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Comment by rwmj | Hacker News Reader

Wikipedia page about the Ingenuity helicopter: https://en.wikipedia.org/wiki/Ingenuity_(helicopter)

I didn't realise it was so large (1.8 kg, 1.2 m diameter rotors). I suppose it has to have the large rotors to be able to generate lift in the thin atmosphere, 1/160th of the density [edit: pressure, not density - thanks Robotbeat] of the earth's atmosphere at sea level according to the article.

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Turns out it’s not quite so bad. 1/160th the pressure doesn’t mean 1/160th density because CO2 is denser for the same pressure, especially Martian temperatures. And Jezero crater is much lower than Mars “sea level.”

This apparently also introduces some serious control issues - with propellers that long and massive, there's substantial lag between control inputs and flight changes. In ground tests in pressure chambers, it was difficult-to-impossible to manually pilot the thing, and even under computer control it's very clearly shakier than Earth-atmosphere drones.

Wow, I never realized it might be 160 times harder to get off the ground on Mars. Perhaps lower gravity helps on the other hand, though the difference definitely seems way lower (please correct me if my physics is wrong).

Yup - lower gravity helps, but by much less than the orders of magnitude by which the thin atmosphere hinders.

its blades rotate over 2000 rpm. it can fly upto 90 seconds consuming 10 to 15 watts. it is meant to be eyes of main rover to guide it.

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