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Missions of unmanned spacecraft Foton-M2 (2005) and Foton-M3 (2007) of 16 and 12 days in duration, respectively, provided an opportunity to conduct the Russian/US experiments with snails (Helix lucorum and Helix aspera), newts (Pleurodeles waltli), geckos (Pachydactilus turneri) and microorganisms (Streptomyces lividans 66, E. coli and others). Besides, Foton-M3 carried a Russian experiment with Mongolian gerbils (Meriones unguiculatus). Objectives of the space experiments were to study the micro-g effects on the living systems' behavior, structure and functioning, post-traumatic regeneration of bone and organs, stable inheritance of plasmid pIJ 702, and melanin pigment synthesis by streptomycets. The survey paper presents the major findings of a large team of investigators.

The paper considers in retrospective the criteria of radiation hazard during space flight, and approaches to safeguarding the radiation safety to crew members adopted in a sequence of Russian and US standards defining the space radiation limits. Based on comparison of the magnitudes of radiation risk in space flight, total radiation risk over lifetime, the risk of fatal cancer, and risk relation to age, the most meaningful and age-independent criterion has been chosen to set limits and admissible total doses over cosmonaut's career. Justification is given to the range of these doses that still ensures socially acceptable levels of health and performance by the end of space career. Impliable dose limits for critical tissues (blood-forming organs, skin, lenticular epithelium) in consequence of a single acute or continuous exposure for a month, a year or career are discussed.