Telescope unfolded in space
The James Webb telescope has travelled 1.5 million kilometres into space on its 29-day journey. En route, it has gradually unfolded, getting ready to take otherwise unachievable pictures of our universe.
The long-awaited James Webb Space Telescope has made it. Postponed by 24 hours because of forecast high winds at the European spaceport in French Guyana, South America, close to the Equator, it launched on Christmas Day 2021 atop an Ariane 5 rocket, starting its journey 1.5 million kilometres into space.
The year’s most important space launch was a complete success. As the massive rocket lifted off, the force from its three large rocket engines accelerated the craft rapidly, breaking the sound barrier after less than a minute and reaching outer space only a few minutes later. In mission control, there was euphoria over the successful launch, which marked the beginning of a 10-year mission.
The telescope, named after former NASA administrator James Webb, is by far biggest, most powerful, and most complex space telescope ever designed, and it promises to revolutionise astronomy by allowing astronomers to peer deeper into space than ever before, to photograph and analyse unknown exoplanets, stars, and galaxies. If all goes to plan, it will be able to provide more information about the history of the universe than we can obtain from any existing equipment on – or off — Earth.
Astronomers waited 20 years
Even though the launch went well, there remained a great deal which could go wrong on the journey towards the space telescope’s destination. The telescope is so big that it only fit into the rocket when folded up, squeezed into the top like a butterfly waiting to leave its pupa. Following launch came a month-long deployment procedure to prepare the telescope before it could finally turn on its instruments. Most of the steps have been controlled from the ground, with NASA’s team checking each stage before proceeding to the next.
The first milestone was the tricky task of unfolding some 750 square metres of plastic membrane in such a way that telescopic rods could perfectly unfold and tension the five-layer sunshield which unfolds to a size of 21.2 metres long and 14.2 metres wide. The huge sunshield is required because the telescope’s instruments can not tolerate heat, and indeed are most efficient in their operation at extreme cold. The sunshield consists of five layers of plastic film that are each thinner than a human hair. Each of the films is lined with an ultra-thin layer of aluminium which reflects unwanted sunlight back into space, so it does not reach and harm the sensitive instruments.
If everything goes according to plan, the sunshield will give the telescope protection corresponding to factor 1,200,000 sunscreen. This means that the temperature on the dark side of the shield will be -225°C. That is still too warm for one of the instruments, so that one is further cooled by liquid helium to a temperature of -266°C, just 7 degrees above absolute zero.
To achieve this unfurling somewhere deep in space is a major engineering task. It was not, as you might think, entirely automatic. While there is a tentative schedule for everything, mission leaders can decide to adjust the timeline along the way. For
29
days is how long it took the telescope to travel to its permanent orbit.
example NASA announced that the Webb team would spend its Sunday (2 January) studying the power subsystems, just to be sure all was in order for the tensioning of each different section. All went well, and the tensioning was complete by 4 January.
Next was the task of deploying the secondary mirror from its stowed position, with long booms swinging it out in front of the primary mirror from which it reflects light on to where the instruments sit. By now the telescope was travelling deep into space, but the secondary mirror deployment was completed on 5 January.
Further instrument cooling is assisted by the next deployment, as the Aft Deployable Instrument Radiator (ADIR) was hinged into position with its large rectangular collection of high-purity aluminium sub-panels covered in honeycomb cells painted ultrablack to create an cooling surface.
That left just the unfolding of the main mirror with its 18 hexagonal segments, each 1.32 metres across. Only 12 of them could be fitted into the rocket in one piece, so the last six mirror segments are mounted on two big flaps that had to slide into place and lock, like leaf sections on a folding dining table. First the port wing, then the starboard were deployed, and on 9 January, with grins you could see through their masks, NASA announced that the James Webb Space Telescope was now fully deployed.
Following a final course correction, the telescope reached its final destination on 24 January. James Webb will spend the rest of its life orbiting a point known as ‘L2’, some 1.5 million kilometres from Earth in the direction away from the Sun. The orbit is quite stable, so that little fuel will be
With the telescope unfolded into its final position, the individual mirrors are tweaked to nanometre precision to bring all 18 segments into perfect alignment. Then the mission can truly begin, with the primary mirror capturing infrared light, which the secondary mirror directs to the instruments.
1 Gold mirrors collect radiation
The primary mirror consists of 18 hexagonal sections made of the strong but light metal beryllium. The mirrors were processed to an accuracy of 20 millionths of a millimetre and plated with gold, which reflects infrared radiation efficiently.
2 Instruments analyse the light
The instruments behind the mirror include infrared cameras and spectrographs. The latter analyse wavelengths to reveal both temperature and chemical make-up of objects at which the telescope is pointed.
3 Sunshield reduces temperature
The instruments do not tolerate heat, and the 150m2 sunshield protects them against solar radiation. The shield consists of five layers of plastic film that reflect radiation, keeping the temperature below -225°C.
required to remain there. Even more importantly, at L2 the telescope will always be able to turn its back on both the Sun and the Earth. Light or heat radiation from the Sun, Earth or the Moon would ruin data from the sensitive instruments, so the sunshield will always block the view of all three heavenly bodies. This will allow the telescope to focus on more remote heavenly bodies deeper into the universe.
But the telescope is not yet ready to take pictures. First it must cool enough for its instruments to become operational, and finally there will be three to five months of adjustments to the 18 hexagonal sections of the primary mirror. The tweaks will be first microns and then nanometers, until perfect alignment in achieved. Only then will the 18 slightly different views of the universe coalesce to give scientists back on Earth access to one magnificently powerful and unique space telecope.
And then – after a hazardous launch, its long journey into space and all the delicate unfurling and deployment of its various sections successfully completed – the James Webb Space Telescope can finally start doing the job for which 1000+ people from 17 different nations designed, built, tested and launched it, and thousands of scientists who have waited 20+ years to receive priceless data from the new viewpoint in space can hope to make astounding new discoveries about the universe in its earliest days.
Large mirror, longer view
There are several key reasons why the new Space Telescope will eclipse the achievements of its predecessor, the James Hubble Sapce Telescope. First and foremost, it is much bigger. Hubble has a circular mirror with an area of 4.5m , whereas James Webb’s multi-edged mirror is equivalent to 25m . The size of the mirror determines how much of the dim light from very remote objects the telescope can pick up. Put simply, the bigger the mirror, the further the telescope can see. A larger mirror also means sharper and more detailed images.
But just as importantly, the new space telescope will not see the universe in the same way as our eyes, nor the way for which the Hubble is primarily designed. Instead, it will observe the infrared universe, which is otherwise invisible to us. That is also the reason why the James Webb telescope is going much deeper into space than Hubble, which orbits at a modest 540km above Earth. Infrared measurements from so close would be affected by the heat radiation from Earth.
The Hubble telescope’s mirror is lined with aluminium, which has been perfect for reflecting visible light and passing it on to the telescope’s cameras. But because the new space telescope is infrared, aluminium or other silvery materials cannot be used. Instead, the mirrors had to be lined with pure gold, which reflects infrared light much more efficiently.
Looking back in time
With its infrared vision, the telescope sees so far into the past that it becomes a kind of time machine that will allow scientists access to the history of the early universe. From its viewpoint 1.5 million kilometres away, it will transmit data to Earth via NASA’s Deep Space Network, which includes huge radio antennas located in the US, Spain, and here in Australia.
Some Australian scientists are eagerly awaiting the telescope’s data, including researchers at the University of Queensland.
“The JWST will go dramatically beyond what any telescope has been able to do – it will see some of the first stars in the universe, billions of light years away,” says UQ astrophysicist Dr Benjamin Pope. “It changes the game on how we observe planets, stars, asteroids, and the universe around us.”
Dr Pope will be involved in several observation projects, observing distant and hard-to-see stars and planets, seeking methods with which to observe asteroids and dwarf planets with greater clarity than ever before, and studying planets at the moment they form around stars.
Meanwhile University of Queensland Associate Professor Holger Baumgardt plans to use the James Webb for a series of observation projects aimed at identifying and studying black holes in distant galaxies.
The use of infrared light means that astronomers will not receive the kind of impressively natural images that we know from other telescopes. Instead the infrared light will be ‘translated’ into something that we can see and interpret. By this method we will be able to see heavenly bodies that have
previously been hidden to us. Unlike visible light, infrared light can pass through the huge dust clouds in which new stars and planets form. With the new telescope, scientists like Dr Pope should be able to observe different stages in the births of stars, and they may even be able to see how dust and gas collects into planets around them. But the most exciting thing about the most powerful telescope ever built is that we really don’t know what it will find. Scientists can search for certain things, but they know that the biggest discoveries of all will most likely come from things nobody ever has even thought to look for. It may also help us ‘zoom in’ on our search for life elsewhere.
Searching for life and first light
Since 1995, astronomers have discovered thousands of new planets orbiting alien stars; indeed it is now clear that planets are orbiting most of the stars in the sky. The next step will be to find out if some of these exoplanets are suitable for supporting life. The James Webb’s infrared cameras will capture the heat radiation emitted by the remote planets and so measure their temperatures as they are photographed. The infrared radiation could also provide data about air quality on the planets. Some of the telescope’s instruments are spectrographs, dividing the infrared light into its individual wavelengths, and the distribution of these wavelengths can be used to determine the gases present in the atmosphere.
In this way, astronomers can learn more about the living conditions on the planet and perhaps even find substanc’s that indicate biological activity. The James Webb telescope may thereby be able to bring us closer to answering whether we are alone in the universe.
Such a large infrared space telescope may be able to uncover another of the universe’s big secrets. It gives astronomers a chance of spotting the very first stars that lit up in the young universe.
The first light emitted by the first stars and galaxies more than 13 billion years ago no longer exists in the form of visible light. As the universe expanded, the light waves were stretched, changing their wavelengths and converting the visible light into infrared radiation. This would now be in the range of wavelengths that the new space telescope is designed to capture.
Astronomers believe that the first stars were very different from the ones we see in the sky now, because the mix of elements was different back then, when the universe contained almost exclusively hydrogen and helium. That could have produced very big bright stars that burned out quickly. They cannot be observed by the Hubble telescope, but the James Webb telescope should be able to detect the stretched light from them and the early galaxies in which they lived.
So far, so good
There is much finger-crossing in space exploration. NASA remembers all too well that when Hubble was turned on, it was out of focus. But so far the US$10bn James Webb Space Telescope is on course to deliver a new era of astronomical observation.
25 m2 is the area of the James Webb telescope's mirror – five times Hubble's.