Space Dosimetry and Space Phantom Experiments

To estimate the space radiation risks for the future planned Mars missions, the radiation fields in the spacecraft and in the habitats on Mars must be fully known. For radiation risk estimations, benchmarking and improving particle and ion transport codes which are currently used for space radiation and shielding calculations, radiation detection and monitoring of the space radiation field as a function of the solar activity, the orbital parameters and the different shielding configurations of the International Space Station (ISS) have been performed and are still ongoing. There are also many ongoing measurements of the spatial and temporal distribution of the radiation field at the ISS. In addition to the measurements at the ISS, important information about radiation environment in deep space was achieved with the Mars Science Laboratory (MSL) spacecraft, containing the Curiosity rover, which was launched to Mars on 26 November 2011, and traveled for 253 days, 560 million kilometers to Mars. The Radiation Assessment Detector (RAD) on the spacecraft showed that the dose equivalent for even the shortest round-trip Earth-Mars journeys, with current propulsion systems and current available shielding, is 0.7 +/- 0.1 Sv, depending on the solar cycle and duration of the mission. Although the dose rate on the surface of Mars is lower than in deep space, measurements with RAD showed that an astronaut would still get around 40% of the dose rate in deep space. If the astronauts are exposed to large Solar Particle Events (SPEs), the dose can reach lethal doses. Effective countermeasures should therefore be developed before performing a manned mission to Mars. The use of human phantoms in space that simulate an astronaut's body, has provided detailed information of the depth-dose distributions, and radiation quality, inside the human body in space. This information is essential for developing more accurate space radiation transport and risk models to be used for evaluating short and long-term radiation risks in deep space and on Mars. Although reports state that background radiation in some high background radiation areas approaches that of the Martian surface, new estimates show that the maximum annual radiation dose in these areas can be much higher than that of the Martian surface. Given this consideration, study of the health effects of exposure to high levels of natural radiation can help scientist better evaluate the risk of radiation in deep space manned missions. This paper presents a short review of some important published space dosimetry and phantom experiments, and discusses some recently proposed counter measures to reduce the health risks of the astronauts on deep space missions.