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James Webb Space Telescope begins final check-outs before science observations

The James Webb Space Telescope is protected from the sun's and Earth's heat by a giant kite-shaped shield.
The James Webb Space Telescope is protected from the sun's and Earth's heat by a giant kite-shaped shield. (Image credit: Kevin Gill)

NASA's next-generation observatory is entering the last stages of preparation before showing scientists an all-new view of the universe. 

Engineers are preparing to make final tweaks to the instruments on board the James Webb Space Telescope as the observatory readies for operations this summer. NASA said the telescope has "calibrations and characterizations of the instruments using a rich variety of astronomical sources" coming up shortly to make sure everything is working before Webb is set loose to examine the early universe.

"We will measure the instruments' throughput — how much of the light that enters the telescope reaches the detectors and is recorded," Scott Friedman, lead commissioning scientist for Webb at Baltimore's Space Science Telescope Institute, said in NASA statement (opens in new tab) Thursday (May 5).

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While no telescope can accurately collect every photon that comes through to it, engineers will still want to know the throughput at several light wavelengths to assess Webb's performance at gathering infrared light, Friedman said.

Friedman emphasized the commissioning is "almost there," as the telescope is in the last two month of the process, which began after Webb's launch on Dec. 25, 2021. Once the instruments are assessed properly, he said, "we will be ready to begin the great science programs that astronomers and the public alike have been eagerly awaiting."

The team has been releasing a few commissioning images along the way, and a notable commissioning target is coming into focus soon: the Large Magellanic Cloud. While Friedman did not say if this galactic neighbor to the Milky Way will be included in early release images, he noted that examining the galaxy will be helpful to calibrate any distortion.

The Webb telescope will also be assessed even further for its sharpness of stellar images, through all of the instruments' optics. Each instrument is working fine with the optics tested so far, Friedman noted, but additional filters and a tool called "diffraction grating" (which spreads light into constituent colors) will also be assessed.

The team will also certify the observatory's target acquisition to make sure the telescope can point with precision down to a hundredth of an arcsecond, which will be useful for exoplanet observations.

"The star has to be placed behind a mask so its light is blocked, allowing the nearby exoplanet to shine through," Friedman said. "In time series observations, we measure how an exoplanet's atmosphere absorbs the stellar light during the hours it takes to pass in front of its star, allowing us to measure the properties and constituents of the planet’s atmosphere."

A last final testing activity will be observing moving targets such as planets, satellites, rings, asteroids and comets. "Observing these requires that the observatory change its pointing direction relative to the background guide stars during the observation," Friedman said. "We will test this capability by observing asteroids of different apparent speeds using each instrument."

NASA plans to update the public on Webb's progress on Monday (May 9) and a livestream of the discussion will be available online (opens in new tab).

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Elizabeth Howell
Elizabeth Howell

Elizabeth Howell, Ph.D., is a staff writer in the spaceflight channel since 2022. She was contributing writer for Space.com (opens in new tab) for 10 years before that, since 2012. As a proud Trekkie and Canadian, she also tackles topics like diversity, science fiction, astronomy and gaming to help others explore the universe. Elizabeth's on-site reporting includes two human spaceflight launches from Kazakhstan, three space shuttle missions in Florida, and embedded reporting from a simulated Mars mission in Utah. She holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, and a Bachelor of Journalism from Canada's Carleton University. Elizabeth is also a post-secondary instructor in communications and science since 2015. Her latest book, Leadership Moments from NASA, is co-written with astronaut Dave Williams. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.