A medical specialty dealing with the physiological, PSYCHOLOGICAL and pathological consequences of space flight, in which the body has to cope with unusual variations in gravitational forces, including weightlessness, a constricted environment, prolonged close contact with work colleagues in very demanding technical circumstances, and sustained periods of emotional pressure, including fear. Enormous progress has been made in providing astronauts with as normal environment as possible, and they have to undergo prolonged physical and mental training before embarking on space travel.