Pushing forward into space can be accomplished either by manned or by unmanned space vehicles (automata). Space flight in manned vehicles is difficult because of the fact that the human organism can only bear small amounts of acceleration, irradiation and changes of temperature. For automata the corresponding ranges are larger. Further, it is difficult to secure respiration and nutrition for a man aboard a space vehicle, to eliminate his excrements, to control the physiological results of weightlessness on muscles and circulation, and to secure that he does not break down psychically. On the other hand, men are less sensitive than automata with respect to the perception of mechanical or electromagnetical vibrations. Only in the relatively small ranges of frequency which are adequate to the human ear and eye a comparable sensitivity of man exists.