As someone who loves the Big Three (Asimov, Clarke, Heinlein) and have read a lot of SF, I pretty much despise Bradbury. There’s no science in his science fiction.

Not much in many of Heinlein's either. Or in Star Wars.

Or even Star Trek to be honest. I don't know why Star Wars always gets passed off as "science fantasy" when it's a more grounded universe than Trek by far - space wizards notwithstanding (which Trek has plenty of.)

Even in a lot of hard SF, a lot of the science is wonky if it falls outside of the author's special interest or area of expertise. Relevant to Asimov, the only reason robots have "positronic" brains in his stories is that positrons were a new discovery at the time and it sounded cool and futuristic to him.

As a Trekkie, fair point. I think Star Trek does fall into the "speculative fiction" category, but Star Wars doesn't. It's just "space opera".

Space opera is still a subset of speculative fiction and science fiction, saying "just" dismisses its influence on the genre as a whole.

A lot of classic science fiction is basically "x with spaceships" where x is the Napoleonic Wars, or feudal Europe or the Wild West or what have you, and the "science" is little more than set dressing.

> saying "just" dismisses its influence on the genre as a whole.

Well, it was meant to be parsed as:

Star Trek is speculative fiction and space opera.

Star Wars is just space opera.

Some space opera is also speculative fiction, but I wouldn't say it is a subset. I wouldn't call some space opera stories speculative fiction at all.

They're all classified as science fiction.

(Yes, yes - there is no consensus on these terms...typically science fiction is considered a subset of speculative fiction, and here I inverted a lot of things).

Early Heinlein e.g. Have Spacesuit - Will Travel, Farmer In The Sky, The Rolling Stones or for non-juveniles, The Moon is a Harsh Mistress have lots of science.

Later works, less so.