Lunar Regolith
Section M 7.
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Lunar Regolith Structural Properties

Lunar Regolith has many unique properties. The most obvious one is that the particles of dirt are very jagged, which causes them to interlock and have inconvenient, or even harmful, effects.

The particles of Lunar regolith don't flow over each other. Unlike Earth sands, lunar dust hasn't been weathered, so the grains are very jagged. Subjected to pressure, such as the edge of a core-sampling instrument or the blade of a shovel, they jam against each other and resist the invader almost like solid rock.

Andrew Chaikan mentioned in his book A MAN ON THE MOON that the dust even caused hay fever in some of the astronauts. The jagged edges irritate the sinuses the same way pollen grains do. We'll need top-notch air filters to cope with that.

The essay in THE LUNAR SOURCEBOOK, section 9.1.6, discusses compressibility of the soil. Generally, the stuff (from Luna 16 and Luna 20 samples) seems to resist compression by pressures up to 1.2 kPa, and then yield dramatically to pressures up to 50 kPa. After that, it won't budge. The impression I get is that at 1.2 kPa, the edges on the grains start to break, allowing them to slip. At 50 kPa, you've crunched it as much as you can and you're into trying to break down the crystalline lattice of each individual grain.

I'm imagining that in a funnel-like device, the jagged edges on the grains would make them resist slipping past each other to sift through the funnel. We might be able to get around this by vibrating the soil so the individual grains bounce off each other.

Incidentally, Russian engineers used a clever technique in building the Aswan Dam that might serve us somewhere along the line. By vibrating the sand at one frequency, they got the sand to flow freely, and at a different frequency the sand compacted so that edges on individual grains fit together. That made it easy for them to move the sand into place, and then lock plain sand together to form a wall strong enough to compete with a similar mass of concrete.

A mechanism to experiment with vibrating moon sand, even a tiny little thing, might be a very useful addition to our manifest for the first flight. We'd need a way to dig up the stuff, dump it into a Oedometer (compression tester), vibrate it, and then dump it out again. A microscope to inspect the grains would be useful, too; easy to add to a television camera. (Mr. Wizard does it, after all.) The crew could deploy a remote-controlled test rig like this and then we could use our robots to test sail samples from all around the lunar base.

Lunar Regolith

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