[gokhan]

Unless other parts of the comet is more flat, that landing gear design seems clearly wrong. It included bolting itself to the surface, if I remember correctly, but it seems almost impossible to fixate three legs with almost no gravity on that surface.

[masklinn]

> Unless other parts of the comet is more flat

It's pretty hard to see the details of a cometary surface from earth. And there isn't much you could do with no gravity and an all-rubble surface either way.

> It included bolting itself to the surface, if I remember correctly, but it seems almost impossible to fixate three legs with almost no gravity on that surface.

Philae had a harpoon for anchoring itself to the surface (with a thruster on the other side to compensate). The harpoon failed to fire. The legs were not intended for fixation, only to dampen the landing.

[gokhan]

Maybe they should put it into a very very close orbit and wait for the micro gravity doing it's work. Maybe large harpoons tangling on sticks every side. It's easy for me to talk at this point, but it's their job to expect that surface. I don't think other comets passing closer by have better surfaces.

I'm following this mission almost from the beginning, amazed by the success despite Philae's short lived life on comet, and think the science aspect of it all is unbelievably great. But that landing moment made all the difference, and it failed to fix it on the surface, hence the criticism.

Would we consider Curiosity mission success if landing put it upside down?

[ragebol]

IIRC, the designers had little idea what kind of surface the comet would have. Could be ice, could be rocks, could be dust.

What kind of landing gear + fixation gear would have been better?

[aruggirello]

INANE (I Am Not A NASA Engineer), but perhaps 4 or better yet more legs arranged in a tetrahedron or analogous polyhedron would better ensure the lander did not get stuck inside a crevasse; an inner rotating body could then bring the lander into a working position. The more the legs, the higher the chance the lander could 'roll' to a lower ground when initially bouncing off the surface, but the optimal number of legs could be determined in advance by simulating the terrain (you wouldn't want it to roll all the way down a slope, ending at the bottom of a crevasse etc.).

Harpoons protruding from each leg could be fired automatically as soon as a stable enough position was detected, or manually when deemed safe; having more legs available could only improve chances of getting a safe fixation.

[dotancohen]

How much mass would another leg have? Which scientific instrument with that mass would you suggest to eliminate for that extra leg?

[krallja]

> INANE (I Am Not A NASA Engineer)

Neither are the people who worked on this lander :)

[whorleater]

Philae had a harpoon to anchor itself to the surface, but ended up malfunctioning. I assume had it actually fired, the engineers balanced the need for extra landing gear and scientific instruments quite well.

[Cogito]

There were three aspects to fixing the landing, to my understanding.

Legs keep it oriented, give a stable platform, and cushion the initial landing.

Top thruster pushes it into the surface, damping any bounce back from the impact.

Harpoons attach to the surface, affixing it permanently.

The top thruster was reported to not work at all, and the harpoons were unable to work by themselves. It's not clear if they would have worked if the top thruster was working as well.