NASA says optical alignment of James Webb Space Telescope is ‘perfect’

Four and a half months later James Webb Space Telescopechristmas day launchengineers achieved near-perfect alignment of its complex optical system, paving the way for final instrument calibration and the release of the first scientific images in July, officials said Monday.

“I am pleased to report that the telescope’s alignment has been completed with better performance than we expected,” said Michael McElwain, Webb Project Scientist at NASA’s Goddard Space Flight Center.

“We’ve basically come up with a perfect telescope alignment. There is no modification to the telescope’s optics that would materially improve our science performance.”

Two images of the same star field in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. The image on the left is from NASA’s now retired Spitzer Space Telescope while the image on the right is from the James Webb Space Telescope. Spitzer, equipped with a single 3-foot-wide primary mirror, was the largest infrared telescope launched before Webb. For comparison, Webb’s segmented mirror is 21.5 feet wide.


On April 18, test images were released showing extremely sharp stars, and on Monday, a new image was revealed showing two views of a star field in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. One image was taken by the much smaller Spitzer Space Telescope, now retired, and the other by Webb’s Mid-Infrared Instrument, or MIRI.

Spitzer’s image shows blurry stars with hints of blur. But the Web’s view shows very sharp stars and clearly defined clouds and filaments extending across the field of view.

“From an intellectual point of view, you can tell that images from the Web would be better because we have 18 segments (mirrors), each of which is larger than the individual segment that made up the mirror of the Spitzer Telescope,” said Marcia Rieke, principal investigator for Webb’s Near-Infrared Camera, or NIRCAM.

“It’s not until you see the kind of picture you’re really giving it until you really take in it and go, wow! Just think what we’re going to learn! Spitzer taught us a lot, but it’s like a whole new world. Just incredibly beautiful.”

Scientists and engineers now plan to spend the next two months carefully examining and calibrating the four Webb science instruments, collecting test images and spectra to verify 17 different operating modes before “cycle one” scientific observations begin this summer.

But first, the team plans to unveil a series of “early launch observations,” or EROs, stunning images of stunning astronomical targets that will showcase Webb’s scientific ability and, in the process, help justify its $10 billion price tag.

The list of potential targets is top secret, but NASA plans to reveal the specific ERO images and spectra in mid-July.

“Their goal is to prove … to the world and to the public that Webb is fully functional and that it produces excellent results,” said Klaus Pontopedan, a Webb project scientist at the Space Telescope Science Institute in Baltimore. “It’s also an opportunity to celebrate the beginning of many years of Web Science.”

He said the goals, chosen by a panel of experts, will showcase all four scientific tools “to shed light on all Web science topics…from the early universe, to galaxies over time, to the life cycle of stars, and to other worlds.”

An artist’s impression of the James Webb Space Telescope naming its major components.


Webb was designed to capture the faint light from the first generations of stars and galaxies to form in the aftermath of the Big Bang 13.8 billion years ago, light that was stretched into the infrared region of the spectrum by the expansion of space itself.

To reach its extremely sharp focus, Webb’s secondary mirror and 18 hexagonal segments of its 21.3-foot-wide primary mirror had to be aligned, each with ultra-precise tilt actuators, with nanometer resolution, an iterative process that effectively fused 18 reflected beams into a point one.

To detect infrared light extending from the first stars and galaxies, Webb must work within a few degrees of absolute zero, a feat made possible by the fragility of Five-layer canopy Which was flawlessly deployed shortly after launch.

Since then, the mirrors and instruments have cooled to about minus 390 degrees Fahrenheit, while MIRI, equipped with a high-tech “cooling cooler” to improve its ability to observe longer wavelengths, has reached minus 449 degrees Fahrenheit, just 6 degrees above absolute zero.

“Overall, the observatory’s performance has been exceptional,” McElwain said. “We’re really in my home extension. At this point, we’re characterizing and calibrating both the observatory and the science instruments.

“In my view, there are always risks going forward, but I have great confidence that we will reach the finish line here, and we will have a great science mission with a massive scientific discovery in the next few months. So I’m just really excited to be at this point.”

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