Running into any spec of dust at those speeds would be quite a bit more severe than a bug on the windshield......
When you accelerate an object (change its velocity, velocity being a two-component vector consisting of speed AND direction) the object moves into a different space-time reference frame. Its clock slows down relative to the clock in the previous frame. ie, its sense of time progressively slows the more it is accelerated.
But in order to change an object’s velocity, an outside force must be applied (F=ma). Without any outside forces being applied, the object would remain in an ‘inertial’ state, move at a constant speed AND direction.
The law of inertia states that an object will remain at rest or in a state of uniform motion (constant speed AND direction) unless acted upon by an outside force.