Question about space debris

[pandadude]

I've read a few times that one of the hazards of space flight and EVA's is collision with space debris. Things that I have read say it is dangerous due to the high speeds required for orbital velocity.

I don't understand why it is such a danger though. If you're in orbit, aren't you also travelling at a high velocity? So although the space debris is travelling at 7kms (roughly), so would your spacecraft, so relative velocity would be small.

What am I missing here? Why is space debris so dangerous?

 

[Bluefinger]

The reason why the debris pose such a danger because they are not all aligned with the orbital plane, nor is the orbit of the debris a within the eccentricity of the spacecraft and ISS orbits. Therefore, any differences in speed could wind up in the km/s region, which in that case, a simple nut would be able to put a fist sized hole straight through the ISS. Also, the danger is for ships attempting to change orbits or entering orbits, as one would encounter differences in speeds once again which allow the dangers to occur.

Also, micrometeorites are quite a problem, as they travel at even higher velocities. A grain of sand sized micrometeorite can still do a lot of damage due to the kinetic energy they possess.

 

[Urwumpe]

Just as example: The typical speed of a dangerous particle is 14 km/s - about two times the orbital velocity, as both orbital velocities add.

At these impact speeds, anything larger than 10 cm can destroy a satellite and badly damage the ISS.

 

[pandadude]

Ah OK. I thought I was missing something simple, and I was!