On Earth people’s lives are usually dictated by a 24-hour rhythm (with about 8 hours of sleep each night). As far as I know this rhythm is determined by chemical processes in the human body which are influenced by the sun (see Circadian rhythm).
However dividing time into 24-hour periods isn’t natural for astronauts on ISS (which make a turn around the earth in about 90 minutes, usually but not always with accompanying sunrises and sunsets).
Do astronauts aboard the ISS still divide time into 24-hour periods or do they use some other regime? What kind of sleep needs does the human body have in space – e.g. do astronauts still sleep for 8 hours at a time or do they sleep for less/more time more/less often? Are all astronauts sleeping at the same time?
Like a lot of things that should be readily available, it's frustratingly difficult to find this on any NASA web site. Fortunately ESA came to the rescue in the form of a blog post about Alexander Gerst.
The crew's schedule is shown onboard using a PC tool called OSTPV (Onboard Short Term Plan Viewer). Gerst was nice enough to post a screenshot of this for one day of his mission. He was on the ISS in 2014, and it shows GMT day 177, so if I did it right, that would be June 26th.
You may wish to view this graphic in a separate window so that you can refer to it as I describe it.
Across the top you see three sets of wall clock time: GMT, Houston time, and Moscow time. The next band shows the day/night cycles predicted for the ISS for this time period. For each crewmember, there is a band labeled with their crew position and name. You can see Gerst's band labeled FE-6 (Flight Engineer 6) and A. Gerst. Referring to his band, you can see the time alloted for him to arise and eat (POSTSLEEP), then his daily activities start, scheduled down to 5 minute intervals.
I am no ISS acronym expert, but some of the activities include IFM (In-Flight Maintenance, fixing something on the ISS), midday meal, and exercise. The day ends with PRESLEEP followed by SLEEP.
At the bottom are the Russian crewmembers, I believe this is really info-only, as they have their own scheduling system.
Other bands on the OSTPV show comm availability, earth observation opportunities, and special crew constraints.
Summarizing, Gerst awoke at 0600 GMT, went to work at 0730, ate lunch from approximately 1310 to 1410, exercised from 1530 to 1830, and called it a night at 1930. Presumably this is a fairly typical (non spacewalk) day as the picture label on the blog post is "typical workday for astronauts".
I hope I addressed all your points, or you can puzzle them out from looking at the OSTPV. You can see that everyone is scheduled to sleep at the same time.
Answered by Organic Marble on November 15, 2021
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