When NASA sent the James Webb Space Telescope (JWST) a million miles from Earth last Christmas Day it did so with one major worry—micrometeoroids.

These tiny particles of space dust have, predictably, already struck the $10 billion space telescope’s 18 beryllium-gold segments, causing irreparable damage not just once, but 14 times, NASA has revealed in a blog.

“We have experienced 14 measurable micrometeoroid hits on our primary mirror, and are averaging one to two per month, as anticipated,” said Mike Menzel, Webb lead mission systems engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The resulting optical errors from all but one of these were well within what we had budgeted and expected when building the observatory.”

The outlier happened in May, when a micrometeoroid struck one of the beryllium-gold segments that makes up JWST’s main 6.5-meter mirror. Classed as as “unavoidable chance event,” it knocked the telescope slightly out of alignment. Engineers were able to adjust its 18 mirrors to correct for the damaged segment.

Space is a dangerous place to operate, with constant threats including cosmic rays from the Universe at large, harsh ultraviolet light and charged particles from the Sun, and micrometeoroids traveling at extreme velocities.

However, JWST’s engineers are already taking evasive action to reduce the chance of the precious space telescope from being damaged further. A working group at NASA concluded that strike in May 2022 was a rare statistical event, but the massive space telescope will hence be faced away from what is now known as the “micrometeoroid avoidance zone.” That means minimizing the time it spends looking in the direction of orbital motion, which statistically has more micrometeoroids moving at much higher velocities.

A particularly risky period is a meteor shower, which are caused by the particles left in the inner solar system by casing comes. It’s a scenario that could become a live issue particularly in both May 2023 and again in May 2024 when Webb travels through Halley’s comet’s stream of meteoroids.

“Micrometeoroids that strike the mirror head on (moving opposite the direction the telescope is moving) have twice the relative velocity and four times the kinetic energy, so avoiding this direction when feasible will help extend the exquisite optical performance for decades,” said Lee Feinberg, Webb optical telescope element manager at NASA Goddard.

The upshot is a reshuffling of JWST’s schedule, with objects observed when it’s safest to do so rather than in order of scientific urgency. An exception to the will be solar system targets, which are far more time-sensitive.

Webb—a $10 billion space telescope that sees in the infrared part of the spectrum—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.

Wishing you clear skies and wide eyes.

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