Sending a rover to Mars is cool—but sending one to Mars along with a helicopter is even better. Yes, that is the plan for the next NASA Mars rover, scheduled for 2020. The idea is to have a driving rover that brings along a small coaxial helicopter. The helicopter will be self-powered and fly for a few minutes a day. The main advantage of the helicopter is that it can scout ahead of the rover and take pictures and stuff—maybe some epic rover selfies. But really, it should be a huge advantage over previous rovers.

Besides being a cool Mars mission, this Mars helicopter is also perfect for some physics questions. Here are some questions and answers regarding this flying robot.

Why doesn't it have a tail rotor?

The Mars helicopter is not your traditional helicopter. For a helicopter with a single rotor (like the ones you usually see on Earth), the tail rotor is required to counteract the change in angular momentum (and the frictional torque from the air) due to the main rotor spinning. Without the tail rotor, the helicopter would spin out of control and crash—or at least get the passengers very dizzy. A coaxial helicopter has two counter rotating blades. Since the two rotors are spinning in opposite directions, the total angular momentum is zero and there is no need for torque from an extra tail rotor.

Getting rid of the tail rotor also does something else—it saves space. You can make a smaller helicopter by using a coaxial rotor. Smaller is better—especially with the limited space on board the rover. Getting a bigger helicopter on the rover would be like trying to fit an overstuffed rolling suitcase in the overhead bin on your last cross-country flight. Also, I should point out that the Mars helicopter doesn't go back to the rover, but it does start there.

Will a helicopter work on Mars?

With regards to helicopter flight, there are two big differences between Earth and Mars. First, the density of the atmosphere on Mars is significantly lower than on Earth (only about 1 percent of our atmospheric density). Second, the gravitational field is also lower on Mars (just 38 percent of the gravity on the surface of the Earth). The lower atmospheric density makes it more difficult to fly a helicopter, but the lower gravity makes it easier.