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How NASA is dealing with micrometeoroids threatening James Webb

In June this year, NASA revealed that the James Webb Space Telescope had suffered from a micrometeoroid impact, in which a small space rock had caused some damage to one of the telescope’s 18 primary mirror segments. Although the damage was not serious enough to interfere with science operations, it did raise concerns about how much damage the telescope could suffer from similar impacts in the future. Now, NASA has shared its plan to deal with the issue of such impacts as Webb ages.

The Webb team knew that some impacts from micrometeoroids would be inevitable, as there are many such small particles in the area where Webb orbits around the sun. The telescope was designed to withstand small impacts, but a NASA working group concluded it was just bad luck that it was hit by a larger impact so soon after its launch in December 2021. An impact of that size was a “rare statistical event,” NASA said, both in that it was larger than most such impacts and that it happened to hit a particularly sensitive part of the telescope.

​​“We have experienced 14 measurable micrometeoroid hits on our primary mirror, and are averaging one to two per month, as anticipated. The resulting optical errors from all but one of these were well within what we had budgeted and expected when building the observatory,” said Mike Menzel, Webb lead mission systems engineer, in a statement. “One of these was higher than our expectations and prelaunch models; however, even after this event our current optical performance is still twice as good as our requirements.”

To protect Webb from such impacts in the future, the telescope will be used in such a way that it avoids facing the “micrometeoroid avoidance zone.” This helps avoid micrometeoroids striking the telescope’s primary mirror head-on, as these strikes are generally faster and are particularly damaging. The telescope will still be able to image all regions of the sky, but it will point at different regions at different times of the year to minimize the risk of impacts. This will begin with the second year of Webb science observations, called Cycle 2, which will start in July 2023.

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