Abstract: This paper addresses the unique safety risk characteristics of space nuclear reactor power sources throughout their lifecycle, aiming to establish a comprehensive safety goal framework tailored for space reactors. The study draws upon safety objective formulation methodologies from terrestrial nuclear facilities while accounting for the distinct operational phases and hazards of space reactors. A systematic three-tiered safety goal architecture—encompassing qualitative, quantitative, and probabilistic objectives—was developed through rigorous analysis of space rectors launch phase risks, research of safety target definitions and rationales from conventional nuclear power plants, integration of quantitative aerospace industry safety data, and review of international space nuclear safety regulations and standards. The qualitative objectives mandate the protection of Earth’s biosphere from significant radiological risk, prevention of substantial contamination hazards to outer space orbits, and avoidance of introducing unacceptable additional accident risks to the spacecraft. Quantitative safety requirements stipulate that the maximum effective dose to any individual from a design basis accident must not exceed 5 mSv, and the risk of reactor failure leading to spacecraft catastrophic failure must remain comparable to risks posed by alternative spacecraft power sources. Probabilistic safety goals establish specific thresholds: the probability of inadvertent criticality during a launch accident must be less than 10⁻³, the probability of reactor failure causing spacecraft catastrophic failure during operation must be below 10⁻², and the probability of spacecraft disintegration during the operational phase must be less than 10⁻⁵. The resulting integrated framework provides systematic guidance for the safety design and risk assessment of space reactors. This structured three-tiered safety goal system provides a systematic foundation for guiding the safety design and risk assessment of space reactors, offering essential theoretical support for developing future safety standards and regulatory guidelines specific to space nuclear power applications, thereby enhancing safety assurance for both terrestrial populations and space environments increasing space activities.