yeah, I guess that is the fallacy with SF. The author can pretty much do anything they want with it.
As several people have posted on another forum in another time, "science fiction is just fantasy with lasers".
This is mostly because in many SF/SciFi stories (there is technically a difference, in that SF is more written and more scientifically accurate than the "whoosh!! ZAP ZAP ZAP!!!" Hollywood-style SciFi genre) use many handwavium (I wave my hands and say "I have inertial compensators for multi-million-G accelerations!! WHEEEE!!!!") items, and explain them with technobabble (think Star Trek explanations of their gear. I would say that the unintelligebility factor cubes with the squaring of the technobabble factor, but don't quote me
).
More "scientifically plausible" items are 'unobtainium'. Note that handwavium/technobabble usually tells you what you can do, unobtainium usually tells you what you can't.
My personal perspective is that- in a hard SF scenario, most industry would still be located on a planet's surface, as 1) that's where most of the people are, 2) it's probably where most of the materials are, and 3) people don't really tend to want to go to a very potentially deadly place to work.
Hence, most of the defenses will be planet based. However, 1) a planet will also likely have its own (probably small) cadre of spacecraft for defense; 2) a planet will likely also have large, very difficult to destroy "battlestations" that would be somewhat analagous to SoaSE:Entrenchment starbases.
Because I would also postulate that highly inhabitable (terran, jungle, ocean, ice, desert) planets are at a premium (or somewhat scarce), just dropping nuclear weapons (or similar, as antimatter just can't be good for a planet's biosphere) or maybe giant planet-killer rocks just isn't a good idea. Mostly because devastating a planet would be bad for everyone. All around.
In contrast, a super-high-intensity conventional warfare would likely also not be the way to go. This is because, as has become apparant, modern, conventional warfare can probably take as many or even more lives than thermonuclear war. As a result (and also because I think this is cooler), I postulate the use of "cap troopers", that is, orbitally-deployed infantry that are "dropped" onto a planet's surface (more like into the lower atmosphere) with "capsules" (hence, "cap"-trooper; also note that I drew this from Heinlein's book Starship Troopers, and not that abomination (in comparison to the book) of the movie.). Such troopers would also be backed by dropship-deployed artillery and armored battlegroups, but the infantry (which are equipped with power-armor, and said infantry also carry "peewee" nukes, capable of destroying local targets, such as: water plants, power plants, distribution centers, manufacturing centers, &c) are the main fighting force.
As a result of the above, it would also happen that for raiding ops, said troops would deploy without armorial (tanks, arty systems) support. This would also make the raids much less costly than a conventional-style attack.
Anyways, that's my take. What do you think Koiju? And, what might you take be?