section_path: Safety concerns/Environmental hazards/Medical issues/Radiation
section_name: Radiation
paragraph_text: Radiation
  
  Without proper shielding, the crews of missions beyond low Earth orbit might be at risk from high-energy protons emitted by solar particle events (SPEs) associated with solar flares. If estimated correctly, the amount of radiation that astronauts would be exposed to from a solar storm similar to that of the most powerful in recorded history, the Carrington Event, would result in acute radiation sickness at least, and could even be fatal "in a poorly shielded spacecraft". Another storm that could have inflicted a potentially lethal dose of radiation on astronauts outside Earth's protective magnetosphere occurred during the Space Age, shortly after Apollo 16 landed and before Apollo 17 launched. This solar storm, which occurred in August 1972, could potentially have caused any astronauts who were exposed to it to suffer from acute radiation sickness, and may even have been lethal for those engaged in extravehicular activity or on the lunar surface.
  
  Another type of radiation, galactic cosmic rays, presents further challenges to human spaceflight beyond low Earth orbit.
  
  There is also some scientific concern that extended spaceflight might slow down the body's ability to protect itself against diseases, resulting in a weakened immune system and the activation of dormant viruses in the body. Radiation can cause both short- and long-term consequences to the bone marrow stem cells from which blood and immune-system cells are created. Because the interior of a spacecraft is so small, a weakened immune system and more active viruses in the body can lead to a fast spread of infection.