Range comes in two flavors - actual and effective. In space the actual range of a missile is, potentially, infinite. Once fired, and assuming it's not captured the gravitational pull of something in the system, then it can drift unpowered until the end of time or it gets captured by the pull of something else and ends up a satellite or impacts upon the surface. Effective range is what the rules in the game are meant to address.
Effective ranges is going to be, for the non-stationary object, the distance that the missile has time left on it's drives to thrust and maneuver. Most versions of the rules have not addressed the type of drives or even if they have the ability to turn on/off, just how many turns of thrust they have. A missile that can turn it's drives on/off can, theoretically, be launched and maneuver for say 5 turns, drift, and then activate its drives during the terminal impact phase. Game-wise this makes for some possible complicated book keeping though, so I think, for RPG gameplay purposes, the effective range is going to be 10turns and then it's taken off the board. The odds of an unpowered missile impacting a ship that has even maneuvering thrusters is quite small (stand-off weapons such as bomb-pumped lasers obviously have more flexibility here). If one wants to argue that you should be able to launch a missile at a station 1,000D distance and hit it, well, one can also argue that you could fire a laser or counter-missile at the inbound missile and assume an automatic hit since that missile is drifting and it's course/position will always be known. While there are numerous alternatives, for gaming purposes its just easier to keep it at 10turns and move on to better things.
Safety-wise, I think it's reasonable to assume every military in space is going to build a missile with a self-destruct built into it. Chances are a force will never be 100% on the offensive, and drifting explosive ordinance is just as much a threat in your home system as it is in an enemies system. Players like to be, well, players, but lets assume most space-going races will share a few similar views on such things. Thus once a missile has lost lock or runs out of drive time its going to self-destruct so that it present no future hazard. Pirates and other nefarious elements are rarely going to be industrious enough to build missiles on their own - they will buy, steal or otherwise acquire them from other sources that will put such safety devices in the missile.
