observatories, as well as flagship Solar System missions like Cassini and Galileo, show that they are extremely productive facilities, enabling thousands of scientists to do forefront research with state-of-the-art instrumentation.

The formal answer to this question is "No" as the guidelines for the survey removed from reprioritization those missions in development. "In development" means in phase C, having passed PDR and been confirmed, which happened to Webb in 2008. However, Webb is a major component of the NASA program, and the Decadal Survey report discussed Webb's role in astronomy. The report, "New Worlds, New Horizons in Astronomy and Astrophysics," identifies three science themes for the next decade: Cosmic Dawn, New Worlds, and Physics of the Universe. As is made clear in the survey, the James Webb Space Telescope (Webb) plays a critical scientific role in the two first themes, and a strong supporting role for the third theme. Many of the survey recommendations build on groundwork to be laid by Webb for the next decade of astronomical exploration. A more detailed description of the role of Webb in the Decadal Survey Report is given in a white paper by Hammel et al., available at:

Community input to Webb comes through several paths. The Science Working Group provides regular input to the NASA Headquarters Program Scientist and the Goddard Space Flight Center Project office. The SWG includes the NASA Project scientists, the principal investigators of each science instrument team and interdisciplinary scientists who are expert in the broad range of science encompassed by the mission. Their contact information can be found at: The NASA Advisory Council Science Committee and its Astrophysics Subcommittee, ( also represents the broad astrophysics community, and provides input on the astrophysics portfolio including Webb to the NASA Advisory Council. Finally, as the operations phase of the Webb mission approaches, the Space Telescope Science Institute will convene a Users Committee to advise on operations aspects.

The National Academy of Sciences recommended the WFIRST mission as the top priority for space astrophysics after JWST.


The JWST 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 over six times as large, 25.4 m 2 (273 sq ft), using 18 hexagon mirrors with 0.9 m 2 (9.7 sq ft) obscuration for the secondary support struts. [26]

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
  • 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)) thus the telescope itself radiates strongly in the infrared bands. [27]

The JWST will operate near the Earth–Sun L2 (Lagrange point), approximately 1,500,000 km (930,000 mi) beyond Earth's orbit. 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 made post-launch repair or upgrade of the JWST hardware virtually impossible with the spaceships available during the telescope design and fabrication stage. Objects near this Lagrange point can orbit the Sun in synchrony with the Earth, allowing the telescope to remain at a roughly constant distance [28] and use a single sunshield to block heat and light from the Sun and Earth. This arrangement will keep the temperature of the spacecraft below 50 K (−223.2 °C −369.7 °F), necessary for infrared observations. [10] [29]

Three-quarter view of the top

Sunshield protection Edit

To make observations in the infrared spectrum, the 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 Earth–Sun L2 point keeps all three bodies on the same side of the spacecraft at all times. [30] 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. [28] 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. [ citation needed ]

The five-layer sunshield, each layer as thin as a human hair, [31] is constructed from Kapton E, a commercially available polyimide film from DuPont, with membranes specially coated with aluminum on both sides and doped silicon on the Sun-facing side of the two hottest layers to reflect the Sun's heat back into space. [32] Accidental tears of the delicate film structure during testing in 2018 were among the factors delaying the project. [33]

The sunshield is designed to be folded twelve times so that it will fit within the Ariane 5 rocket's (4.57 × 16.19 m) payload fairing. Once deployed at the L2 point, it will unfold to 14.162 × 21.197 m. The sunshield was hand-assembled at ManTech (NeXolve) in Huntsville, Alabama, before it was delivered to Northrop Grumman in Redondo Beach, California, for testing. [34]

Optics Edit

JWST's primary mirror is a 6.5-meter-diameter gold-coated beryllium reflector with a collecting area of 25.4 m 2 . 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. [35] 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 is a lack of environmental disturbances of a telescope in space. [36]

JWST's optical design is a three-mirror anastigmat, [37] 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 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. [2] [38] 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. [ citation needed ]

The final segment of the primary mirror was installed on 3 February 2016, [39] and the secondary mirror was installed on 3 March 2016. [40]

Scientific instruments Edit

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. [41]

    (Near InfraRed Camera) is an infrared imager which will have a spectral coverage ranging from the edge of the visible (0.6 micrometers) through the near infrared (5 micrometers). [42][43] 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 located in Palo Alto, California. [44] (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

NIRCam and MIRI feature starlight-blocking coronagraphs for observation of faint targets such as extrasolar planets and circumstellar disks very close to bright stars. [47]

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. [49]

Spacecraft Bus Edit

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. [50] Along with the sunshield, it forms the spacecraft element of the space telescope. [51] The other two major elements of the JWST are the Integrated Science Instrument Module (ISIM) and the Optical Telescope Element (OTE). [52] Region 3 of ISIM is also inside the Spacecraft Bus region 3 includes ISIM Command and Data Handling subsystem and the MIRI cryocooler. [52]

The Spacecraft Bus is connected to Optical Telescope Element via the Deployable Tower Assembly, which also connects to the sunshield. [50]

The structure of the Spacecraft Bus weighs 350 kg (770 lb), and must support the 6.5-ton space telescope. [53] It is made primarily of graphite composite material. [53] 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 planned 2021 launch. The bus can provide pointing precision of one arcsecond, and isolates vibration down to two milliarcseconds. [54] [ clarification needed ]

The Spacecraft Bus is on the Sun-facing "warm" side and operates at a temperature of about 300 K. [51] 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 the shade of the spacecraft sunshield. [51]

Another important aspect of the Spacecraft Bus is the central computing, memory storage, and communications equipment. [50] 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. [50] 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. [50]

The desire for a large infrared space telescope traces back decades. In the United States, the Shuttle Infrared Telescope Facility (SIRTF) was planned while the Space Shuttle was in development, and the potential for infrared astronomy was acknowledged at that time. [56] Compared to ground telescopes, space observatories were free from atmospheric absorption of infrared light. Space observatories opened up a whole "new sky" for astronomers. [56]

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.

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. [27] If not, the background heat of the device itself overwhelms the detectors, making it effectively blind. [27] 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. [27] 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. [27]

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. [57]

Selected space telescopes and instruments [58]
Name Year Wavelength
IRT 1985 1.7–118 0.15 Helium
Infrared Space Observatory (ISO) [59] 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 [60]
Herschel Space Observatory 2009 55–672 3.5 Helium
JWST 2021 0.6–28.5 6.5 Passive, and cryocooler (MIRI)

The James Webb telescope's delays and cost increases can be compared to the Hubble Space Telescope. [61] 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), [61] but by the time it was sent into orbit in 1990, the cost was about four times that. [61] In addition, new instruments and servicing missions increased the cost to at least US$9 billion by 2006. [61]

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. [ citation needed ]

Background Edit

Selected events
Year Events
1996 NGST started.
2002 named JWST, 8 to 6 m
2004 NEXUS cancelled [62]
2010 MCDR passed
2011 Proposed cancel
2021 Planned launch

Early development work for a Hubble successor between 1989 and 1994 led to the Hi-Z [63] telescope concept, a fully baffled [Note 1] 4-meter aperture infrared telescope that would recede to an orbit at 3 AU. [64] This distant orbit would have benefited from reduced light noise from zodiacal dust. [64] Other early plans called for a NEXUS precursor telescope mission. [65] [66]

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. [67] The 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. [15] The result was the NGST concept, with an 8-meter aperture and located at L2, roughly estimated to cost US$500 million. [15] In 1997, NASA worked with the Goddard Space Flight Center, [68] Ball Aerospace & Technologies, [69] and TRW [70] to conduct technical requirement and cost studies, and in 1999 selected Lockheed Martin [71] and TRW for preliminary concept studies. [72] Launch was at that time planned for 2007, but the launch date has subsequently been pushed back many times (see table further down).

In 2003, NASA awarded the US$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 m (20 ft) primary mirror and a launch date of 2010. [73] Later that year, TRW was acquired by Northrop Grumman in a hostile bid and became Northrop Grumman Space Technology. [72]

Development Edit

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 & 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. [74] Goddard Space Flight Center is also responsible for providing the Integrated Science Instrument Module (ISIM). [41]

Cost growth revealed in spring 2005 led to an August 2005 re-planning. [75] 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. [ citation needed ]

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. [75] ESA is contributing about €300 million, including the launch, [76] and the Canadian Space Agency about $39 million Canadian. [77]

Construction Edit

In January 2007, nine of the ten technology development items in the project successfully passed a Non-Advocate Review. [78] 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. [79] 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. [ citation needed ]

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. [80] 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. [81]

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. [82]

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. [83] Final construction of the Webb telescope was completed in November 2016, after which extensive testing procedures began. [84] 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. In June 2018, NASA delayed the JWST's launch an additional 10 months to March 2021, based on the assessment of the independent review board convened after the failed March 2018 test deployment. [20] The review also found JWST had 344 potential single-point failures, any of which could doom the project. [85] In August 2019, the mechanical integration of the telescope was completed, something that was scheduled to be done 12 years before in 2007. Following this, engineers now are working to add a five layer sunshield in place to prevent damage to telescope parts from infrared rays of the Sun. [86]

Cost and schedule issues Edit

Then-planned launch and total budget
Year Planned
Budget plan
(billion USD)
1997 2007 [82] 0.5 [82]
1998 2007 [87] 1 [61]
1999 2007 to 2008 [88] 1 [61]
2000 2009 [46] 1.8 [61]
2002 2010 [89] 2.5 [61]
2003 2011 [90] 2.5 [61]
2005 2013 3 [91]
2006 2014 4.5 [92]
2008, Preliminary Design Review
2008 2014 5.1 [93]
2010, Critical Design Review
2010 2015 to 2016 6.5 [94]
2011 2018 8.7 [95]
2013 2018 8.8 [96]
2017 2019 [97] 8.8
2018 2020 [98] ≥8.8
2019 Mar 2021 [99] 9.66
2020 Oct 2021 [23] ≥10 [36]
2021 Nov 2021 [3] 9.7 [100]

The 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). [61] By October 2019, the estimated cost of the project had reached US$10 billion for launch in 2021. [36]

The telescope was originally estimated to cost US$1.6 billion, [101] 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. [94]

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. [102] [103] [104] [105] US$3 billion had been spent and 75% of its hardware was in production. [106] 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". [102] In response, the American Astronomical Society issued a statement in support of JWST, [107] as did Maryland US Senator Barbara Mikulski. [108] A number of editorials supporting JWST appeared in the international press during 2011 as well. [102] [109] [110] In November 2011, Congress reversed plans to cancel the JWST and instead capped additional funding to complete the project at US$8 billion. [111]

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. [112] [96] Because the runaway budget diverted funding from other research, a 2010 Nature article described the JWST as "the telescope that ate astronomy". [113]

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 and missed budget projections, thus extending the schedule and increasing costs further. [96] [101] [114]

One reason for the early cost growth is that it is difficult to forecast the cost of development, and in general budget predictability improved when initial development milestones were achieved. [96] By the mid-2010s, the U.S. contribution was still expected to cost US$8.8 billion. [96] In 2007, the expected ESA contribution was about €350 million. [115] With the U.S. and international funding combined, the overall cost not including extended operations is projected to be over US$10 billion when completed. [116] 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 US$8.8 billion price tag. [98] In the 27 March 2018 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 European Space Agency (ESA). [117] If this cost estimate exceeds the US$8 billion cap Congress put in place in 2011, as is considered unavoidable, NASA will have to have the mission re-authorized by the legislature. [118] [119]

In February 2019, despite expressing criticism over cost growth, Congress increased the mission's cost cap by US$800 million. [120] In October 2019, the total cost estimate for the project reached US$10 billion. [36]

Partnership Edit

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. [76] [121] The CSA will provide the Fine Guidance Sensor and the Near-Infrared Imager Slitless Spectrograph plus manpower to support operations. [122]

  • 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 Edit

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. [123]

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 Aluminium and steel measuring approximately 24 m × 12 m × 12 m (79 ft × 39 ft × 39 ft) and weighs 5,500 kg (12,100 lb). [ citation needed ]

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. [124] [125] Amber Straughn, the deputy project scientist for science communications, has been a spokesperson for the project at many SXSW events from 2013 on in addition to Comic Con, TEDx, and other public venues. [126]

The JWST 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[127]

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 (−173 °C −280 °F)).

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. [128]

Launch and mission length Edit

As of June 2021 [update] , launch is planned by November 2021, on an Ariane 5 launch vehicle from French Guiana. [3] The observatory attaches 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. [2] Its nominal mission time is five years, with a goal of ten years. [129] 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. [130] The planned five year science mission begins after a 6-month commissioning phase. [130] An L2 orbit is only meta-stable, so it requires orbital station-keeping, or the telescope will drift away from this orbital configuration. [131]

Orbit Edit

The JWST will be located near the second Lagrange point (L2) of the Earth-Sun system, which is 1,500,000 km (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 km (500,000 mi), and take about half a year to complete. [28] 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. [132] This requires some station-keeping: around 2–4 m/s per year [133] from the total budget of 150 m/s . [134] Two sets of thrusters constitute the observatory's propulsion system. [135]

Infrared astronomy Edit

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. [136] 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. [137]

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. [138] 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. [139]

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, [138] such as the molecular clouds where stars are born, the circumstellar disks that give rise to planets, and the cores of active galaxies. [138]

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. [138] 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). [46] [139]

Some of the missions in infrared astronomy that impacted JWST development were Spitzer and the Wilkinson Microwave Anisotropy Probe (WMAP) probe. [140] Spitzer showed the importance of mid-infrared, which is helpful for tasks such as observing dust disks around stars. [140] Also, the WMAP probe showed the universe was "lit up" at redshift 17, further underscoring the importance of the mid-infrared. [140] Both these missions were launched in the early 2000s, in time to influence JWST development. [140]

Ground support and operations Edit

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 US$162.2 million intended to support operations through the first year after launch. [141] 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. [36] Most of the data processing on the telescope is done by conventional single-board computers. [142] 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. [143] 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. [143]

After-launch deployment Edit

Nearly a month after launch, a trajectory correction will be initiated to place the JWST into a Halo orbit at the L2 Lagrange point. [144] [ clarification needed ]

Once in position, JWST will go through the process of deploying its sunshade, mirror, and arm, which will take around three weeks. [145] The mirror is in three pieces that will swing into place with motors. [145]

Watch the video: James Webb Space Telescope Presentation (May 2022).