Now that this thread has been officially exhumed....
I find the most rational writer on the subject of definitions of the genre to be Brian Aldiss ("Billion-Year Spree," et al), even though he still provokes profound disagreement from fellow members of the (perhaps mis-named) SFWA.
For all practical purposes, the genre or catagory of a book or film is where the bookstore or video rental place racks it. Pern books go into the Fantasy racks, Bradbury is stuck randomly in SF or, often, horror, and Vonnegutt is hustled over to the "serious literature" section (leaving the poor clerk to wonder WHAT to do with "Venus on the Half-Shell.") The boundaries are far too fluid to be able to establish firm rules as to what is or is not science fiction. Indeed, I have yet to see a definition for science fiction that couldn't be "broken" by a selected work.
I prefer to look at this as a continuum. To continue the life-sciences metaphor used above, elements and approuches could be considered alleles; Star Wars contains elements of a future technology, offset by a lack of scientific plausibility, it includes a speculative element but the emotional core is rooted in the fairy-tale; in all we might not be able to call the hair blond but she is certainly lighter than many of her sisters; aka, more like science fiction than "The Spy Who Loved Me" though less like science fiction than "Contact."
Personally, I like to expand on one part of Aldiss's central argument, and state that the strongest litmus test for "science" fiction is not technology or era per se, but the presense of scientific method. In the pure vein of science fiction, data is presented, hypothesis are made and tested -- by the writer, by a depicted society, by the protagonists.
The Foundation novels pass because they are an attempted extrapolation of some (admitadly questionable) ideas. Star Wars fails because it merely presents a setting, with no attempt to explain or explore how it got there technologically or socially. "The Black Hole" fails because it begins with what appears to be a scientific premise but turns out not to be based on present (or apparently, ANY,) knowledge. Harry Potter, oddly enough, camps on the doorstep; because of a strong thread of logic and an air of skeptical enquiry that informs the books. Harry does not "trust your feelings, Luke"; he collects data, makes hypothesis and explores them, and the world he lives in does not arbitrarily change the rules to advance the plot.
The biggest loophole in my thumbnail definition is that it includes Agatha Christie and James D. MacDonald (not to say this is ever a BAD thing.) It could also plausibly contain alternate history, historical fiction, and scientific papers.
Pinning down Space Opera is even more notorious. Essentially, though, something becomes space opera because it aspires to be. Like opera, it has conventions that can not be considered "good" or "bad," but can only be considered necessary if you want to be Opera, not "comic opera" or "light opera" or "operatta" or "American Musical." But let me quote directly from Aldiss...
"Science fiction is a big muscular horny creature, with a mass of bristing antennae and proprioceptors on its skull. It has a small sister, a gentle creature with red lips and a dash of stardust in her hair. Her name is Space Opera...
"...Ideally, the Earth must be in peril, there must be a quest and a man to match the mighty hour. That man must confront aliens and exotic creatures. Space must flow past the ports like wine from a pitcher. Blood must run down the palace steps, and Ships launch out into the louring dark. There must be a woman fairer than the skies and a villian darker than the Black Hole. And all must come right in the end."
To sum up; the base structure of EV is more science-fictional than not but it needs a push to be either hard science fiction or space opera. It more than anything is reminiscent of the "Solar Queen" novels by Andre Norton and the "Commodore Grimes" stories of A. Betram Chandler. Martin, I salute you for bringing in the depth and emotion to coax a true space opera out of the beast. It would be a noble experiment to try to do the same for hard science fiction. Just adding scientifically accurate mission texts wouldn't do it. Somehow, the plotting would have to permit extrapolation and change, test and hypothesis. Perhaps some Beowulf Schaeffer situations could do the trick? (The Puppeteers have asked you to go to the neutron star at RC 3824, and find out what killed the previous expedition...)
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"As a weapon of war it leaves much to be desired; but as a spectacle it takes much beating." -- a General observing the disastrous test of the JATO-assisted "jumping" tank.