Every spacecraft in Earth orbit is exposed to a certain flux of natural micrometeoroids and manmade space debris. Collisions with these particles take place with hypervelocity speed.
The damage caused by collisions with meteoroids and space debris depends on the size, density, speed and direction of the impacting particle and on the characteristics of the impacted structure.
Impact analysis techniques fall naturally into two different categories: larger, trackable pieces and smaller, nontrackable particles.
Trackable orbiting objects, whose orbital elements are known, can be propagated along their orbit and their chance of a future collision with another spacecraft or fragment can be assessed. This deterministic approach provides at the same time all relevant parameters of such a potential collision, like impact velocity and direction.
For meteoroids and the abundant smaller space debris particles which cannot be tracked, the risk assessment is supported by statistical flux models as described in the subsequent chapters.