Task and Work Performance on Skylab Missions 2, 3, and 4: Time and Motion Study Experiment M151

THE PURPOSE of the Time and Motion Study was to determine how well man can perform specified tasks under zero-g conditions over the course of long-duration space flights. Among its objectives, experiment M151 studied the in-flight adaptation of crewmen to a variety of task situations involving different types of activity. Training data provided the basis for comparison of pre-flight and in-flight performance.

It was anticipated that in-flight performance of some tasks would be but slightly affected, while the performance of others in the zero-g environment would exhibit more pronounced changes in time and/or in the patterning of the elements comprising the tasks. On the assumption that overall work time would increase in the zero-g environment, initially at least, an additional objective was to determine at what point work efficiency in-flight would be restored to that manifested during the last preflight performance.

The adaptation function, or, the relation expressing the amount of time it takes to perform the same task in successive trials (task time as a function of task trial), was used to evaluate the effect of the Skylab environment on task performance. As graphed, this function is represented by a curve which decreases (i.e., performance time gets shorter) from trial to trial, ultimately reaching a point where successive trials yield similar values (i.e., approach to asymptote). The rate of decrease, which indicates improvement, differs for different tasks. The character of this curve also varies from individual to individual. Unexpected changes in slope or in variability can be used to identify difficulties with hardware, changes in environmental conditions, or alterations in method of performance. Change in performance level or in variability may also reflect fundamental changes in the attitude or physiological condition of the subject. The adaptation function can also be used to identify the point at which in-flight task efficiency is restored to the level of preflight proficiency. It also provides a basis for developing criteria of performance deterioration, specifically relevant to space flights of long duration.

Objective Of Present Report

The specific objective of this report is to present data on those work and task activities encompassed by experiment M151 and common to Skylab missions 2, 3, and 4. The emphasis, then, is on the replication and comparison of crewman performance on flights of varying time lengths. It is thus possible to study the effects of increasing performance trials on the characteristics of the adaptation function. Similarly the effect of increasing zero-g exposure on work and task performance is available for analysis.

Data Acquisition

A Maurer 16 mm Data Acquisition Camera, supplied with SO168 color film, was used to photograph selected tasks on each mission. Two Maurer lenses were employed: a 5 mm lens with wide angle field-of-view to photograph activities in the lower area of the Orbital Workshop where the camera was constrained by close proximity to the filmed activity; and a standard 10 mm lens to photograph activities in the Orbital Workshop forward area. A portable high intensity light was used where onboard lighting was incapable of yielding acceptable photography.

On Skylab 2 all data were photographed at six frames per second to provide reliable criteria for determining the end points of the elements comprising the task. On Skylab 3, frame rates were reduced from six frames per second to two frames per second for some activities in order to con-serve film for an adequate sampling of data over a mission twice the duration of the first. Mass handling tasks were maintained at six frames per second. Skylab 4 data collection followed the same guidelines as those for Skylab 3.

Illumination levels varied from 4 to 9 foot-candles depending on location, and as has been mentioned, the portable high-intensity light was used only where onboard lighting was totally unacceptable for photography. Power conservation practices during early portions of Skylab 2 to relieve power and thermal problems, required some concessions in normal lighting levels, but usable data were obtained.

Because of accumulating radiation damage to film, new lighting criteria were initiated for Skylab 4. The increased use of portable high-intensity light in addition to normal lighting reduced the effects of radiation. Image enhancement procedures were also utilized to counteract radiation damage.

Film Analysis.—Approximately 4350 feet of film were taken on Skylab 2, while more than three times this amount, 14,700 feet, were available from preflight training. Corresponding data for Skylab 3 were 3800 and 10,400; for Skylab 4, 2500 and 6800.

To process this large volume of film a three-level analysis procedure was developed to filter the data into classes according to the depth and detail of analysis required. With this procedure the film as a whole was analyzed, but portions of critical importance were given detailed treatment.

The film was examined on a special film viewer which had the capability of controlling rate of presentation and alignment, while attaining high precision in measuring the dimensions and orientations of the image. In the first level of analysis, each task or activity was broken down into the elements required for its performance. These elements were identified and defined during the training sessions. Along with the basic identifying information, such as date filmed and analyzed, film rate, work activity, et cetera, the first level analysis, gave the element description and the frame number or time at the end of each element.

The second and third levels of analysis built on the data obtained from the first level. More detail was provided and relevant accessory variables were identified. Thus, for each element the second level of analysis included torso configuration, position restraints, restrictions, detailed motion patterns, et cetera. The third level added to the second level such items as crewman elevation, roll and heading, plus details as to elbow, torso, and knee angles. From this information it was possible to reproduce in a quantitative fashion and to a high degree of fidelity the patterning and temporal course of any activity.

The work of the film analyst was facilitated by the use of a Coding Dictionary. The dictionary provided the necessary definitions for identifying, classifying, and measuring the activity as depicted on film. It gave exact instructions for computer coding—the data to assign to specific card fields, the use of various programming cards, and all other programming instructions. The use of the Coding Dictionary maximized the objectivity and accuracy of film analysis.

Task Selection.—Selection of activities to be filmed was governed by a number of rather restrictive criteria. Repetitive and relatively standardized tasks were required to satisfy replication and uniformity conditions. At the same time, relevant and natural, rather than contrived, activities were desired. Consequently, they had to be part of the planned schedule, not added to or modified for experiment M151. Additionally, variety in tasks was sought in order to permit the study of a broad spectrum of human performance.

Activities associated with the preparation and execution of approved medical and scientific experiments met all of these requirements. Thus, the regularities of experimental procedures in other experiments provided M151 with a source of homogeneous data for analysis and evaluation.

Experiment Data Sources.—The experiments and operational activities serving as sources for photographic data are listed below, together with a brief description of some of the activities of interest.

   M092 In-flight Lower Body Negative Pressure. The preparation for this experiment involved the coordinated interaction of two men who utilized both fine and gross motor activity in the unstowing, preparation, and donning of electrodes, probes, and measuring devices. In addition, precision of translation and ingress of the Lower Body Negative Pressure Device was required.

   M171 Metabolic Activity.—This experiment also involved a two-man interaction in the mounting of the ergometer and donning of the restraint system (which was deleted in-flight) and metabolic apparatus. The operations of unstowing, assembling, and connecting required gross motor activity. Specialized restraint systems were utilized.

   T027/S073 ATM Contamination Measurementegenschein/Zodiacal Light.—The removal, deployment, transfer, installation, and retrieval of the photometer (and associated activities) involved two-man interaction (reduced to one-man activity in-flight) in the handling and translation of hardware of very large mass and size. The photometer weighed 95 kilograms and had dimensions of 140 X 50 X 30 centimeters. Gross and fine motor dexterity was involved in the varied activities associated with this operation.

   S190B Earth Terrain Camera.—The removal, preparation, installation, deployment, and retrieval of the Earth Terrain Camera required a one-man/mass interaction utilizing medium-sized hardware. The camera weighed 29 kilograms and had dimensions of 70 X 20 X 30 centimeters. Fine and gross motor activity was involved as well as translation with load.

   S183 UV Panorama.—Photography of this experiment yielded data encompassing unstowage, transfer, installation, and film loading of large hardware which weighed 48 kilograms and had dimensions of 130 X 40 X 40 centimeters. Fine and gross motor activity was involved as well as translation with or without loads of varying size.

   M509 Astronaut Maneuvering Equipment.—One-man maintenance activity involved removal, stowage, unstowage, transfer, and installation of hardware subassemblies. Two-man interaction in donning experiment hardware employed fine, medium, and gross motor activity.

   EVA Suit Donning and Doffing.—Donning of the suit from the liquid cooled garment to pres-surization required two-man interaction involving fine and gross motor activity. Suit doffing involved similar types of activity.

   Food Preparation.—Removal, collection, and preparation of food required relatively gross motor activity. Use of a thigh restraint was involved.

Not all of the data obtained from the tasks listed above were used in this report. The primary emphasis was on comparable data obtained from all three missions.

Sampling and Replication.—Weight and stow-age restrictions placed a limit on the amount of film assigned to experiments. The crowded and complex schedule of an astronaut’s workday presented difficulties for filming the desired experimental trials. These constraints created problems for sampling the experimental trials and allocating them to the Skylab missions.

On the Skylab 2 mission, sampling density was maximized for the initial group of trials of an experiment. During Skylab missions 3 and 4 more emphasis was given to performance towards the end of the mission, to better detect performance variability, should any have occurred due to extended exposure to the Skylab environment.

It will be observed that the final or last trial was not generally used for filming. There were two reasons for this decision. In the first, the well documented "end-effect" was avoided. This effect, observed in traditional learning as well as in isolation situations, reflects the frequently occurring change in attitude of the subject as he realizes that this is his last trial, or last day of isolation. Thus toward the end of a flight, the attitudes and interests of the astronauts were expected to become more focused on "cleaning up" or "getting ready to leave." The second reason was concerned with the practical matter of work slippage. Small but annoying problems could develop during the course of a mission with the result that experimental trials late in the series might have to be sacrificed.

Preflight training involved the crewmen in various types of work and task performance. First, there were walk-throughs, then heavily assisted performances, and finally the crewmen on their own with very little or no assistance from training personnel. These latter performances, the last four or five before flight, were used as baseline or contrast data for comparison with in-flight performance. The data points comprising the baseline extended over a period of many months, from December 1972 to May 1973 for Skylab 2, from August 1972 to June 1973 for Skylab 3, and from November 1972 to October 1973 for Skylab 4. There were, of course, earlier training sessions. In M092, for example, the Skylab 2 crewmen as observers had a total of 25 training sessions; Sky-lab 3 crewmen, 14; and Skylab 4 crewmen, 27. The Skylab 3 crew had the fewest, approximately half the number of the other crews.

Time Measurements.—The time to complete a task was measured in several ways. The most inclusive was Voice/Telemetry Time, the end points of which were either voice recorded by the crewman or automatically indicated by the start-stop controls of a timer. Thus, the beginning of a task may have been recorded by the statement "Started M092 at ," while the completion of M092 data acquisition was automatically indicated by the crewman stopping the experiment timer. Termination was sometimes also announced by voice, as "End M171 at ."

Camera running time included only the time during which activity was being photographed. It eliminated such preparatory activity as, arranging material for the experiment, making final calibrations, and other such activity which was included in Voice/Telemetry Time. Included in Camera Running Time, and in Voice/Telemetry Time as well, were such categories as foreign elements, waits and idles, anomalies, and redundancies. These categories will be discussed in more detail in the Performance Anomaly Section.

Basic element time was the least inclusive of the three measurement procedures, comprising the sum of the times associated with the basic elements.—The basic elements were the set of elements which were necessary to complete the task; they appeared in every performance of the task, preflight or in-flight; and they were performed only by the crewmen to whom the task was assigned. Basic Element Time, then, was comparable from person to person, from mission to mission, and from preflight to in-flight performance. In contrast nonbasic elements were those which sometimes were omitted by the crewmen (e.g., stowage of leg bands), or modified, or done before the camera was activated or after the camera was turned off. In calculating Basic Element Time, such variables as foreign elements, waits, and idles which are defined in the next section were removed from the time for the element in which they occurred.

Element time was the time determined for each element by time and motion techniques.—This included basic as well as nonbasic elements. The time taken to complete each element (ref. 1), at each task performance by each crewman, comprised the fundamental data source from which special analyses were potentially available. As an example, elements could be grouped into classes, such as, fine or gross motor dexterity, translation with or without load, large versus small mass handling.

In the present report Voice/Telemetry Time measurements were included to demonstrate the type of adaptation function they produced. The major portion of the analyses, however, were based on Basic Element Time which provided valid comparisons across missions and between training and in-flight performance. Nevertheless, Voice/Telemetry Time provided a realistic estimate of the time it took to complete a particular in-flight task.

Performance Anomaly.—The time required to perform a given task, subtask or element varies from performance to performance. Differences in method, procedure, or motion pattern are also observed during task performance. These variations are due to a complex set of factors and where they are minor and no assignable cause (or causes) can be discovered, they are characterized as random. However, film analysis frequently reveals identifiable perturbations in task performance which have assignable causes. The situations giving rise to such perturbations have been categorized as: foreign elements, waits and idles, and task-related anomalies.

A foreign element is any activity or motion pattern unrelated to the ongoing task but initiated or caused by the crewman during the performance of the task.—Examples would be a crewman stop-ping his task to take a message or to perform some other and more urgent activity. The time for foreign elements was recorded separately and removed from the time for the element (task) in which it occurred. These intrusive and task-independent activities may be occasioned by human lapses, needs, or distractions and by mechanical or hardware failure.

Waits and idles are characterized by breaks in the work cycle in which the crewman must wait for someone else to work with him, or for a mechanical process to be completed.—Or the crew-man may "take a break," or be idle, that is, non-productive. He may also be engaged in mental activity (e.g., reviewing progress) not observable to the analyst. As was done with foreign elements, waits and idles were removed from the time measurement of the task (or element) in which they occurred.

Task-related anomalies are those activities, initiated by a crewman, or by hardware difficulties, which occur during the performance of a task and are essentially a part of it.—This class is represented by the "fumble," an incorrect procedure or sequence, a dropped object, or other task-related error. The time occupied by the anomaly is usually included in the element time. If it is possible or advantageous to evaluate the causative factors involved, the anomaly can be treated as an element and isolated for more intensive study. As noted above for foreign elements and for waits and idles, task-related anomalies may have human as well as mechanical (hardware) origins. Task-related anomalies are of special importance in that they can point to deficiencies in the man/machine interface and/or in hardware design.

Graphic Results

One of the simplest, and in many ways most effective, methods of presenting experimental results is through graphic procedures. A representative picture of M151 data can be seen in a series of four graphs, figures 16-1 through 16-4, which depict the adaptation function for the basic activities involved in M092 Lower Body Negative Pressure, as these were performed on Skylab missions 2, 3, and 4. Training data comprise the left section of each graph; the right hand portion presents the in-flight results.

Figure 16-1 shows the results for the Pilot and Scientist Pilot as subjects in M092 Prerun Activity. The most striking feature of these graphs is the seeming continuity of in-flight performance as it followed the last preflight performance. The same tendency can be observed in figure 16-2 which summarized M092 Postrun Subject Activity, again for the Pilot and Scientist Pilot on each of the three Skylab missions.

The time to perform the basic M092 Prerun Observer Activity showed a different pattern in figure 16-3. In-flight performance was generally elevated in comparison to terminal preflight training data. This was most clearly shown in the performance of the Commander for each of the three missions.

In figure 16-4, in-flight performance time was at approximately the same level as that for preflight training data. Excepting the preflight performance for the Skylab 4 Scientist Pilot, the data showed very little variation.

Preflight training data for Skylab 3 and Skylab 4 were widely scattered over the 12 months preceding launch. In contrast, most of the training data for Skylab 2 were obtained within the last 5 months before launch.

One important fact emerged from the analysis of the four graphs. Of the 23 in-flight curves presented in the four figures, 18 of them had their initial performance at a level higher than that found in the last preflight trial.

(Scaling reflected the greater importance attached to in-flight performance. Providing larger units for mission days, made it possible for the in-flight performances to be more clearly differentiated among the three missions.)

Statistical Analyses

First Inflight Task Performance.—The first trial of an in-flight task was considered a significant datum for evaluating the effects of zero-g environment on task performance. In one sense, the zero-g effect was already diluted by the time the experiments began because crewmen had been busily working in the zero-g environment during the activation period, and for several days had been slowly divesting themselves of one-g habits and quickly acquiring zero-g maneuverability and expertise. Nevertheless, the previously presented graphs have strongly indicated that the first in-flight trial generally took longer than the last preflight trial of the same task.

To better evaluate the effect of the zero-g environment on the initial trials of in-flight performance, the tasks were subdivided into elements and the times associated with the performance of each element were compared, first trial in-flight versus last trial preflight. The data for these elements were presented in terms of frequencies, namely, the number of instances that time for the first in-flight trial was greater than that for the last preflight trial, and vice versa. The results are found in table 16-I. Thus, in the Skylab 2 mission, 95 elements took longer to complete in-flight than preflight. For 44 elements, the situation was reversed. In 68 percent of the cases, then, the first inflight trial took longer than the last preflight trial.

Although the effect was not so pronounced for the remaining two missions, the results were consistent. When the results of the three missions were combined, it was observed that 61 percent of the first in-flight trials took longer than the corresponding last preflight trials.

Data in parentheses refer to Basic Elements. As shown in the table, percentages based on the basic elements appeared more consistent from mission to mission while summary results based on all three missions yielded almost identical percentages (59 versus 61).

The elements were also categorized into three classes representing tasks requiring fine, medium, and gross motor dexterity. Because of the consistency of results from mission to mission, the data were combined across the three missions. The basic comparisons, first in-flight versus last preflight, were thus available for the three types of motor activity involved in task performance. These are presented in table 16-II.

Although the first in-flight trial generally took longer than the last preflight trial, a result established in the previous analyses, the percent increase was most pronounced for fine motor activity, less so for medium and least for gross motor activity. The percentage differences are small and insignificant but the systematic decrement is important. Such a decrement would reinforce the debriefing comments of the astronauts who reported that the control of small objects caused more difficulty than the control of larger masses.

Return to Preflight Baseline.—It has been noted that the first in-flight trial generally took longer to perform than the last preflight trial of the same task. The question arose as to how long it would take to adapt to the Skylab work environment, or more specifically, how many trials it would take before an in-flight task was done as speedily as it was on the last preflight trial. The criterion of equivalent performance was taken to be that particular trial at which half or 50 percent of the task elements were done as speedily as in the last preflight performance.

The sources for this analysis were the activities involved in experiment M092 (Prerun and Post-run, Subject and Observer), Experiment S073, and Suit Donning and Dofflng. Table 16-III presents the number of activities which, at first or second in-flight trial, were done as rapidly as they were on the last preflight trial. For example, by the end of trial 2, 44 of the 86 elements on Skylab 2 were completed within the time taken on the last preflight trial.

From an overall viewpoint, the results for the three missions were fairly consistent. When the elements were totaled across the three missions, exactly half of the elements returned to preflight baseline (last preflight trial) by the end of the second trial.

The specific mission day on which the criterion was reached could not be precisely determined since some of the activities, such as Suit Don/Doff, were not scheduled as regularly as experiment M092. If one were to take experiment M092 as the more consistent indicator, then the mission day equivalences for the three flights were as follows:

2                                                                    7^th or 10^th day

3                                                                    8^th day

4                                                                    10^th or 11^th day

In general, the second trial of experiment M092 was scheduled within the second week of the mission. It was anticipated, then, that the crewmen should have begun to feel adapted to their work schedules, or should have felt a reduction of the work pressure at about this time. The debriefing comments were not altogether clear on this point. For example, the Skylab 3 crew (and the Skylab 2 crew to some extent) indicated that the critical point in adaptation occurred in the vicinity of 10 days. As for the Skylab 4 crew, one member mentioned a period of a week or two, another a period of a month or so. From an objective viewpoint, however, the data suggested a point in time somewhere in the vicinity of a week or two.

The time period mentioned above was, in many respects, an artifact of work-schedule planning. There was some evidence in the data to indicate that trials were more important than mission days in the evaluation of adaptation to task or work performance. It has been observed that by the second trial, whether performed on the same day or a week later, the time tended to approximate that obtained on the last preflight trial.

In summary, the time to perform a task on the second in-flight trial tended to approach the baseline time of the last preflight trial. For short missions, then, the early repetition of tasks critical for mission success  would seem to be the most effective allocation of in-flight work activities.

Pattern of Task Performance.—It was anticipated that some tasks would be done differently under the zero-g environment than under the one-g training conditions. In particular, it was expected that the pattern of in-flight work activity would differ from that exhibited in preflight training. For the present analysis, the basis for differentiating preflight from in-flight work patterns was the order in which the elements of a task were performed. The standard was the order determined by the checklist. Against this standard were compared the orders in which the elements were performed in-flight and in training. A measure of how closely these orderings corresponded to the standard was obtained by the Spearman Rank Difference Correlation Coefficient.

The following four tasks associated with experiment M092 were used in the analyses:

                   Prerun Subject                (15 element array)

                        Prerun Observer               (27 element array)

                        Postrun Subject               (15 element array)

                        Postrun Observer              (12 element array)

As an example of a typical array, the checklist ordering of elements in the Prerun Subject task follows:

1. Translate to Waste Management Compartment from Data Acquisition Camera                        ---Remote Control.

2. Unstow harness and sponges.

3. Clip harness to garment.

4. Prepare vectorcardiograph harness.

5. Don vectorcardiograph harness.

6. Attach Body Temperature Measurement System cable to harness.

7. Translate to Lower Body Negative Pressure Device from Waste Management                       Compartment.

8. Open seal zipper fully.

9. Adjust plates.

10. Ingress Lower Body Negative Pressure Device.

11. Mate vectorcardiograph to Subject Interface Box on Lower Body Negative Pressure                        Device.

12. Close plates.

13. Zip/adjust seal.

14. Fasten/adjust seat belt.

15. Don Blood Pressure Measurement System.

Spearman correlation coefficients were computed for each trial of each crewman in his capacity as subject or observer. Since number of trials differed in-flight and in training, the number of coefficients for these conditions also differed.

Table 16-IV presents the preflight and in-flight median correlation coefficients "r" for the three Skylab missions. In general, the median preflight coefficients were larger than the in-flight coefficients for all three missions. The results indicated that the crewmen performed preflight tasks more in line with the checklist order than they did in-flight. The result made sense in that a crewman was more likely to follow instructions much more closely during training than after having mastered the task. Once mastery was achieved he could with more confidence experiment with better ways of doing the task. In addition, the crewman’s weightlessness and the weightlessness of the masses he was handling made it more likely for his work pattern to change.

Another trend was also apparent in the data. Whereas the preflight coefficients remained relatively the same for each mission, the magnitude of the in-flight coefficients diminished steadily from the first to the last mission. This, too, was a reasonable result in view of the general transmission of information from one crew to another. In particular, any new and efficient methods of performing in-flight tasks were always transmitted to the crews of subsequent missions. Such methods would have very likely involved the ordering of elements comprising a task.

Despite the differences noted between the pre-flight and in-flight coefficients, both sets were of high magnitude. Coefficients of such magnitude indicated that the order in which the elements of a task were performed, preflight or in-flight, adhered relatively close to the order prescribed by the checklist.

The Spearman coefficients were analyzed also in terms of the function the crewman performed, namely, whether as subject or as observer. Table 16-V presents the median coefficients for these crewman roles, preflight and in-flight, for the three missions. The data indicated not only that the pre-flight and in-flight differences were consistent across the new subdivisions but that there was a strong trend for the Subject coefficient to be higher in magnitude than the Observer coefficients. These results flowed directly from the roles assumed by the crewmen. The subject, once in or attached to an instrument, was constrained by the sequential functioning of the mechanical system much more rigidly than was the observer whose options were more numerous because of his role in the experiment.

In summary, the sequential pattern of a task as described in the checklist, was more rigidly adhered to in training than in-flight. Further, subject activity adhered to the checklist order more closely than observer activity because of the constraints of the instrumental system to which the subject was attached.

Suit Donning Results

Suit donning is of vital concern to crew safety and operation during extravehicular activity. In addition, this activity (as well as suit doffing) has always been of interest to M151 investigators be-cause it requires the full scope of the crewmen’s capabilities from fine motor dexterity, such as the precise alignment of connectors, to gross activities such as placing the helmet and gloves for later use. Crewman interaction is also involved, primarily during the zipper closures of the pressure garment assemblies. As the later crews studied the M151 films of the earlier crews, it was anticipated that significant changes in method from crew to crew would develop. Suit donning was nominally to be performed early, middle, and late in the mission on Skylab 3 and Skylab 4, thus providing some indication of zero-g adaptation.

The Skylab crewmen wore their suits for many different types of training in preparation for their respective missions. In most cases, they received assistance from suit technicians in donning and doffing the suits and as a result had a minimal number of training sessions where they actually simulated the donning and doffing procedures required for the Apollo Telescope Mount extravehicular activities. However, from the exposure of having the suits custom fitted and from having the suits on for various exercises, the crewmen became familiar with the components required for extravehicular activity. During Skylab training, a maximum of only four extravehicular activity suit donning (and doffing) sessions were recorded by M151 for any crew. Table 16-VI presents a summary of Skylab preflight training, with total time shown for 21 basic (and common) elements which must occur in the suit donning activity. The performance number refers to the crewmen donning the suit.

Figure 16-5 presents the graphs of the averaged data in table 16-VI. The outstanding characteristic of the three functions is the terminal point, the time for the last training session before flight. Whatever the differences in the initial training sessions, and these were large among the three crews, the final training performance required about the same amount of time (800-850 seconds) for the different crews. Although there was some inconsistency in the pairing of crewmen during the training sessions, it was felt that this had a minimal impact on the total times. There is certainly every indication that proficiency consistently improved.

Although all three crewmen donned the pressure garment assemblies prior to each extravehicular activity, only the two crewmen who would actually perform the extravehicular activity donned the necessary items specific to extravehicular activity. The third crewman did gain the additional experience of donning and doffing the basic part of the suit but did not participate to the extent of the two extravehicular activity crewmen. The performance number alluded to in this section refers to an assignment as extravehicular activity crewman.

Table 16-VII and a figure 16-6 which follow summarize the in-flight suit donning performances. Only one performance (on mission day 25) was filmed for Skylab 2, but it was the second time the Commander had donned his suit prior to extravehicular activity, while it was the first suit donning for the Pilot as an extravehicular activity crewman. An earlier extravehicular activity on mission day 14, involving the Commander and Scientist Pilot, was required on Skylab 2 during which the Pilot performed a non-extravehicular activity suit don. Three trials were recorded during each Skylab mission 3 and 4, but not always with the same pair of crewmen. The effect of total number of performances, difficulties (on Skylab 4) with the zipping operation because of snug-fitting suits, occasional intrusions of the non-extravehicular activity crewmember into the operation, and the small number of observations, created difficulties in identifying relationships between the timing (number of months or days, before launch) of training sessions and the timing of in-flight performances.

Large differences were found in the average times of extravehicular activity crewmen for the last performances: 669, 740, and 910 seconds respectively. These differences are probably due to factors other than the effect of training schedules, adaptation to zero-gravity, learning, et cetera. Suit fit, for example, could have obvious effects on the time required to don the pressure garment assembly. This may be the reason that the Skylab 4 crewman took longer to don the pressure garment assembly late in the mission. In-flight anthropometric data (ch. 32) from Skylab 4 indicates that the heights of the crewmen significantly increased over the course of the mission and that the greater part of this increase was in the upper torso. This, then, would explain the much longer time required to zip the pressure garment assembly, a fact which M151 data disclosed. Correlation of the results of the antropometric findings and M151 were further substantiated by Skylab 4 crew comments in their postflight debriefings.

On Skylab 4 mission day 7, the Scientist Pilot and Pilot donned their suits (see table 16-VII) with considerable difference in time required; 1192 seconds for the Scientist Pilot and 818 seconds for the Pilot. During this extravehicular activity preparation the Pilot seldom used the portable foot restraint while donning his own suit. He accomplished the suit donning in a free-floating mode or used his hands as a restraint system. Although it appeared difficult or awkward, the time was 31 percent less than that of the Scientist Pilot who remained in the foot restraint while donning his suit.

During the portion of the suit donning task where the crewmen assisted each other, the time taken by the "unrestrained" Pilot to zip the Scientist Pilot’s pressure garment assembly zippers was 279 seconds, while the "foot-restrained" Scientist Pilot took only 222 seconds to zip the Pilot’s zippers. In the first case the Pilot maneuvered around the Scientist Pilot, using the Scientist Pilot to re-strain himself, as he performed the zipping operation. In the second case, the Scientist Pilot had the Pilot free-floating in front of him, and turned him as necessary to put the zipper in the best working position.

Although the Pilot took the shortest time for the total suit donning task, it would appear that in a two man operation, the "operator" should be restrained when working on a task that offers resistance such as a zipper; while restrained he is also in a better position to control the physical attitude of the subject.

Fundamental Time Measures

   Camera Running Time and Basic Element Time.—In addition to accurate time information, photographic methods also provided the basis for understanding why anomalous results could have been obtained. Two time measures based on photography were described in an earlier section— camera running time and basic element time. Although camera running time was the more complete measure, it also included the timing of activities not necessarily relevant to those being observed and measured. More limited in coverage, basic element time provided a measure for making valid comparisons between preflight and in-flight performance, between missions, and between crewmen.

Experiment M092 Prerun Subject data for the three missions were used to give a comparative picture of the two photographic measures. Figures 16-7 to 16-9 present the data for the three missions. The most readily observable characteristic of basic element time was its consistency and stability in contrast to the wide variations exhibited in camera running time. This may be observed most clearly in the respective graphs of the Skylab 2 Pilot (fig. 16-7), the Skylab 3 Pilot (fig. 16-8), and the preflight graph of the Skylab 4 Pilot (fig. 16-9). Despite the lower values obtained with the basic element time measure, it was a sensitive and realistic indicator of changes in the adaptation function. As an example of the value of basic element time, attention is directed to the two curves for the preflight performance of the Pilot of Skylab 3 (fig. 16-8) . The upper curve, representing camera running time, would have indicated that performance became worse with practice. Basic element time, on the other hand, presented a more realistic picture of the adaptation function.

Both time measures, camera running time and basic element time, served important functions in the analyses of crewman task and work activities. Camera running time provided a basis for explaining unusual and unexpected results by isolating and identifying nonrelevant perturbations intruding on the efficient performance of a task. Basic element time served as the fundamental comparative measure and helped in identifying the nature of the differences in performance in-flight and preflight, between missions, and between crewmen.

   Voice/Telemetry as a Method of Data Acquisition.—Because of film restrictions, it was not possible to photograph the totality of trials comprising each of the M151 experiments on the Skylab missions. A procedure was devised to sample those trials most critical to M151 objectives. The partial but carefully sampled data were used to generate the adaptation function which served as the basis for estimating data points not sampled by M151 film procedures.

Data for the complete set of trials would have been highly desirable; they were, however, unobtainable because of the limited amount of film available to M151.

The cooperation of the Skylab 4 crew was obtained to gather and report data on the performance of tasks done repeatedly and regularly over the entire 84-day mission. This involved the major medical experiments: M092, Lower Body Negative Pressure; M093, Vectorcardiogram; and M171, Metabolic Activity. These experiments were scheduled back-to-back in combinations of M092/ M093 or M092/M171 and were performed within 3- or 4-day cycles with each crewman as subject. The result was that virtually every mission day from day 5 to day 83 had at least one of the com-binations M092/M093 or M092/M171 as part of the daily flight plan. The only exceptions were the days the crewmen rested or performed extravehicular activity. Also twice during the mission, two major medical runs were made in the same day to free another day for multiple Earth Resource passes. Although subjects were scheduled on a regular basis, this was not the case for the observers. By the end of Skylab 4, the Commander was the observer for experiment M092 a total of 26 times, the Pilot a total of 23 times, and the Scientist Pilot only 18 times.

Performance time was obtained from the voice records and these indicated the points at which crewmen began or finished a task. In the course of the experiment, telemetry automatically recorded other events, such as calibrations, and these time points provided a check on possible discrepancies in the voice records.

No attempt was made to factor out anomalies or task interruptions present during the nominal run of the experiment. Interruptions caused by air-to-ground communications or other crewmen were considered, in the present analysis, as part of the total time required to perform the task. Other factors, however, not associated with the experiment proper, were eliminated from the tape-recorded time interval assigned to the experiment. These were the special tests which were intro-duced late in Skylab missions 3 or 4. They included Limb Blood Flow, Leg Blood Pressure, Facial Photos and Anthropometric Measurements to study body fluid shifts, venous compliance (chs. 31,32), and changes in body size due to prolonged exposure to zero gravity (ch. 22). In some tests, such as Limb Blood Flow, the time required could be factored out on the basis of telemetry associated with the test. In others, an estimate was determined from baseline data or from in-flight photos taken from M151 data. Early in Skylab 4, the special tests had significant impact on performance because the crew had little or no training on these tests prior to flight.

Accurate Voice/Telemetry data across the three Skylab missions were available in only one segment of the M092/M093/M171 complex of activities. The segment consisted of those activities following the completion of M092 data collection up to the point when M171 data acquisition was begun. In sequence, these activities included:

Time Count—Stop (End of M092)

Cuff/Inflate—Stop/Reset

Perform Hi-Calibration--(Hold 20-25 seconds)

System Select—Off

Tape Recorders—Off

Data Acquisition Camera—On (If required)

Open Marmon Clamp and Lower Body Negative Pressure Device

Remove Legbands and Reference Adaptor from Subject

Close Lower Body Negative Pressure Device and Secure Marmon Clamp

Begin Metabolic Activity Calibration Check

Configure Experiment Support Systems for M171 Data

Electrode Impedance Check

Perform Hi-Calibration (Hold 20-25 seconds)

Vital Capacity Calibration (If required)

Vital Capacity Measurements (3 trials)

Time Count—Start (M171 Data Collection)

The time interval between the two time counts was used to compute averages for the three crewmen acting as observers in each of the Skylab missions. These data are presented in graphic form in figure 16-10. For two of the Skylab missions, 2 and 4, and partially for the third (Skylab 3) the graphs demonstrate the characteristic features of the adaptation function: high initial values and a progressive decrement over the course of the experiment.

The Skylab 2 graph was smoothest and most regular, uniformly lower than the others over the six trials, and decreasing at a relatively slow rate. Of the three graphs, it also suggested the most consistent performance.

The Skylab 4 graph, on the other hand, began at a much higher level and descended in a rapid but irregular manner over seven trials. A sharp increase at the eighth trial reversed the trend momentarily. The rapid descent continued for the last three trials, of which the last two took substantially less time because the Skylab 4 crew had completed some of the required activity before the time period for which it was scheduled. The last two points, then, did not validly indicate the times for the corresponding trials.

The data from the Skylab 3 crew exhibited two radically different trends. For the first half of the mission, trials 1 through 5, the graph was a classic representation of the adaptation function. A sharp increase at trial 6 introduced a relatively stationary level of performance for the remainder of the mission, a level uniformly and substantially higher than that at which the other two crews were performing. The explanation of this anomalous segment of the graph is not readily apparent. Although it was well known that the M092/ M093/M171 sequence of activities was not popular with the Skylab crewmen, the Skylab 3 crew were most direct and explicit in expressing their feelings. They felt it was boring, menial, and nonproductive of at least one person’s time. It may well be that these feelings crystallized midway during the mission with a correlative loss of motivation and a consequent loss of efficiency.

In summary, Voice/Telemetry data were a valuable adjunct in the evaluation of task performance. When the tasks were done in a nominal manner, Voice/Telemetry gave a valid estimate of the actual time expended during the performance of the task. The drawback in using Voice/ Telemetry was that the measure also included everything else that happened within that time period even though it may have had no definite relation to the task at hand. Voice/Telemetry data also failed to correct for such unusual situations as demonstrated in the last two performance trials of the Skylab 4 crew.

Performance Late In Mission

An important objective of experiment M151 was to examine the performance late in the mission for signs of anomalous performance due to the long exposure in the Skylab environment. In terms of the adaptation function an anomalous result would be either a significant increase in time to perform tasks or a significant increase in variability towards the latter part of the mission.

To determine whether these two effects were operating on the Skylab 4 mission, the voice/ telemetry data for M092, M171, and M093 were divided into thirds; the initial third, the middle third, and the final third of the Skylab 4 mission. These data, in the form of means and standard deviations, are presented in table 16-VIII.

As the data in the table indicate, the means for the initial, middle, and final portions of the mission decreased steadily for the three experiments. The standard deviations decreased sharply from the initial third to the middle third and became stabilized at about this period of the mission. The slight increases in standard deviation from the middle to final third for experiments M092 and M171 could be considered as random variations about a relatively stable level. Some substantiation for this conclusion can be found in the standard deviations observed in experiment M093 where there was a decrement from the middle to the final third.

In summary, then, there was no significant evidence for deterioration of performance on Skylab 4 as the mission approached its culmination. As a matter of fact, performance continued to improve while variability did not increase significantly during the final third of the Skylab 4 mission.

Conclusions

The fundamental results from the above analyses can be summarized in several brief conclusions.

Despite pronounced variability in training schedules and in initial reaction to the Skylab environment, in-flight task performance was relatively equivalent among the three Skylab crews.

Behavioral performance continued to improve from beginning to end of all Skylab missions.

There was no evidence of performance deterioration that could be attributed to the effects of long-duration exposure to the Skylab environment.

The first in-flight performance of a task generally took a longer period of time than the last preflight performance. The longer performance time could be the result of a number of factors—stress of last-minute flight preparations, change to zero-g Skylab environment, greater care and caution in the performance of in-flight tasks, and experience of work overload during the early period of the mission.

Performance adaptation was very rapid. By the end of the second performance trial, about 50 percent of all task elements were completed within the time observed for the last preflight trial.

The pattern of work performance changed more in-flight than it did during preflight performance. Three fundamental time measures, ie., Basic Element Time, Camera Running Time, and Voice/Telemetry Time, were shown to have specific application in situations relevant to their use.

Reference

1. KUBIS, J.F., E.J. MCLAUGHLIN, J.M. JACKSON, R. RUSNAK, G.H. McBRIDE, and S.V. SAXON. Task and work performance on skylab missions 2, 3 and 4. The Proceedings of the Skylab Life Sciences Symposium, August 27-29, 1974, app. A.I:349-352. NASA TM X-68154, Houston, Texas, November 1974.

 

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