The lunar portion of the Apollo Program presented entirely different extravehicular activity problems, i.e., 1/6-g and an unknown terrain. Indications were that the cost of walking would be reduced while the cost of other activities would be increased; however, the results and conclusions were by no means uniform. An additional factor of uncertainty was the terrain and surface composition of the Moon and its effect on the metabolic cost of walking. In response to these uncertainties, conservative biomedical estimates of the life support requirements were defined based on the available data, and methods to measure metabolic rate during the extravehicular activities were developed utilizing operational data from the life support system and bioinstrumentation.The objective of this Skylab experiment was to add additional data to the results obtained from the Gemini and Apollo experiments, and further quantify the metabolic expenditures associated with extravehicular activities.
The first set of Skylab extravehicular activities was to deploy the solar panels. After success was achieved, and a considerable capability to perform work in zero-g was demonstrated, the number of extravehicular activities was increased to 10 and the duration of these extravehicular activities was lengthened. These additions included the deployment of the solar panels, erection of a solar canopy, repair of an Earth Resource antenna, replacement of a gyro six-pack, and other vehicle and experiment repairs. An additional extravehicular activity was done to make observations on the Comet Kohoutek.
Skylab metabolic rates were similar to those on the Apollo 1/6-g extravehicular activities. The highest metabolic rate, 500 kcal/h, was reached while the Commander on Skylab 2 was trying to cut a strap that was keeping the solar panels from deployment. The lowest rates were resting rates and these were reached several times during the extravehicular activities, particularly at the times when there was not enough light to continue an ongoing activity during a night pass. Crew comments during extravehicular activities indicated that it was easier to maneuver themselves and their equipment in zero-g than in water tank simulations, but that adequate restraints were more important.
Because of problems with one of the vehicle coolant loops all three crewmen operated from a single coolant supply but the comfort cooling capacity at the loops remained at about 400 kcal/h steady-state. No problems were experienced from overheating. Because of the problem with the vehicle coolant system, the last extra-vehicular activity on Skylab 3 was conducted with gas cooling only. It was of limited scope and duration and no problems were experienced.
When taken as a whole, the Gemini, Apollo, and Skylab metabolic data proved that it was possible, with adequate life support equipment and adequate restraints, to perform varied and extensive extravehicular activity tasks both in zero-g and 1/6-g with considerable real-time flexibility. The capability to work at relatively high levels, up to 500 kcal/h, was demonstrated without physiologic problems provided the life support capability is adequate. The average energy cost of long extravehicular activities was remarkably consistent at about 200 to 250 kcal/h, and appears to be a function of the crew pacing its activity rather than to the effort involved in performing individual tasks.