This question is rather self explanatory so I'll keep I succynct.

A while back Tim Peake photographed a small crack in the cupola of the ISS, which was reportably a paint fleck that collided with the window. According to orbital mechanics (Kepler's Laws I believe specifically) the higher the velocity the larger the radius, and therefore orbital period etc.

How does a paint fleck damage the ISS when it would have to be travelling at a significant (enough to damage the window) relative velocity to the ISS, and therefore a higher velocity, so surely the orbit would be higher than the ISS's orbit and therefore the collision could not occur?

  • 4
    $\begingroup$ What happens if they're at the same orbital height but traveling in opposite directions, directly toward each other? $\endgroup$ Apr 11, 2018 at 22:39
  • 1
    $\begingroup$ Not every orbit is circular. $\endgroup$
    – The Photon
    Apr 11, 2018 at 23:05

1 Answer 1


The fastest bullet travels at about 1.2 kilometers per second. The ISS orbits at about 7.7 kilometers per second. Even a small mismatch in inclination or right ascension means the relative velocity between a paint fleck and an ISS window easily exceeds that 1.2 km/s. A large mismatch could result in a factor ten excess over that bullet speed, or 100 times as much energy.


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