The Mars helicopter is a robotic helicopter being developed by NASA to scout the Martian landscape and return data to engineers on Earth, who can use the data to map out the best route for Mars rovers.
The Mars helicopters are diminutive, about the size of a tissue box. They would be sent out to fly ahead of rovers and use cameras and an array of sensors to scope out interesting features and challenging obstacles, helping rover engineers figure out the quickest and least hazardous route.
The helicopter will have to be lightweight and cannot weigh more than 1 kg, and will likely have a pair of blades spanning 1.1 meters. Such large blades are required due to the thinness of Mars' atmosphere, which will require powerful blades to generate lift.