How a Helicopter Drone Could Fly on Mars

We've gotten pretty smart at telling rovers what to do when they're working on Mars. NASA has more than a decade's experience in directing these machines on the Red Planet, asking them to image rocks, drill into the surface, or drive over varying surfaces. The Curiosity rover is so smart that in some cases, it can identify targets by itself to analyze.
 
But rovers have a big limitation: They stay on the ground. Aerial imaging is only available through satellites that orbit several miles above a rover. While this can provide a large overview of the site, it makes it difficult to anticipate what's just over the next hill or crater.
 
Drones could provide the solution, but there's a problem with them as well. Drones would have to be able to flyautonomously, because there's a several-minute round trip between the time a command is issued on Earth and when it is received on Mars. So a drone has to know when to fly over a hill, or to land when it's low on power; otherwise, the mission could be lost in a moment with a crash.