A Celebration of Human Ingenuity

It flies!

The data is finally in! The engineers and scientists could all breathe again after the seemingly interminable minutes for the eagerly awaited confirmation signal of Ingenuity’s first flight’s success to arrive on their monitors in Pasadena. The few days delay to the start to the flight test campaign made today's result possibly even sweeter. So much so that the elation in the room was not any less palpable than when, just two months ago, Ingenuity's 'mothership' Perseverance had so spectacularly survived its “7 Minutes of Terror”, to reach the Martian surface unscathed.

An aircraft flying on another celestial body is yet another key milestone, not only for aerospace operators and enthusiasts alike, but for humanity in general. Many observers have compared this event to the Wright brothers’ maiden 12-second flight at Kill Devil Hills and Armstrong’s first bold step on our natural satellite. I think few will disagree.

There is also a very direct, tangible link between these three iconic moments of aviation history. A small fragment of unbleached muslin, called “Pride of the West”, used on the wings of the Wright brothers’ aircraft is wrapped by insulating tape around a cable located on the underside of Ingenuity’s solar panel and has now flown on Mars. In July 1969, the Apollo 11 mission had similarly carried a small wood splinter from the Wright Flyer, to the Moon and back.

We are all sharing the joy and excitement with the team at the Jet Propulsion Laboratory - Caltech (JPL) for these first 30 seconds of hover flight. However, we are only catching a fleeting glimpse of the tip of the proverbial iceberg of hard work that took place since the project’s inception in August 2013.

Above: Ingenuity seeing its shadow on the Martian surface - Source: NASA/JPL-Caltech

Mars Challenges

The JPL team had to overcome a plethora of issues that stood in the way of flying a rotorcraft on Mars, starting with the low density of the Martian atmosphere. The surface pressure is about 6.36 millibars (0.6 % the pressure of Earth’s atmosphere) resulting in an average atmospheric density of 0.02 kg/m2, just 1.6 % of the 1.225 kg/m3 value on Earth. To compensate for this rarefied atmosphere, rotor blades need a larger surface area and operate at much higher speeds than required on Earth. This, in turn, comes up against another limit, where rotor tip speeds must stay below ~0.8 Mach, with the speed of sound on Mars being just 240 m/s compared to 340 m/s at sea level on Earth. Tip speeds greater than about ~200 m/s would result in loss of lift, increased drag, and possibly cause destructive vibrations. On the plus side, Mars has a gravity of 3.71 m/s2, practically a third of Earth’s gravity at 9.81 m/s2. This helps offset the aerodynamic performance deficit.

Ingenuity’s coaxial design features two 1.2 meter diameter rotors, with collective and cyclic control on both rotors. With a total mass of 1.8 kg, all the systems and the 350 W power are directly contributing to the helicopter’s flight, as there is no science payload.

The current mission is designed to last for 30 sols (Mars days) with up to five, 90-second flights. The flight time is mainly limited by the 12 Ah battery capacity and more than half of the energy is being used to keep Ingenuity’s systems warm during the cold Martian nights when temperatures can drop as low as -130 °F (-90 °C).

Following this first hover, Ingenuity will open up its flight envelope with horizontal flight and it will be collecting a treasure trove of telemetry that will be so eagerly awaited back here on Earth.

The Next Steps

Scientists and engineers at JPL and the NASA Ames Research Center (ARC) at Moffett Field have already been hard at work designing the next iteration, which could be the Advanced Mars Helicopter (AMH). Although in appearance very similar to Ingenuity, AMH has some remarkable capability improvements as seen from the comparison in Table 1 below.

Keeping the design so close to that of Ingenuity lessens some design risk, by also being able to more directly integrate the lessons learnt from the current mission. 

Technology Improvements over Ingenuity

Continuous improvements in technology are giving the JPL and ARC teams more confidence that a rotorcraft of similar size and configuration to Ingenuity can be designed to carry a useful ~1.3 kg science payload.

One such improvement is using thin airfoils with sharp leading edges that provide a significant increase in performance compared to Ingenuity’s blades. This is primarily due to the use of non-conventional airfoils.

Flight on Mars occurs in the low Reynolds number (Re) (~10?), high subsonic Mach number (~0.8 at the tip) regime, typically not seen with terrestrial rotorcraft. At low Re, conventional airfoils experience laminar separation with no reattachment, which significantly increases drag.

One approach is using biomimicry and emulating winged insects such as the dragonfly that also operate at low Re. These insects’ wings have thin, unconventional airfoil shapes. The sharp leading edges immediately cause the flow to separate and unsteady vortex shedding actually results in a performance gain when compared to more conventional airfoils at very low Re. An increase of up to 41% in peak lift-to-drag ratio can be achieved with optimized airfoils when compared to Ingenuity. Together with this improved aerodynamic efficiency, increased power and battery capacity is what will give AMH the ability to carry a useful payload.

Above: Optimized rotor profile for AMH. Source : NASA JPL and ARC

Mission Scope for AMH

With this resulting increased range, hover time and payload capability, the AMH could be tasked to collect and return soil, rock, or ice samples to a lander or accompany a rover as an airborne scout to assess optimum and safe ground paths. 

Besides being an ‘assistant’ to a rover, some missions may also have the rotorcraft as a standalone science platform. Such a craft has various mission potentials such as mapping, overflights of exposed ice deposits, astrobiology, and meteorology. Compared to satellite imagery an aircraft on Mars could help generate much more highly detailed maps and surveys. Collecting in-situ atmospheric readings also provides higher fidelity data than what can be observed from the planetary orbiters.

Sample collection from locations that rovers would find hard to reach due to difficult terrain can also be considered, with the collected rocks and clays then transferred back to a suitable location for further analysis.

The relatively small size of the AMH makes it possible to package into a legacy aeroshell for the critical Entry, Descent and Landing (EDL) phase. Three legacy EDL systems were investigated including those from the Pathfinder, Viking, and Mars Science Lab / Perseverance missions. The Pathfinder aeroshell is the smallest of the three and also the least costly to launch. The AMH design was thus adapted to allow for rotor blade and landing gear folding to fit inside its tetrahedral petal structure.

Above: Possible packaging configuration for the future AMH and payloads inside Pathfinder’s tetrahedral petal lander. Source : NASA JPL and ARC

The Path Ahead

Planetary scientists are always asking for bigger payloads as this allows a wider range of onboard sensors and experiments. Prior to AMH, another even larger version was being conceived, designated as the Mars Science Helicopter (MSH).

In fact the required performance upgrades required to support the higher payloads envisaged for the MSH are what is being driven back to the AMH design to provide the lifting capability into an aircraft format very similar to the current Ingenuity.

This mission profile chosen for MSH was done to provide flexibility for the scientific requirements but not be excessively challenging to put it out of reach of projected technology. The defined mission is to carry payload of 2.02 kg in an atmospheric density of 0.015 kg/m3 at -50 °C, including the following segments:

a)    30 sec takeoff at hover power

b)   climb to altitude of 200 m

c)    1 km cruise flight to science site

d)   2 min hover at science site

e)   land

f)     sleep for 1 sol, and recharge

The first ‘easy’ option would seem to be to supersize the Ingenuity concept and JPL and ARC have looked at a larger coaxial rotorcraft, with a rotor diameter approximately double that of Ingenuity and AMH.

Another design that NASA is studying is a hexacopter configuration with 0.64 m radius rotors. This has some advantages such as redundancy in case of a single motor failure or rotor damage, an important consideration when maintenance action is not possible. However, even when folded, a hexacopter with these rotor dimensions would not fit in the ‘budget’ Pathfinder aeroshell. Decreasing the rotor size could make it fit, but the higher disk loading would then impact the other interlinked performance parameters.

In just a few days, the scientists and engineers will be poring over the data that Ingenuity is sending back and invariably all these options will be reviewed and reassessed.

And what about us Earthlings…?

This is certainly an exciting time for Mars exploration. The added dimension that aerial platforms can deliver will have a positive impact on the future path of discovery on our planetary neighbor.

Just as the launch of the first Space Shuttle mission, STS-1, 40 years ago on 12 April 1981, inspired a whole generation of scientists and engineers, this test flight campaign will also give a shot in the arm to STEM programs in the United States and beyond.

We will also undoubtedly see other quantifiable benefits as the technological advances that make these engineering feats possible, such as cutting-edge rotor aerodynamics, battery charging and management, lightweight materials and structure design can all contribute to Earthbound VTOL aircraft.

Space exploration has always been at the forefront of human technology, and for the next few sols, a little Ingenuity will be leading the way!

References

• NASA (2021) NASA Ingenuity Mars Helicopter Prepares for First Flight. Available at: https://www.nasa.gov/press-release/nasa-ingenuity-mars-helicopter-prepares-for-first-flight (Accessed: 31 March 2021).
• Radotich, M., Withrow-Maser, S., Gelhar, S. and Gallagher, H. (2021) ‘A Study of Past, Present, and Future Mars Rotorcraft’
• Withrow-Maser, S., Johnson, W., Young, L., Cummings, H., Chan, A., Tzanetos, T., Balaram, J. and Bapst, J. (2020) ‘An Advanced Mars Helicopter Design’, Accelerating Space Commerce, Exploration, and New Discovery Conference, ASCEND 2020

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Note: The views expressed in this article are those of the author and do not necessarily reflect the policy or position of any other agency, organization, employer or company, past or present. The information contained in this article does not constitute investment advice.