Spaceflight exposes people to conditions that do not exist naturally on Earth. Microgravity changes how the body supports itself, while radiation, isolation and distance complicate longer missions.
The effects also depend on destination and duration. Six months in low Earth orbit is not equivalent to a multiyear Mars mission.
Muscles, bones and circulation
Muscles used for posture and movement do less work in microgravity. Without countermeasures, they lose strength and mass.
Bones also experience less mechanical loading and release minerals faster than they rebuild them. Exercise reduces these effects but does not eliminate every change.
Body fluids shift toward the head. This can produce facial puffiness and contribute to changes in the eyes and vision known collectively as spaceflight-associated neuro-ocular syndrome.
After returning to Earth, astronauts may experience dizziness or difficulty maintaining blood pressure while standing as their cardiovascular systems readapt to gravity.
Balance and daily performance
The brain normally combines visual information with signals from the inner ear and pressure on the body. Microgravity changes those signals, causing motion sickness and disorientation during adaptation.
Sleep can also be affected by work schedules, noise, lighting and repeated sunrises. Inadequate sleep can reduce attention, mood and decision-making.
Radiation beyond Earth
Earth’s atmosphere and magnetic field provide substantial protection from space radiation. Crews traveling beyond low Earth orbit receive less shielding from galactic cosmic rays and solar-particle events.
Radiation exposure may increase long-term health risks, including cancer. Shielding, mission planning and monitoring can reduce exposure, but no single countermeasure removes the hazard.
Five connected hazards
NASA groups human-spaceflight hazards into:
- Space radiation
- Isolation and confinement
- Distance from Earth
- Altered gravity
- Hostile or closed environments
These hazards interact. A medical problem becomes more difficult when communication is delayed and evacuation is impossible.
Space medicine therefore involves more than physical fitness. It combines exercise, habitat design, medical support, nutrition, behavioral health and operational planning.
Sources
- NASA Human Research Program: https://www.nasa.gov/hrp/
- NASA Five Hazards of Human Spaceflight: https://www.nasa.gov/hrp/hazards/
- NASA Human Body in Space: https://www.nasa.gov/humans-in-space/the-human-body-in-space/