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Micrometeoroid dings James Webb mirror segment – Astronomy Now

An artist’s rendering of the James Webb Space Telescope with its five-layer sunshield and primary mirror fully deployed after launch on an Ariane 5 rocket. Image: NASA

A micrometeoroid struck one of the James Webb Space Telescope’s 18 primary mirror segments last month, the fifth such impact since the observatory was launched on Christmas Day, causing a “minorly detectable” impact on its performance, NASA announced on June 8 gave.

After a detailed analysis of the fifth and largest impact, the targeting of the segment was adjusted to counteract the degradation, but some reduction in data quality remains.

Despite this, NASA said in a blog post, “The team found that the telescope is still performing at a level that exceeds all mission requirements.”

NASA hadn’t disclosed any of the implications prior to the blog post, and the June 8 announcement surprised many observers, especially considering how smoothly Webb’s checkout and post-launch calibration went.

NASA plans to unveil the first color images of the observatory on July 12, and while it’s not yet clear what “slightly detectable” degradation means in terms of images and spectra, the first photos are expected to enhance Webb’s ability to meet the science targets to achieve the mission, fully demonstrate.

The James Webb Space Telescope is the most powerful ever launched, equipped with a 6.5-metre segmented primary mirror capable of detecting the extended infrared emissions from the first generation of stars and galaxies that glow in the aftermath The Big Bang.

The beryllium primary consists of 18 hexagonal segments coated with a thin layer of gold to maximize reflectivity. They are among the most perfectly formed optical elements that have ever been manufactured. Each segment is equipped with actuators, allowing engineers to make ultra-precise adjustments to fine-tune their orientation and the direction of the reflected starlight.

Given Webb’s open architecture, without the protection of a conventional tube and with the mirrors exposed to the space environment, engineers always expected that the telescope would be hit from time to time by high-velocity, dust-sized particles whizzing through the inner solar system. With Webb’s extremely precise optical alignment, such impacts should be relatively easy to spot.

To ensure that Webb’s gold-coated primary and secondary mirrors can withstand such impacts without suffering significant damage, extensive testing was performed prior to release. But last month’s impact, which occurred between May 23 and 25, was larger than models engineers anticipated.

“Since launch, we’ve had four smaller measurable micrometeoroid impacts that were in line with expectations, and this recent one that’s larger than our predictions of deterioration,” said Lee Feinberg, element manager of the Webb Optical Telescope at NASA’s Goddard Space Flight Center in Baltimore.

“We will use this flight data to update our performance analysis over time and also develop operational approaches to ensure we maximize Webb’s imaging performance as best we can for many years to come.”

https://astronomynow.com/2022/06/09/micrometeoroid-dings-james-webb-mirror-segment/ Micrometeoroid dings James Webb mirror segment – Astronomy Now

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