Effects of Space on Astronauts: What Changes Do They Undergo?

Astronaut Health, and the side effects of space travel

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Published in 03-19-2025

Construction of the International Space Station (ISS) began in 1998. The idea of an international space station was conceived in the 1980s. The ISS is the result of a merger of projects from different countries, including the United States, Russia, Europe, Japan, and Canada.

What happens to an astronaut when they spend a long time in space and return to Earth?

Muscle and bone loss: In space, the absence of gravity causes muscles and bones to lose density. Upon returning to Earth, astronauts may experience muscle weakness and an increased risk of fractures until their bodies readjust to Earth's gravity.

Cardiovascular problems: Without gravity, the heart does not have to pump as hard, which can cause it to become smaller and less efficient. Upon returning to Earth, some astronauts experience dizziness and low blood pressure due to these changes in their cardiovascular system.

Balance and coordination issues: The vestibular system in the inner ear, which controls balance, is affected by the lack of gravity. As a result, astronauts may experience difficulties standing and moving normally during the first few days back on Earth.

The astronauts that were stranded in space for 9 months have officially landed back on Earth. pic.twitter.com/xsqcMFUTWO
— Pop Base (@PopBase) March 19, 2025

Readaptation to Earth: The Challenges Astronauts Face Upon Return

Vision impairment: Some astronauts experience vision problems after long-duration space missions. This is believed to occur because the lack of gravity increases intracranial pressure, affecting the optic nerve and changing the shape of the eyeball.

Skin sensitivity: In space, the skin has minimal contact with surfaces due to microgravity. Upon returning to Earth, astronauts may feel their skin is more sensitive to the touch of clothing and objects, causing temporary discomfort.

Difficulty sleeping: The circadian rhythm is disrupted in space due to the lack of a consistent day-night cycle. Upon returning to Earth, astronauts may take several days to adjust their biological clock and regain normal sleep patterns.

Increased radiation exposure: In space, cosmic radiation is more intense than on Earth, which can increase the risk of diseases such as cancer. Astronauts who spend long periods in space receive significant doses of radiation, which may impact their long-term health.

Post-mission recovery: After returning to Earth, astronauts go through a rehabilitation process that can last weeks or months. This includes physical therapy, fitness training, and medical monitoring to ensure full recovery and minimize the negative effects of microgravity.

Studying these effects is crucial for future long-duration space missions, such as expeditions to Mars. NASA and other space agencies continuously work on strategies to mitigate these impacts and improve astronauts' health both in space and after their return to Earth.