The usual flight rules produce ships (or probes, or EVA gear) that can fly indefinately at a fixed velocity, but if something happens to the flight power (e.g., an attack taking out the drive), the ship stops.
A ship using NSD would have an acceleration, a total amount of delta-v (very high in the case of solar sails, magnetic sails, Bussard ramjets, and reactionless thrusters) and (most importantly IMO) would continue moving when the engines shut off (get sabotaged, explode, etc.)
My current thoughts are to use the Flight for the acceleration, and the max NCM for the total delta-v; and while operating in vacuum would be considered as not moving at non-combat speeds as long as the drive is still functioning and have unspent delta-v. But should there be a modifier or adder for this?
Are there any rules from earlier editions (before 6th, that is)? Does anyone else have any ideas?