James Webb Space Telescope (JWST)

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JWST Full-scale model at NASA Goddard
Credit: NASA

The James Webb Space Telescope (JWST) is an orbiting observatory designed by NASA, the European Space Agency and the Canadian Space Agency. It is scheduled to launch in December 2021.

JWST is planned to be a successor to the Hubble Space Telescope (HST). JWST has a larger mirror than the HST which allows it to see fainter objects and smaller detail. It will also observe longer wavelengths of light (infrared) than the HST. 

 

What will the JWST do?

JWST has been built to look back in time to the early Universe. What did the first stars and galaxies look like? How do stars and galaxies evolve? Do planets like Earth orbit other stars? Can we learn anything about dark matter and dark energy? And many more questions!

The entire telescope has a mass of around 6,200 kg. This is about the same as an African Bush Elephant! It includes a 6.5 metre diameter mirror which will collect light from space.

Artist's impression of the James Webb Space Telescope
Credit: NASA/JWST

JWST’s huge mirror is made of 18 hexagonal segments. These will unfold and adjust to form one large mirror after the telescope has launched. JWST also has a tennis court sized sun-shield. This stops light from the Sun (and reflected off the Earth and Moon) from heating up its detectors. The detectors must be kept at a cool −266 °C to work.

The JWST team have produced a video showing the planned deployment sequence.

 

How will the JWST do science in space?

The JWST will use specially designed scientific instruments to collect the information needed to answer its big science questions. The information is sent back to scientists on Earth. The instruments on board are:

  • NIRCam: A wide field (2.2' × 4.4') near-IR camera covering wavelengths 0.6 - 5 µm;
  • NIRSpec: A wide field (3.5' × 3.5') multi-object near-IR spectrograph covering wavelengths 0.6 μm - 5 µm at spectral resolutions of R~100, R~1000 and R~2700;
  • MIRI: A combined mid-IR camera (1.4' × 1.9') and spectrograph (R~3000) covering wavelengths 5 - 28 µm;
  • FGS/NIRISS: A combined observatory Fine Guidance System and near-infrared imager and slitless spectrograph covering wavelengths 0.6 μm - 5 μm with a 2.2' × 2.2' field of view.

 

How will JWST get to space?

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Lagrange points
Sun credit - ESA, Earth credit - NASA, Moon & graphic credits - NSO

As of November 2021, the launch date is set for December 22 2021. But this may well change. The launch of JWST has been delayed several times. It was originally planned to launch in 2007!

The European Space Agency (ESA) are providing an Ariane 5 rocket to launch the NASA-made telescope into space. The telescope is far too wide to fit into the rocket. The engineers have designed the telescope to fold up to fit into the nose of the rocket.

The JWST will launch from a European Spaceport near Kourou in French Guiana. This location is near to the equator which helps give the rocket an additional push into space!

 

Where will the JSWT observe from?

JWST will be 1,500,000 km from Earth. This is much further away than the Hubble Space Telescope. It will orbit the Sun from Lagrange Point 2 (also known as L2). This is a special location that lets JWST stay in line with the Earth as it moves around the Sun. However, it also means it is too far away to be easily repaired if something goes wrong.

The Sun and the Earth's gravitational pull will stop the telescope from moving around too much. Only small infrequent rocket thrusts will be needed to maintain its orbit at L2. This L2 point also means that the JWST will keep up with the Earth as it orbits the Sun.

There are several Lagrange points. L2 has been chosen because it has the Earth, Moon and Sun behind it, which makes it the perfect 'dark sky' to observe from.

  • L1 offers excellent views of our Sun and is where the Solar and Heliospheric Observatory (SOHO) Satellite is sited.
  • L2 is close to Earth which is great for communications for course corrections and limited fixes.
  • L3 is very far away and is always hidden from us by our Sun, so we may never find a use for it.
  • L4 and L5 are also great sites, except they are very far from Earth, so L2 is the favourite!