UPDATE: Four and a half months after liftoff, the James Webb Telescope has successfully been aligned with its complex optical thanks to a team of skilled engineers. Michael McElwaine, the observatory scientist for the James Webb telescope told CBS News "I'm delighted to report that the telescope alignment has been completed with performance even better than we had anticipated."
On 18 April, the first photos from the James Webb telescope were released and compared to that of the now-retired Spitzer they are incredible thanks to Webb's segmented mirror that measures 21.5ft across - which is 7x bigger than the segmented mirror on the Spitzer.
Its mission is to capture faint light from the first generation of stars and galaxies that formed some 13.8 billion years ago when the big bang occurred. The Webb telescope is currently orbiting the earth from one million miles away and scientists are hoping that within the next few months it will make an exciting scientific discovery.
Original story (24/12/2021) It’s the biggest, the best and the most expensive space observatory ever built, but when the James Webb Space Telescope (Webb) goes skywards tomorrow it will carry into deep space a camera array that’s easily the coolest in the Solar System.
In the works for 25 years, Webb was originally supposed to launch in 2007 and cost US$500 million. It ended up costing US$10 billion. However, if it successfully reaches space and begins operations as planned in 2022, Webb has the potential to change astronomy as we know it.
Following a delay due to the weather, it is now due for a Christmas Day launch from the European Spaceport in French Guiana atop an Ariane-5 rocket at 7:20am EST / 12:20 pm GMT / 10:20pm AEST on Saturday, December 25, 2021. It will be screened live on NASA TV on YouTube.
The next Hubble?
Some call Webb “the next Hubble”, but that’s not correct. While the original space telescope – which launched in 1990 – continues to send back incredible images from its visible light cameras, Webb will have six times more light-collecting power than Hubble, but much more importantly it will add a whole new dimension to Hubble’s astronomical observations by observing almost exclusively in the infrared.
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The cameras on Webb will collect infrared light from the distant corners of the cosmos and capture what the 13.77 billion years old Universe looked like just after the Big Bang. To do that its giant mirror will need to be pointed at faint galaxies for hundreds of hours in order to collect enough light.
Hubble has looked back in time as far as it can. Using its 2.4 metre mirror and a combination of visible light and near-infrared cameras the Hubble Space Telescope has been able to take a slew of incredible images of the early Universe. Its biggest achievements are arguably the Hubble Deep Fields, composite photographs that include small, redshifted galaxies existing when the Universe was just 800 million years old.
Webb will go much further into deep time by using its 6.5 metre mirror and camera to image red galaxies around 250 million years after the Big Bang. It’s hoped that scientists will be able to use the data to probe the structures and origins of the early Universe and to figure out how the complex galaxies they see now actually evolved.
Webb and exoplanets
Although peering closer to the Big Bang is Webb’s headline act, another more recently acquired task of its astronomers will be to use its cameras to study exoplanets, defined as a planet that orbits a star outside the Solar System. While it won’t build on the 4,000+ exoplanets already discovered, Webb will be able to study the atmospheres of those suspected to be Earth-like. As they transit a star and are briefly back-lit Webb will study the light in their atmospheres for traces of methane, water and carbon dioxide. To do that both its NIRCam and MIRI cameras feature starlight-blocking coronagraphs to block the light of an exoplanet’s bright host star.
James Webb Space Telescope’s cameras
This is no ordinary camera array. Webb is designed solely to detect infrared light – a form of heat radiation – emitted by distant stars, planets and the clouds of gas and dust they’re born within. It will see light from the first stars, thought to be about 300 times more massive than the Sun, as well as the earliest galaxies. The infrared skill is important because there are parts of the Universe that are packed with dust and gas, where visible light can’t get through. Hubble hasn’t been able to study these regions; Webb will show us the Universe thus far unseen by any other telescope.
So the four cameras on the Webb – housed in its Integrated Science Instrument Module (ISIM) behind the mirror – have been designed to tease-out as much as possible from the hidden cosmos:
Although it’s NIRCam and NIRSpec that will be doing a lot of the cutting-edge science, it's the MIRI camera that will likely give us incredible better-than-Hubble wide-field astrophotography images.
How and why Webb will keep its cameras cold
While Hubble orbits Earth, Webb will be flying a million miles away. Infrared light is basically heat radiation, which is also emitted by us and by our electronics. So Webb’s cameras need to observe the Universe far from Earth where it’s very, very cold. About four times the distance of the Earth to the Moon, Webb will operate at the Lagrange Point 2, where the gravity of the Earth and Sun combine to create a stable location.
To make it as cold as possible Webb will operate at a shivering temperature of -233 ºC/-388 ºF, which is about 40 Kelvin. However, the detectors inside the MIRI instrument will operate at an even lower -266 ºC/-448 ºF, or 7 Kelvin. That’s critical because it can’t glow brighter than the faint heat signals it’s there to detect. If it does, its images will be ruined by what astronomers call noise. A five-layer sunshield made of kapton will act like a parasol and separate Webb into the Sun-facing side and a cold side. The vacuum between the layers will behave as an insulator.
Webb’s perilous trip to L2 will take about 50 days, but during that trip – and for 27 days afterwards – the sunshield will block the Sun from shining on the cameras, thus allowing them to cool. There’s also a cryocooler on board that will take 19 days to cool down the cameras to their operating temperature (using enough helium gas to fill nine party balloons). This is cutting-edge stuff. “It’s relatively easy to cool something down to that temperature on Earth, but those Earth-based systems are very bulky and energy inefficient,” said Konstantin Penanen, a cryocooler specialist at NASA’s Jet Propulsion Laboratory in Southern California, which manages the MIRI instrument for NASA. “For a space observatory, we need a cooler that is physically compact, highly energy efficient, and it has to be highly reliable because we can’t go out and repair it.”
That’s critical because Webb is on its own after launch. If something does go wrong with its incredibly detailed deployment sequence, or at any time during its mission, then Webb almost certainly cannot be fixed. It’s going to be too far away (though never underestimate NASA!). That’s unlike Hubble, which has had its cameras upgraded several times by visiting NASA astronauts hitching a ride on a Space Shuttle (before they were grounded in 2011).
In terms of risk versus value for your buck, Webb is as big as the bang. The coolest cameras in the Solar System now just need a home in space from which they can change astronomy as we know it.
Further reading:
The best telescopes for astrophotography
The best lenses for astrophotography
