I never played the big MMORPGs (ie. ever-crack) but I do know that some of them have creatures, droids, etc. that follow your character around, doing your bidding.

So why not have a gun/rocket that hijacks a bot and makes it follow you around and shoot anything that attacks you. The better variants of the weapon would be able to hijack better bots. Wouldn't work on nation bots, of course.

To prevent newbie killing, there would probably have to be a "No Pet" zone around stations. Or make the hijacked bots smart enough to not attack friendly targets.

Maybe you could have a small observer drone as a pet, and have it somehow relay sensor data..

I love this idea, but I think it might be prudent to start with just "helper bots" that you can buy - they can repair the ship (like the nano gun thing) or attack attackers, etc. Maybe you have to shoot them out into space and once the enemies are gone they dock again. From there you could expand to more specialized bots - those that hijack collectors or mine asteroids (though I think I remember reading that some large ships can do that already).