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The James Webb Space Telescope: Evolving Hubble for the 21st Century

In 1990, after a fairly long and tortuous process, the Hubble Space Telescope blasted into space aboard NASA’s Space Shuttle Discovery. After a rocky start during which those on the ground found that Hubble’s mirrors were ever so slightly hazy and required what can only be described as giant space spectacles, Hubble began beaming back images of the Universe that simplify took the breath away.

The dazzling, almost surreal, images taken by Hubble were a giant leap forward in terms of telescopic observation, but we are now counting down to the next huge stride forward. Hubble was never designed to last forever, and what’s coming next is set to be even better. 

The James Webb Telescope (JWT) is a joint NASA-ESA-CSA (U.S/European/Canadian) space telescope still under development but scheduled to leave our planet, perhaps somewhat ominously on Halloween 2021. This is very much Hubble’s successor and the astonishing success of the telescope launched over 30 years ago means that it has plenty to live up to. 

A Long Road 

While it certainly seems like the 31st October launch date is now set (with a week window on either side for any adverse weather conditions) the JWT has been here before – several times in fact. The telescope was first slated to depart in 2007, then 2011, 2014 and lastly in 2018. This is the most complex telescope we have ever launched into space and very few would doubt that when it’s finally up and running it will be a tremendous success, but it has been a long difficult path for the JWT. 

This rendering of the James Webb Space Telescope is current to 2015.
This rendering of the James Webb Space Telescope is current to 2015.By Northrop Grumman, is licensed under CC-BY

Early planning regarding Hubble’s successor began in 1986 even before the first telescope had left Earth, with various options and varieties discussed, including the Hi-Z, a 4-meter (13.1 ft) aperture infrared telescope which would have orbited the sun at a distance of 3 au – 1 au being the distance from the Earth to the Sun. 

But things didn’t really get going until 10 years later with the Next Generation Space Telescope (NGST) before being renamed after James E. Webb, NASA’s second appointed administrator between 1961 and 1968. The 1990s saw a serious curtailing of NASA’s budget – well, it was still in the billions of dollars sphere, but certainly fewer billions of dollars. “Faster, better, cheaper” became NASA’s unofficial mantra and what was finally proposed was a low-budget 8-meter (26.2 ft) aperture telescope with a very respectable estimated cost of $500 million ($862 million today).  

After several preliminary concept studies in the late 1990s, NASA awarded the $824.8 million ($1.1 billion) prime contract to TRW. Inc in 2003 to build a telescope with descoped 6.1 metres (20 ft) primary mirror. Later that same year, TRW.Inc was taken over by Northrop Grumman, with the two becoming Northrop Grumman Space Technology.


By this point, the first projected launch date of 2007 was now out of the question, instead, NASA placed their faith in the year 2011. Now that the project had been finalised and the ink had dried on the main contracts, the complexities of who would do what came into play.

While Northrop Grumman Space Technology was the main contractor and would take care of the spacecraft bus and sunshield, numerous other subcontractors became involved, including, Ball Aerospace & Technologies which would build the Optical Telescope Element (OTE), Northrop Grumman’s Astro Aerospace business unit would build the Deployable Tower Assembly (DTA) and the Mid Boom Assembly (MBA) and lastly, Goddard Space Flight Center would be responsible for delivering the Integrated Science Instrument Module (ISIM). 

Now I know much of that won’t make much sense right now, but we’ll go into more depth regarding these components a little later in the video. This was simply designed to give you an overarching view of just how complex building the greatest telescope ever was going to be. 

But believe me, nothing I can say can really describe just how complicated this was all going to be, because once the contracts had been distributed, only then could the hard work of actually designing this telescope truly begin. The challenges surrounding the construction of the JWT were already enormous, but when you take into consideration that some of the technical elements to be included on the telescope have only really reached maturity in the last two decades, we begin to see why things have taken so long. 

In January 2007, seven of the ten technology design items included in the original design passed a Non-Advocate Review, which is essentially a review process of an already approved program or project to mitigate risk. This meant that they had reached an acceptable maturity which in turn led to an acceptable diminishment of risk. In April of the same year, the MIRI cryocooler also passed its required milestone, which effectively pushed the program into the detailed design phase and in March 2008, the project as a whole passed its Preliminary Design Review and a month later its own Non-Advocate Review.  

But still, things were not quite ready across the board. The Integrated Science Instrument Module passed its review in March 2009, the Optical Telescope Element in October 2009, and the Sunshield in January 2010. This was then followed by the Mission Critical Design Review in April 2010, after which the anticipated launch date was put back again to 2015 or at the latest 2018 – but the good news was that the JWT now seemed finally on the verge of construction.  


Blueprints of the James Webb Space Telescope
Blueprints of the James Webb Space Telescope.By NASA’s James Webb Space Telescope is licensed under CC-BY

It’s one of those strange twists that the designing and reviewing of a giant space telescope takes considerably longer than actually building one. The construction of the all-important mirror was done by robotic arm between November 2015 and February 2016, while the JWT as a whole was completed by November 2016.

Hopes of launching in 2018 were dashed when the sunshield ripped during a practice deployment and the sunshield’s cables failed to tighten sufficiently. An independent review was carried out that found a potential 344 single-point failures, it was clear there was still plenty to do. 

The mechanical integration of the telescope was completed in August 2019, and to give you a clear idea of just how long this was all taking, engineers had first hoped this could have been done all the way back in 2007. 

So, as of March 2021, the JWT is finished and undergoing final testing. There is now a growing optimism that this much overdue and vastly over-budget project is finally nearing its departure date. And talking of budgets. Remember how I said back in 2003 the project had an estimated cost of $824.8 million ($1.1 billion today)? Well, in the 18 years since, that figure has grown by almost 10. In October 2019, the cost of the entire project passed the $10 billion mark. 

The JWT 

So we already know it’s astoundingly expensive and incredibly late to the party, but what exactly is the JWT?

The JWT will focus primarily on infrared astronomy, which means viewing astronomical objects through infrared (IR) radiation, though it will carry instruments that will also enable it to see objects in the mid-infrared region. Studying the infrared region comes with plenty of benefits, but simply put, most objects in our universe are too cold and faint to be seen through visible light, but can reveal themselves through infrared. Even Hubble cannot monitor these infrared bands because it doesn’t have the cooling apparatus needed so when the JWT begins operating, it’s perfectly feasible that we will begin to see parts of the universe we’ve never been able to see.  

A JWST NIRCam Detector
A JWST NIRCam Detector by NASA’s James Webb Space Telescope is licensed under CC-BY

The JWT will be sent out and operate close to the Earth-Sun L2 (Lagrange point) – roughly 1,500,000 kilometres (930,000 mi) beyond Earth’s orbit – which is equal to around four times the distance between the Earth and the Moon, of forty times around the equator if you need something a bit more down to Earth. 

The primary component of the JWT is the wonderfully named Spacecraft Bus, which is pretty much exactly what it sounds like. The Spacecraft Bus is where the vast majority of the computing, communication, propulsion, and structural parts are located. The structure weighs 350 kg (about 770 lb) and was constructed mostly from graphite composite material. It measures 3.5 meters (11.5 feet) in length and roughly 6.7 m (22.23 feet) in width.

While we could probably do an entire video on the Spacecraft Bus alone, there’s just too much to go into real depth with, but it does incorporate six major subsystems, the Electrical Power Subsystem, Attitude Control Subsystem, the Communication Subsystem, Command and Data Handling Subsystem, the Propulsion Subsystem, and the Thermal Control Subsystem – so pretty much everything. 

Central to just about everything on the JWT, is its primary mirror, a 6.5 meter (21.3 ft) diameter gold-coated beryllium reflector. It will have a collecting area over six times larger than that on Hubble, measuring 25.4 square metres (273 sq ft), using 18 separate hexagon mirrors grouped together.  

But if you think that the mirror will just pop out ready to go, far from it. The assembled mirror is big, far too big to travel preassembled. When the JWT arrives at its destination, the 18 mirrors will carefully unfold and be delicately positioned using micromotors. In theory, once opened, the mirror will only require updating every few days to retain focus. This will be done with 126 small motors used to carefully adjust the optics. I don’t know about you, but that’s certainly not the kind of job I would want to be entrusted with.    

By orbiting at the L2 point, the JWT will be able to maintain synchrony with the Earth, meaning it will remain a constant distance while avoiding the shadow of the Earth and Moon. With the use of its sunshield, it will be able to keep its operating temperature below the −223.2 °C (−369.7 °F) needed for infrared observations.

When I say sunshield, you might well imagine a giant beach umbrella in space – I know I did – but the sunshield on the JWT is unlike anything we’ve ever seen. It includes a five-layer sunshield, with each layer as thin as a human hair, constructed using Kapton E, a polyimide film, with its membranes specially coated with aluminium on both sides and silicon on the Sun-facing side. The real beauty of it is its delicate folding design, in which it folds 12 times to fit inside the Ariane 5 rocket which will carry it. Once it reaches the L2 point, the sunshield will carefully unfold in space and hopefully encompass an area measuring 14.1 by 21.1 metres (46.4 by 69.2 ft).  


The Integrated Science Instrument Module (ISIM) will provide the JWT with electrical power, computing resources, cooling capability and houses the four main science instruments, which are: 

  • TheNIRCam (Near InfraRed Camera), an infrared imager with a spectral coverage ranging from the edge of the visible (0.6 micrometres) through the near-infrared (5 micrometres). It will also provide information used to align the 18 segments of the primary mirror. 
  • NIRSpec (Near InfraRed Spectrograph) was built by European Space Agency and will perform spectroscopy (studying the interaction between matter and electromagnetic radiation) over the same wavelength range. It principally has three main modes: a low-resolution mode using a prism, an R~1000 multi-object mode, and an R~2700 integral field unit or long-slit spectroscopy mode.
  • MIRI (Mid-InfraRed Instrument) will measure the mid-to-long-infrared wavelength range from 5 to 27 micrometres and comes with a mid-infrared camera and an imaging spectrometer. It also comes with its own helium gas mechanical cooler to keep it below its temperature limit of -267 C (-448F) 
  • FGS/NIRISS (Fine Guidance Sensor and Near-Infrared Imager and Slitless Spectrograph) is the final instrument and one the Canadian Space Agency is responsible for. The FGS will provide the data used to both control the overall orientation of the spacecraft and to drive the fine steering mirror for image stabilization. It also includes the Near-Infrared Imager and Slitless Spectrograph (NIRISS) module for astronomical imaging and spectroscopy in the 0.8 to 5-micrometre wavelength range. 

Mission and Expectations  

To say that expectations surrounding the JWT project are high would be a staggering understatement. After so much money and such a long, drawn-out timescale, an awful lot is weighing on the shoulders of those leading the project. 

The JWT mission comes with four clear objectives

  1. to search for light from the first stars and galaxies that formed in the Universe after the Big Bang
  2. to study the formation and evolution of galaxies
  3. to understand the formation of stars and planetary systems
  4. to study planetary systems and the origins of life

After launching, the JWT will take nearly a month to travel to the L2 Lagrange point, where it will be placed into a halo orbit. It will then begin the painstaking process of unfolding its mirrors, sunshield and mechanical arm, which is scheduled to take as long as 3 weeks. At this point, a series of tests will take place to be sure that everything is functioning as it should – and then, well, we start looking. 

While it’s impossible to predict what we’ll see using the JWT, we can make some broad assumptions, most of which relate to beating cosmic records. Quite simply, if the JWT travels and deploys successfully, we will begin to see things that humans have never seen before. 

Perhaps the most notably will be how far we can look back in time. If that sentence has left you puzzled, then stick with me. When we look out at space, we are essentially looking back in time. The light we see coming from stars takes so long to reach us, we are seeing the past. Even the light from Alpha Centauri, our closest sun apart from our own takes 4 years to reach us. 

This means that when the JWT begins gazing deeply into our universe, it will in effect be looking back closer to the Big Bang – perhaps as close as 200 million years after the events that created the universe. The most distant galaxy we can see, GN-z11, is emitting light that is thought to have originated from 407 million years after the big bang, so the JWT could half this. 

Our understanding of exoplanets (planets outside our solar system) could be revolutionized as we will be able to see and measure planets more accurately than ever before, allowing us to accurately image planets as little as 150% the size of Earth. Lastly, the very first ‘pristine stars’ – made only of hydrogen and helium, the elements made in the hot Big Bang – should also become visible to the JWT, something that has frustrated astronomers up until now.

As I said, we can be sure what the JWT will see, but it has the potential to forever alter astronomy. 

The Next Step   

The Hubble Space Telescope was a gigantic leap forward in terms of our understanding of space and what comes next could be even bigger. The JWT is set to carry enough fuel for a five-year mission, but most assume that with the right kind of fuel management, that could be extended to as long as 10 years. No, we’re not colonising Mars or even walking on the moon, but if the JWT does what is planned, it will be one of the most significant steps forward in astronomical history, a science that stretches back nearly 4,000 years. 

But humans have been gazing up at the stars above us for far longer than that, wondering what it all means and what might be up there. With the JWT, we won’t get all of the answers, but we just might come closer than we ever have.   

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