The performance area of special interest is the human in his or her work role. The study of human work capacity, or ergonomics, has much to contribute to our understanding of how to achieve mission objectives. However, before we approach the task of measuring complex operator performance, we should first describe what is to be measured.
Work Requirements in Space
Although specific enumeration of astronaut work units is beyond the scope of this book, it is possible to suggest various broad categories of work requirements. According to Yeremin, Bogdashevskiy, and Baburin (1975) the duties of an astronaut crew have traditionally involved the following tasks:
Of course, within each of these categories, there are many individual work units that must be mastered and integrated into a total program in order to carry out a particular mission objective successfully. Also, the division of labor within crews has differed markedly as progressively more complex missions have been employed. In the earlier missions, all astronauts were exposed to similar training programs and performed similar operations aboard the craft. However, as the space program has evolved, the responsibilities of crew  members have become more specialized, although considerable cross-training is still given.
Human Performance Abilities
Various attempts have been made to categorize classes of behavior that describe human functioning. For example, Miller (1965) uses such terms as scanning, identification of cues, interpretation, decisionmaking, and short-term and long-term memory. Gagne (1964) suggests discrimination, problem-solving, sequence-learning, identification, etc., as functional categories. Dimensions such as tracking, vigilance, arithmetic, and pattern comparison are used by Alluisi and Thurmond (1965). These categories represent rational, descriptive approaches determined essentially in an armchair fashion. Other investigators have suggested that a small number of descriptive categories is inadequate to systematize the many components that comprise human performance. These investigators argue for an empirically determined taxonomy of human tasks. A refinement of this latter approach would be to identify common elements among the various tasks.
Using experimental-correlational studies and factor analysis, Fleishman (1967) examined a wide range of perceptual-motor performance tasks. His intent was to define the fewest independent ability categories that could be used to describe performance over the widest variety of tasks. The assumption was that complex skills can be described in more basic ability terms. For example, the quality of performance an individual can achieve in operating a turret lathe may depend on the more basic abilities of motor coordination and manual dexterity. Using this logic, Fleishman generated 11 psychomotor factors (e.g., control precision, reaction time, aiming, etc.) and nine factors in the area of physical proficiency (e.g., trunk strength, explosive strength, stamina, etc.) which consistently account for the variance in many performance tasks (Fleishman, 1960, 1962, 1964). While Fleishman's approach has been highly successful in assessing laboratory tasks, the results have been less encouraging when more complex operational settings have been investigated Since we do not yet have a completely satisfactory method of defining the task abilities which underlie various job requirements, we cannot say with complete assurance exactly what human functions define the job of the astronaut in space. We can, however, approximate these requirements.
 One approach to defining the functional requirements of astronauts is provided by Parker, Reilly, Dillon, Andrews, and Fleishman (1965). These authors reviewed and analyzed the technical literature with special emphasis on the factor analytic work of Fleishman. Studies involving regression- analysis models, physical-proficiency studies, and control-dynamics studies were also considered. This process generated a considerable list of basic task dimensions. After making a task analysis of the activities most likely to be required of personnel operating in space vehicles, 18 basic abilities were identified. These 18 abilities were readily classified into six categories: fine manipulative, gross positioning and movement, system equalization, perceptual-cognitive, reaction time, and mirror tracing abilities.
The task dimensions identified by Parker and his colleagues are consistent with similar classification systems suggested by Berlinger, Angell, and Shearer (1964) and by Christensen and Simons (1970). The listing may be taken as one fairly comprehensive representation of the kinds of performance demands made on an operator in space. The next step is to determine how to measure such factors.