This is something I have been thinking about since I read the third Expanse novel, “Cibola Burn”, by S A Correy. Space warfare is a loose, loose proposition.
I started thinking about this idea when Alex and Naomi used the rail gun as a means to save the Rocinate and the colonists ship. I thought “what happens to the projectile”? Given the velocities of such slugs and the lack of friction in space, Newton’s first law says it should just keep going. Just one more small meteorite screaming through the Galaxy. Of course, planetary gravity or collisions with stellar bodies could destroy the projectile, but what if the slugs are shot sufficiently far from such influences.
In addition, when talking about space battles, you have to take into account all the munitions expended, as well as, the debris from destroyed ships. Now consider all the objects NASA and the Air Force track in orbit to protect space launches. At the speeds satellites and space craft travel to maintain orbit, even chips of paint become deadly projectiles. After each space battle, there would be thousands and thousands of such deadly objects left behind requiring additional tracking for normal space flight safety. The more battles you have, the more debris you have to track forever afterwards unless you clean up the area. Just imagine a solar system littered from thousands of space engagements.
So, unless we develop shield technology along with our deep space capacity, we better leave our wars on the ground. Oh, who am I kidding. As usual, we will have our wars wherever we go and then realize the mistakes we made while trying to clean up the mess.