Evolution of the relative separation in a colliding case for HW1 simulations. The collision separation (red) represents the minimum distance between the two asteroid barycenters before they collide given their instantaneous relative attitude and position throughout an integration. The relative separation (blue) shows the actual separation between the two asteroid barycenters throughout the integration. Once the relative separation falls below the collision separation the asteroids are considered to have collided. Here collision occurs just before 0.02 days of integration.