If SF is to be more than just wishful thinking for space groupies, it's going to have to be about more than just space or the future. There are war stories, and love stories, and westerns, and horror, and all kinds of genre fiction, but what keeps them from being just penny dreadful stuff is that they also have some universal story behind them. War is inherently dramatic, but stories just about fighting are strictly for teenage boys. Love is a many-splendored thing, but stories just about romance are strictly for teenage girls. A story must be about the human condition, not about its setting.

Someone (I can't remember who, now) once remarked that good science fiction is about the impact on man or society of technologies or scientific discoveries or cosmic events. I subscribe to this definition.

Using this guideline, a book like Verne's "20,000 Leagues Under the Sea", in spite of its excellent science for its time, isn't really SF since it doesn't analyze the impact and implications of submarine warfare on warfare or commerce or history, particularly as it relates to humans and humanity. It's all about Nemo and his war with the world, sort of a Capt. Ahab in a submersible. OTOH, Wells' "War of the Worlds" is SF because it uses alien invasion as a metaphor for Victorian attitudes on colonialism, racism, cultural clash and conflict. Orwell's "1984" or Rand's "Atlas Shrugged" are novels of ideas which use the future to exaggerate or warn about trends in the present day world. It's not the two-way TV or Rearden Metal that make them interesting, but they are SF.

But whether it's SF or not, what makes it literature depends on whether it tells us something about ourselves, as individuals or collectively. Otherwise, it's just horse opera is space.