Topology
Three Zones, Two Boundaries
Every outpost has the habitat, the surface, and a third zone between them that most plans leave out.
| Zone | Where | Holds | Rated |
|---|---|---|---|
| Pressurized, clean | The habitat | Air, water, food, sleep; no dust | Modeled |
| Unpressurized, controlled | The garage | Lit, thermally managed, dust-excluded, served by umbilicals | Modeled |
| Unpressurized, raw | The surface | Dust, thermal cycling, radiation | Modeled |
Each boundary has its own costs. Between habitat and garage the cost is gas, prebreathe time and dust carried into the breathing air. Between garage and surface it is machine dust, thermal cycling and the consumables a suit or rover spends outside.
The garage is the cheapest capability an outpost can add. Umbilicals for power, cooling and gas make long excursions possible, and longer excursions cut the overhead multiplier: about 2.5× at six hours outside, 1.9× at 10 hours, 1.75× at 12. That is worth about 1.5 crew.
Crossings
An Airlock Vents a Room of Gas Every Time
Gas lost per crossing at a 101 kPa cabin, before recovery.
| Interface | Gas per cycle | Why | Rated |
|---|---|---|---|
| 10 m3 airlock | 11.96 kg | Every crossing vents a room of gas | Modeled |
| Suitport, about 0.3 m3 | About 0.4 kg | The suit stays outside; the person climbs in through the back | Modeled |
| 10 × 10 × 4 m garage | 478 kg | Too much gas to cycle; kept unpressurized | Modeled |
Spacesuits and suitports are on Space Suits.
Life support
Closed Loops Have Flown; Closed Food Has Not
Air and water recovery run on two stations today. Food is still shipped.
| System | Data point | Note | Rated |
|---|---|---|---|
| ISS water recovery · NASA | About 98% of water recovered, 2023 | Urine, sweat and humidity back to drinking water | Observed |
| ISS oxygen generation · NASA | Electrolysis of recovered water | Running since 2007 | Observed |
| Tiangong · CMSA | Regenerative water and electrolysis oxygen | Since 2022 | Observed |
| BEAM · Bigelow Aerospace | Expandable module on ISS | Attached since 2016 | Observed |
| Haven-1 · Vast | Single-module commercial station | In development | Building |
| Starlab, Orbital Reef, Axiom Station | Commercial stations to follow ISS | In development | Building |
| Item | Figure | Rated |
|---|---|---|
| Oxygen breathed | 0.84 kg per person per day | Observed |
| Carbon dioxide exhaled | About 1 kg per person per day | Observed |
| Firm electrical load, four crew | 25 kW, against about 3 kW with no crew | Modeled |
| Volume of a 9 m, 50 m-class landed hull | About 2,800 m3, several times what seven crew need | Modeled |
Once a landed hull becomes a habitat, volume stops being the constraint. The mass budget then goes to shielding, closure, outfitting and boundary hardware.
Burial
Burying the Hull Freezes the Design
Land, unload, trench, place the hull, outfit, pressurize, then bury.
Under several meters of regolith a pressurized hull stays in tension. Depressurize it and the load reverses toward buckling, so routine depressurization is off the table once it is buried. Radiators, penetrations, cable routes, hatches and tanks have to be settled before the shielding goes on; everything important is serviceable from inside or designed never to need service.
Regolith goes over the large habitat. Water, better shielding per kilogram but too much to cover a whole hull, goes around a compact storm shelter inside it, where it is also the strategic reserve.
Buffer gas
The Gas Nobody Breathes
Most of a cabin atmosphere is diluent gas that fills pressure without feeding a fire.
| Destination | Source | Note | Rated |
|---|---|---|---|
| Moon | Little accessible nitrogen | Imported for a long time | Modeled |
| Mars | Nitrogen and argon in the atmosphere | Separated from gas already processed for CO2 | Modeled |
| Titan | Nitrogen atmosphere | Abundant | Observed |
| Carbonaceous asteroids | Ammoniated minerals | Extracted with water | Modeled |
| Helium, anywhere | Not for habitat air | Too scarce; kept for cryogenic purge and leak detection | Modeled |
A world can be rich in water and metals and still poor in the gas that fills most of its rooms. Cycling a large airlock hundreds of times vents tons a tour without recovery; a suitport cuts the cycled volume by another order of magnitude.
How closed
The Resupply Queue Sets How Closed a Loop Must Be
Each added nine of recovery cuts makeup tenfold and costs more hardware, power and maintenance.
| Recovery | Makeup | Fits | Rated |
|---|---|---|---|
| 90% | 1 kg lost per 10 processed | Low Earth orbit, resupply in days | Modeled |
| 99% | 1 kg per 100 | Moon, resupply in days to weeks | Modeled |
| 99.9% | 1 kg per 1,000 | Mars, resupply locked to 26-month windows | Modeled |
| Beyond Mars | Residual covered by stock or local production | Resupply no longer operationally meaningful | Modeled |
Food is different. A greenhouse expected to feed the crew needs stored food behind it in case the crop fails, so the first one carries its own mass plus much of what it replaces. Its real product is reliability data: failure rates, disease, pollination, nutrient-loop stability and the crew time it consumes.
The medical bay scales with evacuation time, not crew size: hours from LEO, days from the Moon, often impossible from Mars. Past Mars, medicine is treatment in place, and autonomous diagnostics become life support.
China
China Runs the Second Closed-Loop Station
Tiangong in orbit and Lunar Palace 1 on the ground.
| Program | Data point | Rated |
|---|---|---|
| Tiangong · CMSA | Three-module station, crewed since 2021; regenerative life support since 2022 | Observed |
| Lunar Palace 1 · Beihang University | Ground test of a closed bioregenerative habitat; a crew of four for 370 days, 2017-2018 | Observed |
| ILRS · CNSA and Roscosmos | Lunar south-pole station; basic model by 2035 | Projected |
Contested
Deliberately Not Claimed
The load-bearing uncertainties, tagged with the confidence they actually earn.
Suitport reliability is the largest open assumption. Hundreds of cycles a tour through a seal exposed to the dust it exists to exclude, with no operational heritage.
The garage is unsized. Its mass, power, thermal load and floor area have not been derived; it is the largest unsized object in the outpost design.
Station recovery rates do not transfer directly. ISS and Tiangong recover water in microgravity with resupply as a backstop; a surface outpost with no backstop needs a reserve of one missed resupply.
Record
Provenance and Data Sources
- Confidence
- Observed for flown, fielded or measured - Building for hardware and programs in development - Projected for announced plans - Modeled for original analysis
- Status date
- Q4 2026
- Data
- NASA ECLSS reports; NASA crew consumables; Vast, Axiom, Starlab and Orbital Reef programs
- China
- CMSA Tiangong; Beihang University Lunar Palace 1; ILRS
- Weakest link
- Garage mass and power