The purpose and vision of NASA's Space Radiation Project (SRP) are to achieve human exploration and development of space without exceeding an acceptable level of risk from exposure to space radiation.
An important safety concern for long-term space travel is the health effects from space radiation. Possible health risks include cancer, cataracts, acute radiation sickness, hereditary effects, and damage to the central nervous system. NASA has been developing ground-based research facilities to simulate the space radiation environment and to analyze biological effects at the molecular and cellular level. These facilities also will be used to understand and mitigate the biological effects of space radiation on astronauts, to ensure proper calibration of the doses received by astronauts on the International Space Station, and to develop advanced material concepts for improved radiation shielding for future exploration missions to Mars.
For over 35 years, NASA has been collecting and monitoring the radiation doses received by all NASA astronauts that traveled into space during the Gemini, Apollo, Skylab, Space Shuttle, Mir, and the International Space Station programs. The data on the amount of space radiation and its composition is now more readily available and well understood.
The primary radiation sources in outer space are the galactic cosmic rays (GCR), protons and electrons trapped in the Earth's magnetic field, and the solar particle events (SPE). The background radiation of the GCR permeates interplanetary space and includes 85% of protons, 14% of helium and about 1% from high-energy (E) and high-charge (Z) ions called HZE particles.
Though the HZE particles are less abundant, they possess significantly higher ionizing power with a greater potential for radiation-induced damage and greater penetration power.
The basic unit of the living organism is the cell. Within the cell, the deoxyribonucleic acid (DNA) molecules contain the information required for the synthesis of intracellular proteins, for cell reproduction and for organization of the tissues and organs. The diameter of a cell is typically of the order of 1/1000 inches. Inside the cell's nucleus, the DNA is tightly wound into a tiny double helix, thousands of times smaller than the cell.
Passage of ionizing radiation can result in direct effect on DNA leading to single strand breaks (SSB), double strand breaks (DSB), associated base damage (BD), or clusters of these damage types. The initial damage caused by the HZE particles at the cell level and to the tissue is unique compared to the damage caused by the terrestrial radiation such as X-rays or gamma rays. Because of their high ionization density, HZE particles also can cause clusters of damage where many molecular bonds are broken in the tissue along their trajectory. The cell's ability to repair DNA damage becomes impaired as the severity of clustering increases leading to DNA deletions and other forms of mutations. The long range of the HZEs allows for the potential damage along a long column of cells in tissue. Since HZE particles are rare on Earth, the prediction of biological risks to humans in space must rely on fundamental knowledge gathered from biological and medical research.
NASA-sponsored research facilities for radiobiology studies are located at Loma Linda University (protons) and at the Brookhaven National Laboratories (heavy ions). At Brookhaven, the NASA Space Radiation Laboratory (NSRL) provides a state-of-the-art facility for NASA-sponsored researchers to perform radiobiology and physics experiments.