In this answer I mention the proposed impact of DART:
- Double Asteroid Redirection Test (DART) Mission
- Double Asteroid Redirection Test
- The Double Asteroid Redirection Test (DART) Element of the Asteroid Impact and Deflection Assessment (AIDA) Mission
DART's impact velocity would be about 6 km/s on a body so small that the momentum transfer is hoped to measurably change its orbit around a companion asteroid.
I wondered about impacts used for other reasons, so I'd like to ask:
What's the highest velocity impact between a spacecraft and a solar system body?
What about for a dedicated impactor (spacecraft component)?