black cell (n.): An originally-improvised form of prison or brig cell used by various independent drifts and starships designed for long-duration flight, a black cell is adapted from an airlock, in which the outer door is not equipped with a docking collar, and the inner door is only controllable from the outside. The prisoner is often (although by no means always) held in as much comfort as a standard cell would provide, supplied with air, water, and food, but always retains the option of opening the outer airlock door and choosing a quick death by spacing.
Opinion is mixed where the use of black cells, improvised or designed, is concerned: whether they are a means of providing their prisoners with an honorable alternative (or, in many spacers’ eyes, a way to spare their comrades the life-support burden), versus offering only a sadistic choice between a quick death and a slow, as they clearly do in those cases in which water and food are not provided. As in the case of so many technologies, it’s the application that determines the ethicality.
– A Star Traveler’s Dictionary