[selven]

Don't think of changing direction, think of changing velocity. Space is a Newtonian movement system, so accelerating 20 meters per second in some direction is just as easy at 0 km/sec as it is at 10000 km/sec.

As for missiles, I really don't like the idea. If I were tasked with building a 22-nd century warship, I would put a few hundred automated anti-missile lasers everywhere, which would fry the missiles before any of them get close enough to darken the hull.