Space radiation hazards are recognized as a key concern for human space flight. For long-term interplanetary missions, they constitute a potentially limiting factor since current protection limits for low-Earth orbit missions may be approached or even exceeded. In such a situation, an accurate risk assessment requires knowledge of equivalent doses in critical radiosensitive organs rather than only skin doses or ambient doses from area monitoring. To achieve this, the MATROSHKA experiment uses a human phantom torso equipped with dedicated detector systems. We measured for the first time the doses from the diverse components of ionizing space radiation at the surface and at different locations inside the phantom positioned outside the International Space Station, thereby simulating an extravehicular activity of an astronaut. The relationships between the skin and organ absorbed doses obtained in such an exposure show a steep gradient between the doses in the uppermost layer of the skin and the deep organs with a ratio close to 20. This decrease due to the body self-shielding and a concomitant increase of the radiation quality factor by 1.7 highlight the complexities of an adequate dosimetry of space radiation. The depth-dose distributions established by MATROSHKA serve as benchmarks for space radiation models and radiation transport calculations that are needed for mission planning.

The radiation environment encountered in space differs in nature from that on Earth, consisting mostly of highly energetic ions from protons up to iron, resulting in radiation levels far exceeding the ones present on Earth for occupational radiation workers. Since the beginning of the space era, the radiation exposure during space missions has been monitored with various active and passive radiation instruments. Also onboard the International Space Station (ISS), a number of area monitoring devices provide data related to the spatial and temporal variation of the radiation field in and outside the ISS. The aim of the DOSIS (2009DOSIS ( -2011 and the DOSIS 3D (2012-ongoing) experiments was and is to measure the radiation environment within the European Columbus Laboratory of the ISS. These measurements are, on the one hand, performed with passive radiation detectors mounted at 11 locations within Columbus for the determination of the spatial distribution of the radiation field parameters and, on the other, with two active radiation detectors mounted at a fixed position inside Columbus for the determination of the temporal variation of the radiation field parameters. Data measured with passive radiation detectors showed that the absorbed dose values inside the Columbus Laboratory follow a pattern, based on the local shielding configuration of the radiation detectors, with minimum dose values observed in the year 2010 of 195-270 lGy/day and maximum values observed in the year 2012 with values ranging from 260 to 360 lGy/day. The absorbed dose is modulated by (a) the variation in solar activity and (b) the changes in ISS altitude.

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To study the radiation environment inside the International Space Station, solid state nuclear track detector stacks were used. Within the BRADOS experiments, Phase 1, seven stacks were exposed at different locations of the Russian segment 'Zvezda' for 248 days in 2001. It was supposed that the radiation field inside the ISS was composed from primary cosmic ray particles penetrating the wall of the ISS and secondaries, mainly neutrons induced by primaries in the wall and other structural materials surrounding the detectors. Based on the calibration made by utilising the high energy neutron reference field CERF at CERN (Geneva, Switzerland), the tracks induced by neutrons were separated from those induced by primary particles. Thus, the stacks, on one hand, provided the secondary neutron ambient dose equivalent. On the other hand, from the analysis of the rest of the tracks, the linear energy transfer spectra were computed and the flux and the dose of the primary particles were determined as shown in this paper.