A report from The Conversation examines the challenges of sleep in space, including the absence of day and night and high noise levels.
Life on Earth has evolved to adapt to the 24-hour cycle of light and dark that stems from the planet’s rotation. From fruit flies to human beings, many organisms spend a significant amount of time resting or asleep. This urge to sleep is determined by the build-up of tiredness and our internal body clock that tells us when it’s the right biological time to sleep. This process is regulated by the complex interaction of many factors such as light, temperature, posture, and feeding. So we tend to sleep when it’s dark, we lie down when we sleep, we don’t eat when we should sleep, and our body temperature drops to a minimum while asleep.
But for astronauts, these factors are disrupted during long-term spaceflight. The low gravity is one major difference: lying down no longer makes any sense, for example, as there is no “down”. Our normal sleeping patterns are disrupted by the lack of feedback from our body’s posture during cycles of rest and activity. In fact astronauts have to take steps to ensure they don’t float around while sleeping in space – they tie themselves into sleeping bags. In order to sleep well, our core body temperature needs to cool. This process is also influenced by body posture and flow of blood around the limbs, which is also affected by low gravity and the absence of “lying down”.