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Comment by mrfusion | Hacker News Reader

I wonder why the helicopter drop was necessary then but not now?

The sky crane maneuver (as JPL called it) was necessary because if they descended propulsively to the surface, it could kick up a huge dust cloud. That dust could land on the rover and damage the instruments. See this awesome video: https://www.jpl.nasa.gov/video/details.php?id=1090

I think there was also concern about the hydrazine-fuelled landing rockets contaminating the site and instruments.

Listening for quakes is not an activity which will be impacted by the surface being gunked up.

The audacity of that.

I like to think some manager saw the army drop a humvee from a blackhawk and asked "why can't we do this, but on Mars?" and nobody came up with a good enough answer so they did it.

Edit: Why is this comment unacceptable?

I always just figured Wile E. Coyote was on staff at the time and had his ACME catalog handy.

Plus this awesome video: https://www.youtube.com/watch?v=gZX5GRPnd4U

I was standing next to one of the engineers who wrote the software for the landing while we were watching on the big screen at Twitter. A few moments after it landed he announced that his code worked and was being deleted to make room for surface operations code.

That's one of those cool things that never gets thought about outside the people directly involved. "Why keep the code required for landing readily available permanently, since it'll never ever need it again." That's one of the aspects that I enjoy about programming Arduino devices. I'm so spoiled to essentially unlimited memory on desktop/laptops (in comparison) that writing code to fit into extremely limited finite amounts of memory becomes challenging in a fun way.

I always wonder if there was any video released of the sky crane tests on Earth. I have to imagine they were done at some point, but I never saw it.

Weight. Curiosity weighs over twice as much as Insight and needed a special heavy lift landing device.

Insight doesn't need it, so no reason to spend the money on it.

I think it's because Curiosity was a rover and Insight is only a lander. A lander can have rockets on the bottom that slow its descent, but a rover can't, as then the wheels won't work. So the "helicopter drop" puts the rockets on a platform far above the rover (so the exhaust won't damage it) and then it flies away once the rover is on the surface.

Spirit/Opportunity were both wheeled rovers, and both landed with something under them; they had ramps that unfolded after landing, and the rover then proceeded to drive off the ramp onto the surface. So I don't think putting things under the wheels is necessarily a non-starter.

(But those rovers, IIRC, did a bounce-and-roll-to-a-stop style landing.)

The difference is that those rovers are a small fraction of the size and weight of Curiosity - the latter probably couldn't have survived a bounce-and-roll.

Curiosity was too heavy for the airbag-style landing: https://en.m.wikipedia.org/wiki/Mars_Science_Laboratory#Entr...

As I recall there was also something about the complexity of having the rover drive off the landing platform which was to be avoided. It would have been several feet of the ground and needed to get down.

I'd guess: Insight isn't a rover and thus less sensitive to a bad landing/getting stuck.

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