[sandworm101]

Lol. SpaceX has landed on prepared surfaces, concrete pads on land or on large barges. They literally have a big X to mark the target. Let's see them land on some random beach, an uneven surface that may or may not subside. But that is still peanuts comparted to the moon's surface.

[JumpCrisscross]

> that is still peanuts comparted to the moon's surface

Sure. I'm not trivialising the problem in an absolute sense. Just going from floating barge or chopsticks to Moon is a simpler set of problems than reïnventing the sort of translational velocity and attitude control needed to get to first base.

[sandworm101]

For selecting and touching down on an unprepared surface, rockets are not the stepping stone. Start with helicopters. It is the same problem: can I land there and what will happen when I put weight on the surface. Try programing a large helicopter to identify and land on a random chunk of rocky terrain. It is not easy. And the bigger/taller the craft, the more difficult it becomes. Then add a 10-second time limit.

[Kye]

Are the sky cranes of Mars viable without an atmosphere?

[ted_dunning]

You say this based on your history of landing rockets on the moon?

And on your history of dealing with the lunar regolith near the poles?

[JumpCrisscross]

> You say this based on your history of landing rockets on the moon?

Actually, mini propulsive landers in lunar regolith stimulant. Yes. In atmosphere and with Earth gravity, both of which make it more annoying and more difficult.

[nomel]

For any of these landings, it's a problem of 3d positional/velocity precision. SpaceX has prove that they can reliably land on a target, usually within meters, with negligibly delta velocity on contact.

In other words, they've proven they have the control systems in place for placing a craft at a precise location, with a precise velocity. What requirement do you see outside of this that are far outside of placement and velocity? Autonomous mapping and adjustments for approach maybe?

Let's not assume they're going to try to use their current earthly landing legs.

> land on some random beach,

They did this I believe two starships ago, when they landed in the ocean. Came to zero xyz velocity some target distance above the water, and hovered for a bit. Unfortunately, the surface tension of the sea couldn't support the weight once they lowered for touchdown.

[literalAardvark]

> 3d positional/velocity precision. SpaceX has prove that they can reliably land on a target, usually within meters

On Earth, which has GPS. On a very highly engineered landing surface.

Landing on inertial guidance on soft regolith is a whole different ballgame.

[nomel]

> Landing on inertial guidance

Which is not the future. Optical/lidar/positioning radio is the future, to make it closed loop (NASA’s Laser Retroreflector Array for high, lidar/optical for low altitudes).

> On a very highly engineered landing surface.

As I mentioned, we shouldn't assume the earthy landing legs are used. That would be a very silly assumption.

From what I can extract from your comment, you believe that the positioning system and landing legs are the issue, rather than the control systems. I suspect both are somewhat related: positioning system to place it over predictable regolith with some, yet-undeveloped, landing legs that need to work at 1/6th gravity.

I'm of the opinion that it's possible/solvable, as is NASA. It would be helpful if you would answer why you think it's not possible: what requirement do you see that make positioning and landing on regolith unachievable for SpaceX?

[1] https://www.nasa.gov/centers-and-facilities/langley/nasas-la...

[literalAardvark]

It may be possible. It may also be that the regolith is too fluffy in that area to support such a large structure without a pad. I don't believe we know.

Athena had multiple laser altimeters on board: they failed to get a fix, perhaps because of the weird surface.

It's my opinion that this isn't something that's easy to do, even for a company that has landed on Earth.