The James Webb Space Telescope is scheduled to enter space on December 18, 2021. Astronomers hope to find the earliest formed galaxies in the universe through it, will look around other planets for Earth-like atmospheres and accomplish many other scientific goals. Marcia Rieke is an astronomer and principal investigator of the near-infrared camera (NIRCAM) on the Webb telescope. Rieke was involved in the development and testing of the camera and the entire telescope.
In order to see the depths of the universe, the telescope has a very large mirror that must be kept extremely cold. But transporting such a fragile piece of equipment into space is not a simple task. Rieke and his colleagues had to overcome many challenges to design, test, and quickly launch and calibrate the most powerful space telescope ever built.
Atmospheres of young galaxies and exoplanets
The Webb telescope has a mirror more than 20 feet in diameter, a tennis court-sized visor to block solar radiation, and four separate cameras and sensor systems to collect data.
It works a bit like a satellite dish. Light from stars or galaxies will enter the telescope opening and bounce off the main mirror onto the four sensors. NIRCam, which takes near-infrared images; near-infrared spectrometer, which can divide light from selected sources into different colors and measure the intensity of each color; mid-infrared instruments, which take images and measure the wavelength of the mid-infrared; and near-infrared imaging gapless spectrometer, which segments and measures the light of any object that scientists point to a satellite.
This design will allow scientists to study how stars in the Milky Way form, as well as the atmospheres of planets outside the solar system; it is even possible to figure out the composition of these atmospheres.
Ever since Edwin Hubble proved that distant galaxies are the same as the Milky Way, astronomers have asked: How old are the oldest galaxies? How did they first come about? How do they change over time? The Webb telescope was originally called "the first optical machine" because it was designed precisely to answer these questions.
One of the telescope's main goals is to study distant galaxies close to the edge of the observable universe. Light from these galaxies takes billions of years to travel through the universe to Earth. Rieke estimates that the images that nircams and his colleagues will collect with NIRCam could show proto-galaxies that formed just 300 million years after the Big Bang — when they were only 2 percent old today.
Finding the places where the first stars formed after the Big Bang is a daunting task for simple reasons. These protocell galaxies are very distant, so they look very dim.
Weber's mirror consists of 18 separate parts that are able to collect more than 6 times more light than a Hubble Space Telescope mirror. Distant objects also look very small, so telescopes must be able to focus light as much as possible. Telescopes must also deal with another complex problem. As the universe is expanding, the galaxies scientists will study with the Webb telescope are moving away from Earth, and the Doppler effect is also starting to play a role. Just as an ambulance passes by and begins to move away from you, the tone of its horn moves down and becomes lower, and the wavelength of light from distant galaxies shifts from visible to infrared light.
Webb is detecting infrared light —it's essentially a giant thermal telescope. In order to "see" faint galaxies in infrared light, the telescope needs to be particularly cold, otherwise it will see its own infrared radiation. That's what heat shields are used for. The heat shield is made of thin plastic coated with aluminum. It is five layers thick and measures 46.5 feet (17.2 meters) × 69.5 feet (21.2 meters) and will keep the mirror and sensor at minus 234 degrees Celsius.
The Webb telescope is an incredible engineering feat, but how do you get something like this safely into space and make sure it works?
Testing and walkthroughs
The James Webb Space Telescope will operate in orbit 1 million miles from Earth — about 4,500 times that of the International Space Station— too far to be serviced by astronauts.
Over the past 12 years, the team has tested telescopes and instruments, rocked them to simulate rocket launches, and tested them again. Everything is cooled and tested under the extreme operating conditions of the track.
The test is followed by a walkthrough. The telescope will be remotely controlled by instructions sent over a radio link. But because telescopes will be so far away — it takes 6 seconds for a signal to reach one direction — there is no real-time control. So for the past three years, Rieke's team has been on a space telescope science institute in Baltimore to conduct a walkthrough mission on a simulator that covers everything from launch to everyday scientific operations. The team even practiced dealing with potential problems that test organizers threw at them, called "exceptions."
Some adjustments are required
The Weber team will continue testing and rehearsing until the December launch date, but the team's work is far from complete after Weber is folded and loaded into the rocket.
The team needed to wait 35 days after launch, let the parts cool down before starting to align. After the mirror is unfolded, NIRCam captures the sequence of high-resolution images for each segment. The telescope team will analyze these images and tell the motor to adjust the segments in billionths of a meter. Once the motor moves the mirror to position, they will confirm that the alignment of the telescope is perfect. This task is critical, so there will be two identical NIRCAMs – if one fails, the other can take over the alignment.
This alignment and inspection process should take six months. Once completed, Weber will begin collecting data. After 20 years of work, astronomers are about to have a telescope that can peek into the most distant parts of the universe.