What, exactly, distinguishes space opera from other science fiction? To qualify as space opera, I think a story must involve space travel more advanced than present-day human technology and it needs to be fast-paced and action-oriented. But that doesn't seem to be enough. Bad science seems to the hallmark of many space operas. I don't think that that means that any work that tries to be scientifically sound, but if serious scientific speculation is central to the story, I don't think it can be space opera. I can't call Hal Clement's novels space operas; scientific rigor is too central to them. When I catch Clement in a scientific error (which is rare), it dramatically affects my appreciation of the story. A scientific error in a space opera is usually something to chuckle at and keep going. Is Catherine Asaro's Skolian Empire series space opera? I'm not sure. Classic space opera also seems to be characterized by cardboard characters and black and white morality. Believable characters with nuance and depth don't make something not space opera, nor does moral ambiguity or good writing in general, but somehow it seems that spending too much time on the character's feelings, motivations, and development do, as does significant, meaningful social speculation or illumination of the human condition. The Honor Harrington series is space opera; the early Miles Vorkosigan books are, but the later ones less clearly so. Ender's Game is not space opera.
Does anyone have any thoughts about what makes space opera? Does anybody care?