Аннотация:A review of space radiation environment from the point of its hazardous impact on spacecrafts is given. The current status of knowledge of the mass and energy spectra of the heavy fraction of the radiation environment in quiet solar daily variations and contribution of the Galactic Cosmic Rays to the average fluxes are analyzed. Further on, the main radiation effects for on-board electronics are discussed. A commonly used Linear Energy Transfer (LET) and Critical Charge conceptions are reviewed and origin of these conceptions at low LETs are discussed stressing on nuclear reactions contribution. The scaling of the integrated circuitry (IC) into deep submicron range and current measures to mitigate the single effect errors rates induced by the cosmic rays on the on-board electronics are discussed.