What Flight 50 Means for the Ingenuity Mars Helicopter

JPL's Ingenuity helicopter is preparing for the 50th flight of its 5-flight mission to Mars. Flight 49, which took place last weekend, was its fastest and highest yet-the little helicopter flew 282 meters at an altitude of 16 meters, reaching a top speed of 6.50 meters per second. Not a bad performance for a tech demo that was supposed to be terminated two years ago.

From here, things are only going to get more difficult for Ingenuity. As the Perseverance rover continues its climb up Jezero crater's ancient river delta, Ingenuity is trying its best to scout ahead. But, the winding hills and valleys make it difficult for the helicopter to communicate with the rover, and through the rover, to its team back on Earth. And there isn't a lot of time or room to spare, because Ingenuity isn't allowed to fly too close to Perseverance, meaning that if the rover ever catches up to the helicopter, the helicopter may have to be left behind for the rover's own safety. This high-stakes race between the helicopter scout and the science rover will continue for kilometers.

Two years in, 10 kilometers flown, and we're well over an hour now in the skies of Mars."
-Teddy Tzanetos, NASA

For the Ingenuity team, this new mode of operation was both a challenge and an opportunity. This was nothing new for folks who have managed to keep this 30-day technology demo alive and healthy and productive for years, all from a couple hundred million kilometers away. IEEE Spectrum spoke with Ingenuity Team Lead Teddy Tzanetos at JPL last week about whether flying on Mars is ever routine, how they upgraded Ingenuity for its extended mission, and what the helicopter's success means for the future of airborne exploration and science on Mars.

IEEE Spectrum: Is 50 flights on Mars a milestone for you folks, or are things routine enough now that you're looking at it as just another flight?

Teddy Tzanetos: It's hugely meaningful. We'll come back to the routine question in a second, but it's very meaningful for all of us. When we hit 10 and then 25 it was big, but 50 is a pretty serious number now that we're 10X our initial flight count. Two years in, 10 kilometers flown, and we're well over an hour now in the skies of Mars. So hitting flight 50, it's a big thing-we're probably going to set up a happy hour and have a big party for the team.

Can you talk about some of the new challenges that Ingenuity has been facing as it makes its way up Jezero Crater's river delta along with the Perseverance rover?

Tzanetos: The core of the challenge here is that the paradigm has changed. When you look at the first year of Ingenuity's extended operations, we were still in the Three Forks area, where the ground was flat. We could get line of sight from the helicopter to the rover from hundreds and hundreds of meters away. Our longest link that we established was 1.2 kilometers-a massive distance.

And then we started to realize that the rover was going to enter the river delta in like six months. It's going to start climbing up through dozens and dozens of meters of elevation change and passing through ravines, and that's going to start presenting a telecom issue for us. We knew that it couldn't be business as usual anymore-if we still wanted to keep this helicopter mission going, not only did we need to change the way we were operating, but we also had to change the helicopter itself.

We owe it to everyone who worked on Ingenuity and everyone who will continue to work on rotorcraft on Mars to try and get everything out of this little spacecraft that we can."
-Teddy Tzanetos, NASA

This realization culminated in the most challenging flight software upgrade we've ever done with Ingenuity, which happened last December. We went into the guts of our algorithms and added two new features. One was the ability to detect and react to landing hazards from the air, which involved handing over a little bit of autonomy back to Ingenuity, with the ability to tell it, Fly to your terminal waypoint and try and land where we think is good, based off of orbital imagery. But if you have better information from your images than what we humans had here on Earth, and you see a hazard, pick a safer site and land there instead." So that's one huge change in what's happening now. And we need that at the river delta because we're no longer flying in a parking lot-besides the challenge of the elevation change, the terrain is different as well, with more, larger rocks that Ingenuity needs to avoid.

The second feature that we added was to include information about the terrain to Ingenuity's navigation filter. When we designed Ingenuity, we assumed we were only going to be deployed on the flat terrain of Three Forks. Therefore, any change in the laser altimeter measurement we could trust to be a real change in the motion of the helicopter, or we could at least filter that into our altitude data. But that's no longer the case. Now, as Ingenuity flies, if the altimeter sees a big decrease in elevation, that could be because the ground is rising to meet us rather than because we're moving down. So since December, we've been telling Ingenuity about the elevation profile across its intended flight so that it knows what the ground is doing underneath it.

Now that both the rover and the helicopter have begun the river delta climb, we're also paying very close attention to our telecom link budget maps. You can imagine every hill or rise that could occlude the line of sight between the helicopter antenna and the rover antenna will have a big impact on your telecom link, and we have wonderful maps from orbit where we can pick a potential landing point and propagate our radio link budget calculation across that point.

We're trying to plan these flights as aggressively as we can to make sure that we stay ahead of Perseverance. We don't want to run the risk of having a situation where the rover may need to wait for Ingenuity-that's not a good thing for anybody. But we also want to provide value for the rover by scouting ahead, and what we hope to do on Flight 50 is to get some imagery of Belva crater, which is this beautiful massive crater to the north of where Ingenuity currently is. We're going to get perspectives that the rover team would not be able to provide for the science team, and it's really exciting for us when there are these moments that are uniquely driven by Ingenuity's capability. We want to go after those, because we want to provide that value while she's still healthy. While we still can. We owe it to everyone who worked on Ingenuity and everyone who will continue to work on rotorcraft on Mars to try and get everything out of this little spacecraft that we can.

One of the best hallmarks of technology success is when you don't realize it, or when it becomes boring. That means the technology is working, and that's a wonderful feeling."
-Teddy Tzanetos, NASA

At one point, NASA was very clear that Ingenuity's mission would come to an end so that Perseverance could move on to focus on its primary mission. But obviously, Ingenuity is still flying, and still keeping up with the rover. Not only that, but we've heard from a rover driver how valuable it is to have Ingenuity scouting ahead. With that in mind, as Ingenuity navigates this challenging terrain, will there be any flexibility if something doesn't go quite right, or will Perseverance just leave the helicopter behind?

Tzanetos: We have to look at the big picture. The most important thing at this point is for Perseverance to collect samples and do science. If you look at everything that needs to be done across all of the rover's science payloads, every sol [Martian day] is precious. And the helicopter team understands that.

We're doing our best to become more efficient, and I think that's a big win that we don't celebrate enough on the Ingenuity team internally-how much more efficient we are today compared to where we were two years ago. Earlier, you mentioned flying becoming routine. I think the team has succeeded in doing that, and I'm extremely proud of that accomplishment. One of the best hallmarks of technology success is when you don't realize it, or when it becomes boring. That means the technology is working, and that's a wonderful feeling.

There's what's called a tactical window that we have between the downlink of the last sol's activity and when we need to uplink activity for the next sol, which is anywhere from five to 10 hours. A certain cadence of activities have to take place during that window, and we need to pass certain checkpoints to get our data uploaded and radiated through the Deep Space Network in time. We've worked very, very hard to minimize our footprint on that timeline, while also being reactive so that we can move quickly on any last-minute changes that the rover team needs us to accommodate. We have to get in, fly, and get out.

Anomalies will happen. That's just the nature of Mars. But when those moments occur, the helicopter and rover teams back each other up. To be clear, no one on the helicopter team wants to cause a delay for the rover. We all want the rover to fulfill its mission, get its samples, and get the science done. If we have a serious anomaly, we'll have to take that one sol at a time. We're going to try as hard as we can to make sure we can keep pushing this little baby as far as we can while still accomplishing the core science mission.

NASA's Ingenuity Mars Helicopter takes off and lands in this video captured on April 19, 2021, by Mastcam-Z, an imager aboard NASA's Perseverance Mars rover. This video features only the moments of takeoff and the landing-and not footage of the helicopter hovering for about 30 seconds.NASA/JPL-Caltech/ASU/MSSS

How do you balance risk to the helicopter against exploration and science goals, or trying new things like pushing Ingenuity's flight envelope?

Tzanetos: That's the fun part! There's no instruction manual. The way we do it is we have a phone call with the core people on the team, and everyone just shares their opinions. The highest priority for us is getting some good scouting imagery for the scientists and rover drivers-we jump at those opportunities. If we're flying through a piece of terrain that isn't particularly interesting, that's when we start looking at the flight envelope developments, right? With flight 49, we're going higher than we ever had before and flying faster than we ever have before. That's not a request from the science community or the rover planners; that's coming from our own internal team where we're trying to release capability piece by piece as the flights go on, because every time we get that win, it's a win for the sample recovery helicopters. So there's that ever-present pressure to push harder, push faster, push higher. And let's also get some wonderful scouting data along the way when we can.

What have you learned about flying helicopters on Mars from 50 flights, that you would have no idea about if you'd been able to do just 5 flights?

Tzanetos: Tons of things. Since I just talked about flying faster and flying higher, and we've now legitimately expanded Ingenuity's flight envelope. There's the lifetime argument, which is obvious-this design has lasted much longer than anyone could have expected, even just in terms of parts and workmanship. Each one of Ingenuity's nearly a thousand solder joints were soldered by technicians at JPL who have the most blessed, precise hands. We'd designed Ingenuity to fly in springtime on Mars, but during the Martian winter, for more than 200 sols the temperature cycled between 20C and -90C and back again. Eventually, it got so cold that Ingenuity's battery would die every night, the heater would stop running, and everything would freeze. That was a massive curveball that we had to contend with, but because of the workmanship of those people, Ingenuity was able to survive.

We now have a stake in the ground to say, Off-the-shelf works, we can trust these things.'"
-Teddy Tzanetos, NASA

Also, dust. We knew that dust would settle on Ingenuity's solar panel, but we've shown that through the process of flying, there's some sort of effect that's helping us to keep our panel clean. It's difficult to put a finger on exactly what it is-maybe the vibration of flight, or the downwash of air passing over the solar panel and into the rotors, or the oncoming air as we move forward. And it wasn't just the dust on the panels; we also got dust in our actuators. Last year, Ingenuity weathered a big dust storm, and afterwards when we tried checking our control surfaces, things did not look good. The motor currents were way too high, and we were left scratching our heads, trying to figure out what to do. We didn't have dust boots around the rotor system simply because we had thought, we're only going to be operating for 30 days, we don't need them."

Our partners at AeroVironment [who worked with JPL on the Mars helicopter design] had one of the swash plate mechanisms lying around, so they spoke to our geologists to figure out what kinds of dust particles might have gotten blown into the swash plate on Mars. We sent them some simulated Mars dust, and they threw it at the swash plate, and then did an experiment to figure out how many times they needed to cycle it before it started to operate properly. Seven cycles got most of the dust out, so we tried that on Mars, and it worked. So now we have a new tool in our tool belt: we know how to clean ourselves. That's huge. And we wouldn't have figured out any of these things had we not gone past five flights.

Looking at the Mars sample return helicopters, how much of their design has been made possible by the fact that Ingenuity has been able to fly this long, and answer these questions that you might not have even thought to ask?

The entire design. I don't think we'd be talking about sample recovery helicopters if Ingenuity didn't fly, period, and if it hasn't survived for as long as it has. You have to keep in mind, Ingenuity is a tech demo. These sample recovery helicopters are a real part of the mission now. If Perseverance has an anomaly in the next decade, these helicopters are the backup-they have to work. And I'm sure that Ingenuity's two years of extended operations provided the evidence necessary to even start talking about the sample recovery helicopters. Otherwise, it would be crazy to think, let's go from tech demo to part of a class B mission within a year."

That's amazing. It must feel really good for you folks to have completely changed what the sample return mission looks like because of how successful Ingenuity has been.

Absolutely. I personally thought to myself, Hey, this is great, Ingenuity has been doing a great job, and this will be wonderful data for the next time we send a rotorcraft to Mars." Which I thought was going to be like ten years later-I thought that Mars sample return would happen with a rover, and then maybe after that, we could throw some helicopters on Mars, maybe a hexacopter with some science payloads on it. Never in my wildest dreams did I ever think, while we're still flying Ingenuity, that we'd be designing the next helicopter mission based on Ingenuity to go to Mars.

More broadly, how has Ingenuity influenced NASA's approach to robotics?

From a robotics perspective, I hope one of the long-lasting impacts of Ingenuity is the adoption of commercial off-the-shelf technology into more NASA missions, and other non-NASA missions into space. This was the first time we flew a cell phone processor, not because we loved the idea about using a part that wasn't radiation hardened, but because we were forced to. We needed a high-throughput processor, and the only way to do that and be lightweight enough was to use a cell phone chip. There was a lot of concern about that-we did some initial testing, but given that we were a tech demo, which means high-risk, high reward, we could only do so much. And here we are, two years later, with this Snapdragon Qualcomm processor that's been running for two years on the surface of Mars, not to mention all the other components like the IMU, the camera, the battery, the solar panels. I think that's one of the unsung victories of Ingenuity. We now have a stake in the ground to say, Off-the-shelf works, we can trust these things." And we can make a stronger argument for the next mission to really enable your engineers and your scientists to have much more technology on board than anything else we've sent into space.

Ingenuity will attempt Flight 50 any time now, with the goal of traveling 300 meters to the other side of a ridge. The landing site may make it difficult to know whether the flight was successful until Perseverance catches up a bit, but we hope to hear the good news within the next few days.