JWST was hit by a small space rock

The JWST in space

JWST suffered a larger than expected micrometeorite impact on its C3 mirror segment. Image credit: NASA GSFC/CIL/Adriana Manrique Guiterrez

After 14 agonizing years of delays and surviving the strain of launch and deployment, the world’s most powerful space telescope faces only one threat remaining: space rocks. NASA announced that the JWST’s primary mirror was hit by a micrometeorite in May. It is the fifth impact large enough to be measurable since the telescope was launched, but the first larger than planned. Fortunately, however, the impact was still small enough to have only a minor effect on image quality.

“Micrometeoroid strikes are an unavoidable aspect of the operation of any spacecraft, which routinely sustains many impacts over the course of long and productive science missions in space,” NASA noted in a statement. The larger the mirror, the more impacts will occur, so the JWST designers were fully aware of the threat. Tolerance for very small impacts has been built into the telescope design, for example by adjusting the position of underperforming segments. Beyond a certain size impact, however, the damage will affect image quality, even if only slightly.

It would have been nice if the first such impact didn’t occur until the scientific work began, so the first images at least were really pristine, but it wasn’t meant to be. Between May 23 and 25, NASA reports, the JWST’s C3 primary mirror segment suffered impact damage beyond its tolerance limit.

Subsequent tests showed, however, that “the telescope is still operating at a level that exceeds all mission requirements, despite a marginally detectable effect on the data,” in the words of NASA.

Consequently, we are still on our way to being dazzled by the first scientific images on July 12, even if they are a little less spectacular than they could have been.

“We always knew that Webb would have to contend with the space environment, which includes harsh ultraviolet light and charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional micrometeoroid attacks on our solar system,” Paul Geithner of Goddard. Space Flight Center said. “We designed and built the Webb with a performance margin – optical, thermal, electrical, mechanical – to ensure it can fulfill its ambitious science mission even after many years in space.”

Having surpassed expectations for how clean the JWST’s optics could be kept on the ground, this impact will still leave the telescope’s overall performance above expectations, NASA claims.

The Internet is not entirely convinced, however.

The risk of impacts is reduced by moving JWST’s mirrors away from incoming meteor showers, at the cost of using up their fuel faster, but little can be done about sporadic micrometeorites like this one.

Always eager to find a coating as silvery as the bracket of a telescope mirror, NASA notes that the primary’s large area and its close evaluation make it “a highly sensitive micrometeorite detector.” Tracking impacts will improve our knowledge of their frequency and size profile.

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