User blog comment:Rozh/Surface-to-Orbit Artillery/@comment-59290-20110327060531/@comment-118.93.233.42-20110414231941

Keep in mind also that most of the energy released by a nuclear explosion is simply deflected in space, making them less effective than in-atmosphere. Then there's the point defence lasers that Covenant ships use to swat fighters and missiles before they get very close - a MAC is too fast a target to hit, and so dense that even if it was the shrapnel would keep going, with a wider spread - like buckshot rather than a single bullet.