The Lunar Reconnaissance Orbiter data is definitive. Shackleton Crater, 21 kilometers in diameter, sits almost precisely at the lunar south pole. The rim receives near-continuous sunlight, roughly 80 to 90 percent illumination depending on the exact position. The permanently shadowed interior contains confirmed water ice deposits. It is the single best location for a permanent settlement on the Moon.

The engineering case is compelling but not simple. The rim elevation varies between 4.2 and 4.8 kilometers above the crater floor. Slopes average 25 to 35 degrees on the inner wall. Building on the rim means constructing on terrain with an average grade that would be illegal for a road on Earth. We need to design foundation systems for a surface where regolith depth is uncertain and bedrock composition is largely inferred from remote sensing.

The LOLA altimetry data gives us sub-meter topographic resolution along the western rim. There are three candidate plateaus with less than 5-degree slopes over areas exceeding 500 by 500 meters. Site Alpha-7, at 89.83 degrees south latitude, shows the most favorable combination: flat terrain, near-continuous line of sight to Earth for communications, and a traversable path down to the permanently shadowed regions within 3.2 kilometers.

I have been modeling thermal cycling at that site. The near-continuous sunlight is a double-edged sword. Surface temperatures on the illuminated rim cycle between roughly minus 50 and plus 50 degrees Celsius as shadows from nearby terrain features sweep across. That 100-degree swing happens on timescales of hours, not the two-week day-night cycle of equatorial sites. Every structural joint, seal, and surface coating must be rated for continuous thermal fatigue.

The Japanese SLIM mission and the Indian Chandrayaan-3 lander both returned data on south polar regolith composition. Anorthosite-rich material with ilmenite concentrations around 5 to 8 percent by weight. That ilmenite is significant. It contains titanium and iron oxides. With the right processing, that is structural metal and oxygen extracted from the ground you are standing on.

My structural designs assume a phased approach. Phase one: robotic preparation of a landing pad using sintered regolith, 50-meter radius, microwave-fused to a depth of 30 centimeters. Phase two: deployable habitat modules from the first crewed Starship HLS. Phase three: excavation into the rim itself for radiation-shielded subsurface habitation. The rim is not just where we land. It is where we dig in.