NASA is developing a harpoon. They aren’t looking for blubber (Star Trek IV taught us not to kill the whales), but for other natural resources, in comets.
This isn’t an offensive weapon. It’s a research tool. The goal is for astronauts to be able to harpoon a comet and bring samples back so that they can study what comets are made of and how they are formed. But, knowing how comets are made could help us learn how to deflect them away from the earth.
And, we’ll leave the tip of the harpoon in the comet. What a nice souvenir.