A Martian Helicopter: Flying into the Future!

From launching the Project Mercury as a beacon of space exploration in 1958 to having the Perseverance rover gassed and geared up, NASA already dons a rather fluffy hat when it comes to surveying the Martian surface. Along the same lines, NASA has now developed a technological marvel that promises to boost planetary exploration. The Mars Helicopter named Ingenuity flies to the Red Planet with hopes of experimenting with a new and potentially better means of transport over there. What makes this mission different from the previous ones? What is so ‘ingenious’ about this chopper, which makes it a historical flight for humanity? Let us dive into the details.

Being ultra-lightweight at around 4 pounds (1.8 kgs), Ingenuity was not designed to fly to Mars all by itself as it couldn’t handle the in-flight stresses and G forces during launch all by itself. Making the chopper capable enough to overcome the latter resistances would have required stronger armor and more rigid materials, which would have contributed to increasing the cost and the weight of the chopper. Neither of these factors is desirable. Thus, Ingenuity was assigned a valet – Perseverance, NASA’s latest Martian rover which carries the helicopter attached to its belly for the entire journey. The rover and chopper combination has been designed to handle vibrational stresses up to 80Gs and survive entry into Mars’ harsh atmosphere. Ingenuity measures about 19 inches (0.49 meters) tall and has a Rotor system span of about 4 feet (1.2 meters), making it about five-fourths the height of a bowling pin.

Perseverance and Ingenuity getting ready for launch

The rover flaunts a wide arsenal of technical systems, including computers, navigation sensors, and a combination of two cameras, colored and black-and-white. To generate power for all these, Ingenuity uses solar energy. A significant portion, two-thirds of the battery, to be precise, goes into maintaining an appropriate working temperature in Mars’ sub-zero atmosphere. CO2 insulation around the electronic boards also helps in this effort. But, the question still persists – why do we even need a helicopter when the exploration is being done efficiently by the rovers?

After having launched and commissioned numerous land rovers and orbiting satellites for Mars, NASA aimed to experiment and test out whether air flights and subsequently powered air transport is possible on a planet like Mars. Being the first of its kind, Ingenuity does not claim to have remarkable off-the-charts features. Even the Jet Propulsion Laboratory (JPL), the NASA subdivision tasked with designing the chopper, was clear with the goal they hope to achieve with this mission.  

According to Bob Balaram, the Chief Engineer behind Ingenuity, Ingenuity is a technology demonstration to test powered flight on another world for the first time. For the first flight, the helicopter will take off a few feet from the ground, hover in the air for around 20 to 30 seconds, and land. That will still be a significant milestone: the first powered flight in Mars’ fragile atmosphere! This will be followed by additional experimental flights of farther distance and higher altitude and the usual Mars exploration by Perseverance rover.

But, as it is with any space mission, there are several arduous challenges. One of the first challenges one might think of is that of the Martian atmosphere. Having an atmospheric density of only 1% of that on Earth, generating even a tenth of Earth’s thrust would be difficult on Mars. Unlike depictions in The Martian, the Mars atmosphere is not suitable for generating the thrust required to elevate a lightweight chopper, let alone blasting humans off into space. While lifting aircrafts weighing thousands of tonnes up on Earth is a cakewalk today, doing the same even for a much smaller one on Mars requires some serious engineering. For perspective, flying the 2 kg Ingenuity on Mars is equivalent to flying a regular-sized helicopter at 100,000 feet above the Earth’s surface. The chopper would have to be built in a way that overcomes the barrier. 

Next, the chopper could not be completely jam-packed with all the surveillance equipment that the researchers at JPL wanted, as keeping it lightweight and maintaining the maximum possible power-to-weight ratio was the primary design priority. Devices such as drilling, complex x-ray, and spectrometers could not even hope to ride on the Ingenuity. This might lead one to think that Ingenuity is scientifically useless. But one must remember that NASA designed this chopper as a prototype to test flight on Mars, not to contribute to Perseverance’s overall goal of studying Mars for biosignatures.

To tackle the atmospheric problem, JPL researchers had two ideas – one, to spin the rotors at extremely high RPMs to generate more thrust and push more air downward, and the second to reduce the overall weight of the chopper. An average helicopter has its triplet of blades spinning at around 500 RPM, which can generate enough lift to push a craft 40,000 feet above the Earth. In the case of Ingenuity, a pair of counter-rotating blades have been designed to rotate between a whopping 2300 and 2900 RPM. This high rate has been tested successfully several times in their own 960 computer fan testing chamber which mimics the Martian surroundings here on Earth.

Schematic for the NASA 960 Fan Testing Chamber

However, even this range has some limitations. This RPM range was explicitly chosen so that the blade tips do not cross the maximum speed of sound, ensuring that the craft’s aerodynamics was maintained and that the chopper won’t have to deal with the trans-sonic flow of air, which can cause instability on Mars. Thus, the design was such that the blade tips stay at 70% of the speed of sound.

When weight is a major consideration, one must do away with any and every redundant part. Although the gravity on Mars is just 38% of that on Earth, which is an advantage to the JPL team, the main design aim was to reduce the overall craft weight and reduce the power consumption required to have Ingenuity take flight. Thus, the chopper carries only the essential components that a self-sustaining flying craft would require on an alien planet. The blades are foam cored with a carbon-polymer based lay-up, with each counter-rotating blade weighing 35 grams only. For sensing its surroundings, it includes the most useful Autonomy sensors like onboard gyros, accelerometers, cameras, altimeters, and an inclinometer.

What makes Ingenuity tick?

Okay, we now have a craft that’s capable of getting into the Martian atmosphere. How does one control it? In the early stages, there was an attempt on a prototype to have a person with a joystick control it while being there near the chopper, kind of like a remote control drone. The problems with this method were plenty. Firstly, we still don’t have Neil Armstrong for Mars. Secondly, joystick control was not as easy as it sounds. The reason was that the Martian atmosphere’s aerodynamics would cause a delay which would hinder the so-called remote pilot to control the chopper effectively. It would prevent correct directional changes as per the drone’s flight course at the exact time and lead to potential crashes or collisions. Teddy Tzanetos, the Test Control Leader at JPL, quotes, “It’s almost unflyable with a joystick”. 

Another method on the table was to pilot it remotely from the command center in real-time, sitting on Earth with a joystick this time. Even this method was refused because of the time delay from Earth to Mars. Any message or signal that has to go from Mars to Earth or vice-versa requires 20 minutes to travel the distance between the two planets, and this made it impossible for real-time flight control from Earth on Mars. Any information about terrain navigation would experience a total delay of 40 minutes from the moment it is transmitted.

For the above reasons, the Ingenuity has been designed as an autonomous flight craft. Using the sensors mentioned previously, real-time estimation is done, which helps generate pathways and course corrections using closed-loop control algorithms. This instructs the blades to change direction and course. The chopper would be rallying signals to and fro with Perseverance and the command center on Earth in the form of code sequences. The blades would be adjusting course, the same way in which a helicopter on Earth changes direction, managing and adjusting pitch and yaw, with the same components used to adjust the blades.

Looking ahead, the first flight of Ingenuity will be a mutual selfie with the rover Perseverance, it’s only companion and command center locally. During these experimental test flights, its performance will help inform decisions relating to considering small helicopters for future Mars missions. They could perform in a support role as robotic scouts, surveying terrain from above, or as full standalone science craft carrying instrument payloads. Taking to the air would give scientists a new perspective on a region’s geology and allow them to peer into areas that are too steep or slippery to send a rover. In the distant future, they might even help astronauts explore Mars.

As NASA states clearly, the project is solely a demonstration of technology; it is not designed to support the Mars 2020/Perseverance mission, searching for signs of ancient life and collecting samples of rock and sediment in tubes for potential return to Earth by later missions. Even the first airplanes designed by the Wright Brothers were just to show that man can fly on Earth. Flying on Mars would be another remarkable achievement for humanity and we might discover something new about the Red Planet as a bonus!

References

https://mars.nasa.gov/files/mars2020/MarsHelicopterIngenuity_FactSheet.pdf

https://www.nasa.gov/feature/jpl/nasas-ingenuity-mars-helicopter-recharges-its-batteries-in-flight

https://mars.nasa.gov/resources/25120/nasas-ingenuity-mars-helicopter-the-first-aircraft-on-mars/

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