UKC

A couple of weeks ago there was a report that NASA intended to use drones on Mars to conduct aerial surveys. The gravitational acceleration for Mars is 3.71ms^-2 - approximately 38% that on Earth. The atmospheric pressure (therefore density) is 30Pa - 0.6% that of Earth. With such a thin atmosphere yet not a significant lower density, surely drones are going to have to work very hard to generate lift - about 63 times as hard in fact. Is this really feasible?

Any thoughts out there?  

I daresay someone more knowledgeable will be along to fill in the details, but as a rough guide:

The lower pressure is not a bad as it seems. If you have a wing (either as a fixed wing, or as part of a helicopter-style rotor), you are pushing it forwards through the air, and it develops both lift and drag.  Lift is good, it's what you want.  Drag is bad, it is what makes it take energy to move the wing through the air. It is also what will break the end off the wing if you move it too fast. Both lift and drag depend on the air pressure. So on mars you get much less lift, but also much less drag.  So you can build a huge, weak wing, and move it quickly, to get the lift you need without drag being a problem. And of course the lower gravity is great.

It'll still be tricky, because they'll need to pack a large wing or rotors into a small spacecraft for the journey there. But in terms of designing a workable wing it's not really much harder than doing one on earth, it's just a different optimisation problem.

The crewed Perlan 2 unpowered sail plane is designed to fly at 90,000 feet - about 1.6% of surface air pressure I think.  That’s in just under 1 g.

I should say that is a Mars relevant flight regime comparing (pressure / gravity).  It’s also intended to carry two peope.

I wonder if the harder part isn’t propeller design - they’ll need sufficient thrust from something highly energy efficient working in very thin air.  

You should email NASA they might not have thought of that...

I think I remember reading that 'copters are theorised to be difficult under those conditions but lightweight fixed wing planes should work well.

Wikipedia's article on the subject doesn't address that directly but most of the serious concepts it mentions are fixed wing craft.

https://en.m.wikipedia.org/wiki/Mars_aircraft

I'm sure there will be Martians complaining of noise pollution and invasion of their privacy.

NASA probably won't be using SI units though, so what could possibly go wrong

Are you sure about those numbers?  In the documentary The Martian, there was still plenty enough wind to cause a big old sandstorm to potentially topple the escape rocket, that meant the crew had to strand the AWOL Matt Damon on Mars for over a year.  Amazing he survived and is still making movies really.

I think Andy Weir was taking a little creative licence there...

https://www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-s...

Which is a shame, because when I looked into it I was rooting for him to be accurate. Love the book and was hoping it would turn out that the wind speeds in storms get ridiculously high or something.

It’s more problematic on Mars with bird restrictions this time of year.

Oh no!  I don't know what to believe in now!