Episode 7: Flying with Ingenuity: the Mars Helicopter

(music)

Narrator: On a cold and wind-swept December day in 1903, in the Outer Banks of North Carolina, Orville and Wilbur Wright flew a powered, controlled aircraft for 12 seconds – the first such flight in the history of the world.

sound effect: aircraft flight

Narrator: More than a hundred years later, in April 2021, another world saw its first powered, controlled aircraft flight when NASA’s Ingenuity helicopter lifted up into the skies of Mars.

sound effect: helicopter rise

Narrator: Teddy Tzanetos, team lead for the Ingenuity mission, says the trickier nature of helicopters made the first flight on Mars even more perilous.

Teddy Tzanetos: Helicopters, in general, you're beating the air into submission from microsecond to microsecond. You have these tiny mechanical parts spinning at 2,500 revolutions per minute. Just take a moment and think about that. It's incredibly fast, which means that when things go wrong, they go wrong catastrophically.

sound effect: helicopter

[1:04] sound effect: whoosh

Teddy Tzanetos: If there's some imbalance in your rotor system, because something broke or fell off, your entire rotor system will explode. That's just true of all helicopters, right? All helicopters are precisely and carefully balanced pieces of art. And the fact that helicopters work to begin with is a testament to just engineering in general, and the beauty behind it.

Narrator: The Ingenuity helicopter was a technology demonstration meant to test whether it was possible to fly a rotorcraft on Mars. Ingenuity hitched a ride with NASA’s Mars 2020 mission, which sent the Perseverance rover to collect rock samples and look for evidence of ancient life. Ingenuity was strapped to the belly of Perseverance during the journey to Mars, and so had to be small enough to fit easily beneath the SUV-sized rover.

[1:54] Teddy Tzanetos: In terms of the dimensions, we have two counter-rotating coaxial rotor blades. The blades themselves are 1.2 meters from tip to tip. The electronics box, which is that silvery-colored box underneath the rotor blade system, that's where our computers are, that's where our battery resides. That's where all of our critical electronic components exist on Ingenuity. It's about the size of a tissue box. The legs come off from that central structure, and then, of course, our solar panel on top. It's a very compact design. On the surface, when we were fully deployed on the ground, Perseverance was able to clearly drive over Ingenuity.

Narrator: A fixed-wing aircraft, like the Wright Brothers Flyer and most planes on Earth today, wasn’t a practical design for the first flight on Mars.

Teddy Tzanetos: With most aircraft, you need a runway. But unless Perseverance was going to spend a couple of weeks paving a pebble-free runway for us, that was going to be a challenge.

Fixed-wing can be a lot more efficient, right? You can glide. You don't have to spend as much energy going from point A to point B. And if you have an anomaly in an aircraft and your motor kicks out, you could glide to safety. But you can't also just stop and hover. On the helicopter side, though, you spend a lot more energy just to hover, but now you can hover. And you can do precision landing precisely where you'd like to land.

[3:14] Narrator: Ingenuity was built to be as lightweight as possible, and yet the team added one extra item, under the helicopter’s solar panel, to provide an inspirational lift to their mission: a postage-stamp-sized bit of muslin fabric that had once covered a wing of the Wright Brothers’ 1903 aircraft. Members of the Wright family and Carillon Historical Park, home to the Wright Brothers National Museum in Dayton Ohio, provided the fabric.

This isn’t the first time Wright Brothers fabric has flown into space. Neil Armstrong brought some of the fabric, as well as a small piece of wood from the propeller, to the Moon in 1969. In 1998, nearly four decades after he became the first American to orbit Earth, John Glenn carried a swatch of the fabric when he flew on Space Shuttle Discovery. Here’s Bob Balaram, chief engineer of the Ingenuity mission.

[4:11] Bob Balaram: I was looking for an artifact to put on the helicopter, and we had considered perhaps putting an American penny – there's one where it has the Wright Brothers Flyer on one side. But then once we realized we could actually get to the real Wright Brothers fabric, we jumped on it.

So, it presented its own challenges. We had to sterilize it just right, and we had to make sure that it wouldn't contaminate the spacecraft. My contamination control and planetary protection engineers went to, I think, JoAnn Fabrics and got some samples so that they could try their heat-sterilization process on the samples first, before actually trying it on the piece of the real Wright Brothers fabric.

And this is the perfect thing to take, not only for me, but for the team as a whole. There's that connection to the past which is always inspiring.

[5:00] (intro music)

Narrator: Welcome to “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory. I’m Leslie Mullen, and in this fourth season of the podcast, we’re following in the tracks of rovers on Mars. This is episode seven: Flying with Ingenuity: the Mars Helicopter.

(music)

[5:57] Narrator: The Ingenuity helicopter is of course not a traditional rover: a remotely-controlled wheeled vehicle that roves on the ground. Ingenuity represents a new generation of robotic explorers, but, in a way, it’s repeating Mars rover history. Sojourner, the first Mars rover in 1997, was a technology demonstration added to the Pathfinder lander mission to test whether we could drive a vehicle on Mars from millions of miles away.

Tech demos are always risky, with high odds for failure, so not everyone at NASA was on board with either Ingenuity or Sojourner. Bob Balaram didn’t work directly on Sojourner like he did for Ingenuity, but as a member of JPL’s robotics group, he helped develop the necessary technology to make the first Mars rover possible.

Bob Balaram: In terms of being a first-of-a-kind system that had skeptics and needed to prove itself, and there wasn't quite the textbook as to how to do it, yeah, a lot of similarities. For its time, it had its challenges and naysayers. We had ours.

[7:07] We are in some ways a tougher problem. A helicopter is inherently an unstable vehicle so that it needs everything to work to keep it in the air. Sojourner had the advantage that if something had failed, it's at least not going to topple out of the sky and smash into pieces. So you could wait and call home if there was an issue.

Narrator: The success of the microwave-oven-sized Sojourner rover got people thinking about more audacious Mars exploration vehicles, including ones that could lift up into the thin, mostly carbon dioxide atmosphere.

Bob Balaram: The idea of a Mars helicopter was quite prevalent in certain communities back in the 1990s. The American Helicopter Society ran a student competition to say, “Take something like Pathfinder, but instead of carrying Sojourner, imagine that if you could carry a helicopter in the same technology, and get it to Mars, what would be your design?

[8:03] So around the same time was a talk being presented by Stanford professor Ilan Kroo, on some of the challenges of flying in a low-density atmosphere. And I attended his talk, and then got to thinking that flying a small thing on Earth – which is what he was trying to do, tiny little micro-helicopters – is the same as flying something larger on Mars, because that's the way the physics scales with the thinner atmosphere you have on Mars.

So Ilan and I wrote a proposal, and a small company in Simi Valley, called AeroVironment, was going to build us a small helicopter. Remember back in the 1990s, you didn't have all these drones that you could just buy, even to just play around with. And so, we were the three legs of that initial research proposal, but it didn't go anywhere.

We got actually favorable reviews from the review people, and we thought we would have had one year of funding. But it was also the year where NASA’s budget was under a lot of pressure. You know, that's always the background story at NASA. So they barely funded anything that year in this particular area. So my little proposal sat on a shelf for about 14 or 15 years.

[9:15] Narrator: In his more than 37 years of working at JPL, Bob is used to working on projects that are so far ahead of their time, they end up taking a lot of space on a shelf.

Bob Balaram: This is the robotics section at JPL where we basically do mobility in all kinds of environments, whether it's rovers or crawlers or walking machines or some flying machines, too. We're always looking to the future, to see what kinds of new mobility technology can we bring?

So along the way, I've worked on things like Mars balloons and Venus balloons. There was even a short-lived NASA idea to go and grab an asteroid and bring it back. Again, there is a (laughs) final report gathering dust somewhere on that one. The ratio of super cool missions to feasible missions is probably 10 to 1. But of those feasible ones, the ones that actually make it all the way to the end is probably like 100 to 1. We do let a thousand flowers bloom, but only one of them gets to the end point.

[10:17] Narrator: The seed of the Mars helicopter idea germinated while NASA was developing the Mars 2020 mission. The team designing the helicopter knew they couldn’t be a burden on the planned rover, but getting Perseverance to adopt Ingenuity wasn’t easy.

Bob Balaram: There were a lot of naysayers, like, “What do you mean, Mars helicopter? That doesn't make sense. You won't be able to fly. The air’s too thin.” It took a lot of courageous people to back us up. There was resistance – correctly so, I think – from the mission that had been asked to accommodate us. That was not something that they wanted to do, so it took some persuasion. And it had to pass all its tests to the satisfaction of the Perseverance folks. So every step of the way, we could have been abandoned.

[11:05] In fact, the way the rover did its belly pan, which is where we are located, there is a version of the belly pan somewhere that doesn't have Ingenuity on it. In other words, it doesn't have all the hooks and things for Ingenuity. Let's say the flight unit had failed a structural test before launch. They would have probably put this other alternative little belly pan onto the rover and flown without us.

So it was every step of the way. First-of-a-kind system – you don't know what’s going to work, what’s not going to work. How much time do you spend refining a design, or is it good enough? How do you make that judgment call? So the metaphor that this is a Wright Brothers moment is not just in the sense that it's the first flight on another planet – which is pretty cool by itself – but the fact that you're going into the unknown.

Our first scale vehicle was unstable, and it took a lot of engineering and analysis of the physics of flying in thin atmospheres for us to understand that instability and work around it. Even our NASA helicopter experts were surprised by that. So they had to also go back to the textbooks, so to speak, to understand the fundamental physics, just to make sure we even have stability in the air.

[12:12] So, it's just across the board exploring a completely new terrain. Nothing was a given. Literally there was a crisis – and I use the word without too much hyperbole – there was a crisis on the project every week for the seven years that it took to get this going. But I got used to that, and kind of thrive on it, actually, because any time there's a problem, there's something fun to solve, right? That's what made it exciting.

(music)

Narrator: One of the biggest pressures of the mission was the lack of air pressure on Mars. Air pressure is the collective force of air molecules pushing against a planet, drawn there by gravity. On Earth, our thicker atmosphere and stronger gravity results in an average surface air pressure of over 1,000 millibars. The 6 millibars of surface air pressure on Mars is a mere whisp in comparison.

[13:07] For a helicopter to fly, it needs enough air for the fast-spinning blades to push against, and because atmospheres get less dense the farther you rise from the surface, helicopters on Earth are limited in how high they can fly. So how could a helicopter ever fly on Mars?

Bob Balaram: Mars has an extremely thin atmosphere – it's equivalent to flying at 100,000 feet here on Earth. If you had a block of air – let's say you spread your arms out wide and made a big cube – here on the surface of the Earth it would be about 2 pounds or so. That same cube of Martian air would only weigh an ounce. Which means that if you want to fly, you have to move that air, which means your blades have to be special for that thin air. And they’ve got to move quite fast in order to push enough air downwards so that you get the lift upwards.

[14:00] Then, even if you build the system that would produce lift, it has to produce more lift than its weight. And not just the weight of the rotor, but everything else you need to carry with it, right? You're carrying batteries and computers and solar panels and radios and wiring and all those things that have nothing to do with flying, but you've got to carry that with you. So basically 4 pounds was pretty much the upper limit. As I've joked, it's very easy to build a Mars helicopter of the same size as Ingenuity and have it weigh 5 pounds, and it would sit on the surface of Mars and spin its blades, but it wouldn't go anywhere.

And so, I was managing the mass on the design down to the gram and sub-gram level. So if my computer guy said, “Hey, I really want 6 grams for this processor,” and there was another processor that was only 4 grams, he and I would have a long discussion before I relinquished 2 grams to him to let him implement a slightly larger processor.

Narrator: Such a lightweight aircraft could be at the mercy of high winds. Because of the thin atmosphere, the winds on Mars aren’t as powerful as winds on Earth, but Ingenuity still needed to be tested to see how it would perform in even the gentlest of Mars breezes.

[15:16] Bob Balaram: When it came time to test how our helicopter interacts with the winds, guess what? There is no wind tunnel that simultaneously does the thin air density of Mars and the low velocities that we were testing. We're not testing winds that are tens of miles per hour. We are testing winds that are a few miles per hour, right? There is no facility in the country that can do that.

And so, yours truly and his team (laughs) built a wind tunnel that we installed in our JPL 25-foot chamber. And it used about 900 CPU fans from your desktop computers to arrange in a square array to basically be a wind tunnel that we could blow air sideways on the helicopter, as it spun its blades up.

[16:02] Narrator: JPL’s 25-foot Space Simulator is a stainless-steel cylinder 25 feet wide and 85 feet high. Normally, spacecraft placed in this chamber are subjected to extreme cold, airless vacuum, and simulated solar radiation to make sure they can survive a trip in outer space. The Ingenuity team turned the chamber into a one-of-a-kind Mars testbed.

Bob Balaram: That facility has the ability to pump down this big chamber to vacuum. In our case, we said, “Please fill it back with carbon dioxide to the same density that's there on Mars.” So we got the atmosphere right, and we did most of the testing at room temperature because that was the cheap and easy thing to do. But we did do a few critical tests where we cooled down that air in the cylinder to Mars temperatures, and so we made sure that nothing funny was happening as the temperatures dropped.

[16:58] Now, of course, the gravity is almost 2.5 times more gravity here on Earth than it is on Mars. So what we did is we basically built an offload device. Think of it as a high-tech fishing line that we attach to the top of the helicopter, and it pulls with an exact constant force equal to the weight difference that we want, so that we get the Mars versus Earth gravity. And it does that regardless of whether the helicopter’s flying up or down. And so, that allowed us to basically understand the behavior without the extra gravity that we get here on Earth, and making Ingenuity think that it was flying on Mars.

We used various fishing line types of cord material and all kinds of very interesting knots to hold that safely. I think we had three reviews on knots, from climbing experts to top mechanical engineers here on Lab and knot experts, to make sure that there were other safety knots and back-up knots. Literally we were hanging the entire project by a thread, right?

[17:57] Ingenuity test: Spin up. (sound of helicopter flying) Steady.

Bob Balaram: So we did many, many, many months of testing in the 25-foot chamber. And once you bump down the chamber and you put on the carbon dioxide, it's not like you can say, “Oh, okay, let's break for the weekend.” No, you're going to test right through the weekend. So there was an entire year where every weekend there was testing nonstop. And the testing would be there late.

And my wife, who's a super awesome baker, she'd bake all these wonderful foods. Any time we were testing, she'd bake for the entire test team. And that's what sustained many of us. So she got an official title on this project called CMO, Chief Morale Officer, working to keep the test team happy.

Narrator: After the well-nourished team developed a helicopter that could fly on a simulated Mars, the aircraft had to go through other tests to make sure it could survive the journey to an alien planet.

[19:06] Bob Balaram: It's not only an aircraft, but it's also a spacecraft. You normally don't think of spacecraft design and aircraft design in the same breath. We had to. So we had to survive launch, which has vibrational G-forces where things get really rattled by the very loud noise that the rockets make, and it just shakes the whole structure up.

(sound effect: NASA rocket launch rumble)

Bob Balaram: And so, there’s structural requirements. You have to be strong in a certain way to withstand entry, descent and landing forces. You have to survive the radiation of space and continue to operate. We had to survive the vacuum of space, and not just survive, but we had to be a good passenger.

In the vacuum of space, gas likes to travel and condense. A lot of materials like adhesives and glues or plastics, you know, if you leave something on your car on a hot day, and sometimes you’ll notice an oily film that may have coated the glass – that's called outgassing, and it’s just like little organics in your system that condense on the coldest thing. Anything sent to space cannot have any of those kinds of things, because you don't want your goo to go and land on this camera lens of this wonderful science instrument that is three feet away.

[20:19] Since we were hitching a ride, we had to be extraordinarily safe to the rest of the mission. It's an astrobiology mission looking for signs of past life. We had to be super-duper clean so that we didn't carry, you know, spores and stuff. So we had to be treated like every other instrument that's on the spacecraft.

Narrator: The space capsule carrying the Perseverance rover and the Ingenuity helicopter was ready to leave Earth on July 30, 2020. During the launch coverage, a 4.2 magnitude earthquake hit Southern California.

Announcer Raquel Villanueva: Ingenuity’s project manager MiMi Aung joins us now to talk about the set of milestones Ingenuity needs to hit in order to take flight on Mars.
[21:03] Ingenuity project manager MiMi Aung: Hi – by the way, we just had an earthquake in this room! But anyway, with that, Mars helicopter demo is motivated….

Narrator: Since the mission was launching from NASA’s Kennedy Space Center in Florida, the quake only rattled those speaking from JPL. After enduring the tremors of a rocket launch and a seven-months-long spaceflight, the mission landed in Jezero Crater on February 18, 2021.

Announcer Raquel Villanueva: We’ve just heard the news that Perseverance is alive on the surface of Mars, congratulations to the mission… (applause)

Narrator: Now that Perseverance had arrived safely, the Ingenuity team had their own, second Mars landing to worry about. Ingenuity was still tucked under the rover’s belly like a baby kangaroo, and needed to hop out. Here’s Teddy Tzanetos again.

Teddy Tzanetos: Right after entry, descent and landing, and Perseverance’s arrival to the surface, the game was on. There were a handful of weeks where the rover was first trying to go through some systems checks. And on the helicopter side, we were confirming that all systems were green across the board, and looking for our first good airfield to fly in.

[22:15] Thankfully, where Perseverance landed in Jezero crater, there were a lot of good locations right nearby where the rover would drop off the helicopter and we would begin our mission. What we were looking for was effectively a parking lot on Mars. We wanted a nice flat surface that the rover could drive to, and would be free of rock hazards. If one of our feet gets stuck on a rock, we'd be landing on a tilt. Or if we landed directly over a rock, a rock could actually puncture our thermal shroud and cause us to have an early end to our mission.

Narrator: Once Ingenuity’s landing spot in Jezero Crater was selected, Perseverance drove over to the center of the area, nicknamed “Wright Brothers Field.” Ingenuity now was ready to be “born.”

Teddy Tzanetos: She's our little baby and she's very tough, but we needed to make sure we took good care of her all the way through delivery to Mars. As soon as Ingenuity is finally separated from Perseverance, there's no way to go back. That umbilical is a one-time separation.

[23:13] We were located under the belly of Perseverance. We had a debris shield, so the first step was dropping the debris shield. Then the rover drove up a little bit. Second step was starting our leg releases, and our launch-lock releases. What those mean are different mechanical restraints that were holding the helicopter in a folded config. And we started our multi-step process to, one by one, unfold the legs, rotate the helicopter to its vertical orientation. During our deployments leading up to the final drop, we were using Perseverance’s camera – there's a camera on its arm that it could look underneath the belly. And that helped us determine, yes, deployments were going well.

[23:57] That final separation, there's effectively just a single bolt holding Ingenuity to Perseverance’s belly. When that bolt snaps, gravity does the rest and Ingenuity falls a handful of inches to the surface. A single circuit, a single wire on the umbilical interface between Perseverance and Ingenuity, went from being a closed circuit to an open circuit. That gave us the indication on the engineering side that, yup, Ingenuity has successfully separated from Perseverance. And from that moment on, Ingenuity is on her own.

And Ingenuity is solar powered. Unlike Perseverance, which has a nuclear-powered energy source, Ingenuity needs photons on its panel. It was critical that soon after Perseverance dropped Ingenuity, Perseverance needed to drive to expose Ingenuity’s solar panel to the Sun.

As soon as Ingenuity was deployed, we're on a clock. The timing is dictated by, A: how much energy you have inside of Ingenuity’s battery, and how much do you need to recharge? But, B: the time windows when you can receive and send commands from Earth to the rover. You can't do that 24 hours a day. So those comm windows when we could inspect the state of the vehicle, identify if Ingenuity successfully dropped, and then send commands to override if needed, only provided us really about 15 minutes in which to react.

[25:17] So it was a very stressful couple of days leading up to that final deployment, and an even more stressful, it was called the “drop-and-drive” activity. Thankfully, everything went smoothly, and we were ready to begin our 30-day tech demo mission.

Narrator: After Ingenuity was safely delivered on the surface of Mars, and the Perseverance rover had rolled a short distance away, leaving the helicopter exposed to the open sky, there was a pregnant pause. Ingenuity was not yet awake. The rover silently faced the helicopter, waiting in the deep quiet of Mars to see what would happen next.

Teddy Tzanetos: It could have woken up immediately after it was dropped, but we built in a delay to allow for a whole series of contingencies that could have occurred. As with all space missions, you want to avoid moving too quickly, because that's when mistakes are made. So we had a good margin window – 2 hours and 15 minutes after the drop – and then Ingenuity woke up. Perseverance was there waiting to communicate, and we established a link, and we were off to the races at that point.

[26:19] Narration: Take note – this 2 hour and 15-minute delay between Ingenuity separating from and then talking to the rover will have surprising consequences later in the mission.

After Ingenuity left the warm embrace of Perseverance, and was going through system checks to make sure everything was working well, Bob was fretting about what came next.

Bob Balaram: The most nervous time I had was when we were dropped off onto the ground from Perseverance. It was not obvious that we would survive the night.

(music)

Bob Balaram: When we were on the way to Mars, we had a separate heater that was energized by the rover, which, with its radioactive RTG source, effectively has power to spare, especially for a small little helicopter. But once we were on our own, it was our battery powering our helicopter. And if the battery was drained so much overnight that by morning, if it wasn't enough juice to keep the computer alive, then we would be in big trouble.

[27:24] We’re a very small object, and it's always difficult for something small to stay warm. You know, you have a small cup of coffee compared to a big barrel of something, it just cools down faster, right? So the helicopter uses almost three quarters of its energy just staying warm through the night. It’s collecting all this energy from the solar panels, harvesting it all day, sticking it into the battery, and then it spends most of that energy depleting the battery to run a bunch of heaters. We couldn't let the batteries freeze out. We couldn't let the electronics get so cold that some little soldered joint somewhere would pop free.

Then on top of that, we really didn't know what kind of winds to expect on Mars that night. And it's the nighttime cold winds that would have really sapped our system.

[28:05] sound effect: wind

Bob Balaram: We had an instrument on the rover called MEDA, which was a weather meteorology station. But it was only just beginning to get commissioned. So we didn't know whether the winds would be twice as much or three times as much. Now, it turned out that the winds are not that bad, and especially the closer you get to the ground, it's even less of an issue. But we didn't know that. So that to me was the most harrowing time.

Narrator: Ingenuity endured its first freezing Martian night on its own, and still had enough power remaining by dawn to run its computer. Now Ingenuity needed to bask in the sun until its solar panels recharged the battery.

[28:56] Bob Balaram: There was indeed a scenario where we could have potentially survived on Mars, but never had enough energy during the course of the day to charge up our battery to the point where we could fly. And you have to fly with a battery that's fairly topped up, because if you don't, the moment the rotors kick in and start drawing high power, the battery voltage will droop and all your electronics will brown out. And you have to be able to have enough energy left to have enough flight time to climb up and do something useful. And so just surviving itself is not enough.

Mission Control 1: This is downlink, confirming battery data has been received.
Mission Control 2: Rotor motors appear healthy. Swash plate servos appear healthy, overall actuators appear healthy…

Teddy Tzanetos: The mission was really about that first flight. We wanted to prove that humanity could build something that could, in fact, fly on Mars. And that first flight – where we took off, hovered, we rotated, came back down, and landed 39.1 seconds later – that is the most important flight of Ingenuity’s entire lifetime.

[30:04] Mission Control: Altimeter data confirms that Ingenuity has performed its first flight, (shouts, applause) the first flight of a powered aircraft on another planet.

Teddy Tzanetos: I was elated. I was extremely excited. And then it quickly came back to business. We still had a job to do. Yes, Ingenuity had flown, but we still needed to assess its health. Was it still capable of flying again? How did all of our subsystems fare? How did our actuators perform, the battery perform, the thermal system perform? Across the board, we quickly dove back into the data to finish the job at hand.

Narrator: Ingenuity’s altimeter data, which tracked how high the helicopter had risen, was the main indication a flight had actually happened.

Teddy Tzanetos: The altimeter data just showed a simple square. So the helicopter rose up, you saw the altimeter data go up. It stayed there, it hovered, had a little bit of noise, then came back down. And when it came back down and stayed at a steady level, we knew that we’d landed, and we stayed upright. That was the key success moment there is to know that, yes, the flight was a success, but we also safely landed. And we remained upright, and we had a healthy vehicle that could again fly for flight number two days afterwards.

[31:19] There's a whole rover imaging team that was in the room adjacent to us. And while our data came down, in parallel, the rover imaging team was also quickly trying to come up with their own secondary confirmation that, yes, flight was a success. So within seconds of having our altimetry data, the imaging team was ready to roll and show the video feed to immediately support that conclusion. It was a beautiful one-two punch of emotion.

(audio: team reacts to video of first flight)

Teddy Tzanetos: A picture is worth a thousand words, and a video is even better.

(audio: team reacts to video of first flight)

Narrator: Perseverance’s video of Ingenuity rising 10 feet, or 3 meters in the air shows the helicopter lift up with unhesitating ease, slightly swaying from side to side as it hovers in front of dusty, apricot-colored hills. The elevation of that first flight had been a careful calculation.

[32:18] Teddy Tzanetos: The thing is, you don't want to be too close to the surface of Mars, because there's ground effect. You don't want to kick up dust, and have that dust then get rotated back into your prop wash. You also don't want that dust to trick your camera system. You want to make sure you're looking at features on the surface to help the helicopter navigate, and if there's clouds of dust or sand kicking around that, that makes things tougher for you. You also don't want to go too high on our first flight, because we didn't want to stress the system when we were just getting started. So 3 meters was a nice Goldilocks range.

(music)

Narrator: The 39 seconds of Ingenuity’s first flight on Mars represented decades of thought and hard work. Teddy’s introduction to the mission, though, was relatively more recent.

[33:00] Teddy Tzanetos: A large part of how I started working on Ingenuity was just some dumb luck. I was working on some research tasks – some ground-based robotics – and I had heard about Mars Helicopter. I knew it was happening at JPL. I was begging my group supervisor at the time, like, “Hey, do you know anyone working on Mars Helicopter? Is there anyone I can talk to? Is there anything I can do?” So eventually I bugged him enough and he said, “All right, come with me.”

He brought me down the hallway and I met with our chief engineer, Bob Balaram, and I gave him a little bit of my background. And he said, “Yeah, there is some work. There's some cables in a closet, if you want to take a look at those cables and figure out how we could use them. Someone had set them up in the past but no one's really owning this right now, if you want to give that a go.” I was like, “Absolutely, sign me up.” And from that moment I just held on tight for as hard as I could, and for as long as I could, and one thing kind of led to the next.

Narrator: That mundane closet of cables was like a magical doorway to another dimension, and the key to opening it was Teddy’s background in Unmanned Aerial Vehicles, or UAVs.

[33:57] Teddy Tzanetos: Before joining JPL, I worked at MIT Lincoln Labs on some UAV projects. And that's really where I got bit by the UAV bug. And then I worked at a startup called the Drone Racing League – it's like NASCAR for drones. So working on the technology to enable human pilots to wear these goggles and race in a first-person-view environment. So it's as if you're sitting in the cockpit of the drone, but the drones are about the size of a shoe box flying at a hundred miles an hour.

(sound effect: drone flyby)

Teddy Tzanetos: And then when I came to JPL, there was a very relevant project, which is A.I. drone racing. Let's pit some of our best human drone pilots against JPL's best algorithms. Really the foundation of the A.I. drone racing was being able to map, and figure out where you are within the map, and then we married that with our JPL software algorithms to stitch together the fastest shortest traversable waypoints for a drone to fly through in an indoor racetrack.

Narrator: Long before Teddy charted flights on Earth and Mars, he was growing up near New York City, a child of Greek immigrants. He developed a fascination with computers and robotics thanks to his father’s work.

[35:07] Teddy Tzanetos: My father was a sewing machine mechanic.

(sound effect: sewing shop)

Teddy Tzanetos: In the nineties and the eighties and going back to the seventies, there was a large textile industry in Manhattan, in New York City. And then things moved overseas after that, but for most of his life, he worked on automation for sewing machines.

When I was a little kid, I would just be in the garage futzing around with pistons and some of his mechanisms for the sewing-machine robots. And then I started getting curious. I was like, “Hey, Dad, how does this work? How does this control this?” And eventually started getting into more complicated questions about electricity and how does electricity work, and eventually, how do computers think? Which is a really profound question that I wasn't equipped as like an eight-year-old to think about. But the idea got me hooked.

[35:53] There's some sort of intent in a computer to do something, right? I remember staring at a CRT monitor and thinking that there was some magical brain, (laughs) and I wanted to understand how did that brain work? And later on, when I actually started learning about computers and learning about coding, I started really, you know, peeking behind the curtain and understanding how cool and how beautiful a lot of the underpinnings of computer technology is.

When I first started writing programs, I knew that I wanted to be in engineering and I wanted to stay in robotics. And that's what I focused on in undergrad and graduate school. Even then, I knew that JPL is where I wanted to be. JPL is, for the robotics world, for the computer science world, it is a very unique place where you can take cutting-edge technology and try and do something groundbreaking with it. Not many people can say, “We're flying helicopters for the first time on another planet.”

So I knew that if I could one day get to JPL, I definitely wanted to. I applied early in my career, and I didn't get it. And later on in my career, after working in industry for a couple of years and a startup, and deciding, you know, “It's time to try again.” And thankfully, it panned out, and I've been having the time of my life ever since.

[37:07] (music)

Narrator: After the Ingenuity team proved it was possible to fly on Mars, the focus of the mission changed to see how far the helicopter could go. The first four flights returned to the original landing site, but by flight five, the team combined satellite images of Mars with scouting images by Ingenuity to select and land in a new spot.

Ingenuity zoomed past its initial timeline, and riskier flights began to be considered. For instance, for flight nine, the team wanted to take a shortcut over hills and craters to head Perseverance off at the pass in a section of Jezero crater named “Séítah.” As chief engineer, Bob decides when to push the limits of the helicopter.

[37:55] Bob Balaram: Ingenuity was designed to fly 90 seconds. Ingenuity was designed to fly over flat ground because we’re a tech demo. Let's bake that into the software, and not make it do undulating ground, because then testing it would have been much more difficult. Flying over undulating terrain presents challenges to the navigation system. We can overheat the motors if you fly longer than the time I was mentioning, 90 seconds. Are we safe to take that flight? For that kind of engineering call is very much my job.

So that big epic flight we did across Séítah, we basically cut across the badlands and went to the other side, many, many days ahead of what Perseverance would drive around the long way.

Narrator: In that 166-second flight, Ingenuity flew the length of almost seven football fields. The helicopter continued to push its limits in the five flights leading up to September 2021, but then was grounded for a month. Mars had entered “solar conjunction,” when the planet’s orbit takes it behind the Sun from our point of view, and Mission Control loses steady communications with our Mars spacecraft for several weeks until the planet peeks out from the other side of the Sun.

[39:08] Around this time, Mars presented yet another challenge to the helicopter team.

Teddy Tzanetos: It was the first time in our mission where we started seeing some impact on the flight readiness of the vehicle because of dust. Which is surprising, looking back on it. We had a 30-day mission on Mars, and we were flying at that point for what, about five months, and had not yet seen any impact of dust or sand. And now, finally, we saw some.

(music)

Narration: The Martian atmosphere is often thick with dust as fine as talcum powder, and larger particles of sand can be tossed up by the wind and dust devils. Such air-borne grit seemed to have drifted into the mechanism that controls the helicopter’s rotor blades, making it harder to operate.

[39:56] Teddy Tzanetos: So because of that, we wanted to just stop and think. And ask all of our experts, say, “Hey, this is what we're looking at. We think there's dust or dirt in the mechanism, but it's still working. We think we just need to clear it out. And our partners at AeroVironment, they had a mechanism at their location. And they threw sand and dirt into it, got it all nice and dirty, and then did a test where they cycled it once up and down.

(sound effects: thrown sand and dirt, rotor cycles)

Teddy Tzanetos: And they cycled it again a second time, a third time, a fourth time. They did it up to seven times. And by the seventh cycling, they noted that the mechanism had cleaned itself out.

That gave us the expectation that if we were to try something like that on Mars, we think that we should be able to clean out the mechanism. ‘Lo and behold, that's exactly what we did, and things worked out great. So another victory in terms of proving firsts on Mars, right? Not only have we flown, not only have we flown at that point for five months, but we now have a new tool in our tool belt where we can clean ourselves.

[41:01] Narrator: The team at JPL also has several engineering models of Ingenuity to troubleshoot issues, still using the 25-foot Space Simulator as a Mars testbed. But in this particular case, they didn’t want to get their models dirty.

Teddy Tzanetos: No, we are not throwing dirt at those. We need to keep those in pristine condition, should we ever need them for future testing. But AeroVironment evidently had some leftover hardware and some prototype equipment, which was representative enough for them to do this test.

Narrator: The dust on Mars causes another less obvious problem for the helicopter. When dust suspended in the air is heated by sunlight, that warms the air molecules and causes the atmosphere to expand, or become less dense. With fewer air molecules available for the helicopter blades to beat against, Ingenuity has to spin its blades faster to generate lift. That can cause the rotor motor to overheat, even on the coldest Martian days.

[41:59] Teddy Tzanetos: Our rotor motor is densely constructed. You have components that are wrapped in these layers that are very tightly packed, so it looks like a hockey puck. And inside of this hockey puck of a rotor motor, you're generating this heat. That heat’s kind of trapped. It doesn't instantly radiate out into the environment. It takes some time to work its way out. Based off that time constant, we can back out how much flight time we have before any one of those parts reaches a specific temperature, at which point now the rotor motor is structurally at risk.

So a lot of work went into making sure we understood what our epoxies were – the glue, effectively, that holds the rotor motor together. And making sure that, for X seconds of flight, we weren't overstressing any one of those components thermally. We had a whole review where we went through everything that could go wrong, if we were to bump up the RPM. So we looked at all of our test results, and we decided, okay, we're going to bump up the rotor rpm from 2537 up to 2700 rpm.

[42:58] We did a high-speed spin activity on the ground, so we just ramped up, ramped down, without actually producing any lift. We didn’t take up off the surface. We wanted to make sure nothing was going to shake itself loose, and the control system was working fine at that higher rpm.

So that's how we dealt with that curveball is, “Hey, density’s dropping, let's spin the blades faster to accommodate.” And there's no free lunch. If you spin your blades faster, our rotor motors were heating up quicker, and that meant that we couldn't fly for as long. But less flight time is better than no flight time, right, so it was a worthwhile trade.

Narrator: Dust is just one of the elements that shifts the air pressure on Mars. The polar ice caps have an even bigger impact. The north and south poles each hold vast amounts of carbon dioxide molecules as dry ice in winter, and the waxing and waning of that ice over the year can alter the air pressure by as much as 30 percent. Ingenuity also has to dance with the swings of atmospheric density over the seasons, as the air is warmed and expands, or is cooled and condenses.

[44:03] A Mars year is almost twice as long as an Earth year, so Mars seasons don’t align with ours. Summer was past its peak when Mars came out of conjunction in October 2021. Ingenuity made several end-of-summer flights, but then on flight 18, Ingenuity lost radio contact with the rover.

(sound effect: rover beeps)

Teddy Tzanetos: There's an antenna on the top deck of the rover. And then we have the helicopter antenna, which is a little whip antenna on top of our solar panel. The key question is, is there any Martian terrain intervening between those two antenna paths?

Based off of our orbital images of the surface of Mars, we know where there are hills and we know where there’s elevation changes. And we knew for this flight that there would be a chance that, on landing, there would be some terrain that might give us a challenge for telecom.

[44:53] Now, what wound up happening is the flight executed, we had beautiful comms while we were airborne. And when Ingenuity went down to start descending, we started losing packets, and we didn't get confirmation all the way down to the surface that landing had succeeded. So we had a radio blackout after when landing should have occurred, and we're just waiting and waiting and waiting. Nothing was coming up, and eventually, we were lucky enough that we got a couple of packets across. So the flight went well.

It was a growth experience for us on the operations team in that we got more comfortable with expecting, potentially, to lose comms on landing. If you don't have it that day, it's okay, no big deal. You wait for the rover to reposition itself, get a better vantage point, and then you could establish comms and get all the data that you were missing.

From a broader sense here, we must get comfortable with that. I think it's just on the natural path of evolution here of, get towards more autonomy. Get towards more trust. Whether or not humans are in the loop, Ingenuity will still do the same thing. I want to be very clear. We are spectators. When it comes to what happens from second to second in flight, we are completely hands off. There is no joysticking. There is no human interaction. Ingenuity is on its own when it comes to dealing with anomalies in flight, dealing with warnings, dealing with challenges. So whether or not we have comms on landing or not, the flight will still perform in the same way.

[46:13] Narrator: Because Ingenuity is so small, it doesn’t have enough power to talk to Earth directly, so all our communications with the helicopter have to pass through the Perseverance rover.

Bob Balaram: This helicopter is basically using the same radio system that your sprinkler system in the garden uses to talk to the controller in your kitchen, or wherever you have it. It’s called a Zigbee radio. A lot of home appliance smart devices use the Zigbee protocol. But it’s all short range, you know, a few hundreds of meters kind of thing.

Narrator: Ingenuity’s limited radio range is like a leash that keeps it tied to Perseverance. Ingenuity needs to stay close enough to not break that connection, but the helicopter also can’t fly too close, or else it risks crashing into the rover if anything goes wrong. The team always keeps Ingenuity at least 164 feet, or 50 meters away from Perseverance.

[47:08] The distance between them threatened to grow much larger, though, when a dust storm grounded the solar-powered helicopter.

Teddy Tzanetos: Really, we were lucky to have our first dust interaction around conjunction, because it gave us the tool kit. And that helped us because then come January 5, January 6, we had a big dust storm coming.

(sound effect wind)

Teddy Tzanetos: And this was an unseasonably large dust storm. Having one of this magnitude in January was rare. We weren't expecting it. So instead of proceeding with our flights, we said, “Hey, we're going to hunker down. We'll leave the helicopter on the surface and we'll try again on the other side of the dust storm.”

So that lasted for about a week. We then expected that we would have to do some cleaning activities, just like last time. We did a series of these blade wiggles, as we call them, to clear the dust out. And we did the first one; it wasn’t as smooth as we wanted. We did another one; it got better. And then we decided we were ready for flight again.

[48:03] Narrator: Thanks to its post-dust-storm cleaning, Ingenuity could now start flying up a storm. The Perseverance rover was heading to what seems to be a dried-up river delta, a 3-mile or 5-kilometer nonstop trek the mission called their “drive, drive, drive” campaign. So the Ingenuity team started their own “fly, fly, fly” campaign.

Teddy Tzanetos: The rover had to go in a counterclockwise direction around Séítah, while we were taking a shortcut across the northwest. We called it the Northwest Passage. I had my own Lord of the Rings reference called the Pass of Cirith Ungol.

Gollum: Careful Master, careful. Very far to fall.

Teddy Tzanetos: I’m a big Lord of the Rings fan. Before we had official names, I figured, “Hey, I'm going to put my own fun spin on it.” So hopefully now this will be immortalized forever (laughs) as the Pass of Cirith Ungol – that Northwest shortcut.

[48:58] So, yeah, for our “fly, fly, fly” campaign, we were racing to get flights 20, 21, 22, 23, 24. And finally 25 was our record breaking 704-meter flight. We were originally trying to get ahead of the rover, but at the very least try and keep up. We didn't want to fall too far behind.

Narrator: Ingenuity travels much faster than Perseverance. The helicopter’s top speed is over 12 miles per hour, compared to the Perseverance rover’s top speed of 0.1 miles per hour. When it comes to speed, they’re like the tortoise and the hare.

Teddy Tzanetos: In a lot of ways, slow and steady does win the race, right? In the long run, of course, that will be true. Perseverance will definitely outlast Ingenuity. But yeah, different speed vehicles for different challenges.

Narrator: Rather than racing, this helicopter hare supports the rover tortoise by scouting ahead, saving the mission time by ruling out terrain that would have caused Perseverance to turn back around. Ingenuity’s daily pace is kept on track with an internal clock.

[49:59] Ingenuity had used its clock to wake up every morning for its first 426 Martian days, which are known as “sols.” As the darker days of winter approached in May 2022, there was less and less sunlight for the solar panels to power the helicopter.

Teddy Tzanetos: What we believe happened on the evening of sol 426 is by the time sunset came around, the battery was around 68 percent state of charge. We calculate now that we needed close to 70 percent so that the components could stay warm overnight and we can keep the mission clock powered.

And what happened on sol 427 is Perseverance tried talking to Ingenuity, and Ingenuity was nowhere to be found. We tried again on sol 428, and again, no reply. And we had come to the conclusion, “Hey, we think we've lost our mission clock. We think we're now resetting every single night.” And that means it's effectively like Groundhog Day, every day Ingenuity wakes up and it thinks it was just deployed from the rover. So every day is like the beginning of its mission.

[51:01] Groundhog Day music + radio announcers: “Ok campers, rise and shine! And don’t forget your booties because it’s COOOOOLD out there!” “It’s cold out there every day, what is this, Miami Beach?”

Teddy Tzanetos: And remember earlier when we were talking about our initial deployment from the rover, I mentioned that 2 hours and 15 minutes? So what we think was happening is once things were warm and charged enough, our electronics booted up, and 2 hours and 15 minutes from that moment, Ingenuity woke up and tried talking to the rover. And we came up with a plan for sol 429 to effectively do a full-day search, where Perseverance just stayed put and tried talking to Ingenuity the entire sol. And because the rover was waiting all day, it was there to catch us, and it established comms.

(sound effect: rover beep)

[51:46] Teddy Tzanetos: We had spent about a week of trying different thermostat settings to see if we could recover into a more normal mode of operations where we wouldn't reset every night. But we quickly came to the conclusion, “Hey, this is our new normal. We cannot fight Mother Nature on Mars.” So the two things happening every night, since sol 426, is our mission clock resets, so that means every morning we need to search for Ingenuity, tell it what time it is, and say “Hey, that's your mission clock. Set it. Wake back up later on in the afternoon and we'll do something useful with you once you've charged up your batteries.”

Lithium-ion batteries don't perform well in the cold. When it gets late enough into the night, after about midnight or two o’clock in the morning, we expect that the battery is low enough where the thermostat is no longer running. And we expect that our components are reaching ambient temperatures. When I say ambient, I mean negative 80 degrees Celsius.

(music)

Teddy Tzanetos: So every night instead of hovering around negative 25, we're now tanking down to negative 80, hanging out there for a couple of hours, and then the Sun rises, then we come back up. And in general, small electronics, when you cold-cycle them – when you bring them very, very cold, and then you bring them warm, and you bring them cold, and you bring them warm – it’s just like a piece of metal where you bend it back and forth and back and forth, and you do that enough times and eventually something will break. So each night could be our last.

[53:08] Now, that's not to say all hope is lost, right? We do have some testing here on Earth that suggests that part of our systems should be able to withstand this cold cycling. We do have cell phone quality components that weren't designed for this, so there's no guarantees. All bets are off at this point. Really, all bets were off after our 30-day tech demo, but even more so now.

Narrator: Ingenuity was grounded the entire month of May as the team worked through technical issues, but then, after charging its solar panels all day, the helicopter was able to make its 29th flight on June 11 as the Sun was setting on the horizon.

Ingenuity is now hunkered down for the winter, which in Jezero Crater begins in late July 2022, just as this episode is released. If communication with Ingenuity is lost, the team has a limited time to recover the helicopter because of its dependence on the Perseverance rover.

[54:03] Teddy Tzanetos: No way do we want the rover to sit there for months on end waiting. The rover has an important job. It needs to go collect samples. It doesn't do the rover mission any good to wait around for months for Ingenuity to see if it survived.

Once the health of Ingenuity starts to degrade, we plan to give it another chance, give it another chance, give it another chance. And then eventually you'll get to a point where we have to call it. This has been a remarkable journey that Ingenuity’s been on for the last year. And we've always known that the mission can come to an end and we're prepared for that. We've been ready for that since sol two of the tech demo.

And it's time to celebrate. When that day comes, I'm going to throw a massive party. We're all due a big celebration for everything that Ingenuity has accomplished. And then we'll get ready for whatever comes next.

(music)

[54:52] Narrator: The success of Ingenuity drives the possibility for more flights on Mars. For instance, one idea NASA is considering is to use small helicopters to pick up the rock samples Perseverance is now gathering, and ferry them to a rocket ship that would launch them on a journey to Earth. And Bob says that despite the thin atmosphere, even larger aircraft could be designed to fly on Mars.

Bob Balaram: One specific idea that's been worked on quite actively for the last three years is to build a science helicopter that may be able to carry about 10 pounds of science instruments. During entry, descent and landing, it would fly away from the back shell and proceed to land by itself. And then it would be able to sustain a mission on Mars where you would really exploit what I call the 3 Rs of helicopters on Mars: reach, range, and resolution.

You'd be able to reach many places that you will never be able to get to with a rover. Then there's range. We can fly tens of kilometers a day with that kind of craft. And resolution. I mean, you've already seen how we can do high-resolution images with a little cell phone camera. Imagine that you had imaging spectrometers. You could take this really high-resolution stuff, maybe not as fantastic as what the rovers can do because they can carry much bulkier things, but definitely much better than a little one-gram camera that we carry on Ingenuity, right?

[56:17] So the big caveat, I must say, that the fact that I mentioned it in some sense no way commits anybody to ever do anything, and these are just ideas.

Narrator: Although ideas for other Martian aircraft are, for now, just dreams of what’s possible, Teddy is committed to seeing more flights on Mars in the future.

Teddy Tzanetos: Just like the Wright brothers led to an explosion of aerospace here on Earth, it's my belief, and I think everyone else’s on the team here, that Ingenuity will do the same for Mars. We've really unlocked a lot more of Mars now for scientists. We can fly down lava tubes, we can fly vertically up cliff walls. Ingenuity has demonstrated we can quickly traverse hundreds and hundreds of meters in a matter of seconds. That blows the doors open in terms of an exploration platform for Mars.

(music)

[57:04] Teddy Tzanetos: My goal is, instead of sending large rovers, we start sending larger aircraft that can give scientists access. If there was a bus in the sky on Mars, what would the scientists want to do with it? And we've designed hexacopter platforms that when it unfolds, it's about the size of a large SUV. And each of the six rotor blades is the size of Ingenuity. So imagine six Ingenuitys in a ring, with a central hub – that's what we're imagining here for a hexacopter platform. And things, I think, will only just scale up from there.

And I really believe that's the way of the future. I'm sure that once human astronauts arrive on Mars, there's going to be fleets of drones buzzing around, helping them out with their daily activities. I'm certain of it. It's really just a matter of time, now that Ingenuity’s left its mark, for the next generation to pick up and start building fleets for the Red Planet.

Narrator: We’re “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory. If you enjoyed this episode, please follow and rate us on your favorite podcast platform. Be sure to check out our other episodes, and NASA’s other podcasts – they can all be found at NASA-dot-gov, forward slash, podcasts.

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