Deep-space observatory prepares for lift-off
Image credit: Nasa
It’s long overdue and well over budget, but the James Webb Space Telescope, Nasa’s successor to the Hubble, is finally eyeing a launch date of 2021.
When the world’s most powerful telescope eventually launches, space scientists will hold their breath. Equipped with the most delicate and sensitive optics ever built, the James Webb Space Telescope (JWST) – a launch that has been delayed by 14 years and is roughly ten times over budget – will probe deeper and further back into space than ever before: revealing first light, the start of the universe, the birth of stars, and possibly the origins of life.
First, the spacecraft and instruments must be brought together for final testing, then travel by ship to South America and hurtle into space to reach a gravitationally stable position, some 1.5 million kilometres from Earth. A massive sunshield with five layers, each thinner than a hair, must unfurl in space, and a vast golden mirror unfold and assemble – like a ship in a bottle. After six months, infrared optics will be fully commissioned, poised to detect the faint signature of objects that shone some 13.5 billion years ago. But if anything goes wrong out there, no one can fix it.
“It brings us one step closer to understanding the origins of life,” says Pierre Ferruit, a scientist who’s working on the JWST for the European Space Agency (ESA). “But what is really exciting is the prospect of discoveries we’re not even expecting – there’s so much room in space for surprises.”
The flagship project is now in the final stages of testing; all instruments have already passed, and the spacecraft element – the bus and sunshield – are in late-stage tests at Northrop Grumman in California. While everything was built by the end of 2016, the optics and spacecraft haven’t yet been fitted together. Once that’s achieved, everything must be tested again. “We’ve never done this before – no one has created an optic as big as Webb in space,” says Scott Willoughby, vice president and programme manager, JWST at Northrop Grumman, the lead industrial partner for the telescope. “Our challenge was to do something that didn’t exist.”
Instruments on board
Four main instruments will detect light from distant stars and galaxies, and exoplanets. Observatories will be fully commissioned six months after JWST’s launch.
Near-infrared camera (NIRCam)
(University of Arizona)
The primary imager on board will detect light from the earliest stars and galaxies in formation, stars in nearby galaxies, young stars in the Milky Way and objects in the Kuiper Belt – a region of leftovers from the solar system’s early history. Equipped with coronagraphs to block out bright light, it will detect dimmer objects such as planets orbiting near stars.
Near-infrared spectrograph (NIRSpec)
(European Space Agency and Nasa’s Goddard Space Flight Center)
Designed to examine 100 objects simultaneously, this spectrograph will search for faint signs of first galaxies that formed after the Big Bang. A spectrograph disperses light from an object into a spectrum – analysis of this reveals the object’s physical properties. NIRSpec has microshutter cells, each as wide as a human hair, which can be controlled individually.
Mid-infrared instrument (MIRI)
(European scientists and engineers and Nasa’s Jet Propulsion Lab, California)
Equipped with a camera and spectrograph to examine the mid-infrared region of the electromagnetic spectrum, MIRI will produce breathtaking astrophotographs. It will also observe redshifted light of distant galaxies, newly forming stars and faintly visible comets and objects in the Kuiper Belt.
Fine guidance sensor/Near infrared imager and slitless spectrograph (FGS/NIRISS) (Canadian Space Agency)
The sensor helps the telescope point precisely to give high-quality images, while the spectrograph will search for signatures of first light in the universe and detect and examine exoplanets.
Sunshield and mirror
The telescope will sport a tennis court-size sunshield and a 6.5m-wide mirror – the largest ever launched into space. The primary mirror is made of 18 segments of gold-coated beryllium; gold reflects infrared light. Each mirror can be controlled with extreme accuracy. Too large to fit unfolded, both mirror and sunshield will unfurl once in space.
A joint project led by Nasa in collaboration with the European and Canadian space agencies, JWST was first conceived back in 1996, six years after Hubble (Space Telescope) was launched to become the largest telescope in space.
But JWST, with a 6.5m-wide mirror, which will provide about seven times the light-collecting area of Hubble, will be able to see far further into space. While Hubble detects visible and ultraviolet light, JWST will detect infrared radiation from objects billions of light years away.
Optimistic estimates first put the cost of JWST at $1bn (£750m) to $3.5bn (£2.7bn), but it has to date cost roughly $10bn (£7.7bn). As it enters final testing, the project is racking up $1m a day, and is forecast to launch in 2021, after an initial launch date of 2007 as well as more recently missed deadlines.
These costs cover the current testing work in California, the Goddard Space Flight Center and the Space Telescope Science Institute in Maryland, where some 300 scientists and engineers will be based. At its peak, says Nasa, the project employed 1,200 scientists, engineers and technicians from more than 14 countries – now roughly half that number are working on the final stages.
“To understand the delays is to understand the ambition,” says a Nasa spokesperson. “We spent most of the first decade of development inventing the technologies and developing the know-how to make such a machine as the Webb feasible.”
As with Hubble, new technology and engineering had to be invented. These included software to keep the telescope correctly positioned with minute precision and new material for the sunshield.
Two of the biggest engineering challenges, says Nasa, have been how to deploy the complex mechanisms that are intrinsic to a large infrared space observatory, and how to ensure instruments will operate in the extreme cold vacuum of space. While the sunshield – the size of a tennis court – will keep the telescope in perpetual shadow at around -223°C, one European-built mid-infrared detector needs to be kept at -267°C and has required a bespoke cryocooler. “These instruments are packed in layers of insulation,” says ESA’s Ferruit. “You have to get the design right – once it’s deployed you don’t get a second chance.”
Temperature requirements have made testing difficult. “Webb had to be built ‘precisely wrong’ at room temperature so that it will be ‘precisely right’ in shape and dimensions in space, so it can be sensitive to faint infrared light from objects in the cosmos,” says a spokesperson for Nasa.
Instruments and optics have already been tested in Houston to see how they will fare in space, and how they’ll tolerate the powerful vibrations and soundwaves during lift-off aboard an Ariane rocket. To simulate a launch, JWST has been bombarded by soundwaves and violently shaken on an electrodynamic vibration table.
Now the spacecraft element is undergoing acoustic, sine vibration and thermal testing, which has included spending seven weeks in a vacuum while passing through a range of temperatures to mimic space’s brutal cold.
Once these tests are complete, the spacecraft element will return to the giant clean room where it was first assembled, where engineers will check whether the sunshield still works. Then two halves of JWST – spacecraft and telescope – will be integrated for a final round of testing and evaluation before launch.
Not all has run smoothly. Nuts and screws on a relatively simple part of the sunshield cover fell off last year after acoustic testing. “All but two washers were recovered following inspections,” says Nasa. “All parts under question were replaced and the spacecraft element has successfully passed its launch environment testing... this is why we test.” Previously tears in the sunshield and leaks in the thruster valves – now resolved – caused delays. “This high level of complexity brings its own challenges,” says Willoughby.
In 2011, the project narrowly escaped cancellation by the US government. But analysts say the ballooning budget comes at the expense of future flagship astrophysics missions.
“There’s both frustration and hope in the scientific community,” says Laura Forczyk, a space consultant and owner of space research firm Astralytical. “The mission is designed to last five to ten years and it’s taken 23 to get to this stage. Researchers have been on standby for years, waiting to get their hands on the data. But I can’t see Nasa repeating the mistake of Hubble at any cost [the telescope required a servicing mission after launch]. They’re taking extra care.”
More uncertainty lies ahead with “things we haven’t done before”, says Nasa. “We rehearse first-time activities with surrogates and simulators to reduce risk, but there’s nothing like the real thing.” These include fitting telescope and spacecraft elements together, testing flight electrics, and a final round of acoustic and sine vibration testing.
Once complete, JWST will be packed down to its launch state – with mirror and sunshield folded and stowed. Just smaller than a bus, the final telescope will be too large to travel by plane, so Nasa will ship it to the launch site. JWST will sit inside specially designed containers and a wide-load trailer tractor will transport it to Long Beach, California, from where it will travel by boat to Kourou, French Guiana, via the western coast of Mexico and through the Panama Canal.
During transit, it must be kept clean and safe from severe bumps and shocks. “Mother Nature will be our biggest hurdle,” says Willoughby. “Weather and unpredictable sea conditions are what we will be paying close attention to.” Once at the launch site, Northrop Grumman will begin prelaunch testing and fuelling before lift-off aboard a European Ariane 5 rocket, described by Nasa as one of the most reliable launch vessels.
For 30 days, the telescope will travel a million miles to what’s known as the second Lagrange (L2) point. Half an hour after launch and after separation from the launch vehicle, it will deploy a solar array, which will provide power, and thrusters will fire to point the solar panels towards the Sun. “So much of what we do is first of a kind,” says Willoughby, who declares himself confident of ultimate mission success. “Every day we’re doing something that hasn’t ever been done before.”
The telescope’s missions
With infrared vision, the Webb will peer back over 13.5 billion years to see the first stars and galaxies forming out of the darkness of early space. There are four main missions:
JWST’s main mission is to examine first light in the universe, looking at objects which formed shortly after the Big Bang, when the universe was a dark, hot soup of particles – electrons, neutrons, protons. Light wasn’t visible until the universe had cooled enough for these particles to start to combine into neutral atoms which allowed light to travel freely. But it would still be perhaps up to a few hundred million years after the Big Bang before the first sources of light would form. JWST’s imaging capabilities and infrared vision will reveal the early universe with unprecedented clarity.
Assembly of galaxies
JWST will look back at the earliest galaxies to understand how the universe has evolved. The spiral and elliptical galaxies scientists see today emerged from different shapes over billions of years, influenced by processes such as the collision and merger of smaller galaxies. JWST will look at what gives galaxies their shapes, how chemical elements are distributed, how central black holes influence their hot galaxies and what happens when galaxies collide.
Birth of stars
JWST, 100 times more powerful than Hubble, will be able to see with infrared vision into massive clouds of dust that are opaque to visible light observatories – through to the clouds of gas where stars and planetary systems are being born. Key questions JWST will address are how do clouds of gas and dust collapse to form stars, why do most stars form in groups, and how do stars release heavy elements back into space?
Origins of life
Since 1992, scientists have discovered thousands of exoplanets – planets outside our solar system. JWST will be able to look at these in depth, in some cases examining their atmospheres. Scientists will search for planets orbiting in the habitable zone of their star, where it’s possible for water and even life to exist. The ultimate goal is to find a planet with a similar atmosphere to Earth. JWST data will also help scientists build a fuller picture of objects in our own solar system.
When the telescope finally launches it will be aboard a European rocket – Europe’s total contribution to JWST amounts to €600m.
European scientists and engineers have made major contributions to JWST – namely provision of two optical instruments – the NIRSpec and the optical bench assembly of the MIRI. Scientists from Oxford and Cambridge Universities have worked on NIRSpec, while UK scientist Gillian Wright led the team responsible for MIRI. Furthermore, a team led by Sasha Hinkley at the University of Exeter will investigate exoplanet imaging after launch.
Building instruments that are low volume, highly accurate, light and stable has been challenging, says European Space Agency (ESA) scientist Pierre Ferruit, who’s currently based in the Netherlands.
He joined ESA in 2010 and has been working on NIRspec since 1999. “Both instruments have state of the art detectors,” he says. Instruments are made from silicon carbide – an area of European expertise. “This material is extremely stable at cold temperatures.”
MIRI – the only mid-range infrared instrument on board – has required specialist expertise, says Ferruit. “It’s been a challenge to keep everything small and light and prepare to keep it cold – at minus 266 degrees centigrade it has to be cooler than the rest of the instruments.”
European member state scientists will also have access to 15 per cent of overall observation time of JWST. Europe will provide a 15 strong team of scientists and engineers at the Space Telescope Science Institute in Baltimore, Maryland, where researchers will analyse data from the JWST once it’s in space. “Europe built these two instruments, we know them, and we will bring the expertise to the operations centre,” says Ferruit.
When the observatory is first commissioned, half a year after launch, Ferruit will work with the team in Baltimore. Membership of ESA is not linked to EU membership, which is good news for UK scientists involved in the project.
While years of delays have been frustrating, Ferruit awaits the project with anticipation. “JWST will deliver unique scientific insights. That’s what all scientists in the space community are waiting for.”
JWST in numbers
Current launch date: 2021
Official mission lifespan: five to ten years
Launch vehicle: Ariane 5
Primary mirror: 6.5m wide, 705kg
Sunshield to protect instruments from sun: 22m by 12m
Current daily cost of mission: US$1m
Man hours dedicated to date: more than 100 million
Distance from earth: 1.5 million km
Temperature of side of JWST facing the sun vs the shaded telescope: 85°C vs -223°C
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