Picture the scene: A small drone the size of a suitcase descends into a dark Martian crevasse—perhaps a lava tube that was formed billions of years ago by volcanic activity on the Red Planet. The drone illuminates its surroundings, recording views never seen before by human eyes as its suite of instruments seeks out signs of past or present alien biology. Finally, its reconnaissance complete, the drone flies back to a landing zone on the surface to transmit invaluable data back to Earth. After soaking up the Martian sunlight to recharge its batteries, it continues its explorations of terrain inaccessible to any other machine.
Far from being some starry-eyed flight of fancy, such a mission could soon become a reality thanks to the resounding success of NASA’s Ingenuity rotorcraft, sometimes referred to as a helicopter or drone—a technology demonstration that has taken place on Mars over the past few weeks. Carried to the planet by NASA’s Perseverance rover, which touched down on February 18, this small machine, weighing a paltry 1.8 kilograms, was the first attempt at controlled aerial flight on another world—more than a century after that same feat was mastered on Earth by the Wright brothers. “We can now say that human beings have flown a rover craft on another planet,” said MiMi Aung, project manager of Ingenuity at NASA’s Jet Propulsion Laboratory (JPL), in a speech to her team from mission control following the successful first flight on April 19. “We together now have our Wright brothers moment.”
With Ingenuity’s success, space scientists are contemplating the roles that aerial vehicles might play in our exploration of the solar system. Few worlds possess the necessary conditions for powered aerodynamic flight, namely an atmosphere and rocky surface like that of Mars or Earth, but there are two others of note. “The general technique of aerial flight is applicable to places like [Saturn’s moon] Titan and Venus,” said Bob Balaram, chief engineer of the Ingenuity team, in a press briefing following the first flight. The latter’s exceedingly high temperatures and pressures pose some unique challenges: “Near the surface it’s closer to swimming,” says Paul Byrne, a planetary scientist at North Carolina State University. Yet flight there is not impossible, which was proved by the Soviet Union’s Vega balloons in 1985. With a rotorcraft called Dragonfly already being developed to visit Titan in the next decade and work continuing on a conceptual successor to Ingenuity, the future looks bright for aerial exploration of alien worlds. “This could be the start of a new era,” Byrne says.
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Ingenuity’s first flight, from a strip of land on Mars’s Jezero Crater that is now dubbed “Wright Brothers Field,” was modest but impressive: the planet’s atmosphere is incredibly thin, just 1 percent that of Earth, so generating lift is exceedingly difficult. “It’s similar to Earth at about 100,000 feet above the ground,” says Ben Pipenberg, an engineer at defense contractor AeroVironment, who helped build Ingenuity. With Perseverance watching from a safe distance, Ingenuity spun its blades at 2,500 revolutions per minute (rpm) to rise to an altitude of three meters, where it hovered for 30 seconds and performed a 96-degree rotation. Then it descended back to the ground, landing on its four legs, with a total flight time of 39.1 seconds.
From there, things got more complex. The second flight lasted 51.9 seconds, reaching a height of five meters. And it included a lateral movement of about two meters—something not attempted in the confines of the test chamber on Earth where Ingenuity first flew in simulated Mars conditions. Flight three saw Ingenuity travel half the length of a football field, some 50 meters, reaching a top speed of just more than two meters per second. The fourth flight on April 30 pushed the envelope once again, with Ingenuity remaining airborne for nearly two minutes—117 seconds—and reaching an impressive speed of 3.5 meters per second as it scouted a potential future landing zone over a round tripof more than 260 meters. Ingenuity’s fifth flight—completed on May 7 and initially planned to be its last—sent it on a one-way trip to the new landing zone to await the arrival of Perseverance, its mother ship.
Now this wildly successful technology demonstration drone is entering a new phase of its mission—a second month-long set of more ambitious operational tests. These tests are meant to show how airborne drones “could play an active role in a future rover science mission,” says Dave Lavery, program executive for Ingenuity at NASA headquarters in Washington, D.C. Although Ingenuity will not directly support the science objectives of Perseverance—namely looking for signs of past life on Mars—it will help scout out the rover’s potential route ahead as the team plans the optimal path through Jezero Crater’s riches. And the craft may photograph nearby locations that are not in the Perseverance’s planned path. There is even a slim chance that Ingenuity could support the rover’s later mission, too—if the craft survives. “We might see about potentially looking over the rim of the crater,” Lavery says.
Much has been made of how these vehicles might one day support human missions, acting as reconnaissance drones for humans to scout out regions of interest near a landing site or carrying tools between locations. In the near-term, prospects of more exciting robotic science are on the horizon—perhaps in the same way that the Sojourner rover in 1997, itself a prototype of wheeled exploration and part of NASA’s Pathfinder mission, paved the way for its successors Spirit, Opportunity, Curiosity and now Perseverance. “I do think we’re going to see some flying vehicles in the future,” says Michael Meyer, lead scientist of NASA’s Mars Exploration Program at the agency’s headquarters. “It will now be part of our portfolio of methods that we use for exploration. There are things you can do with a helicopter that you can’t do with other platforms.”
Examples could include exploring the aforementioned lava tubes or perhaps approaching crater walls—too high and steep for a rover to scale—where a helicopter could take images and perform some up-close analysis as well. Another example could be studying recurring slope lineae, dark flows on Mars that have arguably been linked to liquid water flowing on the surface. Perversely, it is this possibility of water—and the accompanying risk of contamination with bacteria imported from Earth—that essentially prohibits anyone or anything from setting foot (or wheel) there to seek out signs of native Martian life. But a hovering drone could look without touching, offering a novel route of exploration. “A rotorcraft would give us the ability to go and look up close at something that we would otherwise deem not suitable for a rover,” Byrne says, “either because of planetary protection issues or because it’s too dangerous.”
One concept for a possible aerial vehicle beyond Ingenuity is already being investigated. Known as the Mars Science Helicopter, this six-bladed hexacopter would weigh nearly 30 kilograms. And it would be equipped with several kilograms worth of instruments to analyze different regions of the Martian surface and would have the ability to fly for minutes at a time over several kilometers. “We’re trying to learn from Ingenuity and ask ourselves, ‘What could we accomplish if we push it further?’” says Theodore Tzanetos of JPL, who is part of the Mars Science Helicopter concept team. The science such traits would afford would be tremendous, bringing large swathes of the Martian surface suddenly within reach. The current distance record on Mars is held by NASA’s Opportunity rover, which traveled more than 42 kilometers in a little more than 11 years. A helicopter could achieve the same feat in weeks.
Other ideas involve using rotorcraft to perform surveys of exposed water ice on regions of the Martian surface inaccessible to rovers. Drones could dive into Martian valleys such as the two-kilometer-deep Mawrth Vallis, looking for evidence of clays linked to astrobiology, or perhaps use instruments to probe the lower reaches of the Martian atmosphere, says Shannah Withrow-Maser, Mars Science Helicopter vehicle systems lead at NASA’s Ames Research Center. And this could all be done either alongside a bigger rover mission or as more cost-effective and much lighter standalone missions, enabling more widespread exploration of a variety of Martian locales. “I personally would love that,” Withrow-Maser says.
Elsewhere in the solar system, flight options are more limited. One could imagine a rotorcraft in the atmosphere of one of the gas giants such as Jupiter or Saturn, where theoretically flight would be possible. But actually getting there would be an issue. “The problem, of course, is slowing down and the amount of energy that would take” on arrival at the planet, Byrne says. But Titan, Saturn’s intriguing moon with an incredibly thick atmosphere and lakes of hydrocarbons on its surface, is a very tantalizing prospect. In 2019 NASA selected a mission that would attempt to deploy the rotorcraft Dragonfly on the moon. Dragonfly is intended to launch as early as 2026 and arrive in 2034, andits team has been watching Ingenuity’s successes very closely.
“We’ve been following with great interest,” says Elizabeth Turtle, lead of the Dragonfly mission at the Johns Hopkins University Applied Physics Laboratory. “We’re very anxious to see what lessons we can take forward to Dragonfly.” Like Ingenuity, Dragonfly will be flying autonomously, so it will make use of similar onboard image processing capabilities to decide where to land on the Titanian surface. (Ingenuity performs terrain mapping by taking 30 images of the ground per second.) But Dragonfly is a mammoth compared to Ingenuity, weighing nearly half a metric ton and powered by plutonium. And it is a standalone mission rather than a ride along like Ingenuity. “It’s like Perseverance [in scale], except we fly instead of drive across the surface,” Turtle says.
Despite Titan being a much more distant alien world than Mars—with a light travel time from Earth of about an hour, compared with up to about 20 minutes for the Red Planet—flight is relatively easier there. Titan’s gravity is only 14 percent that of Earth and much less than that of Mars, while the moon’s much thicker atmosphere makes generating lift a comparative breeze. “A person could put wings on and soar over Titan’s surface,” Turtle says. Winds on Titan are also much slower, barely more than a kilometer an hour versus tens of kilometers an hour on Mars. And whereas Ingenuity’s blades require 2,500 rpm to lift its fragile 1.8-kg body off the surface, Dragonfly’s half-metric-tonbulk can be lofted just by its rotors spinning at 800 rpm. Titan’s major challenge is its temperature, which averages only about –180 degrees Celsius—hence the need for a long-lived, heat-generating plutonium power source. “It’s certainly cold,” Turtle says. “It’s a nontrivial challenge.”
With Dragonfly on the horizon, and perhaps future missions such as the Mars Science Helicopter in the works, there is plenty to be excited about beyond Ingenuity. This little machine has, for the first time, proved flight on alien worlds is possible—from both a physical and logistical point of view. Now this exciting new era of discovery awaits, and while only a handful of worlds afford the right conditions for this method of exploration, the sky is very much the limit for the science that could be performed by aerial vehicles in these alien skies. “There are things to be sorted out,” Meyer says. “Then I think we’re going to start seeing some new and improved helicopter platforms that can actually carry tempting payloads.”