Can a helicopter fly on Mars?

In the early morning of July 30, an enormous Atlas V rocket fired the Mars 2020 spacecraft into the skies above Cape Canaveral Air Force Station in the center of Florida’s Atlantic coast, beginning an almost seven-month journey to the Red Planet. Any flight to Mars is remarkable, but what makes this one particularly noteworthy is that this won’t be the last launch for this mission. And while the physical scale of the next one — which aims to generate enough lift to bring a four-pound vehicle briefly off the ground — will be much smaller, it will be significantly more monumental. That’s because it will be taking place on Mars itself, and the flight — to be completed by a helicopter — will represent the first time any aircraft has achieved powered flight on another planet.

“The idea of atmospheric flight on other planets has been one that folks have been thinking about ever since we really started to do planetary exploration,” Dave Lavery, program executive for Solar System Exploration at NASA, told Vertical. “The concept is over half a century old, and the problem was . . . initially the access, but then also the technology just was never quite there in order for us to actually attempt it. And that has changed within the past decade.”

Those technology advancements include the development of advanced materials and computing, as well as huge leaps forward in autonomous flight capability.

Still, there are significant obstacles to overcome in building a vehicle that can fly on Mars. Perhaps the largest of these is the planet’s extremely thin atmosphere — just one percent the density of Earth’s — which means there is precious little air against which to generate lift. In Earth terms, it would be like trying to fly at 100,000 feet (30,480 meters).
In selecting a design for the first powered flight on another planet, it’s perhaps not surprising that a helicopter wasn’t the first type of aircraft considered by NASA’s engineers.

An artist’s concept shows NASA’s Ingenuity Mars Helicopter standing on the Red Planet’s surface. The aircraft will arrive on Mars on Feb. 18, 2021, and will become the first aircraft to attempt controlled flight on another planet. NASA Image

“We had been sort of focused on fixed-wing aircraft for many of the prior concepts, and then at some point, someone basically said, ‘Well, why don’t we try a helicopter as well?’ ” said Lavery. “At first, there was a lot of head scratching about well, could that actually work in the Mars atmosphere and is there enough atmospheric density that we actually could get sufficient lift to fly [a helicopter]? And we did a couple of quick calculations and said, ‘Just barely, yes, it will work.’ ”

As the team explored the concept more deeply, they found it was, in fact, a very feasible idea. They considered various designs, including a quadcopter, multirotor, and a more traditional helicopter with a single main rotor and a tail rotor.
However, the final design sees the aircraft (known as Ingenuity) using counter-rotating main rotor blades on a single shaft; one two-bladed rotor on top of another two-bladed rotor; one spinning clockwise, one spinning counter-clockwise.

With a height of 19 inches (49 centimeters), Ingenuity weighs less than four pounds (1.8 kilograms) — but is also strong enough to perform atmospheric flight, and endure the harsh Martian environment.

“The biggest forcing functions associated to lead us to the design we had were a combination of what was the smallest and therefore the lightest we thought we could get the body of the helicopter,” said Lavery. That then dictated the size of the lifting disc required (about four feet, or 1.2 meters).

NASA’s Mars 2020 Perseverance rover stands behind Ingenuity in this artist’s concept. Perseverance is the most sophisticated rover NASA has ever sent to Mars, and will arrive at Jezero Crater with Ingenuity attached to its belly. NASA Image

The team also had to consider how it would be attached to Perseverance, the car-sized rover that is performing the primary work of the 2020 mission — searching for signs of ancient life on Mars, and collecting rock and soil samples for possible return to Earth by a later mission.

A light and powerful design

To keep Ingenuity as light as possible, NASA engineers used composite materials where possible, had the blades constructed with a carbon fiber foam core, and thought outside the box in their choice of advanced computing and avionics components.

“We used a lot of very compact, lightweight electronics components — components that typically you don’t see flown on spacecraft, but in this specific application we really have no choice because of the mass constraint,” Mars Helicopter engineer Jakko Karras told Vertical.

Having a lightweight aircraft makes it easier to get it off the ground, but how do you generate the lift required to do so when there is so little atmosphere? The key for Ingenuity is the speed it spins its rotor blades and their unique shape.
While the main rotor blades of helicopters on Earth generally spin at 400 to 500 revolutions per minute (rpm), Ingenuity‘s blades will be spinning at between 2,800 and 3,000 rpm — closer to the speed of a terrestrial helicopter’s tail rotor blades. By spinning faster, Ingenuity‘s blades can generate more lift.

According to Karras, another important element in the blades’ design is their stiffness. “One of the issues that you get in the thin Martian atmosphere is that if the blades aren’t stiff, they actually start to flap around, as there isn’t as much atmospheric damping — and that leads to stability issues.”The Martian helicopter’s blades also look quite different to the rotor blades you typically see on helicopters, with a thick tapered paddle shape. At their root, the chord of Ingenuity‘s blades (the distance from their leading edge to their trailing edge) relative to their length is about four times the ratio of a terrestrial helicopter’s blades. So, they appear much fatter than a helicopter’s blades would on Earth.

Ingenuity is powered by lithium-ion batteries, which will be charged by a solar panel mounted above the rotor blades as the helicopter rests between flights.

Lavery said Ingenuity is “very much like a terrestrial helicopter” in terms of its general design, with a swashplate, a single power shaft around which the blades rotate, and control capabilities directed by what are, in effect, collective and cyclic inputs.

“So when you think about everything you do to control a helicopter here on Earth, those are the same issues, the same problems that we’re going to have with this helicopter on Mars,” said Lavery.

This is where the aircraft’s advanced computing power comes in, with its artificial intelligence and autonomy capabilities allowing it to fly itself far more easily than a human could. Once on Mars, the helicopter will simply fly along pre-programmed paths having received commands from Earth relayed through the rover.The same problems, but within a much smaller flight envelope. “If you were to attempt to try to real-time joystick fly [Ingenuity], it’s almost impossible to fly it — not quite — but it’s very, very difficult to fly, just to maintain stability of it,” said Lavery.

But while Ingenuity may be similar to a helicopter in many ways, it is also an independent spacecraft — and as such, it has to deal with unique thermal and power challenges. To survive the cold Martian night, it has heaters to keep its electronics and other critical components warm. Thermal insulation provided by thin layers of film (which result in the aircraft’s body looking like a foil cube) radiate heat back inside towards the electronics.

Proof of concept

One of the challenges in developing something that can fly on Mars is in finding a way to replicate Martian conditions during testing. NASA’s got just the device in its Jet Propulsion Laboratory in Pasadena, California — the snappily named “25-five-foot Space Simulator.” Now approaching its 60th birthday (and having been named a National Historic Landmark), the simulator is a cylindrical chamber in which engineers can test some of the extreme conditions of space, or, in this case, Mars.

Air can be pumped out, gasses can be pumped in, the temperature can be adjusted from -195 C (-320 F) to 93 C (200 F), and intense light beamed at whatever is being tested to replicate the solar radiation beyond the protective blanket of Earth’s atmosphere. Over the years, various spacecraft and rovers have cut their teeth in the chamber, including VoyagerCuriosity, and Perseverance.

An artist’s concept of Ingenuity flying through the Red Planet’s skies. The aircraft is expected to attempt its first flight test in spring 2021, about 60 to 90 days after it arrives on Mars. NASA Image

The chamber is just over 25 feet in diameter, and about 85 feet tall — making it well suited to flight testing a small helicopter.

For Ingenuity‘s tests, air was taken out of the chamber to match Mars’s atmospheric density, and the mixture of gasses adjusted accordingly (the air on Mars is mostly composed of carbon dioxide).

The huge Martian temperature swings  — ranging from 60 to 70 F (15 to 21 C) at high noon during the peak of summer on the equator, to -160 F (-107 C) in the middle of night in winter — were also simulated; while a wall of tiny fans replicated potential crosswinds of up to 10 miles per hour.

However, one thing the chamber can’t do is alter gravity. So, to offset the pull of Earth (the gravity on Mars is just one third that of Earth’s), the team attached a line to the top of the helicopter that was hanging down from the ceiling, with a counterweight on the other end.

The first Ingenuity prototype was tested in 2014. Smaller than the current vehicle, it didn’t have any onboard control; instead, it was flown by a human operator outside the chamber.

Two years later, a third prototype saw the aircraft carry its computing and power for the first time.“A key takeaway of that 2014 experiment was that, yes, we can produce the necessary lift to take off, but the control is quite difficult — at least for a human controller to sustain a stable hover in that atmosphere,” said Karras.
A more fully-developed prototype, controlled by a computer, flew in 2016, and it was able to sustain a controlled hover.

“That achievement really demonstrated the viability of doing this on Mars, because we now had essentially a self-contained viable Mars helicopter prototype,” said Karras.

Landing on the Red Planet

The Perseverance rover is scheduled to land on Mars’s Jezero Crater on Feb. 18, 2021. Ingenuity, which will have travelled through space securely attached to the rover’s belly, will be protected during the descent and landing stages by a special debris shield.

Once the rover is safely on the surface, its team will work alongside the Ingenuity team to scout out the surrounding terrain and identify a suitable airfield — a process that will take between 60 to 90 days. The teams will be looking for a relatively flat area, free of rocks and hazards.

When they’ve found the right spot, Perseverance will drop the debris shield, and Ingenuity will be unfolded and deployed. The rover will drive about 100 meters away — a safe distance from which to still be able to communicate and see the helicopter. This will begin the 30-sol (a Martian day — which is about 40 minutes longer than a day on Earth) flight experiment window.

The first flight will be a straightforward demonstration of a takeoff, a stable hover of about 20 to 30 seconds, and a landing. The second flight will see Ingenuity take off, hover, fly to one side for a few meters, fly back, and land in the same spot. The third flight will take Ingenuity a little further away, capturing images as it moves along the flight path, before landing back at the same position.In total, the aircraft is scheduled to perform five flights on Mars, which, like a flight test program here on Earth, will see the aircraft performing increasingly complex maneuvers.

According to Karras, flights four and five aren’t fully planned out yet. They may serve as contingency flights for the first three, but could also be used to take Ingenuity to higher altitudes, faster, further, or in higher winds.

Ultimately, Ingenuity will be able to fly for up to 90 seconds at a time, to distances of almost 980 feet (300 meters) at an altitude of 10 to 15 feet (three to 4.5 meters).

While the rover will be able to provide a view of Ingenuity‘s progress from 100 feet away, the aircraft will also be taking its own pictures using a high resolution color camera (it has another camera that it uses for navigation), and these images will provide those on Earth with an entirely new perspective of Mars.

Of course, being a first-of-its-kind attempt, there are plenty of unknown elements that may impact the mission’s success. Ingenuity has only ever flown in a chamber that simulates Mars; the planet itself will be an uncontrolled environment. Perhaps the team’s model of the Martian atmosphere isn’t quite right, or the control theory behind the collective on the helicopter was wrong, or the dust kicked up by Ingenuity causes more substantial issues than predicted.Ingenuity is, first and foremost, a technology demonstrator. “Its purpose is to go and show that we actually can execute stable controlled flight by an aerodynamic craft on another world,” said Lavery. “If we get that first flight to be successful and we show we actually can do it, that’s what we’re after for this one.”

“A big part of this is to prove that the model that we have built based on what we do know so far about Mars is complete and correct,” said Lavery. “If there’s something there that we just didn’t include in the model, upon which we based the flight characteristics, then we’ll have to go back and learn from this and revise those for future capabilities.”

Leaving a legacy

If Ingenuity proves that controlled flight on Mars is possible, it could open the door to a new era of exploration, according to Jim Watzin, director of NASA’s Mars Exploration Program.

In the near-term, much of the Martian terrain that’s of interest to NASA — steep cliffs, caves, sinkhole depressions — is not accessible with wheeled rovers. Being able to explore these areas with a helicopter may provide crucial answers to questions about the planet’s history.

“But as you look even further, beyond just the exploration activities that we’re doing, and you fast forward to the point in time where we would have human exploration, the ability to scout will become very, very valuable,” Watzin told Vertical. “In fact, if we had it with some of our rovers where we could have scouted ahead, we would have chosen different terrain paths to do our roaming. And so the value of that is just amplified enormously when you’re trying to plan out and control and manage the operation of crewed activities on the surface.”

The excitement about the project among both those at NASA and the general public is palpable. “It’s an incredible project,” said Karras. “We say that it will be a Wright Brothers moment on another planet, so it’s going to be a breathtaking moment when it succeeds.”

On July 5, 1997, the Sojourner became the first rover to explore another planet when it rolled onto Martian terrain as part of the Mars Pathfinder mission. Lavery also worked on that program, and he drew many comparisons to Ingenuity and his hopes for its legacy.

“[Sojourner] was a very small technology demonstrator add-on to a larger science mission, and it was done by a very small, very focused group of folks who were really just trying to prove a specific technology could work,” he said. “When we showed that controlled surface mobility was not only possible, but it was something that we actually understood pretty well and could do on an ongoing basis, that opened the door for every rover since then. . . . Maybe, just like every mission following Mars Pathfinder carried a rover, after this one if it’s successful, every future mission starts to carry a helicopter on board as well.”

Courtesy of Oliver Johnson from Vertical Mag

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