Marcia Rieke is Regent Professor of Astronomy at the University of Arizona. This story originally appeared on The conversation.
The James Webb Space Telescope is scheduled to go to space on December 18, 2021. With it, astronomers hope to find the first galaxies to form in the universe, search for Earth-like atmospheres around other planets, and achieve many other scientific objectives.
I am an Astronomer and Principal Investigator for the Near Infrared Camera – or NIRCam for short – aboard the Webb Telescope. I participated in the development and testing of my camera and the telescope as a whole.
To see deep into the universe, the telescope has a very large mirror and must be kept extremely cold. But transporting fragile equipment like this into space is no easy task. My colleagues and I had to overcome many challenges to design, test and soon launch and align the most powerful space telescope ever built.
Young galaxies and alien atmospheres
The Webb telescope has a mirror over 20 feet in diameter, a tennis court-sized sunshade to block solar radiation, and four separate camera and sensor systems to collect data.
It works much like a satellite dish. Light from a star or galaxy will enter the telescope’s mouth and bounce off the primary mirror towards the four sensors: NIRCam, which takes near infrared images; the near infrared spectrograph, which can divide light from a selection of sources into their constituent colors and measure the strength of each; the Mid-Infrared instrument, which takes images and measures wavelengths in the mid-infrared; and the near infrared imaging slitless spectrograph, which splits and measures light from anything scientists point at the satellite.
This design will allow scientists to study how stars form in the Milky Way and the atmospheres of planets outside the solar system. It may even be possible to understand the composition of these atmospheres.
Ever since Edwin Hubble proved that distant galaxies are like the Milky Way, astronomers have been asking: How old are the oldest galaxies? How were they first formed? And how have they changed over time? The Webb Telescope was originally nicknamed the “First Light Machine” because it is designed to answer these same questions.
One of the main purposes of the telescope is to study distant galaxies near the edge of the observable universe. It takes billions of years for the light from these galaxies to travel through the universe and reach Earth. I estimate that the images my colleagues and I will be collecting with NIRCam could show protogalaxies that formed barely 300 million years after the Big Bang, when they were only 2% of their current age.
Finding the first clusters of stars that formed after the Big Bang is a difficult task for a simple reason: these protogalaxies are very far apart and therefore appear to be very weak.
Webb’s mirror is made up of 18 separate segments and can collect more than six times as much light as the Hubble Space Telescope’s mirror. Distant objects also appear to be very small, so the telescope must be able to focus light as closely as possible.
The telescope also faces another complication: since the universe is expanding, the galaxies scientists will study with the Webb telescope move away from Earth, and the Doppler effect kicks in. Just like the siren d As an ambulance shrinks and gets deeper as it passes and begins to move away from you, the wavelength of light from distant galaxies changes from visible light to infrared light.
Webb detects infrared light – it’s basically a giant thermal telescope. To “see” weak galaxies in infrared light, the telescope must be unusually cold, otherwise all it would see would be its own infrared radiation. This is where the heat shield comes in. The shield is made of a thin plastic covered with aluminum. It is five layers thick and measures 46.5 feet (17.2 meters) by 69.5 feet (21.2 meters) and will keep the mirror and sensors at minus 390 degrees Fahrenheit (minus 234 Celsius).
The Webb telescope is an incredible feat of engineering, but how do you get such a thing safely into space and guarantee that it will work?
Test and repeat
The James Webb Space Telescope will orbit a million kilometers from Earth, about 4,500 times farther than the International Space Station and far too far away to be served by astronauts.
Over the past 12 years, the team has tested the telescope and instruments, rocked them to simulate the rocket launch, and tested them again. Everything has been cooled and tested under the extreme operating conditions of the orbit. I will never forget the time my team was in Houston to test the NIRCam using a chamber designed for the Apollo lunar rover. It was the first time my camera detected light bouncing off the telescope’s mirror, and we couldn’t have been happier, even though Hurricane Harvey was battling us outside.
After the tests came the rehearsals. The telescope will be controlled remotely by commands sent over a radio link. But because the telescope will be so far away (it takes six seconds for a signal to go one way), there is no real-time control. So for the past three years my team and I have been to the Space Telescope Science Institute in Baltimore and performed rehearsal missions on a simulator covering everything from launch to routine science operations. The team has even practiced handling the potential problems that the test organizers throw at us and nicely call “anomalies”.
Some alignment required
The Webb team will continue to rehearse and practice until the launch date in December, but our job is far from over once Webb is folded up and loaded into the rocket.
We have to wait 35 days after launch for parts to cool before starting alignment. After the mirror is deployed, NIRCam captures high-resolution image sequences of individual mirror segments. The telescope team will analyze the images and have the motors adjust the segments in steps measured in billionths of a meter. Once the motors have put the mirrors in place, we will confirm that the telescope alignment is perfect. This task is so critical that there are two identical copies of NIRCam on board – if one fails, the other can take over the alignment job.
This alignment and verification process is expected to take six months. When complete, Webb will begin collecting data. After 20 years of work, astronomers will finally have a telescope capable of scanning the most distant and far reaches of the universe.