The biological dosimetry of the solar UV radiation functioned correctly on the Earth's surface. The aim of the present studies was to extend the dosimetry to the extraterrestrial solar radiation in LEO. Similar to the Earth's surface bacteriophage T7 and polycrystalline uracil thin layers were used as detectors and exposed to the simulated and to the real space environmental parameters aiming to perform the in situ biological UV dosimetry in the space, more exactly on the external pallet of the ISS. The UV detectors have been used in specific cases in thin layer form. In contrast to the Earth's surface the extraterrestrial solar UV radiations contains wavelength components (λ ~ 190-200 nm), which cause photolesions (photoproducts) in the nucleic acids/their components similar to the UV-B photons. However, these wavelengths cause not only photolesions but with a wavelength-dependent efficiency the reversion of some photolesion, too. Our biological detectors measured either in simulation or in situ conditions the resultant of both reactions induced by the extraterrestrial UV radiation. From this aspect the role of the photoreversion in the extension of the biological UV dosimetry and in the survival of the living systems in the space are discussed.