When thinking about velocity I could imagine that the ISS getting hit by some space junk (let it be just a plate of 1 meter in span) with a velocity of some 100 meters per second could be quite fatal.

How is this actually handled? are there some "defensive" systems installed against this kinds of collisions? Or are there just regions that are considered to leave the junk in so it never is interfering with the orbit of the ISS?

If the latter is the case, how is the launching of space vehicles of states like northkorea handled? I could imagine that northkorea wouldn't care much about such convetions. Not to say they might even be happy about "accidently" hitting the ISS with some space junk.


The actual speed of impacts can be up to 14 km/s, it is something quite serious, even for small issues. There are a number of procedures taken to prevent such thing.

The first level is known as the "Big Space" theorem, which is that space is really big, and there isn't that many objects. We are getting to the point where this isn't good enough overall.

The second layer is to detect such objects. There are a number of systems that can do this, the best is the system provided by the US military, called JSpoc, or the public outreach called Space Track. They monitor all objects, and will inform parties, both commercial and government, when a predicted impact might occur. These can be predicted days in advance, and allow an object such as the International Space Station to flee a potential collision. This works for objects larger than 10 cm. These sometimes occur too late to be of help, in which case additional actions are taken, see this article.

The third layer is to protect the space around the space station. This is done primarily for the objects visiting the space station, which are launched into a non-intersecting orbit and slowly transition to the final orbit, to reduce the debris in the area. NASA also requests coordination with commercial entities operating near the space station to ensure they are not going to impact the station.

Another layer is provided by selecting an altitude where the space station is relatively low, reducing the lifetime of debris in the area to only a year or two.

Lastly, there is shielding on the space station that will prevent a small item, say a paint flake or grain of sand sized object, from damaging the station. I understand it works until about a 1 cm object. The shielding is called a "Whipple Shield".

All this being said, there is still a substantial risk of damage. Take a look at this graphic, which shows the relative chance of impact.


Large pieces of debris are tracked from the ground using radar, and the ISS moves to avoid them. (Ars Technica) (NASA). This isn't automatic or spontaneous - these maneuvers are carefully planned from the ground. Also, your hypothetical 1m plate would be devastating to the ISS - anything bigger than a fist-sized rock can cause major damage if it hits the wrong part of the station.

Smaller pieces of debris can't be tracked, but the ISS is designed to survive impacts with most of them. I imagine (but couldn't find any hard sources) that the ISS is designed with redundant systems, and that parts of it can be sealed off in case of major damage.

  • $\begingroup$ What is considered a smaller piece in this context? $\endgroup$ – Zaibis May 11 '16 at 13:22
  • $\begingroup$ Anything smaller than 1 cm, IIRC. $\endgroup$ – Hobbes May 11 '16 at 13:24

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