Just this week, NASA had to postpone a spacewalk on the International Space Station due to concerns of space debris in the area. It’s like waiting to go out to the store until it stops raining. Except, in this case, the rain is rocks, and they’re moving at up to 7 miles per second. We’ve talked briefly before about space debris, a growing issue that space agencies must mitigate, but until we can remove the junk from space, the best we can do is try to avoid it.
To get out of the way of something, you have to know where it is and where it’s going. Some objects can be tracked pretty well. Impressively, the DoD’s Space Surveillance Network can track almost all objects larger than 1 cm in diameter. This covers satellites, leftover rocket parts, and even large nuts and bolts. There are a lot of these things out in space, but thankfully their orbits are extremely predictable. If you know an object’s location and velocity, you know, at any time before or after, where it will be. With almost no force acting on it, its trajectory will rarely ever change. Because of this, NASA and the ISS know well ahead of time if they’re in danger of an impact, and can use small thrusters to adjust their position to avoid a potential incident. It’s like knowing where every car on the road will be at any given time. Equipped with this knowledge, you’d be able to avoid most if not all collisions. But what if the cars are the size of a grain of sand? That’s a bit harder to predict.
In the case of undetectable debris, which just so happens to be the vast majority of space debris, we can’t readily plan for it. So, we have to have protection on the ISS for these collisions. Under its initial development, the ISS had the following goal: any portion of the ship should have a maximum of 10% chance of penetration over 10 years. I’ll be honest this does seem kind of high. But because this is over 10 years, the odds of an impact penetrating the cabin at any given time is relatively low. To achieve this level of protection, the ISS uses a form of the Whipple Bumper. [4]
These are multiple layer barriers made of specially chosen composites and metals designed to vaporize and disperse the energy of the object. These are typically designed for projectiles traveling up to 11 miles per second. The general goal is to break it apart—like turning a bullet into a shotgun burst—this will distribute the energy over a larger area. This dispersion makes it easier for the subsequent material layers to withstand the impact.
There are a wide variety of options to choose from, and the designs have been optimized over the years for different types of impacts. While it is great that we have a layer (or multiple) of protection, there are some areas of the ISS that are more susceptible to impacts than others. For example, it’s hard to get rear-ended in space. The orbit of the ISS is essentially set by its speed. So anything traveling in a similar orbit will have around the same velocity. This means that if it’s coming from behind you, it’s not going that fast relative to you. On the other hand, if it’s coming at you head-on, it’s traveling twice your speed. Because of this, the ISS needs significantly more shielding on the front than on the back.
So at this point we can get out of the way of large objects, and can withstand impacts from smaller ones, but what happens if both these options fail. What is the escape plan for astronauts? The answer is rather simple: lifeboats. Most of the capsules that bring the astronauts up to the ISS can be powered on within minutes. So, if there is an imminent threat of impact, the astronauts can quickly take shelter in a capsule and close the hatch. Should anything catastrophic happen, they would be shielded from the vacuum of space. They can then detach, and create a flight plan to get back down to Earth safely.
All this being said, space is an extremely unforgiving place. One wrong move could end in disaster. Luckily for astronauts, there are loads of fail-safes in place to protect them from the perils outside the spaceship walls. Thank you for reading this week’s edition of It’s Not Rocket Science! Happy Wednesday, see you next week!
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Cover Image: Popular Science
[1] https://www.nap.edu/read/5532/chapter/6#29
[3] https://www.nasa.gov/mission_pages/station/news/orbital_debris.html
Always wondered how they avoid stars. Thanks. And HAPPY BIRTHDAY
Matthew, Thanks for another interesting, engaging and well written article. I look forward to them. Keep up the good work. Best, San Diego Doug