I've been using a homebrewed system and hard sci-fi setting (not originally designed for tabletop RPGs, but for writing stories and as my worldbuilding project) with a group of friends for a while now and they are ready to leave the starting space station. Thus the first space battle comes ever closer, but I'm uncertain whether my ideas on how to do space combat are any good or not.
The setting is very hard sci-fi set several millions of years in the future, so while technology is very advanced (Torch-drives, antimatter, hand-held energy weapons, nanotechnology, genetic engineering, transhumanism), none of the typical soft sci-fi technologies (FTL-drives, teleportation, useful forcefields, ...) exist. This has worked fine so far, yet the players haven't yet come into contact with truly advanced military equipment like spacecraft.
The hard sci-fi nature of the setting means that space combat is an extremely automated process involving a mind-bogglingly rapid dance of probability and vector math paired with deception and elaborate bluffs. Evasive maneuvering, firing solutions, and tactical decisions must be calculated, made and remade in a matter of nanoseconds. This does obviously mean that human intervention in space combat will be minimal.
Thus my idea was that if players can't make tactical decisions, having them win battles because of strategic ones and good preparation would be the way to go. If normal combat would be akin to playing Fortnite, my space combat would be akin to Dota Autochess or LoL's TFT mode: You make strategic decisions and whether they were good or not, you have to live (or die) with the results). I would describe the strategic options the players have and tell them as the spacecraft AI the probability of success, critical success, failure, and critical failure. Thus the space combat would be very narration heavy opposed to usual dice heavy combat.
It is worth noting that in the absence of energy shields and usable spacecraft armor, the negative outcomes would either be vaporization of the party in a nuclear blast, overheating and thus loss of the vessel's combat effectiveness or loss of a critical resource or component (main drive, ejection mass, ammunition, ...), making victory extremely unlikely. This means that space combat will always involve very high stakes, since there are no fantasy means of getting out of bad situations.
My system in general works by adding up all the related stats a player has to a number of dice he can throw for the roll. Each die is considered a success if it shows more one of the upper 50% of its eyes. (if D6: 1,2,3 == Failed_Roll; 4,5,6 == Succeeded_Roll) For minor decisions, like what kind of loot is found I use a "Destiny_Roll". I roll a D20 and ask the player in question if he wants high or low numbers. The result may be a yes/no or how good/bad answer, depending on the situation.
In space combat, they will have flat dice boosts due to their vessel's equipment (adding a railgun or a fresh dagger shield will give extra dice) and maintenance status (attrition during the battle will drain dice if a second round happens). (They will start with an ultra slow solar sailer without armor and only armed with defensive point-defense IR-laser arrays, which is pretty much rock-bottom as far as spacecraft go.) Then they will discuss their battle plan with the spacecraft's AI, where they can use character skills and creative suggestions to gain extra dice. Additionally, the vessel will have limited resources, namely heat-capacity, heat sinks, reaction mass, power, armor, and slugs whose use-up-rate depends on the players' decisions and the outcome of the dice rolls. These plans are made prior to the battle or during downtime. (The bad guys shot a volley of missiles at them and it will be an hour before the next volley arrives, thus the strategy can be adjusted.) Short-term adjustments will be handled via "Destiny_Rolls" and will have little impact.
Player decisions would be whether the vessel should focus on defense or offense, how much resources it may use, which weapons to prioritize, what range to keep, etc. Each of these decisions will give specific buffs to the encounter, which won't necessarily be flat dice boosts (sacrificing dice to gain guaranteed damage on a success, etc.)
What issues might I run into with this system?