System Category
Human Factors
You can ground-test hardware. You can't ground-test what people do to each other after 90 days in a sealed can. This page tracks the constraints that come from inside the crew.
Every engineering system on a spacecraft depends on a human somewhere. People are the load-bearing component that never shows up in the schematics. The question behind all of this research: what makes humans break under pressure, and what can we build around them to keep that from happening?
The Human Factor Map
Psychology and social cohesion. Crews go through a predictable timeline: novelty, then irritation, then factions start forming.
Day 1 → Day 90+ → Collapse risk
Bone loss, muscle atrophy, cardiovascular deconditioning, radiation exposure, and vision impairment.
1-2% bone loss/month → 2 hrs exercise/day
Post-journey recovery. After months of weightlessness, the crew lands at their weakest. That is exactly when the mission demands the most from them.
Arrival = most fragile moment
Health as infrastructure. Just keeping the human body functional in space takes 3-4 hours per person per day.
3-4 hrs/day per person
Stress, sleep loss, elevated CO2, and isolation all degrade decision-making. The crew's thinking gets worse exactly when the mission needs it to be sharp.
Sleep deficit → -25 to -40% cognition
If only one person knows how to fix the water recycler, losing that person means losing the water recycler. With 4-9 crew, this happens constantly.
4-9 crew = near-zero redundancy
Small errors compound in closed systems. Hardware breaks, which stresses the crew, which leads to mistakes, which breaks more hardware. The feedback loop is what kills you.
One failure rarely stays one failure
These factors are all connected.
When one gets worse,
it drags the others down with it.
A physically depleted crew makes worse calls. Worse calls cause more breakdowns. More breakdowns raise stress. Higher stress fractures the social unit. A fractured social unit stops cooperating on hardware maintenance. The loop tightens until something gives. Understanding where to interrupt that loop is one of the biggest open questions in long-duration spaceflight.