Space is very open so you have clear view in all directions. On earth radar works because the distances aren't that extreem. But in space the delay doubles for radar to optical sensors.
If you last defence line track even the smaller projectile or the very fast. Half the response time is good thing. Also it is more stealthy to go passive.
Heat is also a problem. Optical sensors would be full range above and beyound the visual band.

Also stealth is limited obscuring background stars and a modern advanced space ship computer could proces the sensor data to detect the more stealthy . Where high fidelity small arc zoom in sensor inspect the annomalis in 360 spere arc detection.
As such space craft 1 AU away are screen filling.

Kenetic weapons are effective because speed is quadratic factor.
Laser puls canon is means to snipe with a almost 1/3 delays at 100.000KM range.
A space craft build around the canon make sens.

Space craft could be realy big lightweight. With a lot of reduncty to be able to take lots of kenetic hits.
Large spread out sensor array.

It is posible to tweak the fun and game pace with how much and wich fictional tech your wil using in the game.
Missiles are on it own in effective but in swarm over run point defence turrets.
Space shot kun to take out as much sensors. Blind vessel. The a swarm missile get more effective.
It also seams that it might not get a fighter dogfighting gameplay.

I am thinking a lot about this. But there are a whole lot of choices to make.

And practical warfare is a arms race where both parties adapt to what works and what not.
In reality there should also besides the units that worked very well also the dead ends . If tactic change what did not work could become effective.

For this thing the FTL drive. For me that fiction tech should be rather big engine needing a very extreem high energy use. So notting less then a fusion plant or extremer. Especially for the faster FTL.
A agile fighter or drone won't have FTL. Or there smaller very weak once for the upper limit sub FTL.
Like a corvette

Part of a space battle might be fire and forget missile barrages, e.g. millions of small missiles at sub light over a massive area hoping to hit an enemy ship inside a cone shaped area.

You might also see huge minefields several AU across, protecting planets and shipyards and placed across shipping lanes.

If you have a mythos where space travel can only happen along charted paths then this can lead to such tactics along with ambush tactics and other fun things.

Restrict the space that can be travelled or used and the game could become much more fun...

Restrict the space that can be travelled or used and the game could become much more fun...

I think this is a pretty key observation. If we take the drives-like-a-car spaceflight model of most video games, then players are free to fly anywhere at any time with no restrictions, and this obviates most tactical decisions.

If, instead, you are restricted to 'hyperspace routes' and/or flight paths defined by (semi-realistic) orbital mechanics, then you have back the choke points and ambush tactics that make most non-space genres so interesting to play.

In regards to FTL: as far as anything within the realm of speculative realistic sci-fi goes, FTL is pretty much physically impossible. It will always be used in sci-fi though because our solar system is usually viewed as quite boring. I think with enough work though, it's possible to make the Sol system interesting. The big problem with FTL is that it is essentially time-travel.

For example: a potential far-future use for Jupiter would be the extraction of radioactive Hydrogen or Helium isotopes, so you'd could either have large ships in it's upper atmosphere or semi-pernament mining bases. A level inside the atmosphere could be filled with chaotic winds, near zero visibility, and slowly moving harvest-ships in the clouds. Something in low-to-medium orbit, like a transport/control hub for the extraction teams would have an amazing view of its storms.

Anything in high or low-orbit could have some pretty amazing views. Pluto has a thin atmosphere apparently, so there's some color there. Several planets have ice or rock rings, which would be eventful. Mar is mars, so it doesn't need any gimmicks, but throw in some sparse lights from cities on it's dark-side and it's suddenly 1000% more interesting. Any area of space could potentially have unidentified asteroids or comets, whether captured by hurling them from the asteroid belt (for mining), or naturally occurring. X: The Terran Conflict had some interesting Sol system levels.

Space games are always off to chase the splendor of black holes, quazars, and nebulas, which are visibly interesting, but ultimately just inanimate backgrounds or fog - if you're in a nebula. Personally, I think the trade-off of being more immersive is worth the slight loss of visual splendor - especially on an indie budget. Our system has the potential for interesting sights, but the public mind mostly recalls drab Nasa photos.

It will always be used in sci-fi though because our solar system is usually viewed as quite boring. I think with enough work though, it's possible to make the Sol system interesting. The big problem with FTL is that it is essentially time-travel.

But can you make the solar system interesting without also making sub-light function as time-travel?

Our current optimal transit to Mars is somewhere in the region of 8 months, and the window for that only comes around once every 2 years. Newtonian physics doesn't leave us a ridiculous amount of room to optimise that equation - there are diminishing returns to the amount of reaction mass carried vs expended to get there.

It's going to require some careful game design to make fun a game that plays out in a timespan of years for each tactical decision.

I think there are plausible technologies that could speed up travel times. Whether or not the time-factor is relevant depends on the type of game. If you've got a story-based RTS, you can just make levels in different areas and time can be conveniently ignored. If it's FPS based, you can leave somewhat-realistic travel-times "4 years later..." screen fades from black into the cockpit.

As far as tech goes, ion-engines look to be promising. In theory, they could bring travel time to mars down to 40 days, and that's based on current in-development tech. There'd be room to fudge it if you put the storyline 200-400 years into the future.

There are a lot of possibilities. Even if you only upped engine speeds to .5 light speed, you have a travel time from the sun to pluto in 10 hours. In a strictly realistic sense, you'd need considerable speed-up and slow-down times in the span of months though most likely. But.. fudging speed-up/slow-down times is quite a bit different from fudging the laws of physics. Another possibility if something like travel-lanes is needed design-wise is to have some sort of hyper-velocity accelerators. Either a network of them, or only lanes for major routes.

I think the biggest benefit of a realistic system would be a re-birth of what sci-fi used to offer. Sci-fi used to offer a glimpse of what could be. But now, sci-fi has atrophied into following the pattern established by the now-dashed hopes of an era that didn't know light-speed and transporters are utter fantasy. This is why 2001: A space odyssey is still so captivating. Same with Interstellar, despite the black-hole thing.

I think a realistic setting is what we need culturally too in sci-fi. We're at an era where private companies are starting to think about space-tourism and asteroid mining. The US even passed a law that gave permission to private companies to keep what they mine from space. In 50-75 years humanity could finally begin its diaspora into the void.

Travel time seams to get boring long, the time dilation if you get up to fast speed like fusion ion drive accelerating for many years. Boring if you can't accelerate time. If you drop online gaming stick to single player. This problem is solved.
For me this a easy choice as I so not into MMO.
Competive short online sessions I do. But this type of game doesn't need to fall under that.
Co- op maybe. As in crew on the same spacecraft.

But I would more go from making the soft scifi more hardcore.
Then stick to real science and keep that as pure as posible.

But if I keep real space up to scale. Then distances got extreem. Then I need this FTL fiction. FTL may or my not be posible. But if it would be a huge brake trough. I expect that these engines are huge and the powerplant extreem to.
So what I drop is roaming space in a Fighter, with FTL drive the size of ipad? With Cargo bay? And only single seat cockpit?. That a no go for me.
Also Spacecraft is no plane no submarine no naval thing there is something in common with all but also very extreem differences. So it make sense to not start in a fighter that the more airplanes in space combat. But in a spacecraft. You have to travel and trade so it has a lowest and older tech FTL drive. Which is big engine plus power plant. You have cargo bay and living space no cockpit but more small bridge. Which means not agile. So if heaving weapons they are for defence and probaly be mounted on turret. No dogfighting .
My guess pirates in deep space make no sense but do make the game more interresting. So I keep them. If they want to take your ship or cargo the need to match your speed. In that case a docked heavy fighter make sense as gun turrets do come with cost of space mass ammo and power needs.
In this case dogfighting situation do come along. In military combat it isn't about matching speed but take out keeping your main high velocity vector. You see you bogey on sensors screen filling. But not looking out your cockpit.
Another fiction I keep is shield tech. Because combat could be often one hit one kill. How ever there efficiency depend on there tech level mass and have high power need. The heavy fighter or better gunship have the smaller once.

Spacecraft construct. Want some realism there to. fTL works in some specific way so these engines could be part of ship design.
Fusionion drive as main cruise engine. Best power mass and fuel mass ratio.
Fusion plasma thrusters for planet side take of. Best power mass ratio. Less fuel mass ratio.
So with each ship type you need a balanse between these engine.
Less fusion power thrusters no planetside landing capability.

Also in setting where there are centuries of space colonisation mining and exploration and warfare. There are centuries of space ship types with wide tech settings.
For me space craft design would need to be procedural following techlevel.
The problem with design good looking concept space craft. The often conflict with physicaly realistic simulation model of thruster placing and structure strength.

So for planet side landing vessel you wouls see something build around large fusion ion drives.
Or at least see some big fusion plasma thrusters.
I space craft like in the movie Promethiouse make sense.

There is also choice to make on mass. Big FTL or lighter FTL vs landing capability.

FTL may or my not be posible. But if it would be a huge brake trough.

I don't want to debate real physics but less than 300 years ago people thought that if you went faster than 40 mph you'd die from inertial forces.

People less than 100 years ago said it was impossible for a human to break the sound barrier because the shock wave would kill you.

With our current understanding of physics it's impossible to travel faster than light but this doesn't mean it's impossible that we'll ever travel interstellar distances in practical timescales.

After all if a cave man saw you driving a car what would he think? It's science fiction to him, not science fact.

We can't speculate about future science and say "this is believable because it seems like what we have now", that makes no sense because the real world has proved future technology is a thing we struggle to predict and can't ever imagine.

Back when star trek came out they thought that in the 23rd century a computer would still be the size of a large room.

How wrong they were...

I'm surprised no one mentioned drones yet.

When I think of a "realistic" scifi space combat, I tend to think of a more "Drone carrier" ship launching drones out of a railgun at insane speeds, which then seek out targets and communicate that info/attack.

Or maybe fusion powered lasers that disentegrate anything in their FOV?

FTL may or my not be posible. But if it would be a huge brake trough.

I don't want to debate real physics but less than 300 years ago people thought that if you went faster than 40 mph you'd die from inertial forces.

People less than 100 years ago said it was impossible for a human to break the sound barrier because the shock wave would kill you.

With our current understanding of physics it's impossible to travel faster than light but this doesn't mean it's impossible that we'll ever travel interstellar distances in practical timescales.

After all if a cave man saw you driving a car what would he think? It's science fiction to him, not science fact.

We can't speculate about future science and say "this is believable because it seems like what we have now", that makes no sense because the real world has proved future technology is a thing we struggle to predict and can't ever imagine.

Back when star trek came out they thought that in the 23rd century a computer would still be the size of a large room.

How wrong they were...

Sure, but that doesn't mean that these " relative easy" barrier's are broken. That anything can be broken! It could even be that the most advanced godlike alien somewhere in the universe are bound and isolated by limit of C

I'm surprised no one mentioned drones yet.

When I think of a "realistic" scifi space combat, I tend to think of a more "Drone carrier" ship launching drones out of a railgun at insane speeds, which then seek out targets and communicate that info/attack.

Or maybe fusion powered lasers that disentegrate anything in their FOV?

Autonomious drone which also could be used remote. The Pilots are on the drone carrier.

Also with advance tech and miximg tech a fighter drone missile mine got a bit merge.

In space a cruise missile could have FTL so a big engine thus big and expensive missile.

With high velocities there often is no need for warhead. But some mass