The Radiation Biology Department of DLR developed the anthropomorphic phantom experiment MATROSHKA (see picture on the left). MTR is an ESA experimental unit for studies of the depth dose distribution of the different components of the low earth orbit radiation field at the sites of specified organs. It can be positioned outside or inside of the ISS, to simulate either astronaut extravehicular activity (EVA) or intravehicular activity (IVA). MTR consists of a human head/torso-phantom, allowing the accommodation of dedicated active and passive radiation measurement devices. It is designed as a long duration, non-maintainable, space-exposed payload. The objective of the MTR experiment is to determine the empirical relations between measurable absorbed doses and the tissue absorbed doses in a realistic human phantom exposed to cosmic radiation. Such measurements have the highest priority, particularly in view of long-term human space exploration. Once the ratio between tissue/organ doses and surface doses is known for a specific radiation field, it may be used in future exposures to determine the required tissue/organ doses from measurements of just the surface doses: such surface dose measurements are much easier to perform. In addition, a further objective is to enlarge the, still modest, quantity of empirical data that is available for the composition of the radiation field in space. This includes mapping of the radiation environment in space and its variation with time and orbital parameters (such as solar cycle, solar flare events, inclination and altitude) and studying the modification of radiation doses in space by mass shielding (e.g. attenuation, build up and/or activation). The collected data will be used to reduce the uncertainties of risk estimates for radiation-induced cancer and for the refinement of realistic shielding distributions in future spaceflights.
The MTR facility was launched in 2004 and a first exposure was performed for 539 days outside the ISS (MTR 1). A second experimental phase was started in 2006 for the measurement of the radiation environment inside the space station (MTR 2A). The research community is currently preparing the detectors for the third exposure (MTR 2B), again in the Russian Segment (Zvezda), of the ISS. A fourth exposure is currently foreseen for the years 2008–2009 outside the ISS. After completion of the four MTR phases, data will be available for an exposure period of more than 1200 days within a timeframe of 5 years, covering a considerable part of an entire solar cycle.