What future space combat would really look like

Space is big, space is empty. FTA this means everything is easily trackable, not only are thrusters visible from across the solar system (except perhaps if you're headed directly for someone, but the thrust required there would be insane), but even every object in the solar system is glowing in infrared energy and thats background objects, not to mention you've strapped nuclear power plants, life support and whatever other heat producing apparatus onto your ship to make it glow even brighter.

The problem with being visible from a distance means it favours those who can hide. Basically, it favours mines. It's simple strap a laser onto a small rock, bury capacitors inside it and have them charged by solar panels. Why? Because the aim is to one-shot your target somewhere important. The mine is disposable, if it one shots the target you might get lucky enough to use it twice. If not you'll have dozens of others waiting. You've got 3 targets: Power supply (nuclear reactor/capacitor bank/whatever), main engine (you cripple their thrust and they're a sitting duck) and control centre (heck, you're likely able to nail all habitable space in one shot as a space ship is more likely to have a vastly expanded cockpit rather than a whole ship of habitable space)

The other problem with space combat is heat. Before you'd even fire a missile or a bullet, you're going to be aiming infrared lasers on your targets from light minutes away. If a ship is habitated then you only need to get it to the point where the life support can't shift enough heat to keep the air temperature below 40C. In uncrewed ships you're talking hot enough to make processors malfunction, which isn't considerably hotter than people can tolerate. These might cope better as cooling can be dedicated to very small areas.

The problem with space is that objects can get very hot, very fast and unless you bring a lot of material to heat sink and dump, you've got problems.

Space will be a war predominated with mines and heat. There are currently about 25,000 objects in space. If only 1% of these are ship-killer mines, would you attack Earth? Well, you'd need more than 250 ships, assuming you're able to kill all the mines in a very short time before they can refire.

Want to attack a mining base in the asteroid field? Find the rock without the massive laser hiding in it! Furthermore, try to wage an effective assault when you're pulverizing everything within a million kilometers of you, and still have the weapons/energy/heat sink capability to fight your target that has a massive rock of shielding and heat sinking, versus your ship.

What about launching asteroids or comets at your target? Well 1 if it's viable to nudge an asteroid from hitting earth, then it's viable to nudge the asteroid your in so that it's missed.

So the invading force goes into the Oort cloud, picks a chunky rock, attaches a giant thruster to it and begins accelerating it towards c. A day later, the speed of the rock has reached 0.5c.

Hours later, a defending fleet arrives, shoots and kills all the invading bds. The rock however, continues at 0.5c even though the thruster and guidance systems were destroyed. It reaches the asteroid cluster, and hits... nothing. It keeps going to the other side of the solar system, and as its speed was so high, exits orbit.

Accelerating a giant rock to c takes throwing out alot* of gas. The asteroid based civilisation, to prevent random impacts with random asteroids, would've been tracking every object in the belt. One of the rocks suddenly accelerates, I think it will be picked up.

Also, when the asteroid was accelerating, its direction would've been picked up. Once accelerated to c, it will still take hours to arrive at the designated target. The home asteroids simply have to maneuvre away from an intercept course. And no, guidance systems on the accelerated rock won't help. It's travelling at c, and by the time the system finds out the target has moved away, the asteroid would've missed it. Unless the asteroid have 100% maneuverability, and energy to change course whenever, however it likes. But if the asteroid can do that, any asteroid can do that. ;)

So your only option is accelerating the rock from the next system onwards. It will now take years for the asteroid to arrive. To reduce the probability of a successful attack, just have a "random thruster day" every 30 days where all the home asteroids just move randomly to different locations. By the time the enemy asteroid arrives the location of all the home asteroids would've been different. The probability of hitting anything worth hitting will be very low. Even if you have 1000 incoming asteroids.

Also you're assuming you won't get picked up accelerating an asteroid to c in the next system; Remember, asteroids have no atmosphere and 100% visibility. You might miss 1, but 1000? I'd doubt it. if 1000 asteroids are really incoming then you just make every day random thruster day. ;) They have so much energy, you should too.

In truth it is more analogous to a bullet or bomb - point it in the right direction and try and get it there as fast as possible.

Piracy would likely extend solely to the theft of energy resources. Similarly, so would war but on a bigger scale.

Piracy of goods would only extend to things not easily replicable by the present technology, or not easily replicable on many colonies. Even then, you're looking more at the theft of raw materials or for material value. Piracy would likely resemble robbing armoured vans today than any kind of piracy we've seen before, but they'd likely be trying to get precious metals or power like uranium.