Will long space missions make us lethargic?

What kind of effects would a prolonged space mission have on people? To date, only four people have spent more than a year in space. Six people have, however, spent 520 days enclosed in the Mars500 simulator. During that time, they were isolated from all outside contact, except by means that would be accessible in space (including communication delays).

Among the things lacking during their seventeen-month mission was any degree of privacy. The six men had their movements, activity level and wakefulness continuously monitored by wrist devices. In addition, each person was given an alertness test twice a week and a questionnaire about workload, tiredness and sleep quality once a week.

• Diego Urbina looking out from the hatch inside Mars500 facility.
  Credit ESA, 9/11/2010.
  
  
  

Four of the six crewmembers experienced some type of sleep problem, such as poor sleep quality or disruptions of their wake/sleep cycles. As the mission progressed, the volunteers spent less and less time in ‘active wakefulness’. The rest of the time, they were either asleep or sedentary. The drop in activity level was precipitous during the first three months, but continued to fall until the last twenty days of the mission, at which time everyone seemed to perk up. On the plus side, the extra sleep seemed to help the crew maintain alertness when they were awake, because their scores on those tests improved as their sleep time increased. This might be a lesson for all of us.

This mission highlighted a number of issues, as far as sleep goes. For one thing, it’s clear that different people have different reactions to prolonged isolation. Two of the crewmembers developed such skewed sleep rhythms that they were offset (asleep when the other four were awake or vice versa) twenty percent of the time. For another, the increasing amounts of inactivity as the mission progressed could be problematic in a real mission, especially if that quiescence reflects boredom or apathy.

You can see the crew’s triumphant 'return' below:

Basner M, Dinges DF, Mollicone D, Ecker A, Jones CW, Hyder EC, Di Antonio A, Savelev I, Kan K, Goel N, Morukov BV, & Sutton JP (2013). Mars 520-d mission simulation reveals protracted crew hypokinesis and alterations of sleep duration and timing. Proceedings of the National Academy of Sciences of the United States of America PMID: 23297197.