Studies of circadian rhythms in space flight: some results and prospects

Results of the chronobiological experiments carried out aboard the Soviet "COSMOS" biosatellites with beetles, rats and primates indicate a possibility of 1. decrease of the circadian rhythm stability in space flight, expansion of the range of phase "hunting"; 2. shift of the endogenous circadian period in microgravity. Both should result in a higher hazard of desynchronosis in space flight. In the future it is important to investigate systematically the circadian range of entrainment in microgravity, the capabilities of rhythms to adapt to different durations of the day.