August 15, 2022

Alignment of James Webb Space Telescope begins

Alignment of James Webb Space Telescope begins
Alignment of James Webb Space Telescope beginsAlignment of James Webb Space Telescope begins

The James Webb Space Telescope continues to take big strides toward becoming an operational observatory.

Mission team members have begun the three-month process of aligning the $10 billion Webb, which launched on Dec. 25, NASA officials announced today (Feb. 3). 

In the past day or so, for the first time, photons from distant stars traveled through the entire telescope and were detected by Webb’s Near Infrared Camera (NIRCam) instrument, NASA officials said. This was a huge moment in itself, and it lays the groundwork for alignment, which relies on data collected by NIRCam.

“This milestone marks the first of many steps to capture images that are at first unfocused and use them to slowly fine-tune the telescope,” NASA officials wrote in an update today. “This is the very beginning of the process, but so far the initial results match expectations and simulations.”

Related: How the James Webb Space Telescope works in pictures

Webb’s 21.3-foot-wide (6.5 meters) primary mirror consists of 18 hexagonal segments, which launched in a compact configuration and unfolded after the telescope got to space. The alignment process will get all 18 working as a single light-collecting surface, which is no mean feat.

“To work together as a single mirror, the telescope’s 18 primary mirror segments need to match each other to a fraction of a wavelength of light — approximately 50 nanometers,” NASA officials wrote. “To put this in perspective, if the Webb primary mirror were the size of the United States, each segment would be the size of Texas, and the team would need to line the height of those Texas-sized segments up with each other to an accuracy of about 1.5 inches [3.8 centimeters].”

There are seven phases in the alignment process, which will key on imagery Webb captures of the bright star HD 84406. The mission team will take photos of the star with each of the 18 mirror segments, then use that information to shift the segments into their proper positions. 

Today’s update goes into considerable depth about the seven phases and how each will work; you can read the details here.

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NASA views Webb as the successor to its iconic Hubble Space Telescope, which has been circling Earth since April 1990. Whereas Hubble views the cosmos primarily in visible and ultraviolet light, however, the newly launched scope will focus on the infrared — wavelengths that we feel as heat. 

Webb’s optics and four science instruments must stay very cold to do this work; the slightest heat emissions could swamp the faint signals the observatory was designed to study. So Webb sports a huge, five-layer sunshield to block and disperse solar radiation and is ensconced at the Earth-sun Lagrange Point 2, a gravitationally stable spot 930,000 miles (1.5 million kilometers) from our planet that will allow Webb to use that shield effectively all the time.

Alignment isn’t the final step in Webb’s journey to operational status; the mission team will also need to commission the telescope’s four science instruments. That work is expected to be complete by late June or early July, team members have said, at which point Webb will start its highly anticipated science mission. During that mission, the observatory will study the universe’s first stars and galaxies, scrutinize the atmospheres of nearby exoplanets for intriguing chemicals and do a variety of other high-impact research. 

Mike Wall is the author of “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook