The James Webb Super Telescope

26th July 2022 - Last modified 19th October 2023

20 years of Alto. 20 years of science. #10

By Rose Layton PhD, Science Writer

As part of Alto Marketing’s 20 year celebrations, we’re looking back at some of the most important advances in science over this time in our blog series “20 years of Alto. 20 years of science.” And where better to focus this time than a look at the James Webb telescope after NASA released the first images from the most advanced – and the most expensive – telescope ever built.

30 years. £8 billion. 10,000 people. 100 million hours.

This is what it took to build one Super Telescope. Named after the man who headed up NASA during the 1960s when it was preparing to land people on the moon, the James Webb telescope is the most advanced – and the most expensive – telescope ever built.

With NASA having just released the first images from the James Webb telescope, we take a look at how it was designed, built, and launched to explore the furthest reaches of our universe – and what astronomists think we might discover.

From Hubble Beginnings

Back in 1990, scientists launched the Hubble telescope – the first major optical telescope to be placed in space. Five years later, Hubble took one of the most extraordinary images in history. By focusing its camera on what was apparently ‘empty space’ and using an exposure time of 10 days, astronomers were able to see deeper into the universe than ever before. Approximately 10 years after, Hubble took an even deeper image.

Known as the Hubble Ultra Deep Field, the infamous image revealed over 10,000 distant galaxies, some as they would have appeared approximately 13 billion years ago. This is just a few 100 million years after the big bang. But astronomers wanted to see further into space and farther back in history to answer questions that have puzzled humans for centuries: How did it all begin? What happened in the earliest years of the universe? How were the first generation of stars and galaxies formed?

To answer these questions, astronomers needed an incredibly powerful telescope.

Take a Look in the Mirror

Or more accurately, take a look in Hubble’s mirror. To see very faint light, like the light emitted by stars 13.2 billion light-years away, telescopes like Hubble require very big mirrors. The bigger the mirror, the more photons or the more light the telescope can collect.

While Hubble’s mirror was a hefty 2.4 m long, in order to see even further into space, astronomers calculated that the James Webb telescope needed a 6.5 m mirror. The problem? A 6.5 m mirror was far too wide to fit into the largest rocket available.

NASA engineers solved this problem by splitting the mirror up into segments. An early design featured mirrors that looked like petals of a flower. Once launched into space, the petals would unfurl and line up to form one continuous mirror.

The final iteration followed a similar concept but instead of petals, it was made up of 18 hexagonal mirror segments. Before launch, these segments were folded into a shape that allowed them to fit into an Ariane 5 rocket. Once in position, motors on the back of the segment would move them so that they fitted together like honeycomb; aligning to focus light as a single giant mirror.

Shaping the mirrors constituted a massive engineering challenge. In fact, Hubble’s main mirror had been shaped incorrectly resulting in a defect known as a spherical aberration. This meant that the light falling on the outer edge of the mirror was brought to a focus at a different point than the light falling on the middle. Ultimately, this led to blurry images that were much less clear than anticipated.

While Hubble’s mirror was corrected in a service mission in 1993, James Webb’s mirrors would need to be perfect first time. The James Webb telescope was intended to be launched into the second Lagrange point: a gravitational sweet spot that holds the telescope in a special orbit. Being extremely remote (1.5 million km away from the Earth’s surface), there would be no opportunity to send a repair mission.

NASA developed brand new technology to ensure the mirrors were perfect. In this scenario, perfect meant that the mirrors were polished to accuracies of less than one-millionth of an inch. It took 2.5 years to polish perfect surfaces on all 18 mirrors.

To find out more about the James Webb mirror design, check out this article on NASA’s website

The Darkside of the Telescope

The next problem NASA engineers had to solve was how to stop the Sun, Earth, and Moon from heating up the telescope to inoperable temperatures. To understand why heat is such a problem, we first have to understand how light travels through space.

Since the big bang, the universe has been expanding. Therefore, as light travels through an expanding universe, its wavelengths get longer. Light that once was in the visible spectrum eventually shifts to the invisible, infrared spectrum. If the sun is allowed to heat up the telescope, it will emit its own infrared and drown out the faint infrared signals that have travelled through space from distant galaxies.

Space is terrifyingly cold – a brisk -266˚C. Consequently, shielding the telescope from all three bodies would keep temperatures low enough for operation. And this is why Lagrange point is so special – it keeps all three bodies on the same side of the spacecraft at all times. This allowed NASA to design a giant sun shield, that kept the telescope sheltered from all three bodies at once.

Designing a Sunshield

Being approximately the size of a tennis court, the James Webb telescope’s unfurled Sunshield suffers the same problem as a giant 6 m mirror: it won’t fit into one of NASA’s rockets. Thus, NASA needed a way to package it down and fold it out to full size once in orbit.

The James Webb sunshield is made up of five extremely thin (25-50 microns) layers of a material known as Kapton coated with aluminium for reflectivity. The outermost Sun-facing layers are coated in doped-silicon that strengthens the shield, and helps it reflect heat. In fact, the outermost layers are responsible for reflecting approximately 90% of the heat.

Being extremely thin, the shield could be folded into a concertina until after launch. Then, a remote-controlled system of intricate cables, motors, and pulleys pulls out the sunshield to a taut screen that will keep the telescope in the dark – and most importantly, in the cold.

Discover how NASA engineers designed a Sunshield with an SPF of 1 million

Unravelling the Webb of Space

Following the big bang, nothing much happens. Mostly, the universe just cools down. After a few hundred million years of cooling off, some parts of the universe reach a low enough temperature for matter to condense. And, out of this cold darkness, the first stars are born.

But scientists aren’t exactly sure how these first stars came to be. The most widely accepted working hypothesis is that giant clouds of hydrogen, helium, and a small amount of lithium (the only elements formed during the big bang) collapsed under their own gravity to form stars.

It is thought that these first stars were vast, potentially 100 times the mass of our sun. It is also thought that the intense temperatures and pressures in these early stars and their massive supernova explosions transformed hydrogen and helium into a plethora of new chemical elements – the building blocks for new planets.

This intense period of star formation and the initial creation of the elements is what NASA astronomers are interested in. It is hoped that the James Webb telescope will give us a brand-new insight into how are universe evolved in the very early stages of creation.

Recently, NASA released the first images from the James Webb telescope. These images are already revealing types of galaxies we’ve never seen before – and the telescope promises to continue illuminating the far reaches of our universe.