Ron Edwards coined the term fantasy heartbreaker a while ago, which now has some currency (although broader than he initially intended it) among fans. His initial conception of it is one of the many games that is like D&D in almost all of its fundamental assumptions, made some superficial changes, and may have a truly innovative idea or two, but which gets lost in the crowd because ultimately it doesn't offer enough to anyone other than the True Believers™ to play it instead of just sticking with D&D. This is a somewhat nuanced definition, and because it's probably a little too nuanced to be useful, it has evolved such that most people who now say it mean it to be almost identical to the notion of pastiche as used in the fiction and art world. Fantasy heartbreakers are, therefore, D&D pastiches. There's not enough to really set aside, say, Palladium Fantasy from D&D for it to really be a completely different kind of game. It's just a minor variation on the concept of D&D.
Pastiche isn't necessarily bad. I don't dislike, for example, Flash Gordon, which was deliberately created to compete with Buck Rogers. When King Features Syndicate was unable to purchase the rights to make a John Carter of Mars strip to compete with Buck Rogers, Alex Raymond just pastiched it. And Flash Gordon is a wonderful thing in its own right, in spite of the fact that it's clearly (and even admittedly) a pastiche of Edgar Rice Burroughs.
Star Wars is itself also a pastiche, with very similar (albeit somewhat ironic) origins. George Lucas was a fan of the old Republic serials based on Flash Gordon and Buck Rogers starring Buster Crabbe (which by this time resembled each other even more strongly than their older comic strip versions did—which was already quite a lot). He couldn't secure the rights to Flash Gordon, which is what he really wanted to remake, because Dino de Laurentiis held them. So, like Alex Raymond before him, he created his own pastiche version of it. Instead of focusing the action on a single planet, Mongo, he had galaxy-hopping space ships, added WW2 style dogfights, and a weird Zen fantasy wizard element in the Jedi (which were admittedly considerably less weird in the first movie than they later evolved into.) But even this was little more than coopting ideas from Frank Herbert's Dune, probably the Lensmen, and other, older sci-fi pulp stories about psionic powers and whatnot (as an aside, the Green Lantern Corps is often considered to be a pastiche of the Lensmen, although they've overtaken it by an order of magnitude in terms of recognizability to today's audience—just as Star Wars has done to its own sources.)
So, I suppose what I'm saying is that I think the evolution of the term Fantasy Heartbreaker to mean little more than D&D pastiche isn't necessarily a bad thing, because I don't see pastiches to be necessarily a bad thing, although Ron Edwards meant Fantasy Heartbreaker as, if not an insult, at least an expression of disappointment. Then again, Ron Edwards always was kind of a pretentious blowhard, if you read enough of his discussion on the industry. In fact, he's rather famous for it, as are the rest of the commentators over at The Forge, although taking their reputation at face value without checking it out yourself is always a bad idea. In my case, I thought the reputation was more or less warranted.
On a whim, after typing "space opera heartbreaker" into my post yesterday, I did a search to see if anyone else had ever used the term, and what they meant by it. I found a couple of discussions, some from rpgnet, which often (especially in the time period of these posts) mimicked a lot the same attitude common at The Forge. However, they did make an interesting point; Edwards' conception of fantasy heartbreaker requires the big juggernaut that everyone is attempting to pastiche. In the case of much of swashbuckling science fiction, ultimately the juggernaut is John Carter of Mars, at least until people start doing pastiches of what are themselves pastiches—a la, Star Wars as a kind of pastiche of Flash Gordon which is in turn a pastiche of John Carter. In fantasy RPG terms, it's clearly D&D. In the science fiction RPG world... there really isn't a comparable juggernaut, so there's nobody to pastiche.
Now, this doesn't work exactly as I'm describing it. For one thing, RPGs are not (at least they weren't; sometimes they are now) about creating truly original content; they are all pastiches of some existing thing, translated into another medium. D&D could be seen as a pastiche of a bunch of similarly themed pulp sword & sorcery stories, overlaid with some superficial Tolkienisms, and then translated into the medium of the RPG. Therefore, any space opera heartbreaker would be a pastiche of a translated pastiche, if you will. But still; there isn't the same level of there being a single juggernaut in the industry that one can write a pastiche of.
The oldest, and probably best known sci-fi RPG is Traveller, but it hardly compares to D&D in terms of its size or prominence; in fact, it's gone in and out of print numerous times, having to be licensed and rebooted, often into drastically different systems. The first edition was published in 1977; the same year Star Wars was released, and seemingly showing little overt influence from it (I can't find a release month for Traveller, so it may have even come out before Star Wars. If not, it's unlikely that Star Wars played a significant role, however—there simply isn't really enough time. And anyway, the setting that ended up developing for the game is highly suggestive of being a pastiche of Larry Niven's Known Space stories or Poul Anderson's Technic History stories much moreso than Star Wars, although the MegaTraveller update, complete with a Rebellion and Civil War seem to acknowledge that Star Wars was the only space opera setting that many of its customers still cared about. But if Classic Traveller had an Appendix N, Star Wars wouldn't be on it.) TSR was the RPG publishing juggernaut, but their space opera game didn't come out until 1982—Star Frontiers—and while it has a loyal following, it was never really big, and it didn't last in print all that long.
Rogue Trader was another important player, although not until the later 80s, and it turned into Warhammer 40,000; more of a war-game than an RPG (although in its first iteration, it was less so.) 40k is interesting in that it also doesn't overtly pastiche Star Wars, but rather does so to Dune, Lovecraft, Aliens, and Judge Dredd and it bounces back and forth between a kind of Lovecraftian grimness and sly tongue-in-cheek unseriousness. Plus, it picked up a bunch of superficial Tolkienisms—orcs, dwarfs and elfs in space, in particular. Although it's not exactly in the same wheelhouse as RPGs, 40k probably can't be completely ignored just based on its massive size—very popular games, spin-off computer games, and massive collection of novels and other stories. The briefly popular Fading Suns mined a lot of this same territory; perhaps being more overtly Dune and Lovecraft influenced, without the Britishisms of Judge Dredd, for instance. Star*Drive for the Alternity system and is similar in many respects to a Traveller without a Third Imperium.
And finally (and by this, I don't mean to suggest that this brief survey is complete because obviously there were other games as well—these are the ones I was most aware of, so according to my perception, they were the most prominent and/or important), of course, there is West End Games' own Star Wars game. Although I don't know that it was really so popular as to threaten Traveller's place at the putative top of the heap, it's curious that much of what was first developed for the RPG later found its way into the Expanded Universe and became canonical—heck, even after the reboot of the Expanded Universe, much of it remains canonical. Names like Rodian, Twi'lek and others originated here.
Outside of tabletop RPGs, space opera dominates computer games; RPGs, shooters, strategy, all of it. From StarCraft, to EVE Online, to Destiny, to the Mass Effect series, to the old Wing Commander—they're pretty much all space opera if they're sci-fi (unless they're cyberpunk.)
I guess the point of all this is that there isn't really anything that a space opera heartbreaker could be deliberately imitating. You can from a setting perspective be overtly "pastichey" of one or more existing space opera settings, but you can't really do so at a game level with regards to a specific juggernaut that you are unable to get out from the shadow of, as it were. Either every space opera game is a heartbreaker or none of them are.
Of course, in the more expanded definition of fantasy heartbreaker, as it's evolved (where it's more or less equivalent to pastiche) then sure; AD ASTRA is a space opera heartbreaker. It started off overtly as an ersatz Star Wars, with space mapping conventions borrowed and modified from Traveller, and the more I develop, the more I start incorporating stuff that is common to other works in the same general genre; Dune-like elements, 40k-like elements, Known Space or Technic History-like elements, and heck, maybe some cyberpunk or even Stainless Steel Rat elements here and there. A pastiche not necessarily of one particular thing, although Star Wars stands proud as the first and most important element, but its still a pastiche of all kinds of things.
Much the same way D&D itself was, I suppose.
So, what do I really mean by space opera heartbreaker, if I've deconstructed the term to uselessness? Basically, only that I'm unapologetic about the elements that are pastiches, and I don't care if anything in it is particularly unique or innovative. It's about execution, hopefully, not originality.