Asteroid Redirect Mission
What it is: Rerouting an asteroid to orbit around the moon in order to explore its surface and train astronauts for Mars
Status: Anticipated launch in the 2020s
This sounds a lot like Armageddon, but it's not quite the Bruce Willis doomsday-averting mission you're probably imaging. Rather, this is NASA's plan to land an unmanned craft on a near-Earth asteroid, collect tons (literally) of surface samples, redirect the asteroid into a stable orbit around the moon, and return to Earth.
So what's the point of redirecting the asteroid at all? Well, it's actually going to be used for training purposes. Astronauts already in space aboard the Orion will use this opportunity to practice landing on the asteroid and exploring the surface, testing the capabilities needed to successfully navigate a manned mission to Mars.