The James Webb Space Telescope was launched into space on December 25, 2021, and with it astronomers hope to find the first galaxies that formed in the universe, search for Earth-like atmospheres around other planets and achieve many other scientific goals.
I’m an astronomer and the principal investigator for the Near Infrared Camera – or NIRCam for short – aboard the Webb Telescope. I have been involved in the development and testing of both my camera and telescope as a whole.
To see the depths of the universe, the telescope has a very large mirror and it must be kept very cold. But bringing a fragile piece of equipment like this into space is no easy task. There were many challenges that my colleagues and I had to overcome to design, test, launch and align the most powerful space telescope ever made.
Young galaxies and strange atmospheres
The Webb telescope has a mirror more than 20 feet wide, a tennis court-sized sun shade to block solar radiation and four separate camera and sensor systems for data collection.
It kind of works like a satellite dish. Light from a star or galaxy enters the mouth of the telescope and bounces back from the primary mirror toward the four sensors: NIRCam, which takes pictures in the near-infrared; near-infrared spectrometer, which can separate light from a selection of sources into their component colors and measure the strength of each; mid-infrared instrument, which takes pictures and measures wavelengths in the mid-infrared; and the near-infrared imaging spectrum, which splits and measures the light of whatever scientists point the satellite at.
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 find out the composition of these atmospheres.
Since Edwin Hubble proved that distant galaxies are similar to the Milky Way, astronomers have wondered: How old are the oldest galaxies? How were they formed for the first time? How have they changed over time? The Webb Telescope was originally called the “First Light Machine” because it was designed to answer these very questions.
One of the telescope’s main goals is to study distant galaxies close to the edge of the visible universe. It takes billions of years for the light emitted from these galaxies to cross the universe and reach Earth. I estimate that the images that my colleagues and I will be collecting using NIRCam can show the protogalaxies that formed just 300 million years after the Big Bang – when they were only 2% of their current ages.
Finding the first clusters of stars that formed after the Big Bang is a daunting task for a simple reason: These protogalaxies are very distant and therefore look very faint.
The Webb mirror consists of 18 separate segments and can collect more than six times the light of the Hubble Space Telescope mirror. Distant objects also appear very small, so the telescope must be able to focus the light as tightly as possible.
The telescope must also deal with another complication: as the universe expands, the galaxies that scientists will study with the Webb telescope move away from Earth, and the Doppler effect begins. Just as an ambulance siren deflects downward and gets deeper as it passes and begins to move away from you, the wavelength of light from distant galaxies shifts downward from visible light to infrared light.
Webb detects infrared light – essentially a giant thermal telescope. In order to “see” faint galaxies in infrared light, the telescope must be exceptionally cold or else all it sees is its own infrared. This is where the heat shield comes in. The shield is made of thin aluminum-coated plastic. It’s 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 degrees Celsius).
The Webb Telescope is an amazing feat of engineering, but how does one safely transport such an object into space and ensure that it will work?
Test and practice
The James Webb Space Telescope will orbit a million miles from Earth – about 4,500 times more than the International Space Station and far beyond it can be served by astronauts.
Over the past 12 years, the team has tested and rocked the telescope and instruments to simulate a rocket launch and tested them again. Everything has been cooled and tested under the harsh operating conditions of the orbit. I’ll never forget when my team in Houston was testing NIRCam using a chamber designed for the Apollo lunar module. It was the first time my camera detected light bouncing off the telescope mirror, and we couldn’t have been happier—even though Hurricane Harvey was battling us outside.
After the test came rehearsals. The telescope will be remotely controlled by commands sent via a wireless link. But because the telescope will be so far away – the signal takes six seconds to go in one direction – there is no real-time control. So for the past three years, my team and I have been going to the Space Telescope Science Institute in Baltimore and running simulator training missions covering everything from launch to routine science operations. The team has even been trained to deal with potential problems that test organizers throw at us and call them bluntly “anomalies.”
Some alignment required
The Webb team has continued to train and practice until the launch date, but our work is far from over now.
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We need to wait 35 days after launch for the parts to cool down before starting the alignment. After the mirror is unfolded, NIRCam will capture sequences of high-resolution images of individual mirror segments. The telescope team will analyze the images and tell the actuators to adjust the sections in steps of billionths of a metre. Once the motors move the mirrors into position, we will confirm that the telescope’s alignment is perfect. This task is so important that there are two identical copies of NIRCam on board – if one fails, the other can take over the alignment task.
The alignment and withdrawal process should take six months. When finished, Webb will start collecting data. After 20 years of work, astronomers will finally have a telescope capable of looking into the farthest and farthest reaches of the universe.
This story has been updated with launch.
Marcia Ricci, Regents Professor of Astronomy, University of Arizona
This article has been republished from The Conversation under a Creative Commons license. Read the original article.
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