Stage 1 and Stage 2 Habitats:

Humanity’s next steps beyond Earth will not be giant leaps but careful, deliberate stages. Each stage builds the infrastructure and understanding needed to survive and eventually thrive on the Moon and Mars. In space architecture, these are often described as Stage 1 and Stage 2 habitats—two distinct but interdependent phases of human presence beyond Earth.

Stage 1 Habitats: The Era of Arrival

Stage 1 habitats are the first shelters humanity brings with it. These structures are typically lander-based or surface-deployed modules designed for short-term exploration missions. They are limited by what can be launched, landed, and assembled with existing rocket capacity—every kilogram counts.

Think of them as basecamps on another world: self-contained, portable, and rapidly deployable. Their main goals are to provide protection from radiation, dust, and temperature swings while supporting scientific activity and short-duration human stays.

Key examples include:

• NASA’s Artemis Base Camp concepts, which rely on pre-integrated surface habitats.

• ESA’s European Large Logistics Lander (EL3) architecture, capable of delivering pre-assembled shelters or inflatable modules.

• SpaceX Starship-derived surface modules, leveraging reusable landers as living and working platforms.

These systems share a common philosophy: mobility, modularity, and minimalism. They are engineering triumphs of packaging efficiency—high-pressure living capsules that can support human life for days or weeks, but not indefinitely.

However, Stage 1 habitats are transitional. They are designed for exploration, not permanence. Relying entirely on imported materials and consumables, they demand constant resupply and maintenance. Over time, this becomes unsustainable—both economically and logistically.

That’s where Stage 2 begins.

Stage 2 Habitats: The Era of Belonging

Stage 2 habitats mark the transition from exploration to settlement—from surviving on a foreign world to truly living there. Rather than bringing everything from Earth, Stage 2 systems use the environment itself as both structure and resource.

This is where the philosophy of in-situ resource utilization (ISRU) and site-specific architecture takes over. Instead of building on the surface, where radiation and temperature extremes are lethal, we begin to look beneath it.

Subsurface Strategies

Lava tubes, cave systems, and ice formations are natural fortresses against the harsh conditions of the Moon and Mars. They offer stable pressure environments, natural shielding from cosmic rays, and thermal moderation.

By sealing and outfitting these existing formations with inflatable or modular interior structures, we can create habitats that are safer, lighter, and more scalable than anything we can launch from Earth.

On the Moon, lunar lava tubes—believed to be hundreds of meters wide and kilometers long—could shelter entire research bases or even small cities. On Mars, collapsed skylights and ice-filled craters like Korolev present opportunities for hybrid ice-and-regolith shelters.

Engineering Meets Ecology

Stage 2 habitats represent a new design frontier: architecture that interacts with geology, ecology, and robotics. Their construction involves:

• Autonomous mapping and scanning, using lidar and drones to survey caves and voids.

• Inflatable membranes and liners, engineered to seal irregular rock surfaces.

• ISRU-based life support, extracting water, oxygen, and construction materials from local resources.

• Hybrid energy systems, combining solar, nuclear, and regenerative storage technologies.

Rather than imposing Earthly architecture on alien ground, Stage 2 systems adapt to the terrain—transforming caves, tunnels, and ice domes into living ecosystems.

From Shelter to Settlement

Stage 2 habitats are not just shelters; they are ecosystems in microcosm. Once structural safety is achieved, the next step is bioregenerative life support—systems that recycle air, water, and waste through controlled ecological loops.

Projects like MELiSSA (ESA), EDEN ISS, and Biosphere 2 have laid the groundwork for understanding how plants, microbes, and humans can cohabit in closed environments. The challenge now is integrating these systems within the geological shelter of a Martian cave or a lunar tube.

The evolution from Stage 1 to Stage 2 represents a philosophical shift. The first is about getting there; the second is about staying there. One is about endurance, the other about belonging.

Stage 1 habitats are metallic footprints; Stage 2 habitats are foundations for civilization.

Plan R and the Stage 2 Frontier

At Plan R, our mission is to design and prototype Stage 2 habitat systems—inflatable, modular environments that integrate with natural formations both off-world and on Earth. We view the development of cave-based, low-mass habitats as the logical next step in humanity’s evolution of shelter design.

Our work explores dual-use technologies:

• For space, we develop systems that can deploy within lunar or Martian lava tubes.

• For Earth, we apply these techniques to subterranean urban farming, disaster-resilient construction, and sustainable underground living.

By uniting architecture, robotics, and material science, Plan R bridges the gap between the two stages—building not just habitats but strategies for permanence.

Conclusion: From Landing to Living

The journey from Stage 1 to Stage 2 is the story of human adaptation. Stage 1 gets us there; Stage 2 helps us stay. The shift is more than technical—it’s cultural. It marks the moment when humanity stops surviving on new worlds and begins belonging to them.

In the end, the first true Martian city might not shine under an alien sun. It might hum quietly beneath an ancient lava tube—built by robots, grown with life, and designed by visionaries who, like Plan R, believe the best habitats aren’t built against nature, but with it.