Wanted to share a method I used to grind this one out in the endgame, and also because I found myself SUCKING at space combat.
I would agro a sentinel drone on a planet, fly into space and wait for a ship to warp in. Instead of engaging in space I would fly back to the planet and engage there instead.
The sentinel ships would more often than not just sit there, and navigate around very slowly. I think the AI takes on a different set of rules while dogfighting on a planet, made it very very easy to chalk up the 80 kills needed. Once you have taken them out you can go back into space and more should appear. Rinse. Repeat. If they dont warp in, head planet side and agro a drone again and then head back to space.