James Webb Space Telescope: An astronomer on the team explains how to send a giant telescope to space — and why

The James Webb Space Telescope, the largest orbital telescope ever constructed, is set to be launched into space Dec. 18, 2021.
This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.

Marcia Rieke is the Regents Professor of Astronomy at University of Arizona

On Dec. 18, 2021, the James Webb Space Telescope will be launched into space. Astronomers will be able to locate the first galaxies in the universe and search for Earthlike atmospheres on other planets with it. They also hope to accomplish other scientific goals.

I am an astronomer, principal investigator of the Near Infrared Camera (or NIRCam) aboard the Webb telescope. My camera and the telescope have been developed and tested by me.

The telescope must have a large mirror to see into the depths of the universe. It must also be kept very cold. It is not an easy task to get a delicate piece of equipment such as this into space. My colleagues and I had to overcome many obstacles to design, launch and align the strongest space telescope ever made.

The telescope must be large and kept very cold in order to detect galaxies that are far away and older than the rest. (Image credit NASA/Chris Gunn CC BY).

Galaxies young and alien atmospheres

The Webb telescope features a mirror that measures over 20 feet in diameter, a sun shade tennis court-sized to block sunlight and four camera and sensor systems for collecting data.

It functions in a similar way to a satellite dish. The telescope will receive light from a star, or galaxy, and it will bounce off the primary mirror towards the four sensors. These sensors are NIRCam, the Near Infrared Spectrograph and Mid-Infrared Instrument. They can take images and measure wavelengths from a variety of sources and measure their strength. And the Near Infrared Imaging Slitless Spectrograph which splits and measures light of any object scientists point at.

Scientists will be able to use this design to study the formation of stars in the Milky Way as well as the atmospheres on planets other than the solar system. These atmospheres may even have a composition that can be determined.

Here is the NIRCam. It measures infrared light coming from old and distant galaxies. (Image credit NASA/Chris Gunn. CC BY).

Astronomers have been asking: What is the age of the oldest galaxies since Edwin Hubble's discovery that distant galaxies look just like the Milky Way? What caused them to form in the first place? How have they evolved over the years? Because it was designed to answer these questions, the Webb telescope was initially called the "First Light Machine".

The telescope's main goal is to study distant galaxies at the edge of the universe. The light from these galaxies takes billions of year to reach Earth. My colleagues and I are estimating that the images we collect with NIRCam will show protogalaxies formed 300 million years after Big Bang, when they were only 2% of their current age.

It is difficult to find the first aggregations stars formed after the Big Bang. This is due to one simple reason: Protogalaxies appear very faint and far away.

Webb's mirror has 18 segments, and can capture more light than the Hubble Space Telescope. Also distant objects appear very small so the telescope must be capable of focusing the light as precisely as possible.

Another problem that the telescope must deal with is the Doppler effect. As the universe expands, the galaxies scientists will be studying with the Webb telescope are also moving away from Earth. The wavelength of light coming from distant galaxies shifts from visible light to near-infrared light, just as the siren pitch shifts and becomes louder when it passes.

The five layers of silvery material beneath the gold mirror act as a sunshield and reflect heat and light to keep the sensors extremely cold. (Image credit NASA/Chris Gunn. CC BY).

Webb can detect infrared light. It is basically a giant heat telescope. The telescope must be extremely cold to "see" faint galaxies under infrared light. Otherwise, it will only see its own infrared radiation. The heat shield is here to help. The shield is made from thin plastic coated with aluminum. It has five layers and measures 46.5 feet (17.2 m) by 69.5 feet (21.2m). The shield will protect the sensors and mirror from freezing at minus 390 Fahrenheit (minus 23 Celsius).

Webb's telescope is a remarkable feat of engineering. But how do you safely transport it to space? And guarantee that it will function?

Scientists and engineers tested the telescope in a cryogenic vacuum chamber that was extremely low pressure and cold. (Image credit NASA/Chris Gunn CC BY).

Practice and test your skills

The James Webb Space Telescope will orbit one million miles (1.5 million km) above Earth. This is approximately 4,500 times farther than the International Space Station. It is too far away to be serviced with astronauts.

The team has been testing the telescope and instruments over the past 12 years. They have also shaken them to simulate a rocket launch, and then tested them again. All of the instruments and telescopes have been tested in orbit under extreme conditions. My team and I were in Houston to test the NIRCam with a chamber made for the Apollo lunar rover. My camera was the first to detect light bounced off the telescope mirror. We couldn't have been more happy, even with Hurricane Harvey pounding us outside.

Space Telescope Science Institute training and rehearsals are crucial to ensure that the assembly process runs smoothly and that any unexpected anomalies can easily be addressed. (Image credit: NASA/STScI, CC BY)

The rehearsals followed the testing. Remote control of the telescope will be possible via radio links. Because the telescope is so far away, it will take six seconds for a signal from one direction. There is therefore no real-time control. My team and I have been visiting the Space Telescope Science Institute, Baltimore, for three years to run rehearsal missions on a simulator that covers everything from launch to routine science operations. Even the test organizers have thrown some "anomalies" at us, so we practiced handling them.

The telescope must be folded into a small package to fit in a rocket. (Image credit NASA/Chris Gunn CC BY).

Some alignment is required

Webb's team will continue practicing and rehearsing until December's launch, but we are far from finished once Webb has been folded into the rocket.

The parts must cool for 35 days before we can begin alignment. NIRCam will take sequences of high resolution images of each segment of the mirror after it unfolds. The telescope team will examine the images and instruct motors to adjust each segment in steps of billionths or a meter. After the motors have moved the mirrors into place, we will verify that the telescope alignment has been achieved. This task is so critical that we have two identical copies (NIRCam) onboard in case one fails. The other can then take over alignment.

The alignment and checkout should take approximately six months. Webb will start collecting data once the alignment is complete. Astronomers will finally have a telescope that can see into the most distant, farthest reaches of the universe after 20 years of hard work.

This article was republished by The Conversation under Creative Commons. You can read the original article.

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