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A comment on NASA's Perseverance rover will attempt to land on Mars this week. Parent comment

Re:NASA's Perseverance rover will attempt to land on Mars th... by wongarsu on Tuesday February 16, 2021 @08:58PM (#26161678)
Simulating Martian air density is trivial, just build a vacuum chamber, remove the air, add some CO2 up to the right pressure. But simulating less gravity is incredibly hard:

Tethers are cheap but don't really allow free flight. Parabolic flights only give you a few seconds in fairly cramped space, and getting the low air density inside a plane sounds tough. A large spinning laboratory in space that can be spun up to simulate the desired gravity would be a solution, but we don't have that.

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Re:NASA's Perseverance rover will attempt to land on Mars th... by op03 on Tuesday February 16, 2021 @10:01PM (#26162138)
Why would it be complicated though? Is gravity changing a lot? I thought it was just a constant you plug into equations. Air density on the other hand I would think can change for hundred different reasons from one second to the next.
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Re:NASA's Perseverance rover will attempt to land on Mars th... by simonh on Wednesday February 17, 2021 @04:52AM (#26164634)
In context the comment is about simulating the conditions physically, hence discussion of vacuum chambers and aircraft.
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Re:NASA's Perseverance rover will attempt to land on Mars th... by jojobas on Wednesday February 17, 2021 @12:19AM (#26163004)
They still used a tether.

https://www.youtube.com/watch?v=GhsZUZmJvaM

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Re:NASA's Perseverance rover will attempt to land on Mars th... by usefulcat on Wednesday February 17, 2021 @12:13AM (#26162977)
Remove most of the batteries to reduce the weight? Trading flight time obviously. Of course since Martian gravity is only ~.4G, you'd have to remove a lot of weight, so a lot of batteries. On a device that's already been designed to be as light as possible.
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Re:NASA's Perseverance rover will attempt to land on Mars th... by dvdkhlng on Wednesday February 17, 2021 @08:04AM (#26165842)
Unfortunately, changing weight of the helicopter changes also changes inertia and the moment of inertia [1]. On mars, only the gravitational force changes, while inertia stays the same.

That will be somewhat more tricky (or impossible) to emulate on earth.

[1] https://en.wikipedia.org/wiki/Moment_of_inertia

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Re:NASA's Perseverance rover will attempt to land on Mars th... by onethought on Tuesday February 16, 2021 @10:23PM (#26162260)
For the moon practice lander they used a rocket that always pointed down to cancel out enough of Earths gravity to match the Moons gravity. Neil Armstrong seemed to like it :D

They could do something like that.

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Re:NASA's Perseverance rover will attempt to land on Mars th... by KMag on Wednesday February 17, 2021 @04:44AM (#26164567)
> used a rocket that always pointed down

Nit: the Lunar Lander Research Vehicle actually used a CF700 turbofan[0], not a rocket, to partially counter-act gravity.

[0] https://en.wikipedia.org/wiki/General_Electric_CF700

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Re:NASA's Perseverance rover will attempt to land on Mars th... by ggm on Tuesday February 16, 2021 @10:50PM (#26162435)
Neil Armstrong seemed to like it :D

It nearly killed him. I don't think anyone actually liked it, and I bet a lot of people in risk assessment went hard on the "nixon needs to prepare the death letter" story.

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