James Webb Space Telescope: A team astronomer explains how to send a giant telescope into space – and why

The James Webb Space Telescope was specially designed to detect the oldest galaxies in the universe. NASA/JPL-Caltech, CC BY-SA/The Conversation

The James Webb Space Telescope launched into space on December 25, 2021, and with it astronomers hope to find the first galaxies to form in the universe, search for Earth-like atmospheres around other planets, and accomplish many other scientific purposes.

I’m 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 sending fragile equipment like this into space is no simple 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 extraterrestrial atmospheres

Artist’s rendering of the Webb Telescope from a lower angle. Reddish beams indicate incoming infrared light. NASA/The Talk

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 the data.

It works much like a satellite dish. Light from a star or galaxy will enter the mouth of the telescope and bounce off the primary mirror to the four sensors: NIRCam, which takes near-infrared images; the near-infrared spectrograph, which can split 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 whatever scientists point the satellite at.

This design will allow scientists to study star formation 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 resemble the Milky Way, astronomers have been wondering: how old are the oldest galaxies? How did they first form? And how have they evolved over time? The Webb Telescope was originally dubbed the “First Light Machine” because it was designed to answer these 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 that my colleagues and I will collect with NIRCam could show protogalaxies that formed just 300 million years after the Big Bang – when they were only 2% of their current age.

Finding the first aggregations of stars that formed after the Big Bang is a daunting task for a simple reason: these protogalaxies are very far away and therefore seem very faint.

The five layers of silver material under the gold mirror are a sunshade that reflects light and heat to keep the sensors incredibly cool. NASA/Chris Gunn, CC BY/The Conversation

Webb’s mirror is made up of 18 separate segments and can collect more than six times more light than the Hubble Space Telescope’s 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 are moving away from Earth, and the Doppler effect comes into play. Just like the tone of the siren of an ambulance descends and becomes more serious 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” faint galaxies in infrared light, the telescope must be exceptionally 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 aluminum coated plastic. 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 miles from Earth – about 4,500 times farther than the International Space Station and far too far to be serviced by astronauts.

For the past 12 years, the team has been testing the telescope and instruments, shaking them to simulate the rocket launch, and testing them again. Everything has been cooled and tested under the extreme operating conditions of orbit. I will never forget when my team was in Houston testing the NIRCam using a chamber designed for the Apollo lunar rover. It was the first time my camera had detected light bouncing off the telescope mirror, and we couldn’t have been happier – even with Hurricane Harvey battling us outside.

After the trials come the rehearsals. The telescope will be controlled remotely by commands sent by radio link. But because the telescope will be so far away – it takes six seconds for a signal to go one way – there’s no real-time monitoring. So for the past three years my team and I have traveled to the Space Telescope Science Institute in Baltimore and conducted rehearsal missions on a simulator covering everything from launch to routine science operations. The team has even trained to deal with potential issues that the test organizers throw at us and kindly call “anomalies”.

Some alignment required

To fit inside a rocket, the telescope must fold into a compact package. NASA/Chris Gunn, CC BY/The Conversation

The Webb team kept rehearsing and practicing until the launch date, but our work is far from done now.

We have to wait 35 days after launch for the parts to cool down before starting the alignment. Once the mirror is deployed, NIRCam will take high resolution image sequences of the individual mirror segments. The telescope team will analyze the images and have the engines adjust the segments in steps measured in billionths of a meter. Once the motors have moved the mirrors into position, we will confirm that the alignment of the telescope is perfect. This task is so mission critical that there are two identical copies of NIRCam on board – if one fails, the other can take over the alignment work.

This alignment and verification process is expected to take six months. Once complete, Webb will begin collecting data. After 20 years of work, astronomers will finally have a telescope capable of peering into the far reaches of the universe.

This story has been updated with the launch.

Marcia Rieke, Regents Professor of Astronomy, receives funding from NASA. His endowed chair is partially funded by the Heisings-Simon Foundation.

This article is republished from The Conversation under a Creative Commons license. Find the original article at http://theconversation.com.


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