What started as a technology development project at NASA’s Jet Propulsion Laboratory (JPL) in August 2013, has become The Mars Helicopter, a small, autonomous rotorcraft which will travel with the agency’s Mars 2020 rover mission, currently scheduled to launch in July 2020 and be the first heavier-than-air craft on another world.

It took four years of design, testing and redesign to get it to under four pounds (1.8 kilograms). Its fuselage is about the size of a softball, and its twin, counter-rotating blades will bite into the thin Martian atmosphere at almost 3,000 rpm – about 10 times the rate of a helicopter on Earth.

Why so fast? To take off in the thing atmosphere. And it won't be able to go very high. The altitude record for a helicopter flying on Earth is about 40,000 feet and the atmosphere of Mars is only one percent of ours so even on the ground it will be equivalent to 100,000 feet up, said Mimi Aung, Mars Helicopter project manager at JPL. “To make it fly at that low atmospheric density, we had to scrutinize everything, make it as light as possible while being as strong and as powerful as it can possibly be.”

The helicopter also contains built-in capabilities needed for operation at Mars, including solar cells to charge its lithium-ion batteries, and a heating mechanism to keep it warm through the cold Martian nights. But before the helicopter can fly at Mars it has to get there. It will do so attached to the belly pan of the Mars 2020 rover.

Once the rover is on the planet’s surface, a suitable location will be found to deploy the helicopter down from the vehicle and place it onto the ground. The rover then will be driven away from the helicopter to a safe distance from which it will relay commands. After its batteries are charged and a myriad of tests are performed, controllers on Earth will command the Mars Helicopter to take its first autonomous flight into history.