cream wobbly wrote:
webdude wrote:What happens if/when we finally become a space-based race?
You're still going to need an external cycle of roughly 24 hours (give or take 25%) of light approximating Sol's spectrum in order to manage the sleep cycle.
24 hours? Not necessarily. I mentioned spelunking due to the early human chronobiology work done by cavers. That work was predated by work on rats, investigating relationships between hormonal cycles and circadian rhythms. "Natural" human cycles, at least for cavers, have varied from 25-48 hours; none were 24 or fewer hours.
Research on astronaut rhythms is ongoing. See this link from March 2012: http://www.nasa.gov/mission_pages/stati ... -Long.html
Here's another link, with a relevant quote: http://science.nasa.gov/science-news/sc ... st04sep_1/
"...scientists still need to answer some basic questions in order to develop countermeasures against unwanted wakefulness. For instance, what exactly controls the master clock? What intensity of light will trigger it -- and which colors? Does gravity itself provide a cue? All these questions will grow in importance as humans move farther into space.
Take the exploration of Mars, for example. On Mars, daylight is primarily yellowish-brown. On Earth, it's blue-green. How will the human clock respond to the unearthly color of Martian skies? Some research indicates that it could make a difference. Melatonin production, for example, is suppressed more by some wavelengths of light than by others."
One more, an abstract from a 1998 paper:
"J Biol Rhythms. 1998 Jun;13(3):188-201.
Sleep and circadian rhythms in four orbiting astronauts.
Monk TH, Buysse DJ, Billy BD, Kennedy KS, Willrich LM.
Sleep and Chronobiology Center, University of Pittsburgh School of Medicine, PA 15213, USA.
This experiment measured the sleep and circadian rhythms of four male astronauts aboard a space shuttle (STS-78) orbiting the Earth for 17 days. The space mission was specially scheduled to minimize disruptions in circadian rhythms and sleep so that the effects of space flight and microgravity per se could be studied. Data were collected in 72-h measurement blocks: one block 7 days before launch, one early within the mission (3 days after launch), one late in the mission (12 days after launch), and one 18 days after landing. Within each measurement block, all sleep was recorded both polysomnographically and by sleep diary. Core body temperature was sampled every 6 mins. Actillumes were worn continuously. All urine samples were collected separately. Performance was assessed by a computerized test battery (3/day) and by end-of-shift questionnaires (1/day); mood and alertness were measured by visual analogue scales (5/day). Circadian rhythms in orbit appeared to be very similar in phase and amplitude to those on the ground, and were appropriately aligned for the required work/rest schedule. There was no change from early flight to late flight. This was also reflected in mood, alertness, and performance scores, which were satisfactory at both in-flight time points. However, in-flight sleep showed a decreased amount of sleep obtained (mean = 6.1 h), and all four astronauts showed a decrease in delta sleep. No further degradation in sleep was seen when early flight was compared to late flight, and no other sleep parameters showed reliable trends."
After all the work that's been done on astronauts, spelunkers, and extended-dive ocean dwellers, there's still a heckuva a lot we don't know. The ideal light-dark cycles on missions to Mars or other destinations might vary during the trip, according to varying gravitational pulls, trajectory relative to solar angles, etc. Think about that - dynamic vs. static light cycles.
Any time-keeping system we adopt needs to address human needs, including the need to get work done safely, with reasonable alertness and reasonably good moods to minimize social problems.