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All About James Webb Space Telescope: Hubble’s Successor

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The James Webb Space Telescope(JWST) is a space telescope being jointly developed by NASA, the European Space Agency, and the Canadian Space Agency. It is planned to succeed the Hubble Space Telescope as NASA’s flagship astrophysics mission.

James Webb Space Telescope Artist Conception
James Webb Space Telescope Artist Conception (Credit: NASA)

About James Webb Space Telescope?

The James Webb Space Telescope (sometimes called JWST or Webb) will be a large infrared telescope with a 6.5-meter primary mirror. The telescope will be launched on an Ariane 5 rocket from French Guiana on 2021. 

The Webb telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

NASA Administrator James E. Webb.
NASA Administrator James E. Webb(Image Credit: NASA)

The Webb telescope was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in September 2002 after a former NASA administrator, James Webb.

Webb is an international collaboration between NASAESA (the European Space Agency), and the Canadian Space Agency (CSA). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, is managing the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

Optics on James Webb Space Telescope

Webb’s segmented primary mirror has a diameter of 6.6 meters (21.7 feet). Each of the 18 segments is 1.32 meters (4.3 feet) across. The area of the mirror is approximately 25 square meters (270 square feet) and the mass is 705 kilograms (1,550 pounds on Earth).

James Webb Space Telescope Mirror Seen in Full Bloom
James Webb Space Telescope Mirror Seen in Full Bloom. (Image Credit: NASA)

What Webb Telescope can tell us

The James Webb Space Telescope with unprecedented infrared sensitivity, will be able to peer back in time over 13.5 billion years to see the first galaxies born after the Big Bang. The combination of high resolution and infrared-detecting instruments on Webb Space Telescope will reveal stars that are currently hidden even from the powerful Hubble Space Telescope. The wealth of additional star data will allow astronomers to investigate a range of questions, from star birth to star death to the universe’s elusive expansion rate. Webb will help astronomers to compare the faintest, earliest galaxies to today’s grand spirals and ellipticals, helping us to understand how galaxies assemble over billions of years.

Keys Facts About JWST

Proposed Launch Date:December 24, 2021 5:50 PM IST(12:20 UTC, 7:20 AM EST)
Launch Vehicle:Ariane 5 ECA
Mission Duration5 – 10 years
Total payload mass:Approx 6200 kg, including observatory, on-orbit consumables and launch vehicle adaptor.
Diameter of primary Mirror:6.5 m (21.3 ft) approximately
Clear aperture of primary Mirror:25 m2
Primary mirror material:beryllium coated with gold
Mass of primary mirror:705 kg
Mass of a single primary mirror segment:20.1 kg for a single beryllium mirror, 39.48 kg for one entire primary mirror segment assembly (PMSA).
Focal length:131.4 meters
Number of primary mirror segments:18
Optical resolution:~0.1 arc-seconds
Wavelength coverage:0.6 – 28.5 microns
Size of sun shield:21.197 m x 14.162 m (69.5 ft x 46.5 ft)
Temp of sun shield layers:Layer 1:
Max temperature 383K = approx 231F

Layer 5:
Max temperature 221K = approx -80F
Min temperature 36K = approx -394F
Orbit:1.5 million km from Earth orbiting the L2 Point
Operating Temperature:under 50 K (-370 °F)
Gold coating:Thickness of gold coating = 100 x 10-9 meters (1000 angstroms). Surface area = 25 m2. Using these numbers plus the density of gold at room temperature (19.3 g/cm3), the coating is calculated to use 48.25g of gold, about equal to the mass of a golf ball. (A golf ball has a mass of 45.9 grams. Note mass does not equal size!)

The James Webb Space Telescope (sometimes called JWST or Webb) is an orbiting infrared observatory that will complement and extend the discoveries of the Hubble Space Telescope, with longer wavelength coverage and greatly improved sensitivity. The longer wavelengths enable Webb to look much closer to the beginning of time and to hunt for the unobserved formation of the first galaxies, as well as to look inside dust clouds where stars and planetary systems are forming today.


JWST Instruments

The JWST will come equipped with four science instruments that will enable observations in visible, near-infrared and mid-infrared (0.6 to 28.5 micrometers) wavelengths. 

Near-Infrared Spectrograph (NIRSpec)

Near-Infrared Spectrograph, provided by ESA with some elements provided by NASA’s Goddard Space Flight Center. A wide field (3.4′ × 3.6′) multi-object near- infrared spectrometer covering wavelengths 0.6 µm – 5 µm at spectral resolutions of R~100, R~1000 and R~2700. NIRSpec will enable large spectroscopic surveys of astronomical objects like stars or distant galaxies, made possible by the powerful Multi-Object Spectroscopy (MOS) mode that is capable of obtaining spectra of up to nearly 200 objects simultaneously.

JWST’S NEAR INFRARED SPECTROGRAPH (NIRSPEC) (Image Credit: Airbus Defence and Space GmbH)

Near-Infrared Camera (NIRCam)

Near-Infrared Camera, provided by the University of Arizona. A two-channel wide field (2.2′ × 4.4′) near-infrared camera covering wavelengths 0.6 µm – 5 µm with a large selection of filters. NIRCam will also provide key measurements for the in-orbit adjustment of the shape of JWST’s primary mirror segments. It is the observatory’s primary camera that will acquire some of the deepest near-infrared images ever obtained and detect light from the first stars and galaxies. NIRCam also has coronagraphic and spectroscopic capabilities that can be used to characterise exoplanets and planetary systems.


Mid-Infrared Instrument (MIRI)

Mid-Infrared Instrument, provided by a partnership composed of ESA, a consortium of nationally funded European institutes, NASA’s Jet Propulsion Laboratory, and NASA’s Goddard Space Flight Center (GSFC). A combined mid-infrared camera (1.3′ × 1.7′) and spectrograph (R~100 and R~3000) covering wavelengths from 5 µm to 28.3 µm. It also includes a coronagraph. MIRI will support the whole range of JWST’s science goals, from observing our own Solar System and other planetary systems to the study of the early Universe. It is the only instrument capable of mid-infrared observations and as such is cooled to -266 degrees Celsius, which is more than 30 degrees cooler than the other instruments in the JWST observatory, achieved with a cryocooler.


Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS): 

Fine Guidance System/Near-InfraRed Imager and Slitless Spectrograph, provided by the Canadian Space Agency. NIRISS comprises a wide-field  (2.2′ × 2.2′) camera that will be usable in parallel with NIRCam’s main camera to provide additional imaging capabilities, a slitless spectrograph, and a spectroscopic mode that is specially designed for exoplanet characterisation using transit spectroscopy for studying the chemical composition of an exoplanet’s atmosphere. The instrument’s accompanying Fine Guidance Sensor (FGS) will guide JWST to point precisely so that it can obtain high-resolution images and spectra.


The four instruments are housed within the JWST payload module called the Integrated Science Instrument Module (ISIM).

This photograph shows the JWST's Integrated Science Instrument Module (ISIM – the black structure) after the integration of all four of JWST's instruments.
This photograph shows the JWST’s Integrated Science Instrument Module (ISIM – the black structure) after the integration of all four of JWST’s instruments. (Image Credit: NASA/Chris Gunn)

James Webb Space Telescope VS Hubble Space Telescope

The James Webb Space Telescope is referred to as the successor of the Hubble Space Telescope.

Scientific advancement is all about “standing on the shoulders of giants” and the JWST will do just that, as its scientific goals were motivated by the results from Hubble.

The two space telescopes have different capabilities, whilst Hubble primarily observed the cosmos in optical and ultraviolet wavelengths (with some infrared capabilities.) The JWST will primarily look at the universe in infrared. Due to the expansion of the universe, light from distant objects shifts to longer wavelengths at the redder end of the spectrum — known as redshifted, according to ESA. The JWST will observe this infrared light in great detail and shed light on some of the oldest stars and galaxies in the universe.

Another big difference between the James Webb Space Telescope and the Hubble Space Telescope is that JWST will orbit the sun, whist Hubble orbits Earth. JWST will be too far away to be serviced, unlike Hubble which was accessed and serviced by space shuttle missions.

Webb, an orbiting infrared observatory, will complement and extend the discoveries of the Hubble Space Telescope, with longer wavelength coverage and greatly improved sensitivity.

JWST Videos

Launch Animation

29 Days on the Edge

Track James Webb Space Telescope Launch HERE





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