Almost 2 weeks ago, NASA’s Mars rover Perseverance landed on Mars with its passenger Ingenuity. It was the 3rd spacecraft to arrive at Mars in February after visits from UAE (“Hope”) and China (“Tianwen-1”, Engl.: “Heavenly Question”). A total of 49 Mars missions have been conducted so far since 1960:
- 16 flybys
- 28 orbiters
- 18 landers
- 9 rovers
A few of the missions were focused on one of the two moons of Mars (Phobos), where 2 of the landers and 1 rover were supposed to head. There were also 4 penetrators planned in these missions.
Yes, I know, you’re going to say, “Hey Boris, you can’t count!” These numbers don’t add up to 49 missions because there are multiple modules on many of them. Some might consist of an orbiter, but others may contain an orbiter and a lander or even a penetrator or a rover.
Now, what is the difference between these?
- An orbiter orbits the planet (or a moon) and sends back images and other data.
- A lander lands on the planet’s (or moon’s) surface but remains stationary and collects data to send back. A little like a Martian weather station
- The penetrators are designed to crash into the planet’s (or moon’s) surface without surviving but reveal some of the soil beneath the surface for closer studies by rovers.
- Rovers are mobile units that move on the surface to study various things like soil samples, drill into rocks, monitor the atmosphere, etc.
An interactive 3D model of the Perseverance rover. (Credit: NASA/JPL-Caltech)
Many of these systems have multiple sensors such as special cameras, temperature probes, wind speed probes, or spectrometers to analyze the samples they collect. Unfortunately, with all these missions to our closest neighbor, not all of them successfully arrived in one piece or even made it to the start of their mission. Some didn’t even leave the Low Earth Orbit (LEO) where their rockets placed them; others got destroyed during entry into Mars’ atmosphere. Yet humanity didn’t give up! That’s why I think the name chosen for the 49th mission to mars is perfect – Perseverance!
You may not know what makes this mission so special and unique because this will conduct the first “powered” flight on a different planet! This part of the mission is still to come in the next 1-2 months. The NASA Mars mission (Mars 2020) not only carries a rover, but it also carries a robotic helicopter named “Ingenuity.” It is not the first flight as there was a balloon used once on Venus, but history repeats itself as the first flight on Earth was also a hot air balloon
Ingenuity is alive
Or was it “Siemens – Ingenuity for life”? Strange coincidence, but let’s roll with it.
Vaneeza Rupani, a 12th grader at Tuscaloosa County High School in Northport, Alabama, came up with the helicopter’s name. When she was asked why she thought “Ingenuity” would be a good name, she answered:
“Ingenuity would be a good name for the helicopter because that is exactly what it took to design this machine. The challenges faced trying to design something capable of flight on another planet can only be overcome with collaboration and creativity. It takes the ingenuity of an incredible group of people to create something with so many complex challenges.” Speaking of ingenuity, let’s talk about the simulation that you’ve all been patiently waiting for
Simcenter FLOEFD – Ingenuity for flight
Finding a model for the simulation of the Ingenuity helicopter wasn’t that hard. NASA actually provides many of their models in a scaled size for 3D printing on their website.
An interactive 3D model of the Ingenuity helicopter. (Credit: NASA/JPL-Caltech)
As you might know, there are reverse engineering tools in Solid Edge and Siemens NX to get polygon or point cloud models from STL files back into NURBS-based CAD geometry, and that’s what I did with the model I downloaded from the NASA website.
I have to admit; I had a little help as I’m not that familiar with the process of reverse engineering such models and Ben Weisenberger from the Solid Edge team did a brilliant job there. The key geometries for my simulation were the rotor blades. As they are swept-shaped geometries, they can’t be easily created without the right airfoil shape to get roughly the same performance. Since I assumed the 3D model was derived from the original CAD model, the accuracy would be closer to the real thing than starting to design my own blade. Of course, this is just an assumption. In reality, they could look very different and therefore impact the performance. The rest of the helicopter consists of some blocks and cylinders to make out the model’s shape, and it was easier to create them than to reverse engineer it.
With the model done, let’s look into the aerodynamics simulation of the helicopter in flight.
Up, up and away…
But before we start, what’s the weather like on Mars?
There have been missions to Mars with a range of sensors to measure the atmosphere during their entry and landing phase and measurements during the usual day and night cycles. With Mars being only about 10% the mass of Earth, its gravity is, of course, also much lower and just around 0.38g (3.72 m/s²), so 38% of Earth’s gravity. This is important for us as the lift we need to generate is much lower.
But this also has an impact on the atmosphere of Mars. Not only consists the general atmosphere of our worst nightmare with around 95% being CO2, 1.9% Argon, 1.9% Nitrogen, and only 0.15% Oxygen. So really not a human-friendly atmosphere. It also has only pressure of just around 700 Pa during an average day around noon and a planetary average surface temperature of -63°C – basically a cold, toxic and thin air for humans. But luckily for our explorers, the surface temperature in the region the previous Mars missions were conducted can reach mild temperatures above freezing during the day time which is important to our equipment.
Since there is no International Standard Atmosphere (ISA) defined for Mars, I took the liberty to define the Martian Siemens Standard Atmosphere (MSSA) with a pressure of 700 Pa and 5°C at Martian sea level (once we find some sea level)
Looking at the specs of Ingenuity, it weighs 1.8 kg, and the rotor RPM is 2400. To give you some idea of Ingenuity’s size, the propeller diameter is 1.2 m (4 ft), and the height is 0.49 m (1 ft 7 in). Of course, Ingenuity will not fly very high and far, and it is flying autonomously as the distance to earth would be too big for direct control. With communication times ranging from around 3 to 22 minutes between Earth and Mars (one way), any maneuvering could not be done safely. That’ll be like driving through town with a friend and telling him/her to stop 3 minutes after you’ve passed the stop sign. Still, your friend reacts to your command after another 3 minutes, So with the atmospheric data and the RPM of the rotor blade, we can set up the simulation, and there is even a “Mars atmosphere” as a fluid with the right gas mixture for the correct fluid properties in Simcenter FLOEFD.
But would Ingenuity be able to fly on earth as well?
Well, let’s clone the project and adjust the MAAS to ISA atmospheric parameters and rerun the simulation. That’s a change done in less than 60 seconds. Let’s have a look at the results and how Ingenuity would perform on Mars and Earth.
Mars vs. Earth, who will win?
Well, looking at the Goals I have defined for the Lift and Torque on the top and bottom rotors of the co-axial configuration, we can see that, of course, the loads are much higher on Earth than on Mars, and that’s due to the denser atmosphere. Extracting these results from multiple projects based on their goals and plots can be easily done with the Compare feature in Simcenter FLOEFD.
|Force (Z) upper propeller [N]||3.6||364.1|
|Torque (Z) upper propeller [Nm]||-0.4||-33.9|
|Force (Z) lower propeller [N]||3.3||317.8|
|Torque (Z) lower propeller [Nm]||0.4||34.4|
Propeller force and torque comparison table between flying on Mars and Earth.
The torque sign is different between the top and bottom rotor due to the counter-rotation to negate the effects a single rotor would have. Otherwise, the helicopter’s body would rotate, and the whole flight dynamics would be a mess. It would look more like the crashing helicopters in the movies once the tail rotor is damaged and spiral down to the ground. And we don’t want that to happen on our first flight on Mars, do we?
The forces are measured in Newton here, and to see if there is enough lift for Ingenuity to lift off, we need to convert its mass in Newton. Taking the gravity, we would get a weight of 6.696 N on Mars and 17.658 N on Earth.
We can see clearly that on Mars, we have a combined lift of both rotors of 6.869 N, so in the current rotor pitch position, we are slightly above the weight of Ingenuity, and it would slightly rise off the ground.
On Earth, however, we would shoot up from the ground like a rocket on steroids with a combined lift of around 683 N, which is 38 times higher than Ingenuity’s weight. Of course, either the RPM or the rotors’ size and design would have to be adjusted for the earth’s atmosphere. Not to mention that the motors used in Ingenuity would not perform on earth, considering the torque they are designed to provide in the thinner Mars atmosphere. Also, the flight time is limited to around 90 seconds per flight, and the elevation limit is 5m, and it could therefore travel around 50m from the starting point and back.
So Ingenuity would have an RPM limited by the torque the motors can provide, and with that, the RPM is probably not high enough to lift off and therefore only make a lot of noise, almost like a fly on its back buzzing with its wings.
So if you wanted to do a race on Mars and Earth, Earth would lose with the same specs for Ingenuity if not done in a Mars climate chamber as shown in a video from Veritasium. But I also want to share some nice animations in which you can see Ingenuity on Mars with the graphs showing the torque and forces for the top and bottom rotor and Earth. This was simulated in transient with the sliding mesh approach. You can clearly see the effects of the blades passing each other and the impact on each other with their flow on the rotors’ forces and torque. The videos show the results for Mars’ and Earth’s atmosphere.
Ingenuity propeller forces and torques on Mars.
Ingenuity propeller forces and torques on Earth.
Also, an animation of the flow field develops and the blades’ wake with the blade tip vortices.
Ingenuity downwash visualization
The model was done in Solid Edge and simulated in Simcenter FLOEFD for Solid Edge, a fully Solid Edge embedded CFD simulation for designers. Still, such simulations can be conducted with any of the Simcenter CFD solutions.
If you liked what Siemens can do for Martian explorers, check out this video on the Curiosity rover (also a fitting name).
Don’t hesitate to contact Thanh for advice on automation solutions for CAD / CAM / CAE / PLM / ERP / IT systems exclusively for SMEs.
Luu Phan Thanh (Tyler) Solutions Consultant at PLM Ecosystem Mobile +84 976 099 099
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