Prior to Skylab, very little objective information had been obtained concerning the ability of man to sleep in space. Only by continuous EEG (electroencephalographic) monitoring can such information be obtained, and the technical problems associated with acquisition and analysis in space are significant. Before the advent of manned spaceflight, there was some concern about the possible adverse effects of this weightless environment upon sleep characteristics. During the Gemini program, however, it became apparent that fairly long duration space flight was not associated with drastic alterations of sleeping behavior. Astronauts could sleep in space and, on at least some occasions, did so fairly well. In the Gemini and Apollo programs, though, it became clear that in many instances insomnia was a problem. Sleep loss, while not absolute, was sufficient in some instances to result in performance decrements. In some instances, sleeping difficulties resulted in the use of hypnotic drugs to promote sleep and amphetamine-type medication to increase alertness following sleep loss
A complete system for analyzing sleep during space flight was designed for this 'experiment and included data-acquisition hardware, onboard-analysis components, and a capability for real-time telemetry. Automatic analysis of the electroencephalogram (EEG), electro-oculogram (EOG), and head-motion signals was accomplished by onboard equipment. The system's output, consisting of sleep-stage information, was telemetered in near 'real time to Mission Control, where a profile of sleep stage versus time was accumulated. The analog signals (EEG, EOG, and head motion) were also preserved by onboard magnetic-tape recorders, thus allowing a more detailed postflight analysis.
The recording cap was worn during the 59-day mission (Skylab 3). The electrodes, attached inside the elastic cap, were joined by wires to a miniature connector at the vertex, which permitted rapid linkage with the preamplifier assembly. The cap contained seven electrodes; four electrodes (left and right central positions, C l and C 2 , and left and right occipital positions, 0 1 and 0 2) provided a composite EEG channel (Cl and C2 paired and referenced to 0 1 and 0 2 paired); two (one lateral to and one above the left eye) provided one EOG channel; and one served as a ground. Following the sleep period, the preamplifier was disconnected, and the used cap was discarded; i. e., a new cap was used for each recording session.
During a sleep monitoring session, true real-time data was available only during the few minutes when the spacecraft passed over a ground tracking station. Throughout the frequent periods when the spacecraft was out of communication range, the sleep-stage data was accumulated by the spacecraft telemetry recorder and transmitted to ground at a high rate during a subsequent tracking-station pass. The tracking stations, in turn, relayed the telemetered sleep-stage information to Mission Control. Consequently, the data ultimately received during a sleep period was somewhat sporadic, ranging from actual real time to delays of up to several hours. Data-processing equipment in Mission Control collated the incoming data so that the time relationships were preserved, and eventually a complete tabulation of sleep stage versus elapsed time evolved.