James Webb Space Telescope optical alignment ‘perfect’, NASA says

Four and a half months after the James Webb Space Telescopethe day of Christmas launchengineers have achieved near-perfect alignment of its complex optical system, paving the way for final instrument calibrations and the release of the first demonstration science images in July, officials said Monday.

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

“We have essentially achieved perfect telescope alignment. There are no adjustments to the telescope optics that would provide material improvements to our science performance.”

Two images of the same star field in the Large Magellanic Cloud, a small satellite galaxy of the Milky Way. The photo on the left is from NASA’s now-retired Spitzer Space Telescope, while the photo 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 in diameter.


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

Spitzer’s image shows blurry stars with hints of cloudiness. But Webb’s view shows crystal-clear, sharp stars and clearly defined clouds and filaments stretching across the field of view.

“From an intellectual point of view, you can understand that Webb’s images are going to be better because we have 18 segments (mirrors), each of which is larger than the single segment that formed the Spitzer telescope mirror,” said said Marcia Rieke, principal investigator for Webb’s Near Infrared Camera, or NIRCAM.

“It’s only when you actually see the kind of image he delivers that you really internalize and go, wow! Think what we’re going to learn! Spitzer taught us a lot, but it’s like a whole new world. Just stunningly beautiful.”

Scientists and engineers now plan to spend the next two months carefully checking and calibrating Webb’s four science instruments, collecting test images and spectra to verify 17 different modes of operation before beginning science observations of the ” Cycle 1″ this summer.

But first, the team plans to unveil a series of “Early Diffusion Observations,” or EROs, jaw-dropping images of spectacular astronomical targets that will showcase Webb’s scientific abilities and, in doing so, help to justify its $10 billion price tag.

The list of potential targets is a closely guarded secret, but NASA plans to unveil the selected ERO images and spectra in mid-July.

“Their goal is to demonstrate … to the world and to the public that Webb is fully operational and producing excellent results,” said Klaus Pontoppidan, Webb project scientist at the Space Telescope Science Institute in Baltimore. “It’s also a time to celebrate the start of many years of Webb science.”

He said the targets, selected by a committee of experts, will feature the four science instruments “to highlight all the themes of Webb science…from the early universe, to galaxies over time, to the life cycle of stars and to other worlds.”

Artist’s impression of the James Webb Space Telescope with its major components labeled.


Webb was designed to capture faint light from the first generations of stars and galaxies to form following 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 achieve its sharpness, Webb’s secondary mirror and the 18 hexagonal segments of its 21.3-foot-wide primary mirror, each equipped with ultra-precise tilt actuators, had to be aligned with nanometer precision, an iterative process which effectively merged 18 reflected beams into a single point.

To detect stretched infrared light from early stars and galaxies, Webb must operate within degrees of absolute zero, a feat made possible by a fragile five layer umbrella which deployed perfectly shortly after launch.

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

“Overall, the observatory’s performance has been phenomenal,” McElwain said. “We are really in the home stretch. At this stage, we are characterizing and calibrating both the observatory and the scientific instruments.

“From my point of view, there are always risks in the future, but I am convinced that we will reach the finish line here, and we will have a formidable scientific mission with enormous scientific discoveries in the coming months. So I’m just super excited to be at this point.”

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