In that book, a colony on Mercury is attacked through the use of several billion pebbles that were flung into the solar system in a calculated way such that they all converge on the colony several years later and the kinetic energy they gained going down the gravity well combined with the sheer mass is a devastating attack and totally undetectable (a single pebble would just burn up in an atmosphere or be a consideration in colony design on an atmosphere-less planet like Mercury, so why monitor it? Billions of them would form a destructive plasma cloud if aimed at Earth or simply a kinetic energy weapon against Mercury).
Further, the author discounted kinetic energy weapons too easily. A rail gun in space would not have to worry about air resistance limiting the range or impact magnitude of the rail slug, and so would be a very effective weapon in ship-to-ship combat (or more likely, railgun installations on satellites aimed at the intruding ship).
Taken together, I think space warfare wouldn't involve ships as we know it at all. It would be planets firing at each other similar to ICBMs between countries today, with drone-like mobile weapons platforms with stealth that are launched as part of commercial launches and placed via gravity slingshots (and so can be as cold as space until an activation signal is sent to it, allowing stealth tech to actually work). These would be placed near potential enemies and probably allies alike, and would be used both offensively and defensively: if an enemy makes an open attack, they would target the attack itself, if they attack, it would reduce the potential response time, though it could not be as significant in magnitude as a massive attack launched from the planetary surface.
(Warning: The book is really not a good first one to read from Kim Stanley Robinson, as it explores some of the more esoteric elements of the Mars Trilogy even further, with a focus more on how technologies of all types, especially bioengineering and artificial intelligence, would affect societal norms, and is far enough away from our current norms that it'd probably "gross out" people ill-prepared for it. Better to read the Mars Trilogy first and follow the line of reasoning that produces the kind of society in 2312, I think.)
In that book, a colony on Mercury is attacked through the use of several billion pebbles that were flung into the solar system in a calculated way such that they all converge on the colony several years later and the kinetic energy they gained going down the gravity well combined with the sheer mass is a devastating attack and totally undetectable (a single pebble would just burn up in an atmosphere or be a consideration in colony design on an atmosphere-less planet like Mercury, so why monitor it? Billions of them would form a destructive plasma cloud if aimed at Earth or simply a kinetic energy weapon against Mercury).
Further, the author discounted kinetic energy weapons too easily. A rail gun in space would not have to worry about air resistance limiting the range or impact magnitude of the rail slug, and so would be a very effective weapon in ship-to-ship combat (or more likely, railgun installations on satellites aimed at the intruding ship).
Taken together, I think space warfare wouldn't involve ships as we know it at all. It would be planets firing at each other similar to ICBMs between countries today, with drone-like mobile weapons platforms with stealth that are launched as part of commercial launches and placed via gravity slingshots (and so can be as cold as space until an activation signal is sent to it, allowing stealth tech to actually work). These would be placed near potential enemies and probably allies alike, and would be used both offensively and defensively: if an enemy makes an open attack, they would target the attack itself, if they attack, it would reduce the potential response time, though it could not be as significant in magnitude as a massive attack launched from the planetary surface.
(Warning: The book is really not a good first one to read from Kim Stanley Robinson, as it explores some of the more esoteric elements of the Mars Trilogy even further, with a focus more on how technologies of all types, especially bioengineering and artificial intelligence, would affect societal norms, and is far enough away from our current norms that it'd probably "gross out" people ill-prepared for it. Better to read the Mars Trilogy first and follow the line of reasoning that produces the kind of society in 2312, I think.)