If it flew, and that was very much a big if, the little helicopter would take to the skies on Mars five times — max — over a period of 31 days.

But over the past year, the plucky little helicopter known as Ingenuity has taken to the Martian skies 28 times, far exceeding expectations and giving scientists a new vantage point on the Red Planet. Over the past 13 months, it has stayed aloft in total for nearly an hour, traveling nearly 4.3 miles, with a max speed of 12.3 mph and reaching a top altitude of 39 feet.

It’s traversed craters, taken photos of regions that would be hard to reach on the ground, and served as a surprisingly resilient scout that has adapted to the changing Martian atmosphere and survived its harsh dust storms and frigid nights.

Now the engineers and scientists at NASA’s Jet Propulsion Laboratory are worried that their four-pound, solar-powered drone on Mars, may be nearing the end of its life.

Winter is setting in on Mars. The dust is kicking up, coating Ingenuity’s solar panels and preventing it from fully charging its six lithium-ion batteries. This month, for the first time since it landed on Mars more than a year ago, Ingenuity missed a planned communications session with Perseverance, the Mars rover that it relies on to send data and receive commands from Earth.

Will a dust-coated Ingenuity survive a Martian winter where temperatures routinely plunge below minus-100 degrees Fahrenheit? And if it doesn’t, how should the world remember the little helicopter that cost $80 million to develop and more than five years to design and build? Those closest to the project say that as time winds down for Ingenuity, it’s hard to overstate its achievements.

“The helicopter has just far exceeded those initial expectations,“ Lori Glaze, the director of NASA’s planetary science division, told The Washington Post.

Given the thinness of the Martian atmosphere, the scientists and engineers who worked on the Ingenuity weren’t sure the experiment would succeed at all. Thomas Zurbuchen, the associate administrator of NASA’s science mission directorate, said at the time that it was an endeavor that forced NASA to find the “right line between crazy and innovative.”

So when the first flight, on April 19, 2021, was a success, NASA heralded it as a Wright Brothers moment. As a tribute, Ingenuity had a postage-size bit of fabric from the brothers’ aircraft, known as the Flyer, attached to a cable under the solar panel.

Ingenuity flew to Mars tethered to the underbelly of the Perseverance Rover, the star of NASA’s most recent Mars mission. After traveling some 300 million miles over seven months, Perseverance touched down in a dramatic landing in February 2021 under a parachute with a secret code snuck inside that read, “Dare Mighty Things.”

The rover, the size of an SUV, landed at an area of Mars known as Jezero crater, which once held water and could yield clues to the history of the planet and whether life existed there. The rover is gathering rocks and soil samples that NASA hopes will be returned to Earth in a future mission, as well as using its seven instruments to conduct science experiments and test new technologies.

Ingenuity was something of an add-on, a technology demonstration that could prove useful for future missions and allow the space agency’s scientists to explore more of the Martian landscape than they could by land alone.

But flying an autonomous drone on Mars would be extremely difficult. The atmosphere there is just 1 percent the density of Earth’s, so to generate lift, the helicopter’s four-feet-wide blades would have to spin incredibly fast — 2,500 rotations per minute.

“We built it as an experiment,” Glaze said. “So it didn’t necessarily have the flight-qualified parts that we use on the big missions like Perseverance.” Some, such as components from smartphones, were even bought off-the-shelf, so “there were chances that they might not perform in the environment as we expected. And so there was a risk that it wasn’t going to work.”

As Ingenuity kept flying, controllers on the ground started to realize their little project could accomplish big things. Before its fifth flight, they wrote in a blog post that “our helicopter is even more robust than we had hoped. The power system that we fretted over for years is providing more than enough energy to keep our heaters going at night and to fly during the day. The off-the-shelf components for our guidance and navigation systems are also doing great, as is our rotor system. You name it, and it’s doing just fine or better.”

As it continued to perform, the scientists at NASA became increasingly intrigued by the idea that maybe this helicopter could become an integral part of the mission.

“What happened was, and this is really key, after Ingenuity performed so well on those first five flights, the science team from Perseverance came to us and said, ‘You know what, we want this helicopter to keep operating to help us in our exploration and achieving our science goals,’ ” Glaze said.

So NASA decided to keep flying.

On its sixth flight, Ingenuity ran into trouble. The helicopter navigates with a camera that takes 30 pictures a second of the terrain below, each with a timestamp. An algorithm predicts what the camera should have seen at that particular moment based on images taken moments before. Then it calculates the difference between the predicted location and the actual location of features of the ground to correct its position, velocity and altitude.

But on this flight, the timestamps were off. As a result, Ingenuity looked like it was being flown by a drunk driver, “adjusting its velocity and tilting back and forth in an oscillating pattern,” NASA said in the blog.

Still, it was able to land safely within 16 feet of its target because of “the considerable effort that has gone into ensuring that the helicopter’s flight control system has ample ‘stability margin,’ ” NASA wrote. In other words: “In a very real sense, Ingenuity muscled through the situation.”

Flight 9, in July, was also a “nail biter,” as NASA wrote. Not just because Ingenuity broke records for flight duration and cruise speed, but because it flew over a crater, “an area called ‘Séítah’ that would be difficult to traverse with a ground vehicle like the Perseverance rover,” NASA wrote in its blog.

Because Ingenuity was designed as an experimental technology demonstration, engineers designed it to fly over largely flat terrain, more easily navigated by its onboard camera.

For this flight, however, Ingenuity would have to dip into the crater. That required it to reduce its speed and for engineers to tweak the navigation algorithm. The flight was a success, and Ingenuity was able to beam back colored photos of the region, including a location that some think “may record some of the deepest water environments in old Lake Jezero,” NASA wrote.

“Given the tight mission schedule, it’s possible that they will not be able to visit these rocks with the rover, so Ingenuity may offer the only opportunity to study these deposits in any detail.”

Since then, Ingenuity has soldiered on, overcoming obstacle after obstacle. At one point in September, it detected an engine problem during its preflight checkout “and did exactly what it was supposed to do: It canceled the flight.”

About a month later, the problem was fixed, and it returned to flight.

This image of the "backshell" that protected the Mars Perseverance rover and the parachute that helped it descend to the Martian surface was taken by the Ingenuity helicopter on April 19, 2020. (Courtesy of NASA/JPL-Cal-Tech)

This image of the “backshell” that protected the Mars Perseverance rover and the parachute that helped it descend to the Martian surface was taken by the Ingenuity helicopter 

In April, it made another discovery — flying over the parachute that slowed the rover for its Mars landing, it spotted the ruins of the shell that had protected the rover as it plunged toward the Martian surface. There was a pair of human-made objects, sitting on another planet, images that “just blew my mind,” Glaze said. In the past, NASA has been able to spot vehicles on the surface of Mars through an orbiting spacecraft far away. But here were pieces of hardware, close up, in such high-definition that the “Dare-Mighty-Things” encoded into the chute was visible through a thin coating of red Martian dust.

Then, 10 days later, on April 29, it took its last flight to date, No. 28, a quarter-of-a-mile jaunt that lasted two-and-a-half minutes. Now NASA wonders if that will be the last one.

The space agency thinks the helicopter’s inability to fully charge its batteries caused the helicopter to enter a low-power state. When it went dormant, the helicopter’s onboard clock reset, the way household clocks do after a power outage. So the next day, as the sun rose and began to charge the batteries, the helicopter was out of sync with the rover: “Essentially, when Ingenuity thought it was time to contact Perseverance, the rover’s base station wasn’t listening,” NASA wrote.

Then NASA did something extraordinary: Mission controllers commanded Perseverance to spend almost all of May 5 listening for the helicopter.

Finally, little Ingenuity phoned home.

The radio link, NASA said, “was stable,” the helicopter was healthy, and the battery was charging at 41 percent.

But, as NASA warned, “one radio communications session does not mean Ingenuity is out of the woods. The increased (light-reducing) dust in the air means charging the helicopter’s batteries to a level that would allow important components (like the clock and heaters) to remain energized through the night presents a significant challenge.”

Maybe Ingenuity will fly again. Maybe not.

“At this point, I can’t tell you what’s going to happen next,” Glaze said. “We’re still working on trying to find a way to fly it again. But Perseverance is the primary mission, so that we need to start setting our expectations appropriately.”