Near future means cannons
Railguns seem a far more attractive alternative, largely because you can get them going really, really fast. Chemically powered weapons might work for things like flak, but otherwise they won't be able to close the distance quick enough.
whose recoil would knock a ship significantly without countering thrusters, and then fuel might be limited.
It takes an awful lot of force to move an object as massive as a several hundred meter long chunk of armor. Yeah, there'd be some recoil, but I don't see it accomplishing much more than slowly inching you away from your target. Realistically, ships would have to be able to vector the thrust from their engines in virtually any direction in order to compensate for things like recoil, enemy attacks, or just to change direction.
Also consider that objects in orbit move really fast, so even hitting the target would require either sophisticated tracking computers (or maybe not so sophisticated, I know nothing of coding)
Fighting in orbit wouldn't be terribly viable, simply because all you need to do is get to the far side of the planet to avoid any and all fire. Granted, you'd have someone chasing you, you'd have a head start. As ships would likely be built in orbit, any attacker would have the disadvantage of having to travel to the target, which would know for quite some time that an attack was coming. Targeting isn't likely to be a problem at such close ranges. Changing direction completely requires not only accelerating in that new direction, but also completely decelerating in the old one. In other words, it'll take a while. Compensating should be easy.
If we include Navy prototype railguns
I don't doubt that in the "realistic near future," they won't be prototypes anymore. We'll likely have much more powerful variants.
and lasers as seen on experimental anti-missile aircraft
Again, we won't be talking prototypes. We'll be talking a few hundred MJ, which would do some serious damage. It's also the fastest moving weapon possible. Even so, lasers do have an effective range.
Nuclear reactors as seen on Naval vessels could work, though a meltdown in space would likely result in complete destruction of the craft, though it would undoubtedly look really cool.
Fusion would probably be the way to go. Not only is it more efficient than fission, but it's also a lot safer. Meltdowns don't seem likely, but in any case, it seems like some sort of containment systems would be implemented, even if it involved somehow ejecting the reactor.
Armor would probably need to be either very thick or very advanced, beyond that I don't know.
Yeah, I don't know much about armor either. Thickness would be nice, but keep in mind-- the heavier you are, the longer it takes to maneuver. Something that takes a lot of energy to burn through would be good. Maybe something carbon based. Boron might be even better. One thing to keep in mind is that something that protects from lasers may not be great at keeping back kinetic (railguns) or explosive (rockets) weapons. One final consideration is that to get through an armor plate, you have to either hit it hard enough to break it in one shot (not likely; it's not good armor if you can do that) or hit the same segment repeatedly, which would be pretty tough.
More generally, any reason this shouldn't be in Ect instead of BSF discussion?
None at all, actually. I was reading the other thread as a reference while writing this one, and forgot to switch forums. Totally slipped my mind. Sorry about that.