TWH – The launch of the James Webb Space Telescope (JWST) in late December was big news, as it is the largest and most powerful telescope yet to be launched into space.
Arianespace’s Ariane 5 rocket launches with NASA’s James Webb Space Telescope onboard, Saturday, Dec. 25, 2021, from the ELA-3 Launch Zone of Europe’s Spaceport at the Guiana Space Centre in Kourou, French Guiana. Image credit: NASA/Bill Ingalls By NASA/Bill Ingalls – Public Domain
The JWST has an extraordinary and innovative design. It incorporates four cameras, which are also referred to as instruments, that make up what is called the Integrated Science Instrument Module (ISIM). The four instruments include the Near Infrared Camera (NIRCam), the Near Infrared Spectrometer (NIRSpec), the Near Infrared Imager and Slitless Spectrograph (NIRISS), and the Mid-Infrared Instrument (MIRI).
While similar to the cameras on the Hubble Space Telescope, the instruments on the JWST are next-level by comparison. The Hubble’s cameras include the Wide Field Camera 3 (WFC3), the Cosmic Origins Spectrograph (COS), the Advanced Camera for Surveys (ACS), the Advanced Camera for Surveys (ACS), and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).
TWH spoke with Dr. Scott Rohrbach, who is an Optical Systems Engineer at NASA’s Goddard Space Flight Center, about the launch and mission of the JWST. Rohrbach worked on the Integrated Science Instrument Module (ISIM) aspect of the project and led a team of Stray Light Analysts.
As the Optical Systems Engineer for the ISIM, he was responsible for proving that after the cameras were all received from the various organizations that build them, they would work together as a single package without interfering with one another.
“The team at Goddard also performed an additional suite of tests on each camera that the delivering organizations were not able to do,” Rohrbach said. “This involved a three weeks long 24/7 test campaign involving a staff of about 15-30 engineers per shift.
“The reason we have to do tests more than once,” he continued, “is that we first prove that all of the cameras work as expected under space-like conditions (in a vacuum and very cold), then shake the whole system to simulate what it is like to be launched on a rocket into space, and then do all of the same tests again to prove that they will still work after the rocket launch.”
One of the issues the team had to compensate for is “stray light,” which could distort the images captured by the telescope. “Stray light is when light takes a path that you don’t want it to from the front of the camera to its detector,” said Rohrbach. “When you see a scene in a movie where the camera pans close to the sun and there are a series of circles in the image, often called ‘lens flares’ – these are an example of stray light.”
Rohrbach explained the importance of eliminating stray light from the process. “[Lens flares] might look cool in a movie, but if you are trying to look out into the very dark sky you do not want your image contaminated with blobs like that from a bright source of light outside of the picture you are trying to take.
“The team I worked with simulated the possible conditions that stray light could come from and diagnosed a few ‘artifacts’ (images with unexpected results) during the optical test campaigns we ran at Goddard.”
Rohrbach explained why their work in solving issues was so important. “Using these analytical tools, we were able to diagnose a few problems that were not anticipated and devise solutions to fix them before JWST was launched, which was critical, because unlike Hubble, we cannot go fix JWST. It was not designed to be serviced and it is much too far away for astronauts to visit.”
Shown fully stowed, the James Webb Space Telescope’s Deployable Tower Assembly that connects the upper and lower sections of the spacecraft will extend 48 inches (1.2 meters) after launch. Image credit: James Webb Space Telescope – CC BY 2.0
The JWST has been dubbed as revolutionary in the technology it incorporates. Rohrbach highlighted some of the ways it differs from and expands on the tech of the Hubble. It is worth noting that the Hubble was launched in April of 1990, and while it has undergone a series of repairs and upgrades, the technology it utilizes is over 30 years old.
“There are a few ways JWST will improve upon Hubble. First, it collects six times as much light as Hubble and its cameras are more sensitive because they use newer technologies that help to produce much less background [noise].” He explained the advantages this way: “Think of the ‘fuzziness’ that you see when you take a picture with a smartphone in dim light. JWST’s ‘dark’ is much darker than Hubble’s, so it can see dimmer objects.
“The combination of more light and better cameras means that JWST will see things about 100 times dimmer than Hubble can, so it will see things that are not just further away, it will see many more things in our own galaxy, like very dim brown dwarf stars.”
The JWST uses infrared light, and Rohrbach explained why that is significant. “This is important because for galaxies and other objects that are very far away in the universe, the light that comes from them is stretched out. Light that is originally ultraviolet or visible so far away is stretched into the infrared spectrum by the time it reaches us. Another benefit of looking in the infrared spectrum is that dust in space blocks a lot of visible light. That can make for really cool pictures like the iconic Carina Nebula picture Hubble took, but JWST will be able to see inside of those dust [clouds] that make up that nebula to see all of the stars that are forming in that ‘dense’ region of the universe.”
The famous Carina Nebula “Mystic Mountain” photograph, taken by the Hubble Space Telescope. The JWST will be able to see objects within the dust clouds captured here thanks to its use of infrared light. Image Credit: NASA, ESA, M. Livio and the Hubble 20th Anniversary Team (STScI)
Another aspect of the JWST is its ability to observe and explore the structure of planets outside of our solar system and at a level that has previously been unattainable.
“A third capability I will point out (though there are more) is the ability to study planets in our galaxy outside of our solar system, or ‘exoplanets.’
“JWST will be able to directly image ones that are very large and far away from their local stars, but also be able to study the atmospheres of planets as they pass between their local star and the telescope. Light from the local star passes through the exoplanet’s atmosphere and depending on what molecules are in the atmosphere, some wavelengths of infrared light will be absorbed while the rest pass through to JWST.
“These absorption features act like a fingerprint for things like water, oxygen, carbon dioxide, and methane,” said Rohrbach, “so we will be able to tell if those compounds are in an exoplanet’s atmosphere. And planets with those kinds of compounds are much more likely to host life than ones without them.”
There was a lot of coverage in the media about the JWST’s “transformer” qualities due its design to seemingly change its shape by deploying its mirror array after being launched and reaching its destination.
Image from February 2020 when the telescope went through a mirror deployment test. Image credit: James Webb Space Telescope – CC BY 2.0
“The Primary Mirror in JWST is so big that it would not fit in any existing rocket,” said Rohrbach. “So the only way to get it into space is to make it out of smaller pieces that can all fit together inside the fairing–the front of the rocket where our payload sits. Our solution was to make the big mirror out of 18 smaller hexagons and fold the three hexagons on either side backward to fit into the fairing.
“Additionally, the Secondary Mirror needs to be held about eight meters away from the Primary Mirror – again, that will not fit in any of our current rockets, so the legs holding the Secondary Mirror have to also have to fold up. All in all, no space Observatory has ever been designed with so many individual motions needed to just get it started.”
TWH asked Rohrbach how all of this impacted his work. “All that being said,” he replied, “that aspect did not directly impact my work because my job focused on the cameras more than the front-end telescope. But one of the cameras (NIRCam) is actually used to help align the 18 hexagons to one another and make sure the Secondary Mirror is in just the right place. So we needed to test the ability of NIRCam to detect the subtle variations in images from the 18 segments and then be able to sense whether the Secondary is in the right place or not.”
If all of this seems complex and hard to grasp, Rohrbach wrote and produced a musical primer performed by The Chromatics, an a cappella group that he is a part of, whose members are all engineers, astronomers, and teachers.
TWH asked Rohrbach if there was one thing he would TWH readers to know. “There has been a lot of news over the years about JWST being behind schedule and over budget,” he replied, “but the task of building and launching it was never going to be done on the original timeline or cost.”
He noted the likely reasons for this were largely due to a combination of originally low-balling the expected cost to get it started as well as NASA and congressional management accepting that proposal.
“By now, JWST cost only about twice what Hubble cost once it was serviced to repair the initial problems it had, and the total time from concept to launch was about the same for both. But in the end, while Hubble is a 2.4 meter diameter telescope operating at room temperature in low-earth orbit, JWST is a 6.5 meter telescope with six times the collecting area that weighs half as much, operates at nearly absolute zero, helping it to be 100 times more sensitive, and sees five times more wavelengths. So while $8 billion sounds like – and is! – a lot of money, we have an observatory that can do so much more than Hubble.”
The Wild Hunt is not responsible for links to external content.
To join a conversation on this post:
Visit our The Wild Hunt subreddit! Point your favorite browser to https://www.reddit.com/r/The_Wild_Hunt_News/, then click “JOIN”. Make sure to click the bell, too, to be notified of new articles posted to our subreddit.