[crusty old prospector]

I wonder if even sand-sized particles are a risk.

[Red Badger]

Yes, the kinetic energy is enormous..............

[Robert A Cook PE]

Maybe. It depends on the two relative velocity directions: A very small parts in a polar orbit is going to be more important than an equal sized particle also in a equatorial orbit. (Almost no satellites - and thus particles - are in a reversed east-to-west orbit. But those particles coming from explosions and test impact are random directions - if they are not quickly absorbed by the atmosphere.)

And it depends where the impact occurs. On a window or sealing surface at a hatch or a hatch locking mechanism or instrument receiver/sensor is more important than one into a blank hull section.

[Red Badger]

BRAVE AI:

A 0.01 gram of sand travelling at 50kmph is about 2500 Joules of energy, an amount of energy comparable to what a powerful handgun round can carry, potentially causing severe injury to a person even if the energy is absorbed by a bulletproof vest.

[Steely Tom]

I wonder if even sand-sized particles are a risk.

On one Space Shuttle mission, there was visible damage to one of the front-facing windows; this appeared when the shuttle was in orbit. When they got back on the ground, the windows was removed and the damage carefully examined.

The particle that caused it was extracted and analyzed using advanced techniques (neutron activation analysis among them) and was determined to have been man-made; a tiny flake of paint from some other spacecraft.