Why getting hit by space dust is an inevitable part of space travel

Why getting hit by space dust is an inevitable part of space travel

On June 8, NASA revealed that its powerful new space observatory, the James Webb Space Telescope, now sported a small dimple in one of its main mirrors after being bombarded by a larger-than-expected micrometeoroid in deep space. . The news was a little shocking since the impact happened just five months into the telescope’s space tenure – but such strikes are simply an unavoidable aspect of space travel, and more hits are certainly on the way. road.

Despite what the name suggests, space is not exactly empty. In our solar system, tiny bits of space dust pass through the regions between our planets at enormous speeds that can reach tens of thousands of kilometers per hour. These micrometeoroids, no bigger than a grain of sand, are often small pieces of asteroids or comets that have broken off and are now orbiting the Sun. And they are everywhere. A rough estimate of small meteoroids in the inner solar system puts their total combined mass at about 55 trillion tons (if they were all combined into one rock, that would be about the size of a small island).

This means that if you send a spacecraft into deep space, your hardware is sure to be hit by one of these little pieces of space rock at some point. Knowing this, spacecraft engineers will build their vehicles with certain protections to protect against micrometeoroid strikes. They often incorporate something called Whipple shielding, a special multi-layered barrier. If the shield is hit by a micrometeoroid, the particle will pass through the first layer and fragment even more, so the second layer will be hit by even smaller particles. Such shielding is typically used around sensitive spacecraft components for additional protection.

But with NASA’s James Webb Space Telescope, or JWST, it’s more complicated. The golden mirrors of the telescope must be exposed to the space environment in order to properly collect light from the distant Universe. And while these mirrors were built to withstand some impacts, they’re more or less sitting ducks for larger micrometeoroid strikes, like the one that hit JWST in May. Although the micrometeoroid was still smaller than a grain of sand, it was larger than NASA had expected – enough to damage one of the mirrors.

Spacecraft operators model the population of micrometeoroids in space to better understand how often a spacecraft might be hit in a given part of the solar system — and the size of the particles that might hit their hardware. But even then, it’s not a foolproof system. “It’s all probability,” said David Malaspina, an astrophysicist at the University of Colorado who focuses on the impacts of cosmic dust on spacecraft. The edge. “You can only say, ‘I’m so lucky to be hit by a particle of this size.’ But whether you do it or not is up to chance.

Examples of Different Types of Whipple Shielding
Image: NASA

Micrometeoroids have a wide range of origin stories. They may be the remnants of high-speed collisions in space, which pulverize space rocks into tiny pieces. Asteroids and comets are also bombarded over time by space particles and photons from the Sun, causing tiny pieces to break off. An asteroid can also get too close to a large planet like Jupiter, where the strong gravitational pull tears off pieces of rock. Or an object may approach too close to the Sun and become too hot, causing the rock to expand and break into pieces. There are even interstellar micrometeoroids that just pass through our solar system from more distant cosmic quarters.

The speed at which these particles move depends on the region of space they are in and the path they take around our star, averaging around 45,000 miles per hour, or 20 kilometers per second. . Whether or not they collide with your spacecraft also depends on where your vehicle is in space and how fast it is moving. For example, NASA’s Parker Solar Probe is the closest man-made object to the Sun right now, moving at a top speed of over 400,000 miles per hour. “It goes down to the 4-meter line, relative to the Earth, being all the way through an end zone,” says Malaspina, who has focused on studying micrometeoroid impacts on Parker Solar. Probe. It’s also moving through the densest part of a region called the zodiacal cloud, a thick disc of space particles that pervades our solar system. Thus, the Parker Solar Probe is sandblasted more frequently than JWST – and it hits these particles at incredibly high speeds relative to the telescope.

The Parker solar probe allows us to better understand the micrometeoroids around the Sun, but we also have a pretty good understanding of the population around the Earth. Each time a micrometeoroid hits the upper atmosphere around our planet, it burns up and creates meteoric smoke – fine smoke particles that can be measured. The amount of this smoke can tell us how much dust is hitting the Earth over time. Additionally, there have been experiments on the International Space Station, where materials have been mounted outside the laboratory in orbit to see how often they are bombarded.

An artistic rendering of NASA’s Parker Solar Probe
Image: NASA

While JWST lives about 1 million miles from Earth, it’s still relatively close. Scientists also have an idea of ​​what’s out there based on other missions sent into a similar orbit as JWST. And most things that hit the telescope aren’t that big. “Spacecraft get hit by little ones all the time,” Malaspina says. “By small, I mean fractions of a micron – much, much, much smaller than a human hair. And for the most part, spacecraft don’t even notice them. In fact, JWST has already been hit by small micrometeoroids four times before being hit by the largest micrometeoroid in May.

NASA modeled the micrometeoroid environment before JWST launched, but in light of the recent impact, the agency has assembled a new team to refine its models and better predict what might happen to the telescope after future impacts. . Current micrometeoroid modeling will attempt to predict things like how debris travels through an orbit if an asteroid or comet breaks up. This type of debris is more dynamic, Malaspina says, which makes it harder to predict.

Ultimately, however, the prediction will simply give you more knowledge about when a spaceship could be hit by a large speck of dust. One-time impacts like this are simply unavoidable. JWST will continue to blow itself up over time, but it was an eventuality that NASA was always prepared for. “You just have to live with the likelihood that you’ll eventually get hit by a sizable dust particle, and you just do your best with the engineering,” says Malaspina.

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