Ingenuity- Mars 2020 Helicopter, Deployment & Operations Options

[Art Martin]

I'm putting this in the Early Drives category because I believe that one of the primary purposes of these first drives is to find a spot for the helicopter.

Is anyone else wondering like I am just what the terrain needs to look like to set the helicopter down? It sure looks to me that the areas we're in right now are largely free of obstacles for flying and landing with no large rocks. Unless you go for some completely sand covered spot I'm not sure you're going to find any areas any more pristine. Does anybody have any info about what type of zone they are exactly looking for? Since the helicopter is not really designed to be used for investigation of terrain but more as just a proof of concept of flight, I would imagine the choice of area would be wide open and flat.

Here's what I've got so far about upcoming events.

1. The helicopter below the rover limits ground clearance so it is vital that the helicopter phase be early in the drives so the rover is not limited in mobility.

2. The main purpose of the helicopter is proof of concept of Mars flight so the emphasis is not using it for exploration/route planning/research photography but merely that we can sustain flight - take off, fly autonomously, and land safely.

3. Once deposited on the surface, it will take a number of days of check outs prior to the first real flight.

Should we create a new topic that is discussion about the helicopter?

[mcaplinger]

Some interesting info in https://trs.jpl.nasa.gov/bitstream/handle/2...L%2318-3381.pdf -- stuff in JPL TRS is circa 2018 so might be out of date though.

[Pando]

Some interesting info in https://trs.jpl.nasa.gov/bitstream/handle/2...L%2318-3381.pdf -- stuff in JPL TRS is circa 2018 so might be out of date though.

Great info there. One thing that caught my eye was the future use of a helicopter as "Fetcher":

• Fetchers go carry something from one place to another"
• Like collected rock samples to a single pile for Mars Sample Return

[rlorenz]

Great info there. One thing that caught my eye was the future use of a helicopter as "Fetcher":

Unlikely, IMHO. Helicopters do not scale up well.

Beyond the obvious thrust challenge in the thin Martian atmosphere (i.e. classic momentum theory, and the Mach/Reynolds aerodynamic issues common to all aeronautics), there are some other rotorcraft-specific issues that actually are rather challenging for Ingenuity that one only confronts when one gets into the real details of design and test.

First is heat transfer. The thin atmosphere gives almost no cooling. The Ingenuity motors have parts made of beryllium to act as a heatsink, but even then I think overheating is actually the limiting factor on fliight duration, not battery energy.

Second is aeroelasticity. There's a similarity parameter called the Lock Number (that I hadnt heard of until I started working with rotor people on Dragonfly) that is important in assessing the structural damping of blade flexing. Again, the thin atmosphere is the problem, it provides no damping so blade oscillations can build up.

Both of these issues get worse as you scale up. So at the NIAC / Powerpoint / student-final-year-project level, yes you can mock out neat-looking hexacopters and stuff in the 10-20 kg range and they look like they should fly, but once you really start poking into the thermal and mechanical design, I bet even those would not work out.

[fredk]

The thin atmosphere gives almost no cooling. The Ingenuity motors have parts made of beryllium to act as a heatsink, but even then I think overheating is actually the limiting factor on fliight duration, not battery energy.

That's interesting, and surprizing. Since the rotors must produce comparable downward thrust on Mars as on Earth (to within an order of magnitude, anyway, considering the lower gravity), via a much greater rotor velocity, I might've guessed that the cooling effect of that air would be comparable too. I guess that means that thrust doesn't scale the same as conductive cooling with air density.

[rlorenz]

That's interesting, and surprizing. Since the rotors must produce comparable downward thrust on Mars as on Earth (to within an order of magnitude, anyway, considering the lower gravity), via a much greater rotor velocity, I might've guessed that the cooling effect of that air would be comparable too. I guess that means that thrust doesn't scale the same as conductive cooling with air density.

Thrust goes as rho * V squared. So for a given thrust and disk area, Martian density 50x less means the downwash has to be 7x faster

Power goes as rho * V cubed. So to generate that thrust we have to put 7x more power through the motor

But the heat transport goes as something like rho * V, so we have 7x less heat removal for a given temperature difference.


Now of course the disk loading of Ingenuity is a factor of a few less than typical small terrestrial drones, to make these effects a bit more manageable (and keep the rotor tips subsonic, etc.) but you can see the scaling really points to overheating being an issue for sustained operation at low density