The total time accumulated each day in 'activation tasks accomplished' divided by the number of 'man-hours available' for work was defined as the efficiency ratio (ER). The 'man-hours available' was simply a measure of the total crew time awake during the activation phase of each flight. If every waking moment were spent on activation tasks or repairs, this ratio would be unity. However, since the many essential tasks of food preparation, eating, sleeping, personal hygiene, and housekeeping were excluded, the efficiency ratio was less than one. When considering a normal day on Earth has 16 hours of possible work time, split evenly between useful work (8 hours) and other "overhead" or housekeeping functions, an average day would have an efficiency ratio of 0.5 by this definition.
The results of the Skylab data show that on seven of the nine activation days, the efficiency ratio average was just over 0.54. Only on mission day 2 of Skylab 3 and mission day 3 of Skylab 4 did it drop significantly below this value. Mission day 2 of Skylab 3 was the day in which this crew felt most handicapped by motion sickness. On this day there was an attempt to provide the crew with about 2 hours of rest in midday, although they were required almost immediately to respond to a Master Alarm indication of low bus voltage. Much of the scheduled rest period was then spent in tracking down the source of the large power drain.
The Skylab 3 crew had been awake on mission day 1 for a total time of 22 hours (only 7.5 available for activation), followed by 18 waking hours on mission day 2. These long days may well have contributed to reduced efficiency on mission day 2, as well as the motion sensitivity. Assuming that an ER of approximately 0.54 is 'normal,' it was estimated that the time lost due to reduced efficiency was approximately 7.0 man-hours. Similarly, the Skylab 4 crew on mission day 3 may have lost about 4.7 man-hours, at least some of which was due to motion sensitivity.
Crew performance can be viewed from another aspect by examining how many man-hours of activation tasks remained incomplete at the end of the scheduled activation interval. For the three crews respectively, 0.1, 13.5, and 4.8 man-hours of work remained incomplete. For all three flights, essentially all of these remaining tasks were completed by the end of mission day 4. Although 13.5 man-hours of activation tasks remained to be accomplished at the end of mission day 3 on Skylab 3, additional repair tasks of 12.9 man-hours had been completed. The Skylab 4 crew completed an extra 4.2 man-hours of added tasks in their activation phase. These results indicate that all three crews were able to deliver, in the first 3 or 4 days of their respective flights, rather close to the amount of work they had been scheduled to accomplish preflight.
A comparison that examined productive work accomplished in the first few days of flight with that accomplished later, when adaptation was complete and the routine well established was produced. In order to make this comparison other operational tasks performed later in the missions, in addition to the direct performance of experiment operations, had to be accounted for. These operational tasks include physical exercise, some 'post-sleep' activities related to experiments, television, photography, and repairs. When these tasks were added to the specific experiment operations, the Skylab 3 crew delivered over 31 man-hours of productive work per day, and increased this to about 36 man-hours per day toward the end of the mission, which would correspond to an ER equal to 0.75. These numbers relate to a 'normally' efficient activation day of about 26 man-hours per day of work accomplished.
A summary of the results shows that all three of the three-man Skylab crews accomplished activation work at an efficiency ratio of about 0.54, equivalent to 26 man-hours/day, assuming they were all awake for 16 hours and asleep for 8 hours each day. On 1 of the 9 total days spent all or partially in activation, mission day 2 of Skylab 3, the crew efficiency dropped about 25 percent (ER equal to 0.41), attributable largely to transient motion sickness. After experiment operations began, the Skylab 3 crew soon accomplished similar work tasks at a rate in excess of 31 man-hours/day, increasing to about 36 man-hours/day toward the end of the mission. The Skylab 4 crew accomplished work in these same categories at a rate of about 28 man-hours/ day early to above 33 man-hours/day late in their mission.
The researchers concluded from the results that the improvement in productivity seen throughout the mission came about for two reasons. First, the crewmembers had more extensive training and proficiency in experiment operations as compared to activation tasks, and second efficiency improved as experience was gained in zero gravity living. The activation tasks were to be performed only once by each crew and consisted of many largely unrelated activities. Each crew had the opportunity to practice the full procedures in their trainers at the Johnson Space Center only a few times prior to launch. However, training for experiments and especially those consuming the most time (solar, medical, Earth Resources) was very thorough and extensive. Still, operations in zero gravity could not be precisely simulated preflight, and a further training improvement was noticed during the course of the mission. More time became available to experiments because the time required for the 'overhead' tasks of food preparation, eating, and housekeeping was reduced as experience was achieved in the routine of zero gravity living.
In conclusion the results show that a relatively modest amount of crew time may have been lost due to motion sickness on Skylab missions 3 and 4 but that each crew's performance was never substantially impaired for more than 1 day.
During the three activation intervals, less than 12 man-hours were lost to reduced efficiency (including the effects of motion sensitivity) while almost 200 man-hours of productive work were delivered. A very substantial improvement in work rate was found, however, for tasks in which simulation and training time was extensive and for tasks of a repetitive nature which allowed zero-gravity operations to be optimized.