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Vibration research is reviewed from the point of view of how this environmental stress affects different types of human performance capabilities. The oscillatory motions normally called vibration range from 1–30 Hz., and the motion may be either sinusoidal or random. In terms of subjective discomfort, the lowest tolerance level for vibration occurs at about 5 Hz., the frequency at which resonance of large body organs is most severe. Visual acuity is severely impaired by vibration frequencies in the range of 10–25 Hz. Manual tracking capability is most seriously affected by vibrations at 5 Hz. and below, as are other motor capacities. Tasks involving primarily central neural processes, such as reaction time, monitoring, and pattern recognition, are highly resistant to the effects of vibration.

Among the important tasks of an astronaut will be the visual search for other vehicles in a co-planar orbit for purposes of rendezvous. Human data for minimum visual acuity can be used to compute the maximum sighting distance using information about target size, background, luminance and target contrast. But this distance is valid only if the astronaut knows the exact location of the target satellite and can fixate on it with foveal vision. For a dynamic search situation it is more meaningful to compute a probability of sighting using additional data or assumptions about peripheral visual acuity, eye fixation frequency, search area, and target closure rate. A method is described for computing probability of sighting. An example is provided for application of the method to a search situation for the approximate situation of a space rendezvous with a target comparable to the NASA Gemini vehicle.