A small helicopter opened a new chapter of space exploration this morning when it lifted off the surface of Mars, marking humankind’s first powered flight on another planet. The 19-inch-tall chopper called Ingenuity kicked up a little rusty red dust as it lifted about 10 feet off the ground, hovered in place, turned slightly, and slowly touched back down. The flight lasted only about 40 seconds, but it represents one of history's most audacious engineering feats.
“A lot of people thought it was not possible to fly at Mars,” says MiMi Aung, the project manager of Ingenuity at NASA’s Jet Propulsion Laboratory (JPL). “There is so little air.”
The wispy atmosphere at Mars’s surface is equivalent to an altitude of about 100,000 feet on Earth—much higher than even the most capable helicopters can fly. The highest helicopter flight in history occurred in 1972, when French aviator Jean Boulet flew to 40,820 feet at an airbase northwest of Marseille.
The Martian helicopter experienced a setback on April 9, when the craft’s onboard computer shut down early during a test to spin the two rotors at high speed. After reviewing the data, the team at JPL adjusted the command sequence that is sent to the spacecraft to start the rotors, allowing them to complete the high-speed spin test on April 16. And at 3:34 a.m. ET on April 19—in the midafternoon local time on Mars—the helicopter successfully completed its first flight.
In the future, similar flying machines could scout new areas for rovers and astronauts, collect samples from hard-to-reach places, and traverse dozens of miles over the span of days to provide a new perspective of the Martian landscape.
Only four pounds on Earth, which is 1.5 pounds on Mars, Ingenuity has been operating on its own since April 3, when the car-size Perseverance rover deposited it in a flat area clear of debris. A small solar panel tuned for the relatively low levels of sunlight charges the helicopter’s batteries during the day, and electric heaters keep the vehicle warm during nights that can plunge to -130°F.
To achieve its short foray into the Martian atmosphere, the little rotorcraft relied on a tiny processor like those in cellphones, autonomous navigation technologies from self-driving cars, eight lithium-ion batteries, and lightweight composite materials. Its two carbon-fiber rotors, which span four feet from tip to tip, had to spin up to about 2,500 rotations per minute—roughly five times the speed of a normal helicopter rotor—to lift off the ground.
Now that Ingenuity has taken its first flight, the team can plan a second, which will likely perform the same hovering maneuver but a bit higher and for a bit longer. They are about halfway through a 31-day window to test the helicopter, using Perseverance as a communication relay to Earth before the rover drives off to begin its search for past life on Mars. Up to five flights are planned, building up to a trip down a 50-foot-long flight zone and back.
“It boggles your mind,” says Thomas Zurbuchen, NASA’s associate administrator for science, “flying for the first time in history a helicopter on Mars.”
“Don’t tell me anymore it’s not possible”
In 2015, the Mars helicopter team was preparing a presentation for NASA headquarters to ask for funding to build a prototype known as a “risk reduction vehicle.” They had already flown—and crashed—a one-third scale model in a vacuum chamber at JPL. For these tests, the chamber was pumped down to low pressure and filled with carbon dioxide to replicate the atmosphere of Mars.
As Aung was preparing for the presentation, something clicked. Humans could not “joystick” this helicopter directly because it would fly millions of miles away on another planet, and there is a communication delay of about 15 minutes between Earth and Mars. The vehicle would have to fly itself, which meant developing a lightweight computer that could rapidly assess the craft’s position and adjust the rotors accordingly.
“It comes down to how quickly the vehicle has to respond to perturbation,” Aung says. The helicopter could face wind gusts up to 22 miles an hour, along with changes in pressure that make it difficult to maintain stable flight in the thin air.
But it was a problem that Aung knew her team could solve. The one-third scale model had already demonstrated that lift was possible on Mars, and Aung, an electrical engineer who specializes in autonomous technologies, knew that the electronics of the 21st century had come far enough to build a small computer that could fly the helicopter.
“After that moment, it was all like, Don’t tell me anymore it’s not possible.” Aung says. “What’s in our way?”
Convincing NASA headquarters took a bit more than a presentation, though. The agency funded the prototype, which in 2016 underwent a series of tests. The first was simply to hold the vehicle in place inside the vacuum chamber, spin up its rotors, and measure the torque and lift to make sure the math matched the team’s models.
When the prototype was held in place, though, the forces from its rotors could interact with the ground and the test stand. That interaction produced vibrations that could affect the vehicle’s control systems and cause it to rip itself to pieces—the same effect that has been known to cause full-size helicopters to break apart while trying to take off.
“We had everything to lose,” Aung says. “If we broke apart like that at any time, we could have been cancelled.” Even if the program continued, a failed test at this point could have prevented the team from completing the helicopter in time to fly in the belly of the rover, which was scheduled to launch during a planetary alignment of Earth and Mars in July 2020. “Perseverance was going with or without us.”
The test worked, and the math checked out. The prototype was able to fly, hover, turn, and land in the vacuum chamber, demonstrating that not just lift, but autonomously controlled flight was possible on Mars.
“We got the aerodynamics challenge handled,” Bob Balaram, chief engineer of Ingenuity, remembers thinking at the time. “Now we got to build the rest of the spacecraft.”
Carbon fiber and fishing line
Mass is the enemy of flight, particularly on Mars. Every extra gram on the Ingenuity helicopter increased the amount of lift and thrust the rotors had to produce.
“You need to be very light,” says Teddy Tzanetos, the deputy operations lead for the helicopter. “Ingenuity is 1.8 kilograms, and it was an engineering feat to get everything we needed jam-packed into those 1.8 kilograms.”
Much of the helicopter, including its rotors, landing legs, and fuselage (a small box to hold the electronics), was built by AeroVironment, an aerospace contractor based in Simi Valley, California. The company builds military drones as well as experimental aircraft for NASA, such as the solar-powered flying wing Helios —which, unlike helicopters, has flown up to about 100,000 feet.
Ingenuity’s two carbon fiber rotors spin in opposite directions, canceling out the torque that would turn the helicopter if it had only one rotor. (On a conventional helicopter, a tail rotor is used to counteract the torque from the main rotor.) These rotors not only had to be large and exceptionally light, but also very stiff to prevent them from flopping around and disrupting the airflow.
The landing legs, also made of carbon fiber, presented another “interesting challenge,” says AeroVironment senior aeromechanical engineer Ben Pipenberg, who has been working on the Mars helicopter since the start of the program.
“The gravity on Mars is about one third of what it is here on Earth, and you have to be pretty careful that, when you land, you don’t really bounce,” he says. The legs also had to fold up so Ingenuity could fit snugly under the belly of Perseverance for the flight to Mars. “That would be an unfortunate way for the whole thing to fail—either the legs don’t deploy when we’re trying to get off the rover, or after landing it bounces and it flips over.”
Mars’s light gravity presented other challenges as well—namely that it cannot be perfectly simulated on Earth. A full, exact copy of the Ingenuity helicopter was tested in JPL’s vacuum chamber in 2018. The team could drain the atmospheric pressure and pump in the right gases to create the kind of air you find on Mars, but there is no way to adjust the gravity. To compensate, the team used what they called a gravity offload system.
“You can think of it as a fishing reel with some fishing line attached to it, a motor, and a very precise torque sensor,” Tzanetos says. The line was attached to the helicopter with a “very secure knot tied there—several knots, as backup,” and the precision reel pulled up on the helicopter to mimic the low gravity of Mars.
A second complete prototype went through environmental testing, proving that it could survive the vibrations of a rocket launch and the frigid temperatures of the Martian night. By early 2019, the team had built the actual helicopter that would fly to Mars, testing its flight capabilities twice in the vacuum chamber.
“The next time we fly, we fly on Mars,” Aung said after the tests.
“Hundreds of helicopters going around Mars”
Now that Ingenuity has conducted its first flight, humankind is one step closer to making flight a regular part of planetary exploration. “My dream is that aerial vehicles become the norm for exploring space,” Aung says.
The team thinks of Ingenuity as the aircraft equivalent of the Sojourner rover, which became the first vehicle to drive on Mars in 1997. Like Ingenuity, Sojourner was carried to Mars by a larger science spacecraft, the Mars Pathfinder lander.
“The science community didn’t like it,” Zurbuchen says of Sojourner. “They said, Hey we can do everything that we want to do on landers.”
Less than 25 years later, NASA has not one but two car-size rovers exploring the surface of Mars. Both the Curiosity rover, which landed in 2012, and Perseverance are unraveling the planet’s unique geologic history and seeking out signs of past life. Perseverance is also preparing to collect the first Martian rock sample that will be returned to Earth, which could be crucial to finally learning if Mars was ever inhabited.
Future helicopters could serve as scouts for the rovers and eventually for humans, and they could explore areas where rovers and people simply cannot go—deep canyons such as Valles Marineris, which stretches more than 2,500 miles, or the steep slopes of Olympus Mons, which is about two and a half times the height of Mount Everest.
“I could envision hundreds of helicopters going around Mars,” says Charles Elachi, the director of JPL from 2001 to 2016 who oversaw the start of the Mars helicopter program. “I can envision one of the future missions where we have a lander, we have dozens of helicopters on it, and these helicopters will fly and cover a whole large region and bring samples back.”
Teams at JPL are already thinking about larger helicopters, Elachi says, which could carry heavier payloads and survey wider areas. “The rovers now can go a number of miles in a year, but a helicopter could go a number of miles in one day,” he says. “The potential payoff is huge.”
For now, the team will be poring over the data from the first flight to plan Ingenuity’s additional runs—and perhaps taking some time to think about the future of flying machines on other worlds. “Everywhere we can fly, where there is atmosphere,” Aung says, “it should become a norm that we send rotorcraft to fly there.”