The James Webb Space Telescope

The James Webb Space Telescope JWST

A new era of space observation is about to begin, the James Webb space telescope is a revolution in the study of our universes' history. It will enable us to look further than ever before, allowing us to gaze upon the earliest galaxies to form after the big bang. However, the JWST is not only about to take us billions of years into the past, it will also enable us to examine exoplanets with more accuracy than ever before.


America (NASA), Europe (ESA) and, Canada (CSA) have come together to create the largest, most powerful, and most expensive telescope in history with an estimated cost of $10 USD Billion {1}, and it now has a finalised launch date 18th of December 2021, after being delayed for years. On this date the JWST will launch in its' folded configuration, from an ESA launch pad in French Guiana, carried by the Ariane 5 launch vehicle which will provide roughly 26 minutes of thrust and put the JWST on a trajectory towards its destination the orbit of the 2nd Lagrangian point L2 (A point of force equilibrium between the Sun and Earth).

The L2 point is great for space observation as it puts the Earth, Moon, and Sun behind the telescope providing a clear view of deep space, whilst still allowing easy communication with Earth, however, the L2 point orbit is unstable, and this means that the orbit will decay over time and the JWST will 'fall' into an unwanted orbit. To keep the JWST in the L2 orbit it's required to perform an orbital correction burn roughly once a month, unfortunately, this gives the JWST a limited life span in the L2 orbit as the fuel it consumes is finite .{2}

The Trip to L2/ The 14 Days of Terror

In its month-long journey to the L2 point the JWST will have to complete the so-called 14 days of terror. This refers to the 14 days over which the JWST will unfold its self, but first, approximately 3 minutes after detaching from the Ariane 5 launch vehicle the JWST will 'automatically' unfold its solar array. We say automatically as this action is one of only 2 actions the JWST will ever perform on its own, without commands being sent from a control centre on Earth. The second on these automatic actions occur approximately 90 minutes later, at this time the gimbaled high gain antenna will deploy this is how the JWST can receive its next instructions from Earth.

Now that the JWST can receive data from Earth commands can be sent for it to begin its unfolding processes.


First approximately two and a half days after launch the JWST will unfold its forward sunshield boom, and approximately 10 hours later the aft sunshield boom will also deploy, followed by the port and starboard mid-booms. The sunshield, which will face towards the Sun, Earth and, Moon at all times will not only enable to JWST to block light from our star, making it easier to observe fainter signatures in deep space but will also act as a buffer from the Suns' intense heating effects.


There are 5 layers to the sunshield once it is fully operational and correctly tensioned, and this means that while the sun side of the JWSTs' heat shield will be approximately 383K (109C), the other side (the cold side) of the sunshield where all the instruments are will be approximately 36K (-237C) thanks to the way the sunshield is designed this incredible temperature delta (346C) happens over less than 1.8 meters.

Another two and a half days will pass before all the sunshields membranes are released and tensioned correctly, the sunshield will then be fully operational.


A further day will pass before anything else happens. At this point approximately 6 days post-launch, the secondary mirror support structure will be deployed, 3 long booms extend the secondary mirror out in front of the primary mirror, this secondary mirror enables light collected by the primary mirror to be reflected and focused onto the telescope's instruments. The process of deploying the secondary mirror takes around 7 hours.


The final part of the telescope to be deployed over a week into the journey is the primary mirror segments. In its folded configuration the JWST has to reduce the cross-section of its mirror, and this has been achieved by using 18 gold-plated hexagonal segments which when deployed can fit together to produce a larger mirror analogue, the benefit of using smaller segments is that they are each individually controllable allowing for far more accurate reflection of the incoming light onto the secondary mirror.


The deployment of the primary mirror begins with the port side segments unfolding into place, followed by the starboard side, each wing holds 3 mirror segments and takes approximately 3 hours to completely unfold. over the coming week the JWST will continue its journey to L2 and the individual mirror segments with be manoeuvred into place to make sure that they work correctly.


James Webb Space Telescope

Along the journey the JWST has to perform 3 mid-course correction manoeuvres, these manoeuvres are to enable to JWST to reach L2 at exactly the right speed and trajectory to quickly establish its self in orbit, the first of these manoeuvres must occur between 12.5 and 20 hours after launch and is the most important, it a continuous burn on the onboard thruster which could last a few hours.


The second burn fine-tunes the trajectory after launch and its duration will depend on the performance of the Ariane 5, this second burn is performed around 2 and a half days after launch.


The third and final manoeuvre burn is performed 29 days after launch with the JWST fully deployed this burn is an insertion burn into L2.


During this whole period the JWST cannot turn towards the Sun as it would damage the delicate onboard instrumentation. Even without turning around for the first few weeks orbiting in L2 the JWST will just be cooling down in a controlled manner using electrical heaters situated at certain important parts of the instrumentation, as well as turning on all the equipment which hasn't already powered up, the following 5 months will be spent correctly aligning the optics and calibrating the instruments. {5}

Why is the JWST going to be revolutionary?

The James Webb will enable us to explore a massive range of questions, because the JWST will mostly be making use of the infrared spectrum, which humans cannot naturally see, but, will also be able to operate in the red (and some yellow) parts of the visible spectrum, and this will enable to JWST to 'see' light emitted by the very first luminous objects in the early universe.


It is able to identify this old light as it has become 'redshifted' and we now see what was once visible light as infrared, this 'red shifting' occurs when an object is moving away from the observer. The light 'stretches' increasing the wavelength shifting it towards the red end of the spectrum, coincidentally we can use this same method to identify that the universe is expanding.

The JWST will be the most powerful tool ever created to study our universe, it will be used to study the planets in our solar system as well as exoplanets and stars millions and billions of light-years away. It can be used to determine the origin and evolution of such planets and stars and in doing so will enable us to understand more about the Earths own history, and it will also able to observe exoplanets in the habitable zone of their stars. It is powerful enough to determine if and where a planet may have liquid water on its surface, this can be done using a technique called transmission spectroscopy, which is a technique of examining the starlight absorbed by the planet to learn about the chemical composition of the atmosphere. {7}


{1} - U.S. GAO

{2} - NASA

{3} - Wikimedia

{4} - Solar Array | Flickr

{4a} - Sunshield Tests| Flickr

{4b} - Primary Mirror| Flickr

{5} - Deployment Explorer Webb/NASA

{6} - Shutterstock

{7} - Webb Fact Sheet