I've got an idea about boarding parties on spaceships but it's based on the continued existence of infantry, and infantry weapons that are designed to function in an open-system environment. The question is in a world where:
orbital bombardment is a thing and in fact a common first resort weapon.
environmental damage caused by bombardment can be mitigated to the point where it's just not a consideration.
- the vast majority of primary industry and manufacturing are in orbit so on-planet resources and infrastructure are not important targets.
Is there actually a reason to have large-scale armies that can invade worlds? There will always be reasons to have small units for assassinations, extractions, and espionage/sabotage missions on planet but that's a very different skill set and weapons philosophy to massed infantry which is what I'm interested in.
Edit: just so it's clear any group that is using orbital kinetic bombardment as a first strike weapon does Not care about civilians, neither casualties or survivors, at all. Sorry I thought that would be obvious.
Edit 2: MichaelK's quite right I haven't given enough context for really concise answers, there's a lot of good material here anyway but I like clarity too so background and hopefully a clarification of the question as well: In the universe I'm working on humanity started to spread to the stars with FTL starships centuries ago and has colonised a reasonably large number of star systems, with heavy colonisation out to 15 Light-years and rumours of colonies as far away as Canopus, FTL is limited and does not extend to direct communications. Conflict between/within human colonies is rare but tends to be catastrophic, there are rules of war and a "stellar navy" of sorts that can enforce some penalties but the reality of the war courts is that living victims get results and you're pissing into the wind trying to get convictions without them. This reality leads to really devastating bloodshed when a conflict "goes hot" because neither side really wants to leave anyone standing on the other side, it's in their interests not to. So orbital bombardment is a weapon that is actually useful because of it's indiscriminate nature.
Planets play less and less of a role in civilisation the further you go from Earth, orbital factories take advantage of orbital materials to create goods that largely spend their consumer lifetime in space. Planets make good living space for populations because artificial gravity is still expensive and/or awkward, and those who stay on-planet for work contribute to co-ordination and logistics within light-speed communications range. Planets can also be used to grow luxury real foods like meat and cereals that can't easily be grown in space. Almost all infrastructure is in orbit, including power for Arco-cities on planet.
Now on a planet using high-power kinetic weapons isn't much of an issue, you can get away with stray rounds etc... they'll come down somewhere, in space you don't have that option, a stray round powerful enough to punch through armour based on astro-engineering hardsuits that protect from micro-meteors can punch through civilian structural members potentially trashing the target and the boarding crew. From my point of view if the only troops who see regular action are in boarding actions where those risks are a constant consideration, and it's been like that for generations, then people being people they'd come up with projectile or energy weapons that function there but if planetary infantry are still a big thing then boarding parties wouldn't get the same attention and would have to go a different route. So is massed planetary infantry a working model when trashing everything at the bottom of a gravity well is not only feasible but also in some ways preferable?