The physical and psychological rigors faced by astronauts during missions are immense; between the isolation, heavy workload, and separation from Earth, the loneliness of space has previously manifested itself in depression, mental irregularities, and possibly even hallucinations.

The life-altering effect of seeing the earth from space is almost equaled by the everyday stresses of carrying out a mission, and NASA now considers psychiatric conditions to be among the top threats during long-term missions.

In the 1970s, the crew of NASA’s Skylab 4 were placed under enormous pressure, and one day long hours, exhaustion, and disagreements with mission control led them to shut their radio off. They passed the day watching Earth roll by and ignoring NASA completely.

A Russian mission in 1976 saw the crew manning the Salyut-5 station return early due to reports of a foul smell onboard. Their replacement crew boarded with breathing equipment and checked the whole station over. No issues were found and the replacements noticed nothing wrong with the air quality. NASA eventually deduced the smell to have been a hallucination due to interpersonal issues and psychological problems that were reported later.

In addition to the external stresses experienced by humans during spaceflight, some studies show that the brain may work differently in reduced gravity environments. After all, we evolved to work efficiently at ground level.

Data on this effect is spotty, as you must get into space with an EEG to do the experiments and that comes with all the stresses discussed above; but experiments conducted in parabolic flights – designed to simulate weightlessness – have shown similar results. It appears there is a drop in mental ability without the presence of gravity; and while this drop does not yet seem significant, it could affect decision-making in emergency situations or combine with stress to threaten missions over long time periods.