The James Webb Space Telescope

Text by Divan Muller
Photographs Courtesy of NASA

Much has been said, although perhaps not enough, about the significance of the recently launched James Webb Space Telescope. What is so special about this telescope, and what will it reveal?

History

During the 1960s, ‘70s and ‘80s, NASA (National Aeronautics and Space Administration) launched several space telescopes in its Orbiting Solar Observatory programmes. These satellites made a number of notable discoveries from low Earth orbit, before re-entering the Earth’s atmosphere. Well, in terms of returning to Earth, at the end of its mission, one of these space telescopes was destroyed by an anti-satellite missile fired from an F-15 Eagle.

Since then, many other space telescopes have been launched, with the most significant of these being the Hubble Space Telescope (HST). Developed by NASA, with assistance from the European Space Agency, the HST was launched in 1990. Over the past 30 years, Hubble has made incredibly important discoveries, including ones relating to the size and age of the universe, black holes, the size of the Milky Way, and many others. Of course, most will remember the HST for its incredible images of spectacular objects in the universe. With the Hubble Deep Field, Hubble Ultra-Deep Field and Hubble eXtreme Deep Field images, captured in 1995, 2004 and 2012 respectively, the HST discovered thousands of galaxies in a seemingly insignificantly small portion of our night sky.

Although it has been maintained and upgraded though Space Shuttle missions, the HST’s mission will ultimately end within the next two decades, when it will re-enter Earth’s atmosphere.

The James Webb Space Telescope

It is astonishing what has been discovered by the 32-year-old HST, but one has to wonder, what could be unveiled by a more modern, better positioned space telescope?

The James Webb Space Telescope (JWST) was named after James Edwin Webb, who served as NASA’s administrator during the Mercury and Gemini programmes of the 1950s and ‘60s. Planning and development of the telescope began in the mid-1990s, with the launch originally scheduled for 2007. With challenges in terms of funding and components being redesigned, the launch date was pushed back numerous times. At last, on 25 December 2021, the JWST was launched into space by a European Space Agency (ESA) Ariane 5 rocket, from Europe’s Spaceport in French Guiana. At the time of writing, the JWST had unfolded its mirror array and was well on its way to the second Lagrange Point (L2). According to NASA, Lagrange Points are “areas where gravity from the sun and Earth balance the orbital motion of a satellite. Putting a spacecraft at any of these points allows it to stay in a fixed position relative to the Earth and sun with a minimal amount of energy needed for course correction… In the case of L2, this happens about 930,000 miles [about 1,500,000 km] away from the Earth in the exact opposite direction from the sun. The Earth, as we know, orbits the sun once every year. Normally, an object almost a million miles farther out from the sun should move more slowly, taking more than a year to complete its orbit around the sun. However, at L2, exactly lined up with both the sun and Earth, the added gravity of the two large bodies pulling in the same direction gives a spacecraft an extra boost of energy, locking it into perfect unison with the Earth's yearly orbit.”

There are several advantages to having the JWST located in L2. With the telescope always being in the same relative position, it is easier to communicate with it. The telescope uses infrared light to capture images of distant objects in the universe. Of course, infrared light is heat radiation, so to operate effectively, the telescope needs to be cool. The JWST uses a sunshield to keep it below -225 degrees Celsius, but to be effective, the sun and Earth need to be in the same direction, which is the case in L2. Also, according to NASA, “With the sun and the Earth in the same part of the sky, the Webb telescope will enjoy an open, unimpeded view of the universe. In comparison, the Hubble Space Telescope is in low-Earth orbit where it goes in and out of the Earth's shadow every 90 minutes. Hubble's view is blocked by the Earth for part of each orbit, limiting where the telescope can look at any given time.”

Equipment

The amount of detail a telescope can see is directly related to the size of its mirror. As it happens, the JWST has the largest mirror ever launched into space. It has a diameter of 6.5 m and is made up of eighteen hexagonal mirror segments. These mirrors are made of beryllium and coated with a layer of gold. The gold layer has a thickness of about 700 atoms. These materials are ideal for collecting infrared light. In addition to cameras for capturing images, the James Webb uses spectrographs to break light into colours for analysis, as well as coronagraphs to block starlight and observe planets. Its four scientific instruments are: the Near Infrared Camera (NIRCam), the Near-Infrared Spectrograph (NIRSpec), the Mid-Infrared Instrument (MIRI), and the Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS). In terms of resolution, the telescope would be able to see an object the size of a football from a distance of 550 km. It could detect the heat signature of a bumblebee at the distance of the moon from Earth. Six reaction wheels are used to turn and aim the telescope. Its sunshield has a size of about 21 m by 14 m.

According to an Interesting Engineering article, the James Webb might be the most challenging object ever launched into space. “When creating something like the Webb telescope, designers maintain a list of elements that would have severe, mission-disrupting consequences if any one of them were to fail.” The Galileo probe sent to Jupiter in the 1980s had about thirty single-point failures, while a Mars landing has about 100. According to the article, the TWST’s list of single-point failures is 344 items long. “One of the biggest challenges facing Webb isn't the sheer number of single-point failures, it's that so many of them are interconnected.”

Producing the James Webb required 40 million hours of work by thousands of scientists, engineers and technicians from Austria, Belgium, Canada, Denmark, France, Germany, Ireland, Italy, the Netherlands, Spain, Sweden, Switzerland, the United Kingdom and the USA.

While collaborating with NASA and the ESA, the Canadian Space Agency (CSA) contributed the Fine Guidance Sensor (FGS), which allows the telescope to point at and focus on objects of interest, as well as the NIRISS, a scientific instrument that helps study many astronomical objects, from exoplanets to distant galaxies. In return, Canada will receive a guaranteed share of the telescope’s observation time.

The telescope should begin conducting experiments before the middle of 2022, and its mission is planned to last from five to ten years. The James Webb Space Telescope is an incredibly ambitious and complex initiative, but this project will no doubt produce images and information that will literally change the way we see the universe.