Meteoroid hits main mirror on James Webb Space Telescope

Impact at the end of May bad enough to garble data, but NASA isn't worried

The James Webb Space Telescope has barely had a chance to get to work, and it's already taken a micrometeoroid to its sensitive primary mirror.

The NASA-built space observatory reached its final destination, the L2 orbit, a million miles away from Earth, at the end of January.

In a statement, NASA said the impact happened some time at the end of May. Despite the impact being larger than any that NASA modeled and "beyond what the team could have tested on the ground," the space agency said the telescope continues to perform at higher-than-expected levels. The telescope has been hit on four previous occasions since launch.

James Webb's primary mirrors make up the gold-colored array that occupies a good portion of the telescope's body. Those 18 gold-plated mirrors are carefully aligned at the nanometer scale to reflect infrared light to James Webb's cameras, a process that took months for scientists to complete from ground control.

The C3 mirror, which took the hit, will have to be adjusted to counter the distortion and noise that resulted from the impact.

"Engineers have already performed a first such adjustment for the recently affected segment C3, and additional planned mirror adjustments will continue to fine tune this correction," NASA said. Micrometeoroid impacts like this one are "considered an unavoidable chance event," the agency said.

Micrometeoroids are small – often less than one millimeter – but they move so fast relative to spacecraft orbiting Earth that they can cause craters visible to the naked eye. Space debris of that size has a typical impact velocity of 10km/s (22,369mph), while meteoroids, typically considered to be larger than a grain of rice, hit at double the velocity.

Spacecraft like James Webb are designed to withstand these types of impacts, but there are limits to what can be done to minimize them above a certain scale, especially when dealing with rocks traveling 6-12 miles a second. Herein lies the bright spot for NASA scientists, who are accustomed to dealing with mission-altering problems. 

"As a result of this impact, a specialized team of engineers has been formed to look at ways to mitigate the effects of further micrometeoroid hits of this scale," NASA said.

Along with protecting James Webb, NASA wants to use the telescope to better understand the dust and micrometeoroids whipping around the solar system, particularly at the L2 point where the telescope sits. L2 is considered a "sweet spot" for galactic observation, and other space agencies have plans to deploy missions to the same area.

To those worried that this impact will delay or hinder Webb's work – and those hotly anticipating the first images scheduled for release in July – NASA said it's still on schedule. ®

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