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Hello everyone who have answered / commented on my question. Thanks for showing interest. What I was looking for is whether NASA or any other agency attempting to land something (any object) on moon, had anticipated that the object can "sink" into moon soil and knowingly took the risk and invested Time and money, Or they had crash landed objects on moon, and studied lunar soil in detail before deciding to go in for soft landing.

By the way, can anyone recommend any site (or many sites) which would give "absolutely in depth" knowledge about all lunar missions? (Knowledge pertaining to design aspects of equipments on board).

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The uncrewed Surveyor probes landed on the moon before Apollo did. They provided visual images of the landscape and pictures of soil samples that were dug up robotically. All the visual indications were that the terrain was fairly firm:

enter image description here

Surveyors also took pictures of their own footpads to see how deep they went into the soil:

enter image description here

The ground pressure of the Apollo LM, with its meter-wide foot pads, was only about 25% more than that of the Surveyor probes, so it would not sink much more deeply.

In particular, a marshy consistency would be very unlikely given the extreme temperatures (the ground alternates baking in bare sunlight for two weeks, then radiating heat away to bare space for two weeks) and lack of atmosphere.

The worst-case plausible scenario was that there would be a deep layer of dust fine enough to act like a fluid, but the Surveyor imagery showed large particles.

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  • $\begingroup$ I somehow always forget the existence of the Surveyor missions, but it makes sense, They were racing ahead to get to the moon ahead of the soviets but they didn't cut corners on it. On the other hand, Even assuming fluid-dust was possible, as long as the spacecraft sank reasonably evenly and didn't tip over, they could probably have still returned to orbit in the upper stage as intended. $\endgroup$
    – Ruadhan2300
    Nov 22, 2018 at 9:25
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    $\begingroup$ There is a ?Larry Niven? science fiction story about this. The expectation was that moon dust would vacuum weld together, but Mars has enough atmosphere to prevent vacuum welding. $\endgroup$
    – Martin Bonner supports Monica
    Nov 22, 2018 at 10:29
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    $\begingroup$ Martin Bonner are you thinking of the Clarke novel "A Fall of Moondust?" $\endgroup$
    – Organic Marble
    Nov 23, 2018 at 0:21
  • $\begingroup$ Act like a fluid? Weird phrasing... how do fluid-like solids act in a vacuum? $\endgroup$
    – Magic Octopus Urn
    Jul 2, 2019 at 19:43
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In addition to Russell Borogove's answer, it is worth mentioning that the Soviet Luna 9 soft-landed on the moon four months before Surveyor, and transmitted panoramic photographs of the surface back to Earth. According to the Wikipedia article, the mission confirmed that the lunar dust could support a spacecraft.

https://en.m.wikipedia.org/wiki/Luna_9

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