Human Factor — Cognitive
The Decision Layer
Spacecraft run on human judgment. Sleep loss, CO2, and isolation all eat at it.
What Degrades Decision-Making
Sleep Disruption
-25 to -40%
Reaction time and clear thinking drop significantly after sustained sleep deficit. ISS crew have historically averaged about 6-6.5 hrs/night despite 8.5 hrs scheduled, with recent missions trending somewhat higher (~7 hrs) under improved scheduling. On a ~90-minute orbital cycle, the sun rises and sets 16 times a day. Your body's internal clock has no idea what to do with that.
Chronic Stress
Cortisol +
Elevated cortisol narrows your attention, makes you either too cautious or too reckless (depending on the person), and weakens working memory. Confinement, constant awareness of danger, and tension with crewmates all feed into it.
CO2 Levels
1,000+ ppm
Even moderately elevated CO2 makes complex thinking harder. The ISS regularly runs at levels (2,000-5,000 ppm) that would set off building ventilation alarms on Earth. Cognitive studies show measurable impairment above 1,000 ppm. See The Air Constraint for the full CO2 picture.
Monotony + Isolation
Month 3+
When nothing changes in your environment, your brain dials down its alertness. Attention drifts and reaction times slow. Then an emergency hits and you need the opposite of what your brain has been doing for months.
The Compound Effect
These factors stack up. A crew member at month 4 of a Mars transit is dealing with all of this at once:
- Running on 6.5 hours of sleep, badly timed
- In a fight with two crewmates that hasn't resolved in three weeks
- Breathing 3,000 ppm CO2
- Bored to the point of dullness
- And now the water recycler is throwing an alarm
Communication Delay
At Mars distance, a radio signal takes 4-24 minutes one way. Round-trip: 8-48 minutes. Houston cannot help in real time. Every critical decision has to be made by a cognitively compromised crew with no ground support.
Group Decision Decay
Tired, stressed groups make different mistakes than tired, stressed individuals. Everyone starts agreeing too easily. People with good objections stay quiet. The loudest person wins the argument instead of the right one. In faction-split crews, people may withhold information the group needs to decide well.
The crew that has to make life-or-death calls is also the crew that's been awake too long, breathing bad air, and stuck in the same room for months.
Checklists cover the failure modes you anticipated. The dangerous ones are the failures nobody planned for. Those need a rested, creative crew. At month four, that's exactly what you don't have. That's when bad calls become cascades, and when the skill map determines whether anyone on board can recover.