Just who do those comets think they are, huh? HUH? All cruising around the solar system, leaving their dirty ice trails everywhere. NASA's gonna go in and show them who's boss, and the agency's bringing in the big guns to do it. Literally.
This giant harpoon gun (a ballista, technically) is what NASA engineers get to fool around with at work, since building spaceships is apparently not enough fun. This weapon is six feet tall, and made from a pair of leaf springs taken off a truck. A half-inch steel cable cocks the thing with up to 1,000 pounds of force, and they have to point it at the floor 'cause if they pointed it at the ceiling, the harpoon would likely blow straight through the roof and fly for about a mile before punching a giant hole through the chest of some hapless bystander.
So that's pretty awesome, then, but why exactly is NASA building medieval siege weapons? Well, it turns out that the safest way of collecting a sample of material from a comet is to stay as far away from it as possible, and the best idea that NASA has come up with is to send a space probe to a comet and then have it fire a harpoon with a sample collection tip at the surface. The harpoon will bury itself in the comet, and then the spacecraft will reel the center section of the projectile back in, bringing some comet stuff along with it.
We should point out that NASA won't be sending this particular harpoon gun to go after comets. Instead, they'll probably use an explosively-launched version to minimize size and weight. In fact, the plan is to take along a whole rack of harpoon launchers with different explosive charges so that the ideal velocity can be selected for whatever the surface composition of the comet turns out to be, or to allow the spacecraft to defend itself in the event that the comet is actually an alien death ship in disguise.
This harpoon sample-retrieval system is being developed for a potential future mission, and you can check out what that might look like in the video below.