On Monday April 19th at 9pm Australian Eastern standard time, the Ingenuity helicopter — which landed on Mars with the Perseverance rover in February — took off from the Martian surface. More importantly, it hovered for about 30 seconds, three metres above the surface and came right back down again.

It may not sound like a huge feat, but it is. Ingenuity’s flight is the first powered flight of an aircraft on another planet. It marks a milestone in the story of human space exploration.

While the Apollo 11 spacecraft famously touched down on the Moon, upon re-launch it simply had to exit the Moon’s gravity and return to Earth. To sustain flight within the environment of a world with no atmosphere, however, is a different story.

The now historic Ingenuity helicopter took six years to make. We can understand why, once we understand the complexities of what was required.

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Why local flight on Mars is a big deal

There are several technological challenges to conducting a helicopter flight on another world. First, and most significantly, helicopters need an atmosphere to fly.

The blades, or “rotors” of a helicopter must spin fast enough to generate a force called “lift”. But lift can only be generated in the presence of some kind of atmosphere. While Mars does have an atmosphere, it’s much, much thinner than Earth’s — about 100 times thinner, in fact.

Read more: The Conversation