Space Micrometeoroid That Hit Webb Telescope Caused Permanent Damage, Say Scientists

Scientists are reporting that damage sustained to the James Webb Space Telescope (JWST) during a micrometeoroid strike in late May 2022 may be worse than first thought.

In a new paper published in the wake of Webb’s incredible first images last week a group of scientists outlined the performance of the space telescope during its commissioning phase.

They reported problems that “cannot be corrected” as well as a “small effect on the telescope throughput, which is not yet measurable.”

Writing about the projected lifetime of the Webb telescope the report said: “At present, the largest source of uncertainty is long term effects of micrometeoroid impacts that slowly degrade the primary mirror.”

As previously reported Webb’s primary 6.5-meter mirror comprises 18 beryllium-gold segments. One of them, called C3, was struck by small dust particles between May 23 and 25, 2022.

Since launch Webb has been struck by five other, smaller micrometeoroids. One minor strike per month is roughly what engineers predicted pre-launch.

“After initial assessments, the team found the telescope is still performing at a level that exceeds all mission requirements,” said Thomas Zurbuchen, Associate Administrator at NASA’s Science Mission Directorate, in a tweet after the C3 strike.

However, the new report suggests that the damage to the C3 segment could be more serious than first thought.

“Of the six micrometeoroid strikes detected thus far through wavefront sensing, five had negligible effects,” reads the report. Wavefront sensing refers to the aberrations found in Webb’s optics. “By contrast, the micrometeoroid which hit segment C3 in the period 22—24 May 2022 UT caused significant uncorrectable change in the overall figure of that segment.”

Moreover, the report said that this event “exceeded prelaunch expectations of damage for a single micrometeoroid, triggering further investigation and modeling by the JWST Project.”

Although it may have enough propellant to last 20 years—a decade longer than previously expected—the engineers who designed Webb know that its mirrors and sunshield will unavoidably slowly degrade from micrometeoroid impacts.

It’s also expected that Webb’s detectors will be gradually damaged by charged particles while its sunshield and innovative five-layer insulation will degrade from space weathering.

Since its mirror is exposed to space micrometeoroid strikes are difficult for Webb to avoid. “Inevitably, any spacecraft will encounter micrometeoroids,” reads the report, which described “six localized surface deformations on the primary mirror that are attributed to impact by micrometeoroids.”

Was the “C3 impact” a fluke? “It is not yet clear whether the May 2022 hit to segment C3 was a rare event or whether the telescope may be more susceptible to damage by micrometeoroids than pre-launch modeling predicted,” said the report.

It’s hoped that it was merely a once-in-several-years event, but the team will now investigate the micrometeoroid population in Webb’s vicinity, how impacts affect beryllium-gold mirrors and how it mitigates further strikes.

A possible solution could be to minimize time spent looking in the direction of orbital motion, which statistically has higher micrometeoroid rates and energies, said the report.

A $10 billion space telescope that sees in the infrared, Webb launched on Christmas Day in 2021 and has since February been orbiting the L2 point about a million miles/1.6 million kilometres from Earth.

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