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Comment by lisper | Hacker News Reader

I wonder if there's a reason they didn't design the lander with some sort of energy-absorbing material (something analogous to the crush zone in a car) on the bottom of the landing pads to prevent bounces. I thought I'd "wonder out loud" here because someone on HN might actually know the answer.

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The legs were actually designed to dampen the impact and use that energy to drive ice screws into the comet: https://www.youtube.com/watch?v=-77-Z_DHTlY#t=1m40

I see. Thanks!

Its landing was supposed to be softened by a thruster, which didn't work, and it was supposed to be held fast upon landing by harpoons, but they also failed. They presumably did use some shock absorbtion, but it was probably engineered under the assumption that at least some of the rest of the landing system would have worked.

The thruster, if it had fired, would actually have propelled the lander towards the comet. The idea is that it would hold the lander in place against the ground, not slow the lander's descent.

Really too bad the harpoons failed. Why I wonder?

http://image.slidesharecdn.com/rosettamediabriefing16octbiel...

The thrusters to counteract the force of the harpoons were bust.

Apparently the propellant they used was found (after launch, unfortunately) to be unreliable in a vacuum.

http://www.wired.com/2013/10/in-space-no-one-can-hear-your-n...

Ouch. This strikes me as a particularly avoidable mistake.

It's not that they don't work in vacuum, it's that they don't work after a decade in extremely cold vacuum.

... unlike a not-so-harsh room-temperature vacuum ;)

OK, after a decade extremely cold and in a vacuum.

Spec of the anchoring system: http://www.esmats.eu/esmatspapers/pastpapers/pdfs/2003/thiel...

ten years at near absolute zero?

From the article it seems they assumed the comet surface would be a soft layer of dust, absorbing the impact

in the initial race to the moon it was widely speculated that the moon was covered in a deep layer of ultrafine dust, and any spacecraft landing on it would be liable to sink. Arthur C. Clarke's novel "A Fall of Moondust" was based on this thinking.

It seems astronomers have a bias towards assuming dust will cover stuff. Perhaps this says something about their office space.

I thought they calculated the amount of dust that based on the current rate dust accumulation and extrapolating based on the believed age of the universe. It's a little surprising we have not corrected that thought since the moon landing.

Who's to know why they were wrong — it's just amusing to see the same error come up again. I prefer the theory that they look around their offices and extrapolate ;-)

They weren't wrong, there's plenty of dust on the comet. The first photo of the initial landing site is visible precisely because of the shadow cast by a giant cloud of dust kicked up by the lander.

They were wrong about the amount of dust, not the presence of dust -- as was the case with the moon landing. There's plenty of dust on the moon, too, just not oceans of it.

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