Radiation Hazards in Space and effects on Human
Radiation is a well-recognized primary concern for manned spaceflight and is a potentially limiting factor for interplanetary missions because the biological effects from exposure to radiation in space has serious occupational health risk for astronauts on long-duration missions. Radiation is the energy in transit in the form of high-speed particles and electromagnetic waves. Mainly it can be divided into two categories - ionizing radiation and non-ionizing radiation. Primarily, space radiation consists of ionizing radiation which is energy carried by several types of particles and rays (electromagnetic radiation) given off by radioactive material, X-ray machines, and nuclear reactions. This energy can impel electrons out of molecules with which they interact, thus creating ions.
An ionized particle causes injury to living organisms when high energy protons, cosmic rays, x-rays, or gamma rays penetrate and split apart cell molecules which can kill or damage the cell. In addition, particles passing through an obstruction such as spacecraft walls can ionize particles within those walls, creating another hazard called secondary radiation. Heavy cosmic ray particles such as the nuclei of carbon, oxygen and iron atoms do the most damage because they carry greater positive electrical charges than protons, causing more ionization within the cells. A single heavy cosmic ray particle can kill a cell. Protons, however, do the most overall damage because there are so many of them. They comprise the substance of most cosmic rays.
The Galactic Cosmic Rays (GCR) contain highly ionizing heavy ions that have large penetration power in shielding and tissue and are unlike any radiation to which humans are exposed on Earth. A solar particle event from a large solar flare produces very high ionizing radiation doses over periods that sometimes last a few hours or several days. A major Solar Particle Event (SPE) could expose astronauts in free space to life-threatening dose levels in a few hours. Both the GCR and the SPE also contain significant numbers of high-energy protons, capable of large penetration and important nuclear interactions. A small fraction of SPE may produce extremely large doses leading to early radiation sickness or death if adequate shelter is not provided. Improved risk prediction and mitigation of radiation risks is essential to achieve exploration goals.