Photo credit: NASA/JPL-Caltech

It's not a bird or a plane: It's a semi-autonomous space helicopter.

On April 19, 2021, the short-range Mars helicopter Ingenuity took off for the first time. As a powered flight being guided over the surface of another planet, Ingenuity was a much-anticipated exploration milestone. While the landing was soft, safe and by most accounts spectacular, Ingenuity's evolution from futuristic concept to a flight-ready vehicle strapped to the belly of a Mars rover was anything but easy. In fact, the many bumps, blips and pockets of turbulence encountered by the space helicopter over its 20-year journey to being launched reads more like the Wright Brothers' run down the dunes of Kitty Hawk than most people know.

Flight of Infancy

As is often the case with invention, the Mars helicopter Ingenuity was a slow-growing idea. JPL engineer Bob Balaram read the 1999 "mesicopter" proposal to NASA's Innovative Advanced Concepts (NIAC) and was inspired to design one for Mars. He sought out a partnership with Stanford University and private aerospace company AeroVironment. Together, they built prototype space helicopter blades. Fifteen years later, when JPL director Charles Elachi requested proposals for Mars-exploring drones and helicopters, Balaram dusted off his rotors and got to work.

Small but Mighty

Like the Mars Skycrane, the space helicopter is part technology demonstration — something that had never been tried in the field and could only be partially tested before deployment. As a demonstration of technology, Ingenuity earned its name from start to finish.

Very few robots that make it to Mars are this small. That's not for lack of trying, mind you. Less is more when it comes to launching mass at high speed. However, until Ingenuity, no one had successfully jammed space-worthy navigation, telecommunication, cameras and sensor arrays — not to mention batteries and heaters — into a flying box. A generation after the original NIAC mesicopter proposal, miniaturization made this feat possible.

Ingenuity, which weighs far less than most human children at birth, can lift off Mars using the power budget of a few 100-watt bulbs. As NASA notes, because it is so light, all the necessary power can be generated by a single solar panel perched above the rotors, which charges six lithium ion batteries.

It's Flight, Jim, but Not as We Know It

Part of the reason Ingenuity can alight so easily is that Mars has less gravity than Earth. That would be great news for flying fans if Mars also had Earth's thick atmosphere. Unfortunately for space helicopters, the Martian atmosphere is scant at 1/100th of the air pressure at our sea level, as NASA points out.

For things that like to take off and land, the key to success on the red planet is to go big — or more specifically, to go wide. To help them catch enough air to slow down, Perseverance and Curiosity both had large-diameter parachuting systems. For its size (14 centimeters by 16 cm by 20 cm), Ingenuity has huge rotor blades. They extend 60 cm from the center for a total length of 1.2 meters each. That's a lot of blade for a little body. They are also double-layered and rotate in opposite directions, giving the helicopter both stability and control.

Stiff blades and spinning rotors are an Ingenuity special design, flying in the face of Earth helicopters. To keep weight at a minimum, the propeller blades are made of foam at their core. A carbon fiber coating holds each blade together while keeping them light. The coating also makes them very stiff. Here, our helicopter blades sag when the vehicle is not in flight. We get away with that here because a floppy blade cutting quickly through Earth air will straighten out, like a whip. Martian wind wouldn't straighten a flag, much less a helicopter blade.

Large, stiff blades solve some of the flight challenges for a Martian helicopter, but not all. Even when the blades were holding their shapes, the batteries were charged and the vehicle weighed less than four American footballs, there was still the problem of how to generate thrust to pull enough air through the blades to hover the helicopter off the ground.

In a very real way, "spin fast, go faster" is another Wright brothers invention. For the propellers on their flights, the brothers used thin, long pieces of twisted wood, as NASA reports. They placed two of these behind the wings of their aircraft, spinning them fast — 350 times a minute — to create a pressure difference from the front to the back. The pressure difference pulled air through the plane and created the thrust they needed to travel hundreds of feet over the dunes that first day. Using that principle, Ingenuity can still launch, even with 1/100 an atmosphere to bite into — if its blades rotate faster.

By rotating more than 2,400 times a minute, 10 times faster than helicopter blades on Earth, Ingenuity pulls through enough Martian atmosphere to support its 90-second flights. If it rotated any slower, the space helicopter wouldn't get off the ground. Any faster, Ingenuity cold come close to breaking the Martian sound barrier. That barrier is lower because of the thinner atmosphere. Such a sonic boom would be quite an earful for Perseverance, which, like any helicopter parent, is never far away. On April 30th, JPL scientists recorded the sound of Ingenuity's blades and rotors: a steady hum against the background of fine dust shifting over the flat Martian plane that's come to be known as Wright field.

Collect Calls

The physical ability of a vehicle to get off the ground is just one of several keys to a successful flight. Piloting the craft — not crashing, and heading in the right direction — is also important. In the case of robotic exploration, there's the collected observations to relay back to base. How can we give Ingenuity, or any small vehicle, the power for communication and navigation without weighing it down with heavy transmitters and big batteries?

Part of the solution was to give Ingenuity the power to make some of its own decisions. The first interplanetary helicopter flies and lands on its own, sends transmissions, moderates its own energy supply and keeps itself warm through the bitter Martian days and nights, according to NASA. The other part of the solution was to treat it like any valued explorer by making sure it was never completely alone.

Like Wilbur Wright racing along on foot while Orville made that first flight, Perseverance serves as Ingenuity's communication relay. The Mars rover, which cradled the helicopter under a dust shield for the better part of a year, transmits instructions from the pilots back on Earth. It also sends Ingenuity's photos and weather data back.

In the end, Ingenuity can fly for up to 90 seconds for distances of up to 300 meters, per NASA. Future Mars helicopters will likely travel further afield, stay aloft longer and take more detailed observations, aiding human and robotic explorers alike in their quest to find water, life and each other.

One Small Hover for a Robot, One Giant Leap for Science

More than 117 years after Orville and Wilbur Wright lifted humankind off the ground with wings and propellers, a 1.8 kg space helicopter carried us even closer to becoming a true interplanetary species. The ability to fly — really fly — a vehicle semi-autonomously from hundreds of millions of kilometers away has a huge impact on our ability to plan space missions — not just to Mars, but to Venus, Europa, Titan and anywhere a small, highly mobile craft would be an asset (i.e. basically everywhere). The deep-space, remote piloting skills we're learning don't stop at helicopters, either. They apply to drones, submarines and even entire launch vehicles.

The proposed Mars sample return mission, slated to be launched in 2026, will feature many more new and as-yet untested technologies. Chief among those will be another first flight: this time, the Mars Ascent Vehicle (MAV). Using solid propulsion instead of solar power, the MAV will bring the Martian soil collected by Perseverance back to Earth. Planetary scientists will interrogate those samples for the possibility of life on Mars, so we can protect ourselves from it and it from us.

They'll use what they find to develop methods of water extraction and plant growth to see what sort of future we can create from the building blocks of another world. With five flights over 30 days, Ingenuity proved that bold, transformative technologies can be built for environments far, far away — and in spite of never having been there before, can hit the ground running.

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