2 weeks Ago
Butch Wilmore and Suni Williams, the two astronauts stranded in space for nine months after their experimental space craft had technical issues, will be coming home soon. But what effect could living on the International Space Station (ISS) for months, instead of the eight days they were due to be there, have on them? Astronauts face numerous physical and psychological issues during their time in space, and the transition back to Earth can be equally demanding. The sensation of weightlessness experienced by astronauts is not due to the absence of gravity but rather the state of continuous freefall.
The ISS orbits the Earth at a speed of approximately 28,000 kmph (17,500 mph). At this speed, the station is constantly falling towards the Earth but also moving forward at a rate that matches the curvature of the Earth. This creates a state of perpetual freefall, where the astronauts inside experience microgravity.
In this environment, objects and people float because they are all falling at the same rate. In the microgravity environment of space, the human body undergoes significant changes. One of the most profound effects is on the musculoskeletal system.
On Earth, our bones and muscles are constantly working against gravity, which helps maintain their strength and density. This lack of mechanical stress causes bone density to decrease. Astronauts can lose up to 1-2% of their bone mass per month, particularly in weight-bearing bones like the spine, pelvis, and legs.
This bone loss increases the risk of fractures and osteoporosis. Similarly, muscles weaken and shrink due to the lack of resistance. Without the need to support the body against gravity, muscles, especially those in the legs and back, begin to atrophy (waste away).
Astronauts can lose up to 20% of muscle mass in a few weeks. This muscle loss can lead to decreased strength and endurance, making physical tasks more challenging. To combat these effects, astronauts undergo rigorous training and follow strict exercise regimens both before and during their missions.
Preparation begins months, if not years, before launch, with astronauts engaging in strength training, cardiovascular workouts, and flexibility exercises. On the ISS, astronauts spend about two hours each day exercising to maintain their bone and muscle health. The exercise equipment on the ISS includes an Advanced Resistive Exercise Device (ARED) .
This simulates weightlifting using vacuum cylinders to create resistance. It allows astronauts to perform squats, deadlifts, and other strength-training exercises. Astronauts also run on a treadmill while strapped in with bungee cords to keep them in place.
This helps maintain cardiovascular fitness and leg muscle strength. A stationary bike provides a low-impact way to maintain cardiovascular health and leg muscle strength. After spending months in the weightlessness of space, returning to Earth's gravity can be a jarring experience.
Astronauts often describe the sensation as feeling incredibly heavy and weak. The transition back to gravity affects various systems in the body. The vestibular system, located in our inner ear, helps control balance and spatial orientation, is disrupted by the lack of gravity.
Upon returning to Earth, astronauts may experience dizziness, vertigo, and difficulty walking. It can take several days to weeks for their balance and coordination to fully recover. In microgravity, fluids in the body shift towards the head, leading to facial puffiness and decreased blood volume in the legs.
Upon returning to Earth, this fluid redistribution can cause astronauts to feel lightheaded or faint when standing up. Again, it can take weeks for the cardiovascular system to readjust. The process of rebuilding bone density and muscle mass can take several months.
Astronauts continue their exercise regimens and undergo physical therapy to aid in their recovery. Despite these efforts, some bone loss may be permanent, and muscle strength may never fully return to pre-flight levels. The absence of a natural day-night cycle in space can disrupt astronauts' circadian rhythms, leading to sleep disorders.
Poor sleep quality can result in fatigue, irritability, and impaired cognitive function. Being confined in a small space with limited social interaction can lead to feelings of loneliness and isolation. The lack of privacy and constant proximity to the same group of people can also cause interpersonal tensions.
To mitigate these psychological effects, astronauts undergo extensive training and receive psychological support before, during, and after their missions. On a positive note, many astronauts experience the "overview effect," a cognitive shift that occurs when they view Earth from space. This perspective can lead to a profound sense of interconnectedness and a heightened awareness of the fragility of our planet.
As we look towards future missions to the Moon, Mars, and beyond, understanding and addressing these challenges will be crucial for the success and well-being of astronauts. Dr James Williams is a reader in science education and communication at Sussex university.
