The above solution is great, and works well. However, if you missed that part and have yet to unlock this, another great place is on chapter 13 the Lunar Base. However, you must have grenades in your inventory because there aren't any pickups in this area. If you have some saved up like I did though, right when you put on the moon suit and enter outside, you will come to the top of a hill looking down on 3 of those flying drones. Easy place to throw grenades and let them float towards them and blow them up. You only need need 5, so just restart the checkpoint and you are right at the top of the hill looking down on them. Easy peesy!