Being an astronaut looks like an exciting and glamorous career. But have you ever thought about the dangers that these people face by being exposed to extreme conditions, such as radiation and microgravity?
Living and working in microgravity can impact your whole body in different ways. On the other hand, the human body is capable of adapting its physiology to survive in diverse conditions.
“[S]paceflight poses unique medical problems due to prolonged exposure to a combination of stressful stimuli, such as acceleration forces, radiation, and weightlessness. In particular, the latter condition is a critical feature of [spaceflight] and has effects on human physiology which were quite unexpected at the beginning of space exploration,” The National Institutes of Health describes.
What is microgravity?
Microgravity is the condition in which people or objects appear to be weightless.
You may have heard that there is no gravity in space. This is not quite true. In fact, a small amount of gravity can be found everywhere in space.
Gravity becomes weaker with distance. The International Space Station orbits our planet at an altitude between 320 and 400 kilometers (200 and 250 miles) above the Earth. At that altitude, Earth’s gravity is about 90 percent of what it is on the planet’s surface.
The real reason people and objects float in orbit is because that they are in free fall. On Earth, objects with more air resistance fall more slowly than objects able to slip through air more easily. In a vacuum, gravity makes objects fall at the same rate.
Sometimes, astronauts have to spend months in microgravity, so NASA and other space agencies carefully study the effects of microgravity in order to keep astronauts safe and healthy.
“Astronauts who live on the space station spend months in microgravity. Astronauts who travel to Mars also would spend months in microgravity traveling to and from the Red Planet,” NASA reports.
What are the health consequences of microgravity on the human body?
Effects on the cardiovascular system
Under gravity, standing upright, fluid distribution creates higher arterial pressure in the feet (200 mmHg) than in the head (70 mmHg) relative to the heart (100 mmHg).
“On Earth, with its normal gravity, all changes in posture — such as when lying down, sitting, or standing as well as changes in activity levels such as through exercising — require the heart and vascular system to regulate blood pressure and distribution by adjusting the heart rate (beats per minute), amount of blood ejected by the heart (or stroke volume), and constriction or dilation of the distributing arteries. These adjustments assure continued consciousness by providing oxygen to the brain or continued ability to work, with oxygen going to the working muscles,” NASA describes.
In space, blood redistribution toward the head causes altered responses of the nervous and endocrine systems.
Besides that, the increased fluid within the skull increases brain pressure, causing hearing loss, brain edema, and deformation of the eye known as Spaceflight Associated Neuro-ocular Syndrome (SANS).
Acute exposure to microgravity can also cause symptoms of anorexia, vomiting, nausea, and headache, also known as space motion sickness. Fortunately, astronaut’s bodies can adapt to this in 48–72 hours.
Effects on the musculoskeletal system
Because of microgravity, astronaut’s muscles are not required to support their body weight. Due to reduced use, they may suffer from muscle atrophy. This can make them unable to do physically demanding tasks while on a mission.
It’s the same sensation you feel after spending the whole day laying down, and then try to take a walk right after. It feels like your muscles can’t perform their job correctly.
In order to preventing these health problems, astronauts exercise regularly, providing much-needed exercise in the microgravity environment.
Fluid distribution caused by microgravity affects the blood supply to the eye with an impact on its vascularization. That’s why some astronauts may suffer from blurred vision, requiring them to wear glasses during the mission.
Orientation and balance
Gravity is the fundamental reference that tells us which way is down. To accomplish that function, we have receptors in our inner ears that act as our guidance system, helping to track the orientation of our bodies.
Microgravity makes astronauts lose this reference, so they can feel disoriented and have difficulty coordinating their movements.
“In space there is no gravitational force telling the inner ear which way is ‘up’ and ‘down’. So while our eyes can certainly see a ceiling and floor in the spacecraft, our brains cannot register this. This causes nausea and dizziness. Some astronauts experience headaches and vertigo,” the BBC reports.
How can astronauts adapt to microgravity effects?
Astronaut’s nervous systems usually adapt very quickly. By the third day of the flight, most of them can’t feel the discomfort they felt when they first arrived in space.
Once they return to the Earth, they will have to face another process of adapting their physiological systems to gravity again.
“On return to Earth, gravity once again “pulls” the blood and fluids into the abdomen and legs. The loss of blood volume, combined with atrophy of the heart and blood vessels that can occur in space, reduces the ability to regulate a drop in blood pressure that happens when we stand on Earth. Some astronauts experience orthostatic intolerance — difficulty or inability to stand as a result of light headedness and/or fainting after return to Earth,” NASA describes.
The human body is an incredible machine that can do amazing things. Of course, it requires a lot of training and dedication, and this is something at which astronauts excel.
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