Glossary

The model produces a feasibility score from 0 to 100 for a given mission profile, blending consumables, physiology, psychology, decision quality, and skill coverage. Higher means more survivable. Below ~60, the model predicts the mission configuration becomes unsustainable before its end date.

A constraint set by physics or biology that you cannot negotiate around. CO₂ at 5% impairs cognition regardless of training. Bone loss happens regardless of motivation. Hard limits are the floor of what is possible.

All the inputs for a scenario: crew size, duration, destination, recycling efficiency, exercise compliance, privacy ratio, and the rest. You set these, and the model uses them to produce a feasibility score.

Whether a mission profile clears all twelve subsystems' minimum thresholds for the planned duration. A viable mission is survivable. It is not necessarily comfortable.

A pre-configured scenario the engine ships with (Mars transit, lunar Gateway, deep-Mars surface) to give you a starting point instead of a blank form.

The site's centerpiece simulator at /scenario. Takes a mission profile in, runs the model across all twelve subsystems, and returns a feasibility score with per-system breakdowns and the modeled failures that drove it.

One of the twelve domains the framework tracks: food, water, air, body, fracture, decay, awakening, continuity, decisions, skills, cascade, unknowns. They are modeled together because they couple. See cascade effect.

The minimum-population thought experiment. Scale your household to 150 people indefinitely without resupply: what breaks first? It's the calibration check that turns abstractions into concrete numbers.

A specific value where a subsystem flips from "stressed" to "broken." This is where the engine's smooth math suddenly turns into real consequences.

Anything the crew uses up that has to be resupplied, recycled, or grown. Food, water, oxygen, filter media, drug stocks. This is the bottleneck of every long mission.

The hardware that pulls carbon dioxide out of the cabin air. Short missions use lithium-hydroxide canisters. Longer ones use regenerable amine beds. When scrubbers underperform, that is the single most common cause of "the air problem."

How hard a CO₂ scrubber is working, expressed as a fraction of its rated capacity. Above 1.0 it cannot keep up, and cabin CO₂ starts climbing. See lethal threshold.

The point past which death becomes the expected outcome. CO₂ above ~10%, O₂ below ~12%, sustained core temperature above ~40°C. These are the bright lines.

Generating breathable O₂ from cabin water (electrolysis) or exhaled CO₂ (Sabatier reaction). This closes the loop on the air system. Efficiency is rarely 100%. The gap is what eventually kills you.

Reclaiming drinkable water from urine, sweat, and atmospheric condensate. The ISS achieves around 93%. A Mars-class mission needs higher. The closer you get to 100%, the more painful each percentage point becomes.

What fraction of a consumable the system reclaims each cycle. This number drives nearly every mass budget on a long mission, which is why the scenario engine treats it as a primary lever.

How this site frames the water margin: input minus losses minus recycling shortfall, tracked across the whole mission. It goes negative faster than people expect.

The maximum calories per day a closed-loop food system can produce. It is set by growable surface area, lighting, nutrient cycling, and crew labor. Below the ceiling you are fed. At it you are rationed. Above it you are losing weight.

Closed-loop, regenerable life support designed for missions over a year. Shorter flights use stored gas and water. Longer flights have to regenerate. Beyond low Earth orbit, this is required.

Your bones lose mineral density in microgravity, roughly 1-2% per month in the hips, spine, and legs without active countermeasures. Some of that loss is permanent.

Your muscles shrink and weaken in space, especially in the legs and back. This reverses partially on return to gravity, but sometimes not fully.

Your heart and blood vessels adapt to a low-load environment. On return to gravity, crew cannot stand up without help until their vascular tone recovers.

The effective free-fall environment of orbit. There is still gravity. You just have no surface to push against. This drives every other body-system change on this list.

The total ionizing dose a crew accumulates from galactic cosmic rays and solar particle events. This is the hard physical-risk ceiling on any deep-space mission. Shielding helps. Nothing eliminates it.

Vision changes from intracranial pressure shifts during long missions. The eyeball flattens, the optic nerve swells, and your prescription changes. The exact mechanism is still under active investigation.

Calories burned per person per day, set by activity level, body mass, and ambient temperature. This drives the food budget, and the food budget drives nearly everything else.

Our umbrella term for everything a crew does daily to keep their bodies from falling apart: exercise, nutrition, resistance loading, sleep schedules. Skip any one of them and health measurably erodes.

What fraction of the prescribed daily exercise the crew actually completes. The scenario engine treats this as a lever because it is the one mitigation crews try to negotiate down. And they always do.

The overall drift in body capability over a mission: less bone, less muscle, less vascular reserve, slower reflexes. These are modeled together because they move in lockstep.

The predicted moment a small isolated crew flips from "irritated but functional" to "structurally fractured." Typically 90-180 days into isolation, though the variance is wide.

The first ~30 days of a mission, when everything is new and morale runs artificially high. This phase hides the problems that surface later. Real psychological data only starts being meaningful after it ends.

Roughly days 30–90, when small frictions start compounding. Confined-environment psychology starts mattering. The first phase where the mission can actually go wrong from interpersonal causes.

The point past day ~120 where motivation, mood, and group cohesion drop sharply unless actively maintained. Polar winter-over data is the closest analog we have.

Sub-groups within a small isolated crew aligning against each other. Documented in Antarctic stations, submarines, and analog studies. Predictable above ~6 crew members.

Robin Dunbar's estimate (~150) of the maximum stable human social network size. You can know about 150 people well enough to maintain real relationships. The site's 150 test takes this seriously as the upper bound on a self-sustaining colony's interpersonal cohesion.

The phased model of crew mood and cohesion across a long mission: novelty, irritation, fracture risk, endurance wall, return adjustment.

Slow shifts in habit, hygiene, communication, or decision quality that emerge over months of confinement. Hard to notice from inside the crew. Easy to see in the data after the fact.

Operational isolation: no realtime communication, no evacuation option, no external help. The default state of any deep-space mission. Distinct from social isolation in the conventional sense.

Measurable decline in reaction time, working memory, and decision quality under chronic stressors like sleep loss, elevated CO₂, and sustained anxiety. Your brain still works. It just works worse.

The way chronic stress drags down everything else: sleep, immune function, gut health, decision quality, interpersonal patience. It acts as a multiplier on every other risk on this list.

The progressive deterioration of group decisions under prolonged isolation. Manifests as slower consensus, more interpersonal weight, less risk tolerance. The reason ground control matters even when the crew technically doesn't need it.

Chronic shortfall against the 7-9 hours crews actually need. This is the single biggest amplifier of every other psychological and cognitive problem on this list. It has been endemic on every long-duration mission to date.

The framework treats morale as a lever, something you can actually influence. Privacy, food variety, communication latency, and meaningful work all feed into it. Ignoring morale does not make it go away. It just defers the cost.

When exactly one crew member knows how to do something critical. If that person goes down, the mission loses the capability entirely. This is what the skill model is built to detect.

Having at least N+1 crew trained on each critical skill. The minimum N depends on mission length and risk tolerance. Always more expensive than expected.

Deliberately training crew on skills outside their primary role to build redundancy. Costs ground time. Pays back in mission resilience.

The mix of roles, skills, and personalities chosen for a mission. This is modeled as a multi-axis input, because a head count alone tells you nothing. The wrong mix can break a mission that has the right hardware.

The number of humans on the mission. The simplest input to the engine, and the one that changes nearly every other constraint in ways that are not proportional.

The minimum group size needed for some emergent property to kick in. Dunbar bonding needs ~150. Genetic viability needs ~500-5000. Sustainable role coverage needs ~30+. Different questions have different thresholds.

A long-term settlement designed for indefinite occupation. The physics are different from a mission: it must sustain itself or it dies. There is no "we'll resupply next year" version.

The smallest group that can persist genetically and culturally over generations without external input. Estimates range from ~500 to ~5000 depending on what you're optimizing for.

Closed-loop on every consumable, with no resupply, indefinitely. The strict definition. Almost no proposed colony architecture currently meets it.

The variation in the colony gene pool over generations. It drops without active management, even at population sizes that feel like they should be large enough.

Reduced fertility and increased disease susceptibility from a small breeding population over generations. The biological floor under minimum viable population.

Documented zero-G mammalian reproduction is essentially absent. The most basic continuity question, can humans actually reproduce off Earth, has no real answer yet. This is the blocker on any generational mission.

When one subsystem's failure propagates into others, often in surprising ways. This is the framework's central thesis: the twelve subsystems are coupled. A CO₂ scrubber failure is an air problem today. Six days later it is a cognition problem.

A specific instance of the cascade effect: a documented or modeled chain of one failure causing the next. Visualized in the cascade simulator.

The specific way a subsystem can break: hardware, supply, human, environmental. Each subsystem has multiple distinct modes, and each mode produces a different cascade signature.

A physical component breaking — pump, valve, scrubber bed, sensor, seal. The failure category every flight engineer plans for.

Crew error, incapacitation, illness, or death. The failure category every flight engineer plans for less rigorously than they should.

A component, whether hardware or human, whose loss takes down a whole subsystem. Redundancy is supposed to eliminate these. Budgets quietly leave them in.

Things we know we do not know. Radiation effects on multi-year cognition, partial-G physiology, long-term gut microbiome stability. These are listed and tracked. Each is a flagged risk that can eventually be studied.

Things we do not know we do not know. You cannot plan for these. You can only leave margin for them. This is why no mission plan, however careful, is ever sufficient on its own.