• 28 Apr 2021 01:25 AM
• 1

Ingenuity Takes Off On Mars

By Robert W. Moorman
Vertiflite, May/June, 2021

The miniature Mars helicopter Ingenuity begins its month-long mission following its successful first flight on the Red Planet.

April 19, 2021 — a day for the record books: the successful first flight of an aircraft on another planet. Lifting off from the surface of Mars to a modest 10 ft (3 m), NASA’s diminutive Ingenuity helicopter made a humble start that holds huge significance for future flights.

“We have been thinking for so long about having our Wright Brothers moment on Mars, and here it is,” said MiMi Aung, project manager of the Ingenuity Mars Helicopter at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We will take a moment to celebrate our success and then take a cue from Orville and Wilbur regarding what to do next. History shows they got back to work — to learn as much as they could about their new aircraft — and so will we.”

The successful first controlled flight of an aircraft on another planet more than justifies the $80M budget for Ingenuity’s portion of the Mars mission. The mission and the first flight have also reawakened the public’s interest in space exploration and the potential role for vertical flight elsewhere in the cosmos.

Preparing for Success

Since NASA began exploring Mars, it has sent five rovers that landed on the surface, including Perseverance. Four operated successfully and sent back valuable data for future endeavors. This mission is markedly different, with a fragile co-axial rotorcraft sharing equal billing with the robust 2,260-lb (1,025-kg) Perseverance. Weighing just 4 lb (1.8 kg) on Earth and 1.5 lb (680 grams) on the Red Planet, Ingenuity has a rotor diameter of about 4 ft (1.2 m). Its solar panel, mounted above the rotors, charges its Lithium-ion batteries, which use about 350 Watts of power and provides enough energy in one Martian day for one 90-second flight.

Rotorcraft can certainly add a helpful component to a planetary exploration mission. “Using a helicopter is a faster and more effective means for mapping than the rover,” said Joshua Ravich, Ingenuity’s mechanical engineering lead at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “The helicopter opens up a lot of potential for exploration of Mars.”

After entering the Martian atmosphere with a heat shield on Feb. 18, 2021 — slowing to 1,000 mph (1,600 km/hr) — Perseverance deployed a 70.5-ft (21.5-m) diameter parachute at an altitude of about 7 miles (11 km) to begin the next phase of deceleration. With the thin Martian atmosphere, the parachute could only slow the vehicle 200 mph (320 km/h). At an altitude of about 6,900 ft (2,100 m) above the surface, the rover separated and fired up the descent stage rockets, slowing to its final descent speed of about 1.7 mph (2.7 km/hr).

The vertical landing itself was made after the descent stage conducted what NASA called the “skycrane” maneuver. With about 12 seconds before touchdown, at about 66 ft (20 m) above the surface, the descent stage lowered the rover on a set of cables about 21 ft (6.4 m) long, while the rover unstowed its legs and wheels for landing. As soon as the rover sensed that its wheels had touched the surface, it cut the cables connecting it to the descent stage, which then flew off to crash a safe distance away from Perseverance.

Thus, after traveling 293 million miles (471 million kilometers), the autonomous Ingenuity Mars helicopter, attached to the belly of the Perseverance rover, landed safely, at the 28-mile (45-km) wide Jezero Crater, just north of the Martian equator.

The Perseverance Rover then conducted several days of checkouts, taking its first test drive on March 4. An important task for the team was finding an appropriate field from which to take off and land Ingenuity within a designated flight zone. Luckily, aerial photos showed a relatively flat field with few boulders near Perseverance’s landing site, according to Ingenuity chief pilot Håvard Grip during a post-landing press briefing. The 10-by-10-ft (3-by-3-m) “helipad,” within a 33-by-33-ft (10-by-10-m) airfield, is contained within a much larger flight zone.

The next challenging step of the mission was releasing Ingenuity from underneath Perseverance and driving away without damaging the rotorcraft. The complexity of the task is noteworthy. First, the rover ejected the debris shield that protected the helicopter during the flight to Mars, the descent and landing.

The rover then went through a series of steps that transitioned Ingenuity from its horizontal cocoon to a vertical position, followed by carefully depositing the drone on the surface. This deployment process took six Martian sols (six days and four hours on Earth). Following deployment, the rover drove to its observation area, its “twitcher’s point,” a safe 211 ft (64 m) away called “Van Zyl Overlook,” named after Jacob van Zyl, the team’s longtime colleague and JPL leader. Van Zyl, who joined JPL in 1986 and was instrumental on the Mars mission, died unexpectedly in August 2020.

Below is the step-by-step process the team took to deploy Ingenuity to the surface.

Sol 1: The team activated a bolt-breaking device, which released the locking mechanism that held Ingenuity firmly against the rover’s belly during launch and landing.

Sol 2: The team fired a cable-cutting pyrotechnic device, which enabled the mechanized arm that held Ingenuity to begin rotating the craft from its horizontal to vertical position. During this task, Ingenuity deployed two of its four landing legs.

Sol 3: A small electric motor finished rotating Ingenuity until it latched, which brought the rotorcraft to a full vertical, final configuration. At this point, Ingenuity was suspended 5 inches (13 cm) over the Martian surface, with only a single bolt and several tiny electrical contacts connecting it to the Perseverance.

Sol 4: The final two legs were snapped into position. The Wide Angle Topographic Sensor for Operations and eNgineering (WATSON) took “confirmation shots of Ingenuity as it incrementally unfolded into its flight configuration.”

Sol 5: Perseverance charged Ingenuity’s six battery cells.

Sol 6: The team confirmed that Ingenuity’s four legs were lowered and locked, and conducted final checks.

“This is the first time that Ingenuity has been on its own on the surface of Mars,” stated Aung. “We now have confirmation that we have the right insulation, the right heaters and enough energy in its battery to survive the cold night, which is a big win for the team. We’re excited to continue to prepare Ingenuity for its first flight test.”

Ingenuity could only withstand one frigid Mars night if its solar panel didn’t charge properly, according to JPL. Martian night temperatures can drop as low as -130°F (-90°C).

“We are in uncharted territory, but this team is used to that,” explained Aung, who has been with the Ingenuity program since its inception. “Just about every milestone from here through the end of our flight demonstration program will be a first, and each has to succeed for us to go on to the next.”

Members of that pre-flight press briefing team included Lori Glaze, Director of NASA’s Planetary Science Division, NASA Headquarters; Bobby Braun, Director for Planetary Science, JPL; J. (Bob) Balaram, Ingenuity chief engineer, JPL; and Farah Alibay, Perseverance integration lead for Ingenuity, JPL.

Alibay noted the risks before deployment. “Once we start the deployment there is no turning back,” she said prior to the task. “All activities are closely coordinated, irreversible and dependent on each other. If there is even a hint that something isn’t going as expected, we may decide to hold off for a sol or more until we have a better idea what is going on.”

After it dropped Ingenuity, Perseverance drove 16 ft (5 m) away and verified that the rotorcraft and rover were communicating via their onboard radios.

Balaram said before this final task, “Once we cut the cord with Perseverance and drop those final five inches to the surface, we want to have our big friend drive away as quickly as possible so we can get the Sun’s rays on our solar panel and begin recharging the batteries.”

Everything went as planned. No problems were reported by mission control. Now released, Ingenuity is powered solely by its solar array.

Lift Off!

Although NASA had initially announced a launch date of April 11, checkout tests two days before revealed a problem. On April 12, JPL announced that it had come up with a “software solution for the command sequence issue identified on Sol 49 (April 9) during a planned high-speed spin-up test of the helicopter’s rotors… This software update will modify the process by which the two flight controllers boot up, allowing the hardware and software to safely transition to the flight state.”

Finally, on April 19, everything was ready.

As planned, the solar-powered helicopter became airborne at 3:34 a.m. EDT (GMT-4) — 12:33 Local Mean Solar Time — to take advantage of the Martian noon for optimal energy and flight conditions. Altimeter data indicated Ingenuity climbed to its prescribed maximum altitude of about 10 ft (3 m), maintained a stable hover for about 5 seconds, pivoted about 96 degrees and hovered for another 20 seconds. It then descended, touching back down on the surface of Mars after logging a total of 39.1 seconds of flight.

After the data was transmitted from the helicopter to the rover, it was then beamed back 173 million miles (278 million kilometers) to Earth, where JPL confirmed at 6:45 a.m. EDT to the millions around this world who were waiting to hear about the first flight on another world.

“From everything we've seen so far, it was a flawless flight,” Grip said. “It was a gentle takeoff, at altitude, it gets pushed around a little bit by the winds, but it really just maintained station very well, and it stuck the landing, right in a place where it was supposed to go.”

The first three flight tests are to focus on basic hover and flight capabilities. The helicopter will eventually fly as far as 160 ft (50 m) downrange and back to the starting point. Each flight is not expected to exceed 90 seconds.

While Ingenuity is designed to survive windstorms, the team isn’t planning to fly in high wind or dusty conditions, said Ravich. Perseverance has equipment onboard to alert mission control of any weather anomalies.

Materials that Ravich shared with Vertiflite indicated that, based on the Earth-based testing and simulation that NASA JPL had performed, Ingenuity was expected to achieve a maximum altitude of about 16.4 ft (5 m). Horizontal translational velocity of up to 4.5 mph (2 m/s) was planned; accounting for the harsh Mars winds, its true airspeed was limited to 22.4 mph (10 m/s).

If those tests are successful, there is a possibility that Ingenuity could be pushed beyond initial goals, possibly on the final flight.

Engineering Ingenuity

Ingenuity was started in August 2013 but was only formally added to the Mars mission in May 2018.

Several design criteria had to be met before Ingenuity could be part of the Mars mission. Maximum gross weight had to be light enough to be carried into space and to fly in the thin Mars atmosphere. In addition, the rotors had to be large enough to generate sufficient lift, according to Balaram. Mars’ atmosphere is around 100 times thinner than Earth’s, with over 95% carbon dioxide and 2.7% nitrogen, though gravity is only one-third that of our home planet.

Several hours of testing a one-third-scale model in a 25-ft (7.6-m) diameter chamber filled primarily with carbon dioxide to simulate the Mars atmosphere supported the hypothesis that Ingenuity could sustain flight on the Red Planet. The model used twin, counter-rotating blades to whip through the thin Martian atmosphere at 2,500-3,000 revolutions per minute, which produces a tip Mach number near 0.65-0.7, similar to manned helicopters on Earth.

Before the first flight, Balaram said: “We will be looking at engineering performance. We hope that Ingenuity will help expand our aerial mobility on Mars.”

Maintaining flight above Mars with a low Reynolds number (Re) is one of several areas to be examined. The Re is the ratio of air density to its viscosity. In the case of Ingenuity, the Re is the product of the density, the rotor blade chord and the velocity over the blade, divided by dynamic viscosity. The Re for Ingenuity is nominally around 11,000, compared to about 5 million for a conventional helicopter on Earth.

“The engineering challenge is to have enough blade area and chord Reynolds number to generate lift in the thin Mars atmosphere at minimal size,” said Dr. Anubhav Datta, associate professor at the University of Maryland. “The two-rotor, two blades per rotor design is the most compact configuration to meet those needs.” Datta helped JPL and AeroVironment carry out dynamic stress analysis during the Ingenuity design phase. (See also the sidebar, A Little Bit of VFS in Ingenuity)

Early in the program, tests revealed that sustained flight of Ingenuity could not be achieved with a desktop pilot using a joystick, due to the long delays between transmission signals. Ingenuity had to be autonomous, obeying general commands that transmitted from JPL to a Mars Reconnaissance Orbiter, down to Perseverance, and over to Ingenuity. Controlled and sustained flight could be achieved with the help of onboard sensors and high-speed computers. Ingenuity is designed to execute the flight maneuvers autonomously.

Future Flights

As this article was being completed, NASA’s JPL was reviewing the data prior to additional flight tests.

If the overall mission is successful, rotorcraft drones could become valuable assets for future missions in mapping the surface of Mars, scouting routes for rovers and exploring sources of life and water — the key ingredient to maintaining a long-term presence on the planet.

Ingenuity carried a tiny piece of muslin from the Wright Flyer that made the first controlled, powered flight on Earth, at Kitty Hawk, North Carolina, on Dec. 17, 1903. That flight lasted only 12 seconds and only reached an altitude of about 8 ft (2.4 m).

“Now, 117 years after the Wright brothers succeeded in making the first flight on our planet, NASA’s Ingenuity helicopter has succeeded in performing this amazing feat on another world,” NASA Associate Administrator for Science Thomas Zurbuchen said. “As an homage to the two innovative bicycle makers from Dayton, this first of many airfields on other worlds will now be known as Wright Brothers Field, in recognition of the ingenuity and innovation that continue to propel exploration.”

Larger, more robust and capable offspring of Ingenuity could offer what rovers and satellites cannot — a close-up aerial view of Mars’ topography. High-resolution photos and video could advance and expedite science on the Red Planet.

Asked if humans could be carried on a Mars rotorcraft, Ravich said, “We could do it probably. Ultimately, it is a power-versus-mass problem.”

Balaram said that his team has started looking at future Mars helicopter designs with 10 times the mass and capable of carrying about 10 lb (4.5 kg) of instruments.

A current NASA-funded research study theorizes that between 30% and 99% of Mars’ water is trapped in minerals in the planet’s crust, countering the long-held view that most of the planet’s water evaporated into space. Ingenuity could aid Perseverance in validating this research.

While Ingenuity was not designed for a lengthy mission and prolonged exposure to the harsh elements on Mars, the rotorcraft could be useful beyond 30 days.

Provided Ingenuity passes its five flight tests and remains operational, why not extend the mission a few weeks to see if it can fly higher and farther? Further tests of the craft’s turning and mapping capabilities could be valuable for future rotorcraft-included Mars missions. The information also could be shared with the team of the 2026 Dragonfly mission to Saturn’s largest moon Titan (see “Titan’s Dragonfly: To the Heavens and Beyond,” Vertiflite Nov/Dec 2019).

During the pre-first flight press briefing, the question of how long Ingenuity could last and whether the mission could be extended indefinitely elicited back-to-back short answers from Braun and Glaze. “It is not conceivable” for the Ingenuity to last a long time, said Braun, an authority in the development of entry, descent and landing systems. Glaze added that Ingenuity was designed to last for “as long as we needed it to.”

“Even if Ingenuity flies once for only 20 seconds, it is still an enormous victory, and a landmark accomplishment in my mind,” said Datta before the inaugural flight. “Our concern is always the local gust conditions, particularly with no aerodynamic damping in flap,” he added.

Another worry was how to cool Ingenuity’s motors with the lower air density on Mars. As for speed, the maximum design speed for Ingenuity is 10 m/s. So, testing Ingenuity at higher speed was unnecessary, said Datta.

A Broad Team

The Mars Ingenuity team is comprised of personnel from JPL, NASA Ames Research Center and NASA Langley Research Center.

JPL is responsible for the fuselage and integrating various onboard systems. NASA Ames and Langley brought the expertise in rotorcraft design, control system identification, computational capabilities and operational experience.

AeroVironment, an innovator and manufacturer of unmanned aircraft systems (UAS), under contract by JPL, designed Ingenuity’s propulsion system, as well as the composite landing gear.

Lockheed Space Systems in Denver designed and manufactured the Mars Helicopter Delivery System (MHDS), which transported and deployed Ingenuity for flight on Mars. “We had to figure out how to hold onto all the moving parts with minimal rover resources, such as actuation signals, available to us,” recalled Jeremy Morrey, Lockheed Martin MHDS principal engineer. “We had a wicked challenge to do more with less.”

Switzerland-based Maxon said its DCX and BLDC motors were used for “numerous mission-critical tasks.” Six Maxon DCX motors controlled the pitch angle of the rotor blades for flight direction.

Qualcomm, Snapdragon and SolAero provided design assistance and vehicle components.

Mission Success

As of this writing, NASA had met the primary goal of this mission — to prove that rotorcraft flight on Mars was possible. The team also gathered revealing data to determine the viability of future missions with rotorcraft flight on other planets and moons.

While not a specific goal of this Mars mission, some yet-to-be-realized rotorcraft design or technology could come from the data gathered. High-altitude rescue by hovering helicopters could be achieved by what is learned from the Ingenuity’s flight tests, said Ravich.

JPL hasn’t determined if or when another Mars rotorcraft mission would occur or whether it will precede or succeed Dragonfly’s mission to Saturn’s largest moon, Titan. That flight, which will take eight years to reach Titan, will include the 1,000-lb (450-kg) Dragonfly coaxial quadcopter.

Dragonfly, NASA’s fourth New Frontiers mission, has a two-fold purpose. The overarching goal is to help answer the basic question that has flummoxed scientists, astronomers and lay people for millennia: How did Earth evolve to become habitable? The second goal: determine how effective rotorcraft can be as a tool for exploring other planets.

Whether Ingenuity lays the foundation for future, more ambitious helicopter-included missions to Mars and beyond remains to be seen. But its successful first flight and the data gathered from the Ingenuity mission will likely cement rotorcraft’s role in future planetary missions.

Continue reading the sidebar, A Little Bit of VFS in Ingenuity.

Note: As this article was going to press, Ingenuity completed a second flight on April 22. Lasting 51.9 seconds, Ingenuity climbed to 16 ft (5 m), hovered briefly, then translated sideways 7 ft (2 m). After coming to a stop, it hovered in place and made turns before heading back to the center of the airfield to land.

“Because the data and imagery indicate that the Mars Helicopter not only survived the second flight but also flew as anticipated, the Ingenuity team is considering how best to expand the profiles of its next flights to acquire additional aeronautical data from the first successful flight tests on another world,” NASA stated.

Ingenuity's third flight was made on April 25. NASA reported that it continued to "set records, flying faster and farther on Sunday, April 25, 2021 than in any tests it went through on Earth. The helicopter took off at 4:31 a.m. EDT (1:31 a.m. PDT), or 12:33 p.m. local Mars time, rising 16 feet (5 meters) — the same altitude as its second flight. Then it zipped downrange 164 feet (50 meters), just over half the length of a football field, reaching a top speed of 6.6 feet per second (2 meters per second)."

Vertiflite will continue to cover this historic mission with future reports on Ingenuity’s flight tests. 

About the Author

Robert W. Moorman is a freelance writer specializing in various facets of the fixed-wing and rotary-wing air transportation business. With more than 30 years of experience, his writing clients include several of the leading aviation magazines targeting the civil and military markets. He can be reached at rwmassoc325[at]gmail[dot]com.