James Webb Space Telescope instrument gets ready to probe the universe's chemistry

The James Webb Space Telescope's NIRSpec (Near-Infrared Spectograph) during assembly at NASA's Goddard Space Flight Center in Maryland.
The James Webb Space Telescope's NIRSpec (Near-Infrared Spectograph) during assembly at NASA's Goddard Space Flight Center in Maryland. (Image credit: NASA/Chris Gunn)

NASA's James Webb Space Telescope is preparing for a deep-space chemistry experiment.

During the observatory's commissioning and ongoing mirror alignment, Webb's Near-Infrared Spectrograph (NIRSpec) team successfully finished initial check-out and characterization of three mechanisms that are key for the instrument to do its work.

"The NIRSpec team will continue their commissioning efforts. The whole team is very much looking forward to the start of science observations this summer," several NIRSpec representatives wrote in a Webb blog post (opens in new tab) Thursday (March 3).

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Once operational, NIRSpec will split the light from targets that Webb observes into what scientists call spectra, measuring the amount of light with specific wavelengths. This fingerprint can teach astronomers about galaxies, exoplanets and other objects, shedding light on properties such as mass, temperature and chemical composition. 

With NIRSpec, Webb can take spectra of up to 100 galaxies at the same time, making observations much more efficient since collecting the light photons from such distant objects will take the observatory hundreds of hours.

NIRSpec's three key mechanisms are a filter wheel assembly, a grating wheel assembly and a refocus mechanism assembly, the Webb blog post stated. 

Here is how the instrument will work: The grating wheel spreads light from a target of interest into its colors (wavelengths) to make a spectrum. The filter wheel reduces contamination by blocking wavelengths outside of what scientists are interested in looking at. Then the refocus mechanism will adjust and sharpen NIRSpec's focus.

Engineers checked out each of these assemblies separately, starting with the filter wheel assembly to make sure its eight positions in forward and reverse directions are working.

"At each position, we recorded a set of reference data," NIRSpec officials wrote. "This data showed us how well the wheel was moving, and how accurately it settled into each position. Between each ... position, we downloaded 'high-capacity buffer' data from the positioning sensors, and the NIRSpec team analyzed the data. The data showed that the wheel moved very well even in the first attempt."

Next, Webb engineers recorded the reference data of the grating wheel assembly and cycled the positions in much the same way, showing that everything was working correctly.

Then with the refocus mechanism assembly (RMA), engineers also did an initial data collection before commanding the mechanism to move forward "a few hundred steps from launch position," the blog post said.

This gif shows the “before” and “after” images from Segment Alignment, when the team corrected large positioning errors of its primary mirror segments and updated the alignment of the secondary mirror.

This gif shows the “before” and “after” images from Segment Alignment, when the team corrected large positioning errors of its primary mirror segments and updated the alignment of the secondary mirror. (Image credit: NASA/STScI)

"After the initial move," the NIRSpec team added in the blog, "we commanded the RMA mirrors to their previous best focus position. Successful completions of this test showed us that the RMA is a well-behaved and healthy mechanism."

Amid the instrument checkout, Webb mirror alignment is continuing in its fourth phase, focusing on "coarse phasing" that measures and corrects small height differences between individual mirror segments, the blog post noted. The telescope remains in excellent health after its Dec. 25 launch and has enough fuel for at least 20 years of operations.

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Elizabeth Howell
Staff Writer, Spaceflight

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. Elizabeth's reporting includes an exclusive with Office of the Vice-President of the United States, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and (soon) a Bachelor of History from Athabasca University. Elizabeth is also a post-secondary instructor in communications and science since 2015. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: https://qoto.org/@howellspace