Why getting hit by space dust is an unavoidable aspect of space travel - The Verge

NASA revealed that its James Webb Space Telescope was hit by a larger-than-expected micrometeoroid. But the space environment is filled with space dust, and any spacecraft that goes to space is probably going to get hit.

On June 8th, NASA revealed that its new powerful space observatory, the James Webb Space Telescope, is now sporting a small dimple in one of its primary mirrors after getting pelted by a larger-than-expected micrometeoroid out in deep space. The news came as a bit of a shock since the impact happened just five months into the telescope’s space tenure — but such strikes are simply an inevitable aspect of space travel, and more thwacks are certainly on their way.

Despite what its name implies, space isn’t exactly empty. Within our Solar System, tiny bits of space dust are zooming through the regions between our planets at whopping speeds that can reach up to tens of thousands of miles per hour. These micrometeoroids, no larger than a grain of sand, are often little pieces of asteroids or comets that have broken away and are now orbiting around the Sun. And they’re everywhere. A rough estimate of small meteoroids in the inner Solar System puts their combined total mass at about 55 trillion tons (if they were all combined into one rock, it’d be about the size of a small island).

That means that if you send a spacecraft into deep space, your hardware is certain to get hit by one of these little bits of space rock at some point. Knowing this, spacecraft engineers will construct their vehicles with certain protections to shield against micrometeoroid strikes. They’ll often incorporate something called Whipple shielding, a special multi-layer barrier. If the shield is hit by a micrometeoroid, the particle will pass through the first layer and fragment even further, so the second layer is hit by even smaller particles. Such shielding is usually used around sensitive components of spacecraft for extra protection.

But with NASA’s James Webb Space Telescope, or JWST, it’s trickier. The telescope’s gold-coated mirrors must be exposed to the space environment in order to properly gather light from the distant Universe. And while these mirrors were built to withstand some impacts, they are more or less sitting ducks for larger micrometeoroid strikes, like the one that hit JWST in May. Though the micrometeoroid was still smaller than a grain of sand, it was larger than what NASA anticipated — enough to cause damage to one of the mirrors.

Spacecraft operators model the micrometeoroid population out in space to get a better understanding of how often a spacecraft might get hit in any given part of the Solar System — and what size particles might be thwacking their hardware. But even then, it’s not a foolproof system. “It’s all probability,” David Malaspina, an astrophysicist at the University of Colorado focusing on cosmic dust impacts on spacecraft, tells The Verge. “You can only say, ‘I have this chance of getting hit by this sized particle.’ But whether or not you ever do, that’s up to chance.”

https://www.theverge.com/2022/6/20/23168039/micrometeoroid-space-dust-spacecraft-impact-debris-jwst

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