It's a clever idea, really. One probably reason why not, though: budget.
Besides, separation was originally supposed to be much more commonplace, but IIRC it was felt it slowed the plot too much so any desire to show other "mission modules" probably would have went out the door with that.
Besides, separation was originally supposed to be much more commonplace, but IIRC it was felt it slowed the plot too much so any desire to show other "mission modules" probably would have went out the door with that.