Radiation Risks and Countermeasures for Humans on Deep Space Missions

The radiation environment encountered in space differs much in nature from that on Earth, with contribution of protons and high energetic ions up to iron, resulting in radiation levels far exceeding the ones present on Earth. Accurate knowledge of the physical characteristics of the radiation field, the solar activity and the mission length, which influence the radiation risks for humans on deep space missions, e.g. to Mars, is therefore very important. It has been estimated that the transit times for a human mission to Mars vary from 5 to 7 months each way, with a typical figure of about 6 months for a long duration stay on Mars, up to 8 - 10 months each way for a short duration stay on Mars. That means that the astronauts will be exposed to a harsh radiation environment for at least 2-3 years. This paper describes the radiation environment in deep space, some of the radiation health risks astronauts are exposed to on long term missions, as well as the requirements and limitations of physical protection for reducing these risks. Since it has been shown that physical shielding alone is not adequate for long term deep space missions [1], [2], we also present the need for new effective methods of biological protection, e.g. ground-based in vitro preflight screening of the candidates for evaluation of the magnitude of their adaptive responses. Furthermore, methods for boosting the immune system of astronauts and the possibility of using medical counter-measures are discussed. Notably, the use of vitamin C as a promising non-toxic, cost-effective, easily available radiation mitigator, is described.