South Pole vs. Tranquility: Site Selection as Civilizational Choice

The Case Isn’t Close

Any discussion about the first lunar settlement site should be honest about the math. Doing so requires acknowledging that, from an engineering perspective, the south pole is the clear winner. It has near-continuous solar availability, in the range of 80-90%+, in several locations around the rim of the Shackleton crater and the adjacent de Gerlache crater.¹² Periods of darkness are infrequent and brief, with the longest observed to-date being about 3-5 days, compared with 14 days at the equator.¹ That’s a categorical difference in energy system architecture for power-constrained early operations.

The south pole craters also contain permanently shadowed regions (PSRs) with confirmed water ice deposits.³ That ice becomes drinking water, oxygen via electrolysis, and hydrogen for fuel - the ISRU holy grail. These resources are all survival-critical for any remote outpost. Any site without them must import them from Earth or transport them from extraction sites with severe cost penalties.

The south pole also has a stable thermal environment. The equatorial regions experience temperature swings approaching 300°C between lunar day and night — from roughly +120°C to below -170°C. That kind of repeated thermal cycling fatigues materials, stresses joints and seals, and shortens the operational life of any hardware exposed to it. Polar sites, by contrast, maintain far more stable thermal environments: permanently shadowed regions are effectively temperature-stable, and sites along crater rims with near-constant illumination experience temperature swings of perhaps 60°C - nearly a 5x reduction in thermal cycling amplitude, and far less frequently since periods of darkness are fewer and comparatively brief. These effects compound exponentially according to a power law (the Coffin-Manson relation). Accordingly, and strictly accounting for fatigue due to thermal cycling, the expected operational life of hardware at the south pole would be, conservatively, in the range of 10x longer for ductile metals, 100x+ for electronics solder and integrated circuit interconnects, and 10,000x+ for brittle materials like ceramics.⁴

There is a reason why Artemis is targeting the south pole. Every serious proposal from JAXA, ESA, Roscosmos, and private industry points in the same direction. Given current transport economics and power technology, the case is not close enough to argue against honestly.

What “Optimal” Means

“Optimal,” though, depends entirely on what you’re optimizing for. In the first phase of lunar settlement, it makes sense to optimize for energy reliability, resource accessibility, and operational simplicity since dependence on Earth resupply is prohibitively expensive. The south pole excels at all three of these compared with any equatorial site. But the first phase of lunar settlement is not the end state. It’s the foundation upon which future life on the Moon can be built.

Bootstrapping an outpost is not the same as building a permanent settlement where people choose to live. Historical precedent shows that first settlements are often chosen for survivability rather than quality of life. Subsequent settlements can be built with more consideration toward meaning and permanence. There are many examples of this, but to pick one: Moscow was chosen for its survivable, defensible location. Then Peter the Great built St. Petersburg on a swamp to project a different vision for Russia, one built around meaning and culture, and to serve as a gateway to Europe. After he moved the capital there, it became the center of Russian political and cultural life for over 200 years. Those considerations will exist for the Moon, too.

The Starship Inflection

The south pole’s resource advantage is largest under current launch economics. However, that advantage diminishes as launch costs decrease, making other factors more competitive. Right now, launching a payload to low-earth orbit (LEO) costs around $1,500 per kilogram. Landing that payload on the Moon is significantly more expensive, because to do so requires moving the payload into lunar orbit and then landing it safely on the lunar surface. NASA estimates this mass ratio or location factor at approximately 7.2.⁵ Accordingly, transporting payload from Earth to the lunar surface costs over $10,000 per kilogram at the current best prices available using the Falcon Heavy rocket. This is already an improvement of several orders of magnitude from the shuttle era. Still, at these prices, anything you can produce locally is worth producing locally. Water ice at the south pole isn’t a nice-to-have, it’s what makes the economics of permanent settlement viable at all.

In the future, though, launch and transport costs will continue to fall. As this happens, the price differential between import and local production shrinks significantly. SpaceX’s Starship is projected to decrease launch costs by an additional one to two orders of magnitude. According to Elon Musk, SpaceX’s own targets for Starship are in the range of $10-20 per kilogram to LEO. Assuming more realistic launch costs and economic timelines, that may look more like $100-200 nearer term.⁵ Factor in the lunar surface location factor and you arrive at estimates between $70-1,400 per kilogram. At those prices, even if only partially achieved, the south pole’s resource advantage becomes less decisive, and other factors become more competitive. The resource case doesn’t disappear - the south pole’s solar exposure and water ice will remain valuable. But lower launch costs eventually make nuclear power a more viable option everywhere and importing resources no longer prohibitively expensive. Cheap launch doesn’t eliminate the south pole’s advantages. It makes them less decisive.

What Tranquility Has That Shackleton Doesn’t

Tranquility Base is where humanity first set foot on another world. That’s not a triviality. Every major human civilization has recognized that the sites of founding moments carry weight that reshapes how communities understand themselves. The first human steps on the Moon happened at 0.67°N, 23.47°E. That’s a fact about the world that doesn’t expire.

Tranquility has a stronger operational case than many people realize, too. The Mare Tranquillitatis is located near the lunar equator, which provides several operational advantages. Equatorial sites are accessible from low lunar orbit (LLO) roughly every 90 minutes. NASA had to design the entire lunar Gateway program around the south pole’s limited accessibility - requiring a far more complex Near-Rectilinear Halo Orbit (NRHO) trajectory and correspondingly complex orbital infrastructure that offers south pole site access only once every roughly 6.5 days.⁶ On top of this, surface access from NRHO adds an estimated delta-v budget of up to 1400 m/s or more for a round trip.⁶ Propellant mass requirements grow exponentially with delta-v, meaning less payload can be delivered by the same vehicle.

Additionally, Tranquility, being on the equatorial nearside, has visibility to Earth almost constantly, reducing the need for expensive communication infrastructure. The south pole, by comparison, has direct line of sight to Earth only about half the time, in two week windows, meaning communication will rely on relay satellites.¹ The south pole is also rugged, with deep craters and steep slopes, and limited flat areas for landing or building. Recent research published in Science Bulletin identifies just 0.6% of south pole terrain as suitable for landing.⁷ Tranquility lies on the vast basalt plains of the lunar surface, where there is far more abundant flat land. For a burgeoning settlement to scale up operations and enable more cargo deliveries, landing and building area is critical.

Tranquility has easier and cheaper communication and landing, and can sustain a far higher operational tempo from simpler orbital mechanics. Operational advantages alone cannot build a civilization. Communities cohere around shared history and symbolic geography. Settlers at Tranquility would wake up where humanity first walked on their new world. That’s a foundation for something that Shackleton, optimal as it is, simply cannot provide.

The Right Sequence

Lunar settlement isn’t a binary choice. It’s a sequence. This is how terrestrial civilization developed — operational posts become cities, symbolic sites attract habitation that resource sites alone don’t generate, and the map of human settlement reflects both engineering necessity and human meaning.

Humans should settle near the south pole first, because the engineering case is compelling and the constraints of our current capabilities demand it. The first permanent settlement establishes the operational foundation, proves the life support model, develops key resource and ISRU competency, and establishes Earth-Moon logistics.

There will be a second settlement, though, and the location for it matters just as much as the first. As launch economics shift and the south pole’s resource advantage becomes less decisive, Tranquility’s operational strengths — easier orbital access, simpler communications, higher landing tempo, and abundant flat terrain — become competitive on engineering terms alone. Add the historical weight of the site where humans first set foot on another world, and the case is strategic, not just sentimental. The question is whether the second settlement will be chosen as deliberately as the first.

Footnotes

1. Illumination conditions of the lunar polar regions using LOLA topography. Mazarico et al. 2011, Icarus. Abstract can be found here ↩ ↩² ↩³

2. Preliminary quantification of the available solar power near the lunar South Pole. Ross et al. 2023, Acta Astronautica. Abstract can be found here ↩

3. Detection of Water in the LCROSS Ejecta Plume. Colaprete et al. 2010, Science. Full paper can be found here ↩

4. Derived from application of the Coffin-Manson relation to observed temperature differentials between sites. ↩

5. Take Material to Space or Make It There? Jones 2023. Full paper can be found here ↩ ↩²

6. Enabling Global Lunar Access for Human Landing Systems Staged at Earth-Moon L2 Southern Near Rectilinear Halo and Butterfly Orbits. May et al. 2020. Full paper can be found here ↩ ↩²

7. Navigating the lunar frontier: one hundred landing sites at the south pole for future mission challenges. Feng et al. 2025, Science Bulletin. Abstract can be found here ↩