In this contribution an important problems that astronauts have to face when planning their interplanetary journey are presented. As important factors of risks were mentioned environmental dangers, such as: meteoroids, microgravity and cosmic radiation. The second source of hazards are biological and existential, which include space sickness and methods of life maintenance in the space, oxygen acquisition from water, spacecraft air quality maintenance, recommendations for decompression sickness, fatigue and sleep disorders prevention. One of the crucial problems during manned mission is the loss of mass and density bones. The paper also describes the psychological aspects, which are a vital element in planning the cure in the way it makes it more effective and keep their good mental health as distant space may be depressing.
To calculate a risk level, for each of the analysed factor, the Preliminary Hazard Analysis (PHA) has been used. This method allows to determine the value of risk based on the knowledge of the probability of its occurrence and possible effects. The obtained risk values are within the limits of acceptable risk, some of them can be reduced after a more thorough analysis or introduction of additional safeguards.
On the basis of the analysis contained in the article, it can be concluded that the majority of threats can be effectively minimized or completely neutralized. Some of the risks are unpredictable and avoidable, but the probability of their occurrence is low.