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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Suggested Citation:"Productivity in the Space Station." National Research Council. 1987. Human Factors in Automated and Robotic Space Systems: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/792.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

OI)UCI'IVI]Y IN THE SPACE STATION Raymond S. Nickerson ~)I3tJCIION Cat is productivity? How do we measure it, predict it and control it on earth? To what extent can that knowledge be extrapolated to a space con ~ c? What do we not know about productivity on earth that might be found out--and is worth finding out--through research? How might the expected findings be applied to space? How should the research be directed to ensure its applicability to space? Are there important questions about productivity In space that earth-based research is not likely to held answer? d I wish I could promise to answer these questions here. Unhappily, I cannot. These are the kinds of questions that I have had In mind, however, in preparing this paper. In what follows ~ will focus first on the notion of productivity and on how it has been measured and manipulated in earth environments, and then turn to the question of productivity in space, or more specifically, the Space Station. The paper ends with a set of recommendations for research. WED IS ~OOtJCr~? Productivity is an elusive concept. It seems straightforward enough when one begins to consider it. It is Gary to think about the productivity of chickens or dairy cons in terms of eggs laid or milk produced per unit time; here we are dealing with output in a very literal sense. And it does not tax one's imagination to think about comparing the output of the one producer with that of the other. To do this we need a way to describe eggs and milk quantitatively in the same terms. whichis not difficult. Since eggs and milk are valued as foodstuffs, we could describe them both with respect to their nutritional ingredients. But quantifying productivity only In terms of output is not very useful from an economic point of view, and as it relet== to chickens and cows as producers it would be grossly unfair to the chickens; we must also take into account how much chickens and cows consume IN order to produce a given amount of nutritive capital by means of eggs and milk respectively. And to round out the picture we must factor into the equation not only what the producers -at, but 31

32 other resources upon which the Or continuing production depends. To do all this we may find it convenient, since not all the factors that must be considered are nutritional, to quantify everything in monetary terms. But this gives us no serious problem. The situation is still fairly simple concepts ally: chickens and coos produce foodstuffs that can be given a monetary value, and to do so they consume resources that have a monetary cost; productivity can be thought of in terms of the value of what is produced and the cost of producing it. This all makes intuitive sense. When one tries to apply the same type of thinking to human productivity, one has no trouble as long as the human activity involved is analogous to laying eggs and giving milk, in the sense of producing tangible goods that can be Bled to satisfy basic human needs, and consuming resources in the process of doing so. The picture gets Aces clear quickly, however, when what is produced is not so tangible--perhaps not even readily identifiable--and not easily quantified in monetary terms. How does one measure the productivity, for example, of the teacher, the scientist, the poet, the philosopher, the salesperson, the physician, the corporate executive, the athlete, the entertain~r—or the astronaut? Lack of definitional precision has seldom been a great deterrent to the use of words, and "productivity" is no exception On this regard. It is a popular word in economics, and like "truth" and "keautv.~' ~ ~ ~ ~ __ _ . _= . _ = ~ = _ _ ~= . ~ _. ~ ~ , , ,~l~l~ =~1~1 of mu=1 w == "~ -em, was amp- 1~ menu=. Within the literature pertaining to space exploration, one finds references to Increases in the productivity Of spacecraft crews resulting fans charges ~ displays, control pry or other variables, but seldom is it clear ~c~y ~t this means. the word is also seen ~ughout ache human factors li~ture more generally; although Muckier (1982) has changed that ache unconstrained way in which it is use here mans ; - c mar A; PP;~10 - ~ A;c~ ;~ ~ A;= ~~' =~ ^. — &~ - ~' ~ =~ - - ~ ~11 ~1 ~''~ ~11~e ~ petit, pr~uctivi~ is often use more or less as a synonym for performance; if performance improves, by nearly any criterion, productivity is did to go up; if performance degrades, productivity is said to go da an. Sometimes the word is given a precise quantitative mean mg by virtue of the variables that are involved in its measurement. Indices of productivity are typically expressed as a ratio where the numerator is some measure of output (what is produced or the value of same) , and the denom m ator is some measure of input (what is amp up in the production process or the cost of same). What constitutes input and output, and how they are quantified, differs considerably frwu case to case, however; and changes in productivity indices over time can sometimes be difficult to Interpret (Badly, 1986). Moreover, often the word is used as though it were intended to connote a quantitative entity, but there is no clue as to what the input and output variables are or how they could be measured. go concepts that are closely plated to productivity are Chose of Production and efficien - . ~uctivi~r implies production, or more specifically, product arid pricer. Activity is an attribute of a producer; and a producer, by definition, is one who prices sc~thir~. At is product may be tangible (paper clips, a household

33 appliance, an airplane) or intangible (an educational service, entertainment). A producer may be a person, a person-machine system, a team, a factory, an industry, an economic sector (agriculture), a nation, the world. But although productivity and production are closely related concepts they are not the same. AS we have noted, productivity is usually expressed as a ratio of some measure of output or product value to same measure of input or production cost, and the goal, in most cases, is to make this ratio as high ~= possible. Production usually refers only to output quantity. Given these connotations, it is Busy to imagine production Increasing or decreasing independently of changer in productivity. If, for example, a manufacturer produced 10 percent more items in a given year than in the preceding year, but doing so required a 15 percent increase in the number of employees, we might my that production increased while the productivity of the employees declined. The concept of efficiency, like that of productivity, relates Output to the resource consumed in obtaining it. Efficiency has to do with getting the mast out of given resources; the challenge is to organize a production process so as to munlmize wasted effort. A process is said to be made more efficient when the unit costs of output are decreased or when the consumption of a fixed amount of resources yields a greater output than before. Techniques for measuring the efficiency of assembly line workers were among the earliest contributions of engineering psychology to the manufacturing process and have been used expensively in the work place. These have typically involved analyzing production tusks into observable components. The development of tack-analysis techniques Hal received considerable attention from human factors engineers (Van Cott and Kincaid, 1972; Woodson, 1981~. Such techniques have been more readily applied to psychomotor tasks than to basks that are primarily cognitive in nature or even those that have major cognitive components. Attention has been focused increasingly, however, on the problem of analyzing cognitively-demandin; tasks, as an increasing percentage of the tasks performed by people in the work force are defined more by cognitive than by psychomotor demands. We cannot hope to settle terminologies issues here. More Over, definitions are of limited utility when dealing with terms that are widely used, with a variety of connotations, within a field. For present purposes, prcOuctivity will be taken to be very close, but not quite identical, in meaning to efficiency. An entity (person, group, system) will be considered highly prc*uctive when it uses its resources to = advantage in accomplishing its goals. One can be efficient in the sense of not wasting resources simply by using those resources very sparingly, but that type of efficiency could be counterproductive if resources are husbanded to the point of precluding getting the task done. To be productive one has to use one's resources and use them well. As a working definition of productivity I will use: effective and efficient use of resources in accomplishing a goal. The emphasis is on both effectiveness and efficiency. A prc~uctive system is one that

34 gets the Intended job done and does so with a munlmum of wasted effort and resources. I do not mean to split hairs here in making a distinction between efficiency and productivity; if one's idea of efficiency incorporates effectiveness, then ~ see no objection to thinking of efficiency and productivity as more or less synonymous. Effort and rescuracs can be wasted as a consequence of many factors, such as poor training, lack of motivation, mismanagement, faulty organization, mlsscheduling, and a host of others. Productivity will be said to increase when either more is accomplished with no increase in consumed resources or the same objectives are attained with a smaller expenditure of resources. These are still somewhat imprecise notions, but not so imprecise as to be useless. In the Space Station context, as elsewhere, when modifications in design or operating prcce~ures have big effects on productivity, there probably will be no difficulty in getting a consensus that productivity has really been improved. When Masks are performed more easily, more reliably, and with fewer costly errors, most interested observers will probably be willing to describe what has happened as an increase in productivity, and even if not, they a ~ likely to agree that changes for the better have occurred. It seems to be generally assumed, if only tacitly, that anything that improves human performance (increases speed, accuracy, reliability) probably Increases numan pro~uct~v~y. This appears to me to be a reasonable assumption, and a very useful one. Frequently in this paper, the discussion focuses on variables that influence performance, the justification being the assumption that what affects performance for better or worse will affect productivity in a comparable way. ASSESSING PRO WCTIVITY It is helpful in the present context to distinguish between the problem of determining what the level of productivity is at any given time and that of determinirg Nether pr~uctivi~ is Wing, or has Carded. One might assume that the second prowlers is more clifficult than the first, inasmuch as a = of ~e, or difference, is derived frmn the more fi~nt=1 measure of absolute value: to determine whether pr ~ uctivi~r is rare or less this weak than it was last, one simply takes the difference between this week's measure an] last week's. But this is so only if one wishes to know the magnitude of the difference. If one is content to know only the direction of the difference, it may not be necessary to know the individual magnibudes, at least if the magnitude of the difference is relatively large. One does not have to know the precise weight of each of two objects to know which one weighs more, especially if the difference is siz-=hie. Productivity as a Percentage of Capacity ~uctivi~ is sometimes quantified In terms of performance relative taxing. Centesis done, maxi~outputorperformanceis~

35 as the starers against which to evaluate the actual output or performance, whether the performer is an individual, a system (say a factory), or an economy. Thus one might encounter the claim ~t the pr 0uctivit~r of a given industry In a particular region is currently at about 70 percent, which would mean that that industry is operating at 70 percent of what, under certa m assumptions, is the maximum possible. Economists often refer to how close to capacity factories and other manufacturing facilities are operating. The ability to specify hew close to capacity some entity is operating presupposes a metric in terms of which to quantify the operation. Determining what constitutes maximum capacity can sometimes be a complicated and controversial pr Mess. Further, maximum must be understood as maximum within a particular context. The maximum output of a given factory, for example, could mean maximum obtainable with the present tooling, layout, manpower and stock; alternatively it could refer to what would be obtainable if one or more of these constraints on output were relieved. As applied to individual human beings, capacity con not== the best (which often, but not always, equates to most) one can do ~ a given situation, the limit of human performance--or, more accurately, the limit of the individual performer. Conceptually, there are two ways to determine capacity in any given instance: one is to derive it free theoretical considerations; the other is to measure performance under ideal conditions. Neither works very well. While information theory once provided a basis for the hope of defining capacity theoretically, it prayed to be a false Elope, and psychologists have not yet found or developed an alternative that can do the job. Ideal conditions for performing a given ta~k--which Mold have to include an optimally motivated performer--have proved also to be easy to conceptualize but difficult if not impossible to actualize. Differential Productivity Differential productivity in a business context is sometimes measured in terms of changes In the number of employees or amount of employee time required to get a fixed amount of work done, or conversely by changes in the amount of work accomplished by a fixed staff. Thus a retail company is said to have doubled the productivity of its bill collection departments when it managed, by computerizing its operation, to place the same number of reals with a 50% reduction in staff. And the productivity of an insurance company is described as increasing fivefold when the number of policies issued per employee per year increased by a factor of five (Bower, 1986~. Studies of individual human productivity In specific job situations have often focused on the performance of individuals relative to the performance of other individuals on the same task. It is possible to say that A is more productive than B without saying anything very precise about how productive eight individual is relative to a larger frame of reference. Measures of white-collar productivity typically do not yield absolute quantities, but do permit comparisons among similar

36 organizations (Drucker, 1986). In the Space Station program, attention will probably be focused primarily on differential productivity (the cost of attaining some production objective in space relative to that of obtaining it on Perth; or the cost at one time relative to that at another). While it would be interesting to be able to relate productivity to some theoretical maximum in this context (e.g. by relating production to some measure of capacity), it is not clear how to do that. Fortunately, it is not necessary to be able to quantify maximum productivity in order to determine whether one is moving toward or away from it. That is not to suggest that assessing differential productivity is likely to be an easy task. Several investigators have commented on the variability of measurements of productivity, especially those that relate to individual'' human productivity, and on the resulting need to make many measurements over a considerable period of time if reliable numbers are to be obtained (Muckier, 1982~. It is especially difficult to measure productivity in intellectual tasks, inasmuch as methods for assessing cognitive performance are not well developed. When a person is staring cut of his office window, it may be impossible to tell whether he is idly daydreaming or is engrossed in "productive" thought. And even if he were known to be daydreaming, it would not follow necessarily that that time was lost from a productivity point of view. One widely held view of p,~blem-solving distinguishes an "incubation" period in the problel`-solving process during which progress is made on a problem in spite of--perhaps because of--the fact that the individual is not consciously focusing on the problem to be solved and there are numerous examples of scientists and other thinkers reporting insights that have occurred when they were not actively engaged in working on the problem. Whatever methods are developed for measuring productivity must take guality--as well sac quantity--of output or work into account in some way. In manufacturing operations, product quality affects measures of productivity to the degree that items that fail to meet a preset standard become rejects. The importance of quality control in this sense is obvious and the difficulties that some industries (e.g. the manufacturing of computer microchips) have had are well known. this type of linkage between quality and quantity is a fairly gross one however. Differences ~ quality tend to be ignored so long as the quality is not sufficiently low to necessitate rejection. In nonmanufacturing activities the relationship between quality an] quantity is even more tenuous, in spite of the fact that here one might expect qualitative dif^=erenm~s In output to be both large and important. Quality will certainly be an important consideration in the Space Station context. m e quality of the experiments that are done, for example, will be at least as important as the number.

37 Workload and Its Assessment In a complex system the operation of which deperxis on functions performed bar both people end machines and, especially, by people and machines in interaction, high productivity will rehire that workloads be at or near c ~ imal level. Significant overload will r educe productivity through increases in the frequency of human error; significant underload will mean wasted rcsawrocs at best and possibly direct negative impact on productivity resulting from boredom, inattentiveness or other diffim~1 ties arising from feelings of being underutilized or unimportant to the operation. Workload and its assessment will be important considerations, therefore, in efforts to understand, measure, or control productivity In space. As in the case of efficiency, the workload carried by an individual is much easier to measure when the task is primarily physical than when it has major cognitive components. As Wierwille et al. (1985) point out, a major consequence of the increasing automation of modern systems is a shift in the role of the human cgerator away face. manned control and toward monitoring and performance evaluation, and this Hal complicated considerably the problem of quantifying the operator's workload. How can we hope to determine how har5--how close to capacity an individual is working when most of what he is doing is ment=1 activity that is not directly observable? The measurement of mental workload has been recognized by human factors researchers as a major challenge to the field and this recognition has stimulated considerable activity (Chiles and Alluissi, 1979; Eggemeier, 1980; X~lsbeek, 1968; R bray, 1979; Parks, 1979; Sheridan and Simpson, 1979; Singleton et al., 1971; Williges and Wierwille, 1979~. Work in the area is still in the exploratory and formative stages, however, and there has not yet emerged a theory or even a widely agreed upon set of concepts and measurement procedures that are needed to provide a sense of stability and coherence. An indication of the magnitude of the problem and of the current status of work on it is provided In the Proceedings of a NATO Conference on Month Workload published In 1979. Johannsen (1979:3) cpened the conference with the observation that "there exist too many conflicting ideas about the definition and measurement of workload", and expressed the hope that the conference would produce a consensus among participants on a definition and on a procedure for workload assessment. In his preface to the conference prcocedings, Moray (1979:VIII), the organizer, acknowledged that these hopes were not realized, but noted that participants from various disciplines did come to "very similar Inclusions about the validity, usefulness, ark promise (or lack of each) for a wide variety of methods for approaching the assessment of workload in the human operator". It is unfortunate that the proceedings does not contain a summary of these conclusions. It does contain, however, a report from each of five participant groups, classified an experimental psychology, control engineering, mathematical modelling, physiological psychology and applications. m e experimental psychologists summarized the fir conclusions this way: " m e concept [mental workload] reflects a genuine dimension or

38 dimensions of human experience in daily work...it is a concept absolutely required for the adequate analysis and description of such hanks Flasks that are not necessarily physically demanding but that are experienced as exhausting and stressful nonetheless] and for predicting, at the design stage, the future performance of such [automatic and semi-automatic man-machine] systems... On the other hand the concept is at present very ill-def~ned with several probably a; c0; ~~ maim; ~= ~1~- `~ an... There is no satisfactory theory of 'mental workloads' (Johannsen et al., 1979:101). Johannsen et al stress the multidimensional nature of workload, and deny the appropriateness of trying to quantify it as a scalar variable. They specifically rule cut the possibility of meaningfully comparing different tasks with respect to workload, except when the tasks are very similar in structure. The conclusions drawn by the experimental psychologists in the NATO workshop clearly caution against any expectation that the problem of workload measurement will be resolved soon. They are equally clear, however, ~ supporting the view that workload is an essential concept if we are to understand the role of human beings in mcdern systems and design tasks that impose reasonable demands on their capabilities. It could prove to be an especially important concept in the context of the Space Station because of the unusual cognitive demands that that environment will represent. A detailed under standing of those demands insofar as possible in anticipation of the depicyment of the station ~ surely must be a primary objective of the human factors effort In this program. One of the approaches that has been used to identify performance measures that are sensitive to workload has been to take a variety of cancli~te measures in situations in which workload is intentionally varied and SCQ which of then vary with workload manipulation (I i arm Wierwille, 1983; Hicks arx] Wienville, 1979; Wierwi1le arm Connor, 1983; Wier~rille et al., 1985~. =dh of this work has beer done in flight simulators. Candidate n ~ sates that have been studied include opinion scales (subjects' ratings of the task in terms of specified descriptors), physiological measures (heart rate, respiration rate, pupil diameter, eye-blink frequency, eye-fixation fraction), measures of performance on secon ~ tasks (time estimation, tapping regularity), and measures of performance on the primary task. A limitation of this approach is that viable measures, at best, reflect difference= in workload; they do not provide an indication of how herd or how clod to capacity one is working in any particular case. Many of the sues of pilot workload have made use of post flight questionnaires. ~ Ruse this approach is heavily dependent on memory, Rehmann et al. (1983) explored the possibility of having subjects report how hard they are working periodically while performing a tank. Workload judgements did change in this case with controlled changes in task difficulty, but this measurement technique has the disadvantage that it could interfere with the performance of the primary back, especially when the latter is very demanding. The intrusiveness of the measurement process has been a major drawback of many approaches to workload assessment, and especially those that make use of a secondary back (Rolfe, 1971; for a summary of

39 nearly 150 sties using sorry tasks see Ogden et al., 3979~. One way ~ avoid the use of an intrusive task arx] also dependence on ache subject's merry is to monitor physiological indicants of workload that can be darned automati~A.]ly. Israel et al. (1980) have argued that some of the ~ysiologim=1 measures that have been tried; ~ vanic skin response, heart rate variability, and pupil diameter reflect changes in autonomic nervoll,= system activity and so are sensitive to changes in emotional state independently of their origin. As a physiological measure that is more likely to be indicative unambiguously of Wharves in tile cognitive Innards of a bask, they propose the everlt-related brain potential and, in particular, its Iate positive or p300 eminent. Widens (1979, also has argued for the use of evoked ~ , _ __ ~_~ _~ _ TO ~ ~l _~ fit ^~\ ~ ~ =~_ O~ ~~ ~~_~ pO`ell~lals . Reseal en ad . t 11:1UUJ presently coma [LIEU one e~er~nc supporting the idea that this measure does vary with task demands and that obtaining it need not interfere with the primary task. While it would be imprudent to conclude from these data that electro-physiological monitoring of workload will be effective in the Space Station, the possibility deserves further exploration. Varying workload for experiments purposes is probably not feasible within the Space Station context, or at least the amount of this type Of experimentation that can be done will probably be very limited. It will be essential to attempt to have workloads be as close to ideal as they can be made freon the very beginn mg. Of course when evidence indicates that an initially established workload is not ideal, the workload should be changed ~ the indicated direction, and keeping track of such changes can provide some of the data that would have been obtained from controlled experimentation. The goal must be to minimize the need for such changes, however, which requires being able to predict the effects of different workloads from data obtained In earth environments. DEIERMINPNTS OF PRO WCTIVITY Ah ~ e seems to be a consensus among investigators that productivity is a function of many variables, and that attempts to affect it that focus on one or a small subset of those variables and ignore the others run the risk of doing more harm than good (MucX1er, 1982; Sutermeister, 1976). Among the determinants of productivity that would ~ ve to be included In any extensive list are the following. Human Capabilities and Limitations A great bead of information has been compiled about human Capabilities and limitations and is available in various engineering psychology handbooks. What is known in this regard clearly sets bounds on what ~ . . ~ ~ . ~ . . . ~ ~ numan ne logs Ln general can he expected to co In SpeCl~lC rack situations. Individual differences are also germane to the question of human productivity. People differ widely with respect to both physical and mental capabilities, and the productivity of individuals is bound

40 to vary with the degree to which then' individual capabilities match the demands of specific Basks. Aptitude testing and job screening and selection procedures are based on these assumptions. Task Demands Evidence supports the intuitively appealing idea that people work best when the demands upon them are neither too great nor too small. This is one form of the "in verted-U hypothesis" regarding the relationship between workload and performance, which holds that performance of a given task is optimal for a workload level that is ~~ermediate between one that is excessively Hugh and one that is so low as to promote ha,... fM~ I h 1~:~ . W^1 If:_ 1 C)7~2 1 C)7A ~ _~. `~-~_~, An_' I_ ~~, '=~. The detrimental effects of overloading are somewhat better documented than are those of underioading (Weiner, 1975; Weiner et al. 1984~. The possibility that underioading can affect performance negatively takes on special significance, however, in the context of systems in which humans function primarily as supervisors of automated processes. Motivation One can hardly doubt that motivation affects performance. It Is cI-a In particular that performance suffers when motivation is very low. What is less clear is how performance is affected when motivation bed untruly high. Merest in = ~ motivation that is relatively law at We outed will at certainly lead ~ i~pr~ed performance, but what has - ns when motivation that is arcade very high is mcreas ~ still further? Is there such a thing as trying too hard? Wanting too badly to succeed? Some investigators believe there is, and that when motivation is extremely high it has a debilitating effect. This is another form of the inverted-U hypothesis mentioned above; except that in this case the performance determinant of interest is motivation rather than task demands. It may be that the detrimental effects associated with Motivation becoming too high are better attributed to anxiety over the possibility of failing; fear, especially den it beds panic, unsubtly can cause performance to deteriorate. Ac cording to thin vicar, if privation becalms arbitrarily high but is not accompanied by such fur, we Ward not nosily expect perforate to fall off. The distir~tion between very high motivation and fear of failure may be an important one in the Space Static context; it scud be helpful ~ have a better understarxlir~ of the rules of these variables as determinants of pr~Ctivi~r and performance. Physiologic State Fatigue has lord been recognized as a factor in ricing proclivity in many settings (Simpson and Weiser, 1976). indeed it he been

41 defined Operationally as a decrease In performance as a corpulence of pronged activity (~lsb~k, 1971~. Math of the resort on this topic has focus on the problem of schooling rest breaks in such a way as to minimize fatigue (Bechtold et al., 1984; <;anaro and Bechtold, 1985~. The tasks involved in these studio have often been physically strenuous and the results are of limited applicability to tasks that are primarily cognitive in nature. Exceptions include sties of the performance of aircr~rs over extended periods (Carmen, 1971, 1973~. A major question of relevance to productivity in the Space Station is how productivity might be affects by the various physiological effects that can be expected from prolonged living ~ the Space Station environment. Little is yet known about the physiological consequence-= of living in such environments for longer than a few weeks at a time. Training Performance, especially of complex Basks, obviously improves with training and practice. An aspect of the relationship between training and performance that is especially important relative to the Space Station context has to do with the obscuring of differences by ceiling effects. The fact that one has, through practice, gotten to the point of being able to perform a Desk without error is not compelling evidence that one has really mastered the task. The true test may come when that task must be performed under stress or in concert with competing demands on ones resources. To make the point another way, the fact that boo people perform a given bask equally well under acoommo~atlng conditions is not good evidence that they will perform it equally well under stress. Capabilities and T.;m~tations of Machines Just as the capabilities and limitations of the humans in a complex system help determine the productivity of the system as a whole, so do the capabilities and limitations of the machines involved. Unlike the capabilities of human beings, those of the machines that are available for use In the Space Station can be expected to evolve even over the next few derides. Initial plans for the use of technology in the Station take this fact into account. Plans to use artificial Lnt~lligence, for example, explicitly note the unlikelihood that this technology will be used extensively for operational purposes during the initial years of the program. However, provision is being made for its incorporation as the technology matures to the point of being reliably applicable. We would expect that as machine capabilities are extended and improved, a major consequence would be increased productivity of the Space Station as a whole. Nether this proves to be the case and, if so, exactly how rein to be seen.

42 Person-~6hine Function Allocation An i~ortant~eterminantof system productivity, es distinct f~iboth human productivity are] machine productivity, ~st be the way in which system functions are assigned to people and to marines. Several methods for function allocation have been Revels (for a review, see Price et al., 1982~; but none of them is widely used by system designers (Mbutemerio and Cron, 3982; Price, 1985~. Investigators have argued that it is not realistic to expect it to be feasible to allocate function by formula anytime soon, if ever, because the problem is too complex and si~l~tion-dependent (Price and Pulliam, 1983~. Allocations typically are made in an ad-hoc fashion on the basis of human judgment, aided perhaps by efforts of eng peering psychologists, beginning with Fitts (1951), to distinguish between generic functions that machines do better than people and those that people do better than machines. While the number of functions that people can perform and machines cannot is likely to grow ever smaller with continuing advances in machine intelligence, it is likely to be some time before machines can match people in their ability to integrate information in so many forms flus so many sources; to respond as effectively and adaptively to such a wide range of unanticipated situations; to make judgments of relevance, reliability and importance; to draw upon a large store of common sense, sac well as ~hni~1, knc:'wledge; and to follow imprecise instructions and work ~ high-level goals. And if machines acquire Ruth capabilities In time it does not follow that they Should assume these functions In all cases. The question of what functions can be auto maker and that of what functions should be auto many may have different answers. This fact has not received the attention it deserves. There may be reasons not to auto mete functions that are autc=atable from a technological point of view. These include reasons of cost effectiveness, human preference, and the need to maintain human skills at a high level in case they are needed in the event of system failure. One function that we can presumably assume will be a human one indefinitely is that of high-level goal-setting. Value judgments, including judgments of what goals are worth working toward, will hopefully remain the purview of human beings, no matter how clever the machines become. m is probably means also, at least for the foreseeable future, retaining the role of deciding to what extent the behavior of the clever machines is consistent with those top level goals. Design of Person=Nachine Interfaces In very complex systems like the Space Station, many functions are performed neither by people nor by machines independently, but by people ark miadhino£; interactively. This being so, the ad~apy of the designs of the interfaces through which information passes between the machines ark their users will be a major determinant of pr~ctivity of the people, the machines, ark the Space Station as a whole. The design challenge for the Space Station is compliant by the fact that the

43 intent is to acoc~mcdate a large fraction of the anthroQc metric spectrum. It is here, in the design of interfaces, that human factors researchers and engineers are likely to have the greatest impact on productivity. A great dean has been learned about Interface design as a consequence of human factors resc arc h in other contexts (Nickerson, 1986). A significant general conclusion to be drawn from this research is that designers' tuitions uninformed by human factors research are often wrong. A second similarly general conclusion is that small differences in interface design can often have very large effects. m is area deserves a great d~1 of emphasis in the Space Station prearm. Organizational Factors Gunn (1982:115) has claimed that, in the case of manufacturing, the major opportunity for improved productivity is not to be realized by mechanizing the work of making or assembling products, but rather "in organizing, scheduling, and managing the total manufacturing enterprise. m e most important contribution to the productivity of the factory offered by new data processing technology is its capability to link design, management, and manufacturing Into a network of commonly available information". Gunn's emphasis on the importance of a single integrated information system, serving various needs of a manufacturing operation, applies with as much, if not greater, force to the Space Station context. Information will be the life blood of the Station. How the information that supports the various functions will be organize] and accessed will be a critical aspect of the Station's ~ . _ . . . . . . . . cleslgn. representation abound. How these problems are addressed Is certain to have Implications for productivity, which is not to suggest that those implications will be -any to make explicit. problems of o ~ zation, access, updating, protection, and · · . ~ Scheduling Factors Scheduling is a particularly important problem for any operation that involves numerous interdependent processes that proceed partly in series and partly concurrently. The problem is exacerbated by the fact that an unanticipated delay in the onset or completion of any given process may have implications for the timing of other processes. Small perturbations can ripple and grow into major problems producing inefficiencies at best and sometimes serious difficulties. Dynamic rescheduling of mLlti-process operations of any complexity usually ret computer involvement. Educing the scheduling algorithms, hammerer, is still a human aCti~ri~r art one that ryes a great bear of ingenuity, if major inefficiencies are to be avoided.

44 Social and Interpersonal Factors The linkage between social or interpersonal factors and productivity may be indirect, but there can be no doubt of its importance. Interpersonal difficulties among people who must work cooperatively as a group can seriously impair the smooth functioning of the group; conversely, when the members of the working group genuinely like each other and enjoy working together, there can be equally substantive positive influences. Interrelationships cutside the working situation, and sudden changes in them, can also have profound effects. A new emotional relationship, illness or death of a loved one, an unresolved dispute with a friend or acquaintance are obvious cases in point. Such factors can affect performance not only through changes in morale or motivation, but also by diverting attention fr~u the demands of one's job. The above list of determinants of performance could easily be extended, but it is representative of factors that have been studied. Much is known about how these factors relate to performance and thus to productivity in earth environments. Much remains to be learned too, however, and while the themes may seem familiar, the new context of space gives the problems new dimensions. While all of these factors are likely to prove to be important in space, none represents a greater cpportuni~y and need for research than those that involve the way people will relate to and interface with machines, especially in view of the rapidity with which the capabilities of the latter are changing. qHE SPACE STATION Anticipated Functions and Uses m e Space Station is expected to serve a variety of functions. Cheese include serving as a laboratory for scientific experimentation and data gathering, manufacturing and processing of materials (e.g., crystals and pharmacauti~a~s), servicing of satellite and other' space vehicles, providing a staging platform for other space missions, and serving as a base for constructing large structures for use In space. m e station Is viewed as being important not only to scientific and commercial enterprises but to the further development of space technology. Event Duly the station is expected to serve as an extraterrestrial control and service center for numerous unmanned sat=~lit== orbiting in a variety of inclinations and altitudes. Serving as a control and maintenance center could include deploying, retrieving, repairing, and reconfiguring other sat=~lit== or spacecraft (JSC, 1979, N~SA-ASEE, 1985~. Considerable interest has also focused on the role the Space Station could play as a development and evaluation platform for automation, robotics, knowledge-based systems and other emerging technologies that make intensive use of computer-based rascurces.

45 E~im~nary Design and Action Considerations The station is ted ~ evolve in at Act two ways. As a physical plant it will increase in size and became more cc~r~ex as yes are aced and desirable Edifications are identified. sting pus will also Charge as a cons ~ ence bat h of ex`~rien~= ga Bed In operating it and of technologic~l develoFments. In the interest of facilitating the evolution of the physical plant as new desiderata are identified, design plans ~~l for mc~N1arity an] expandability. the living-working Aces are an interconnected set of 4 pressurized cylinders, each of which measures 35-40 feet in length and 15 feet in diameter. The sizes of the Hackles are constrained by the requirement that at least the initial ones be prefabricated to fit in the cargo bay of the space shuttle. Two of these Locales are to be living quarters and two are to be laboratories. Each living Locale will acocmrDdate 6-8 people. A fifth Locale similar in design is called a logistics module and will be used for transporting equipment and supplies between earth and the station. Each of the modules is equipped with detachable units to facilitate reconfiguration. servicing and replacement. Safety is, of course, a major concern. And this problem has the added dimension that mishaps that would have relatively minor consequences on earth could be di.C=~trous ~ space. m e possibility of fire in the spacecraft is a major worry for obvious reasons. mis concern dictates many aspects of spacecraft design. Among the safety pro visions that have been specified in preliminary design documents are: safe exit from any of the pre8ssurize] modules; isolatability of each mcdule fries the others: sufficient food, waste management, control _ . _ , _ , a a e '8 e _ , _ 8 _ a, e 8 , ~ _ _ and communications, and life support facilities an any three-mcUule cluster to sustain crew and make rescue possible. Concern for safer also dictates that ash of the trainer regimen focus on possible 1 functions. In addition to the issue of safe=, that of habitability is receiving considerable attention (Clearwater, 1985; Clearwater and X = per, 1986). Ibis issue b ~ es much more in ortant for missions of extended periods than for those of a few days' duration (Wise 1985, 1986). The question is how to use color, texture, lighting, spatial arrangements, window placements, and other design features/ within the constraints of other requirements, to make the various Space Station modules, and especially the living modules, plot place= in which to spend long periods of time. It is intended that the Space Station be as self-oontained as possible. Consequently, much attention is being given to recycling of supplies, such as water, and to on-orbit maintenance and repair. Arouse the kind of constant and extensive ground control monitoring that has characterized short *oration missions is not feasible for a permanent station, much attention is also being given to the objective of giving the station crew a high degree of autonomy and independence ~ its day-to-day operation. And because the intent is to make the station attractive to the private sector arm useful for cc~ial ventures, the operating policies will have to take account of the

46 desires of the station's clientele. There is a strong interest in assuring human productivity in the Space Station errviro~nt, which stems in part freon the anticipated high cost of manned flight. Uniqueness of the Space Station _ . . . . . Newell, in the preceding paper, has highlighted thirteen "hard constraints" that may be expected to hold independently of the specifics of the station's design. The list makes clear the enormous challenge the Space Station program represents. It also points up the fact that the uniqueness of the space station environment stems not so much from any given constraint or small subset of them, but from the set as a whole. For any given constraint, one can point to one or more other environments or situations with which we have some experience that shares it (e.g. nuclear submarines, submersible laboratories, off-shore oil platforms, polar excursion, scuba and deep-sea diving, incarceration--prisoners of war--and time spent at sea by shipwreck survivors). Some of these environments or situations share several of the constra Ants in Newell's list, but none of them shares the entire set. This is an important point. Suggestive evidence regarding the expected effects of some specific constraints in the Space Station may be found On the results of studies of other environments that share those constraints; and situations that have been studied include extended submarine patrols (Weybrew, 1961; 1963) and wintPring-ov~r parties ~ the Arctic and Antarctic (Gunderson, 1963, 1974; Gunderson and Nelson, 1963). But extrapolating what is known about the effects of any given constraint or even small subsets of them may Overlook important effects of interactions. It is not prudent to assume, in the absence of supportive evidence, that the effects will simply add. It is easy to imagine conditions under which constraints that individually would have minor effects would, in combination, produce major ones. Many of the constraints in Newell's list have implications for productivity, either Erectly or indirectly through, say, morale. Mhlti-manth crew residences and infrequent physical communication cutside the station, for example, could result in feelings of isolation, deprivation or bore dam, or interpersonal tensions among the personnel. limited resources and scare could become uncomfortably - ~ _ . . . . . . · · . restrictive In time. weightlessness can produce nausea, headache, stuffiness and other physical discomforts, as well as spatial disorientation. If challenged to extend Newell's fist of constra~ntsto incorporate other characteristics of the Space Station Iron that are likely to be especially important from the point of view of pr~Uctivi~r, carxli~tes for consideration wed include the following: High degree of interactivity, and especially cognitive coupling, between crew and equipment. Computer mediation of control actions and displays. Criticality of information systems. Nabs for aiding or augmenting of human thinking for

47 troubleshooting and decision mating. Importance of human-in achy e interface designs. Need for contin',~1 concern for safety. Need for ability to de=1 with unanticipated contingencies. Shared responsibility of flight-control decisions between ground and flight crews. Need for some operating procedures and principles to be negotiated with customers; in some cases, perhaps, while in orbit. Heterogeneity of Space Station inhabitants (different languages, different cultures, different professions, cliff--rent amounts of technical training and flight experience). importance of satisfying ways for inhabitants to spend free time. Stress. a variable that could have significant implications for productivity. Consider, for example, the second one. Ih the Space Station most of the control actions that are identified by humans will actually be effected by computers and most of the information provided to the human operators will be provided via comput~r-generatei displays. Focusing only on displays, for the moment, it is easy to see how the ubiquitous computer mediation represents an important departure fry more conventional displays. A major concern in the operation of any high performance vehicle is that of keeping the operators aware of those aspens of the system's state that are critical to its Operation. In conventional aircraft most indications of system state (altitude, bearing, airy, fuel reserve, etc.) are indicated by fixed displays each of which is Each of t-hese ~racter~sti~ deserves attention as . . . . . . · . . . . . . . . . . . dedicated to a particular indicant; when the pilot wants to check the plane's altitude, he looks at the altimeter, which is always in the same spot and displays always and only altitude: a little area of the cockpit is totally dedicated to the objective of keeping the pilot aware of how far off the ground he is. In the Space Station, most of the information that crew members receive will be delivered on ccmputPr driv ~ displays that are used for more than one purpc set Display functions that were once implemented in hardware will now be implemented in software, and the type of information that is available in a specific spot on a control console will vary from time to time, dep q on what piece of software is controlling the display device at the moment. This shift from hardware to software implementation of display functions has some implications for the problem of keeping crew members aware of system state. Productivity in the Space Station Productivity can have several connotations relative to the Space Station. It can refer to the impact of the Space Station program as a whole on the GNP or GWP. It can refer to the use of the Space Station by industry in production and manufacturing. It can refer to the

48 performance of individual humans or person-machine complexes. Also, there may be a diversity of goals relating to the measurement and control of productivity in the Space Station. It may be desirable, for example, to measure the productivity of an individual, a person-in achieve system, a team, or an entire station over some specified period of time. One goal ought be to achieve some targeted productivity on average over extended durations. Another Night involve being able to achieve peak productivity for short periods when needed. [m pact on National or Worldwide Prc~uctivity Considerable emphasis is being put on the potential commercial uses of the Space Station an] the assumption that it will have beneficial long-range effects on the economy of the participating nations. The 1986 report of the National Commission on Space, Pioneering the Space Frontier, proposes that the space program have three mutn;~ly-supportive thrusts: · Advancing our understanding of our planet, our Solar System, and the Universe; 0 Exploring, prospecting, and settling the Solar System; · Stipulating space enterprises for the direct benefit of the people on Earth (p. 5~. - The third of these thrusts is directly relevant to the idea that the space program could have implications for national and international p~uctiviW. Whether productivity gains will be realized will depend, of course, on whether the savings due to better quality control more than offset the cost of getting materials to and from space and any other increases resulting from conducting the operations in a space environment. To have a significant impact on national or international productivity will require a continN mg operation of considerable size. me impact on certain industries could be significant relatively quickly, however, if the cost effectiveness of space-based manufacturing is conclusively demonstrated. The space program could also affect productivity on earth in a variety of ways. Exploration of the ear~h's atmosphere and surface with photography (e.g. LAND6AI) and other sensors can produce information that can affect productivity by producing a better understanding of weather patterns, energy sources, climatic trends, and so on. Industrial Productivity In Space The combination of zero-G and vacuum In space is expects] to facilitate production processes for which it is critically important to control for convection forces or airborne impurities. Among the materials and products that are of Interest In this context are "shaped crystals,

49 semi-conductors, pharmaceuticals, biologi~als, strategic materials, plastics, films, oils, alloys and mixtures, ultra pure metals, composites, glasses, membranes, metal foam fibers, m~crosPheres, . , . ceramic/metal, and matrix materials"' (NASA-ASK, 1985:9). A major industrial interns in space is the prospect of growing superpure crystals (e.g. gallium arsenide) for semiconductors in an environment free of convective turbulences. Interest ~ conducting such operations in space stems from the assumption that the quality of the products will be much easier to control (Chau~hari, 1986). It is expected to be possible to grow much large crystals, for example, and to have a much smaller reject rate. Individual Productivity in Space Individual productivity the effectiveness and efficiency with which the individual participants in the Space Station program carry out their assignments is of special interest to the human factors community, inasmuch as the other types of productivity are contingent to no small degree on how well individuals function in their various roles. All of the determinants of productivity mentioned earlier in this chapter represent important considerations for the Space Station, as they do for any complex system. The following are also among the more significant issues relating to individual productivity that are very likely to arise in this context. redundancy and backup: Many of the functions performed by the Space Station crew will be sufficiently important that provision will have to be made for backup in case an individual becomes incapacitated. The necessity to rely on backup capabilities cculd have implications for productivity, depending on the adequacy of the backup procedures and the extent to which reliance on them has a ripple effect to ether functions. Use of aids, intelligent and otherwise: Where will be a need in the Space Station to augment human cognitive abilities In various ways. Decision-making aids, troubleshooting aids, memory aids, will be needed in various contexts. Error recovery: It must be assumed that in a manned Space Station human errors will occur. The standard approach to minimize disastrcus consequences arising from such errors is (~) to attempt to build in fail-safe procedures so as to make it difficult to commit the errors in the first place and (2) to buffer operator actions--postpon m g their effects--so that when an error is made, there is an opportunity to correct it. There is an obvious tradeoff here between safety and short-term productivity. Fail-safe procedures and previsions for failure recovery are likely to slow operations down. In the long run, however, their costs may be more than offset by what they save if they prevent errors with serious consequences.

50 · Information accessibili=: lhe operation of the Space Station is expected to be highly pressurized. bile criers may be assay to have had extensive training in how to bend with various contingencies that may arise, it is not safe to assume that all the information they will ever need is stored in their heads. Availability of precisely the right information at specific moments could prove critical not only to productivity, but in some instance= to safety or even survival. A recent report from a NASA sponsored workshop identifies a system that explains or assists In the use of other tools as perhaps the single most important tool from the standpoint of Eve autonomy and recc==ends the development of a real-time maintenance information retrieval system that could provide astronauts information on demand relating to End tasks as they are being performed (NASA-ASEE, 1985~. life-support systems: Although very great progress has been made in improving the design of space suits aver the years of the space program, the suits currently in use for extra-vehicular activity still greatly restrict the wearer in various ways. Mbrale: Excepting complications arising fn~m~otion sickness, morale has not been a major problem affecting performance of crews in flight in the space program thus for. But the publicity surrounding the flights and the relative brevity of their *orations have ProkeblY sufficed to keen the morale generally high. , ~ , _ _ _ _ When people are On space for months at a time and the work becomes less of an adventure and more of a job, it will not be surprising if morale becomes an issue, an] one that could affect productivity, from time to time. In addressing these and related issues, it is useful to bear in mind that while the Space Station will differ from other environments in numerous ways, many of the issues that relate to productivity in this environment are of more general interest because of the Or relevance to earth environments as well. The question of how various types of information are best represented on computPr-~riven displays is a very general one, for example. And it takes on considerable practical significance in view of the fact that 40 to 50 percent of all American workers are expected to be using electronic terminal equipment on a daily basis by 1990 (Giuliano, 1982~. Unquestionably designers of Space Station displays should benefit fern the many ongoing efforts to package information more effectively for use in office, industrial, and other earthbound contexts; we expect also, however, that efforts to get the Space Station displays just right because being almost right may not be good enough in this oontext--will yield knowledge about display design that will advance the state of the art in a general way.

51 The Evolving Role of humans in Space A here has been and continues to be a debate about the advantages arx! disadvantages of a space program that includes manned Spacecraft as ~ to one ~t does not. That debate will not be rehearsed here, beyond noting ~t ~nents of a Grinned program have argued ~t having harms in Apace is unnecessary for many aspects of Apace exploration and providing for their safety delays the program arxt increases its costs (e.g. Van Allen, 1986a, by whereas proponents of a manned p Ingram have presents a variety of an ~ ts in favor of it, among them cur inability to provide machines with some human abilities that are seen as critical, especially in responding to unanticipated events. Of particular relevance in the present context is the argument that has been made that the presence of humans in space will contribute positively to the productivity of the program as a whole. In this paper a manned program is taken as given. the problem then becomes that of designing a Space Station environment and operating procedures that will insure both the safety of the crew and the sumacs of its e ~ mlSS1011S . The h~nan's role In Apace he eked arxt diversified over the life of the Space program flus et al., 1982~. In the earliest flights the role was primarily that of passer~er In a highs y automated or grcun5-controlled~vehicle. As experience was gained and the flights became more ambitious the crews took on more of the responsibility of piloting the spacecraft. Still later, the crew's role was enlarged to include functions unrelated to piloting, such as perform m g scientific experiments and repairing malfunctioning equipment. Specific ta-=ks that have been performed by crew members include monitoring of the various spacecraft s ~ teas t guidance and control, propulsion, environment=] control, and life support); guidance and control during rendezvcus and docking; landing and taking-off of lunar module (about 10,000 key strokes are required to complete all elements of a lunar landing mission, according to Loftus et al., 1982~; assembly, ma mtenance and repair (especially of scientific instruments); aiming of scientific instruments and conducting of experiments; mob taring of data quality; and housekeeping. The ability of the crew to perform maintenance and repay' operations and to ha ~ e unexpectc] subsystem failures of various types has been demonstrated in severed missions, including Gemini, Apollo 13, Skylab, and Spacelab (Garriott, 1974; Garriott et al., 1984). Especially in the Skylab and Saab programs crown on numerous occasions were able to repair ~1functioni~ equipment that was essential to we planned experiments. As Garriott et al. (1984) have suggested, we importance of the function should be reflec ~ in the training of the crew designed to familiarize them with the equipment and how to repay' it. The ways in which the crews participated in the research activities of the Skylab and Spacelab programs have also been reviewed by Garriott (1974) and Garriott et al. (1984). An important idea emerging from these reviews is the following one. To the extent that craw members are to act ~ half of scientific investigators located on ache grow,

52 this function may go more satisfactorily if there has been more opportunity for the crew members to work with the scientists prior to the space mission. As the human's role has expanded and diver ified, the need for specialized capabilities and talents on space crews has increased, and consequently the crew members are less and less interchangeable. In the Shuttle program, specialization is recognized explicitly in the terminology, which distinguishes between mission specialists and payload specialists. In prolonged flights, like those anticipated for the Space Station, there will be an even greater need for certain specialized skills than has been the case heretofore. It may be necessary, for practical reasons, to have specialists who are also able to function effectively as crew members outside their area of specialty. An important problem in plank ng the crew requirements for the Space Station will be that of assuring that collectively the crew has all the knowledge and skills that success and safety will require. What is difficult about this tank is specifying the knowledge and ingenuity that will be required to deal with whatever unexpected contingencies arise. While it is not possible, of course, to anticipate everything that could happen, one step that can be taken in this direction is to attempt to identify the major types of problems that could arise (e.g. problems in the station's electrical system, medical problems among the crew, etc.) and to make sure that there is expertise within the crew to dean with problems in those areas. Same of the activities the Space Station's crew will perform will take place outside the spacecraft. Such extravehicular activities (EVAs) may include the changing of focal planes and other servicing of the Bubble Space Telescope (HST), the Gamma Ray Observatory (GRO), the Advanced X-Ray Astronomy Facility (ADOLF), and the Shuttle Infrared Telescope Facility (SIRI1F). . · · .. · . . (For a tabular summary of extravehicular activity on spaceflights through the Skylab III, see Lofted et al., 1982.) A major component of the cost of Elk activity stems from the large amount of time required to make the transition from the environment inside a pressurized space capsule to that outside it (Howard et al., 1982~. Pressure inside the Space Station is 14.7 psi; that ~ the pressurized suit is 4.3 psi (King and Rouen, 1982~. muse of the magnitude of this difference it is necessary for astronauts, in order to avoid the bends, to cheer cut the nitrogen in there body tissues by breath m g pure oxygen for 3 or 4 hours before exiting the spacecraft. m is procedure could be eliminated if the pressure maintained by the suit were above approximately half that maintained inside the cabin; thus immediate exit upon donning a space suit WaNld be possible if either suits were designed to maintain 8 psi and Thins were kept at 14.7 psi as they currently are or cab ~ pressure was maintained at about 8 psi and Suits at 4.3 psi, as they now are (NASA-ASEE, 1985). Extravehicular activity represents a special challenge with respect to productivity for a variety of reasons, including the following: ~ Severe constraints on mobility and dexterity imposed by the

53 pressurized space suit. bionic viscid id *ue ~ part to restrictions on head Cements frown the helmet and space suit. Greasy reduced tactile fe~adk to the harts because of pressurized giggles. Free floating or tethered (and easily tangled) tools. Limited voice communication with ~n-station crew. Problems associated with personal hygiene and comfort; most serious perhaps are the problems of defecation for males and defecation and urination for female=, but the general problem surfaces ~ numerous other, perhaps less serious' guises as well: it ~ very difficult to scratch one's nose or any other itch ~ an ED suit. · Problems of mating and drinking. To the degree that the Space Station is an automated system that is monitored by human be logs and dependent on canny eve ~ ide in case of subsystem malfunctions, it will pose the same kinds of challenge as other systems of this type. One such challenge is that of assuring that the human monitors are adequate to the task. The monitoring and controlling of dynamic systems are quite different tasks, and there is scme evidence that people who have net had experience as manner controllers are less effective at detecting small changes in system dynamics than are those ho have (Bessel are] Wickens, 1983; Wickens and Bessel, 1979, 1980; Yours, 1969~. Another' ~lenge relates to the dependence on human monitors for back up in case of system failure, ark that is the pebbles of ma~ntainir~ the human skills needed to perform complex functions that are very seldom performed under normal Operatic conditions. How does one keep crew members highly skilled at complex tasks that they seldom, if ever, have to perform? According to Jones et al., (1972), the most important functions aboard present spacecraft involve diagnosis and decision making, an] retention of diagnostic and decision mating skills represents our greatest gap in knowledge about task retention at the present time. A major challenge for extended space missions, especially those involving long periods of time simply getting to a destination (e.g. interplanetary travel) will be to keep a crew and other inhabitants of the space vehicle occupied In meaningful ways when there is little essential work relating to piloting or maintenance of the vehicle to be done. Work that is invented just for the sake of killing time is unlikely to be very satisfying. It will be important for individuals to perceive the ~ tasks as serving same useful purpose. Some time will have to be spent in doing housekeeping chores and some will be viewed as leisure, but it will undoubtedly prove to be necessary to have significant fractions of most days occupied with activities that are perceived as important to the mission or to other valued goals. Scientific experimentation and research could occupy much of this time, at least for those individuals who are scientists by profession or who would derive satisfaction from participating In scientific work. me problem of leisure time is considerably more complicated for expended missions than for those of short duration. In the former

54 case, one ~st be concerned not only with provision of short periods of free time at frequent intervals (e.g. daily) but also with the new for sc~rne~ing analogous to holidays or weds and vacations on earth, arm with the question of how to ensure ~t individuals firm it possible to spend that time to good advantage both freon their point of view ad ached of the mission. The Close Coupling of remans awl Muters In 1983, ache Space Systems Division of Me NASA Office of Aeronautics and Space Technology convened a super workshop (co Sponsored by the African Society for Engineering Education) at Stanford University to sod the Cole of autonomy ~ space. Me workshop report was issued in lg85, and he= been referenced here as NMA-ASE:, 1985. Participants in the workshop included professors form universities amass the country. "me workshop sought to generate Orations on autonomous systems and hen functions as well as on a Apace technology program Hebrew toward symbiotic use of machines and h~nans" "me principle objectives of the 1983 Sumner study wee to examine mte~ctions of humans ad highly automated systems In the content of specific tasks envisioned for the Space station, to search for opting combinations of hens and machines, arm to develop methodologies for selecting l~ma~i~ systems" (N~A-ASEE, 198S:2~. Participants In the workshop concluded from their stuffer "that machines will nak replace humans in space and that artificial intelligence (AI) systems will not have major impact on initial station design." To be sure, some aspects of the operation of the Space Station- maintenance of orientation, control of in-station environment, po Ming of antennas and solar panels--will be done completely automatically, at least under normal circumstances. Moreover, the role of automation and artificial =~1 ligence will increase as these technologies mature. But for the foreseeable future, and perhaps indefinitely, a great many aspects of the cgeration of the Station and of the performance of various missions will require the interaction of people with machines. An increasingly common mode of interaction will involve supervisory control, which is viewed by some as intermediate between the use of teleoperators an the one hand, and roLcts on the other (Thief and Khrtzman, i983~. In the case of Operators, the human has a 'virtual" hands-on relationship but at a distance, as it were. In the case of rctots, the relationship is of a qualitatively different type and may be remcbe both with respect to distance and time. m e robot is given a capability by its designer to function relatively autonomously, albeit ~ accordance with principles incorporated in its design. In the case of supervisory control, the human is linked to the machine in real-time, but controls its cgeration only at a relatively high level. The human provides generic commands, which the system then translates into lower-level commands to the effecters that will, if all goes well, get the job done. How generic the commands are that the human operator

55 provides deperxis on the system. me higher the level, the closer one cams to rcibotics, are! at scare point the distinction between the Awes Disappears. me fact that so many of the functions in the Space Station will be perform by people arm machines ~ irlt~ction mans that the design of the various workstations and person-me chine ~n~cerfam~s will be of central Importance. mere exists a su}=tantial literature, ash of it ~ design guide form, that is highly r ~ event to this proble`` a ~ that should be a major resource for designers of Space Station workstations and displays. But because the Space Station will be extending the frontiers of technology An several ways, designers will also have to consider questions for which answers have not yet found their way Onto design guides, and in some cases may nct have yet been asked. Moreover, as Loftus et al. (1982) po lot out, the ultimate design objective of any manned spaceflight program is never that of optimizing the crew-to-spacecraft interface, but rather that of achieving overall program effectiveness; and given the numerous constraints within which such programs must function, this may mean that compromises will be necessary in various interface designs. Decisions about such compromises, and selections among various possible tradeoffs, should be made with the best understanding possible of their implications. Among the issues relating to workstation and interface design that will be of special concern in the Space Station context are the following: · How to design multifunction input-ou~put devices so as to preclude confusion among functions. How to lay out the various display and input devices so as to ensure ease of location, interpretation and use. How to design the control and feedback interface-= for teleoperator systems. Haw-to design the various input-output procedures (cc mmand and query languages, menus, abbreviations, symbols) so as to maximize their usefulness and m m Itemize human error. . . . Many of the human factors issues relating to the design of workstations and interfaces will center on the question of how to get information--precisely the right information in a notable format and at the appropriate time--from a person to a machine or from a machine to a person. So in addition to the important questions of the physical designs of displays and input devices, there will be many issues relating to the design of methods and procedures for interacting with information per se. When will it make sense to use query languages as opposed to menus for searching ~ data base? Query languages put a greater learning burden on the user than do menus, but probably ~ e faster for experienced users, because menus typically force one to go all the way down a tree step by step even when one knows precisely what one wants to ask at the beginning. When menus are used, how should they be structured? This question subsumes a host of others, and although the lower-level questions sometimes seem to have intuitively obvious answers, research often

56 reveals tavern ~ be more complicated In they appear. Consider the apparently simple matter of deciding how many items to straw on a single node of a menu hieramby. For a system with a given namer of possible ~ points, there is a ~cradeoff between ache rn~xr of Options one sees at a given node in the hierarchy arm ache nor of nodes required ~ get form the start ~ the finish. This breadff~-vemus~ep~ Tradeoff has been the focus of ~ research Away et al., 1981; Miller, 1981; Seppala and Salverx~y, 198S). File the results have not led ~ an unequivocal conclusion, there seems to tee some agr~nt that menus that have very few items per level (say less than four) tow generally to be inefficient (TP£1 and McGregor, 1985; Seppala and Salvers, 198S). The scion is cca~li~, hover, tar the fact ~t hair much breadth one can hen ~ e effe ~ ively will probably depend on how much experience one has had with the system. This may be an argument in favor of permitting a menu structure to modify itself to match the experience level of its user. Much research effort is currently being devoted to the development of natur21-language front ends for information systems. It seems likely cat na~cur~ language systems with limit but useful capability will be available by the time the Station is operational. This is not to suggest that the reality of nlatura1 language capability will make other males of interaction ~ solete. The assumption that natural language scold be the preferred mcde of interaction with a data base in all cases is not beyond question; there is some evidence that more structured and constrained query languages may give superior performance An certain instance= (Small and Weldon, 1983; for a review of human factors considerations that pertain to the design of query languages, see Ehrenreich, 1981~. - Speech is also becoming increasingly feasible as a mode of communication between people and machines and could find at least limited use On the Space Station. The technology for synthesizing speech is improving steadily and although the best synthetic speech is still noticeably different flair human speech and typically some whet less intelligible, people get quite good at Understanding it with only modest amounts (a few hours) of listening (Schwab et al., 1985~. Speech understanding by computer is not so far along, but progress there is also being made. m e technology for isolated word recognition probably is sufficiently mature to be used in a Space Station context, and more ambitious uses of speech understanding technology may be feasible by the time the Station becomes operation21. Stress and Performance In Space Efforts to anticipate how humans will perform on extended space missions have focused on certain ways in which the spar. environment differs from more familiar environments on earth and on various types of scissors that c ~ ~ have either acute or mutilative lor~-term effects. Some of the characteristics of the Space Station environment may themselves be stressors, if not oontinucusly, at least under certain conditions. It will be convenient, therefore, to begin this

57 section with a brief discussion of stress in general terms and then to consider specific environments characteristics or stressors that might be expected to affect performance and hence productivity significantly. Affects of Stress on Performance Stress is likely to be a factor An The Space Station and to affect productivity in several ways. First, under the best of circumstances the Station and its personnel are always at risk. While we would not e ~ individuals to spend every waking moment worrying about safety, it would be surprising indeed if there were not a constant underlying sensitivity to the tenuousness of the situation; this might be considered a type of chronic stress. Second, from time to time, a _ c ~ _ _ , ~ . ~ ~ . ~ _. a ~ ~ ~ ~ individuals or the entire occupancy of the Station may be stressed acutely ~= a consequence of an unanticipated event or situational change. Third, stress may also be caused by factors that are relatively-long lived, but not necessarily chronic. These include confinement and social isolation, sensory-motor restriction, interpersonal frictions, dissatisfactions with certain aspects of one's duties or the Station's operating procedures, and anxieties about events or situations on earth. The list of possibilities is easily extended. Acco ~ g to Sharit and Salvendy (1982) most of the definitions of stress that one finds in the literature reflect biases related to the scientific orientation of the writers and fail to capture the many-faceteS nature of the phenomenon. Fidell (1977) has noted that some authors who have written about stress have avoided defin mg the term (e.g. Broadbent, 1971; Welford, 1974) presumably on the assumption that the word is intuitively mearingful: most of us know what it means to be stressed from personal experience. In his review of effects of stress on performance, Fidell (1977) classified stressors as physical, physiological, psychological, and social. Lazarus and Mbnat (1977) used the last three of these categories but not the first.) In the first category Fidell include d thermal (heat, cold, humidity) mechanical (vibration, acceleration, fluid pressure) and sensory (noise, glare, odor, deprivation) and ingested or inhaled substances (drugs, noxious fumes, insufficient oxygen). As physiologist stressors he listed mLscu10skeleta1 fatigue, sleep deprivation, age, disease, and illness. As psychological stressors he distinguished between cognitive (information or perceptual under/overload) and emotional types (fear, anxiety, insecurity, frustration). me social stressors in his list were occupational factors (e.g. career pressures) organizational structures, major life events, crowding, and solitude. Fidell also pointed out that stress is sometimes thought of as an effect and sometimes as a cause. It is assumed to be an effect, for example, of a perceive] threat to one's safety or the imposition of a task that exams onets ability to perform. On the other hand, it is sometimes identified as the cause of poor performance or of otherwise inexplicable behavior. It is also sc~netimes~vi~red as the cause of certain types of medical problems such -

58 as ulcers, colitis, and cardiac arrhythmias. Effects of stress on performance are not easy to summarize. Mild to moderate stress for short durations can have a beneficial effect in many situations, possibly as a consequence of increased alertness and the energy spurt that comes with the greatPr-than-normal production of adrenaline and other hormones. Excessive stress can produce detario,ation of performance. Frequent experience of stressful events tends to be acoompanled by atypically high incidence of illness of various sorbs (Norman et al., 1985~. A relatively unexplored aspect of effects of stress on performance relates to how performance changes after a temporary stressor has been removed. The study of effects of stress is further complicated by the fact that people adapt or acocc=odate to stressors, especially if they are only moderate in degree and relatively invariant over time. Noise, for example, can be a stressor, but people who work in a continuously noisy environment seem to adapt to it so that its effects as a stressor diminish greatly or disappear. Unexpected substantive change in the level or characteristics of the noise, however, may have disruptive effects. Leventhal and Lindsley (1972) distinguish between danger control and four control as two types of concern that one may have in a threatening situation. Concern for danger control is focused on the threatening situation and on how to rectify it. Concern for fear control is focused on the fear response and on how to keep it In check. Both are legitimate concerns and training in preparation for e ~ ed space missions should take both into account. Stress is likely to be an important factor in the Space Station and its effects on productivity could be substantial. Moreover several stressors may be cgerating simultaneously, producing complex interactive effects, and the stressors will be interacting also with other variables in ways that cannot be foreseen. In the remainder of this section, several of the stressors that could be-especially important in the Spare Station environment are briefly noted. Exactly how these factors, especially in combination, will affect performance art productivity is not known; that their effects will be substantive, however, seems highly likely. Weightlessness Weightlessness has been emphasized as a major feature of a spacecraft environment that could give rise to physiological problems such as altered fluid and electrolyte balances, and deconditioning of specific systems such as the cardiovascular, m~sculoskelet=1 , metabolic, and neuroendocr~ne systems (Lindsley and Jones, 1972). Problems of these types have net yet been shown to be sufficiently severe to preclude prolonged space missions; on the other hand, how they will manifest themselves ~ long duration missions remains to be seen. In retrospect many, perhaps most, of the observe] short-term effects of weightlessness on human functioning probably were predictable, but many of them were not predicted. In thinking about what it would be

59 like in a weightless environment, one may find it easy to imagine being able to float freely in space and fail to realize that it will also be difficult to stand on the floor, sit in a chair, or maintain any fixed position without restraints. Who would have thought to ask whether it waNld be possible to burp? Or whether it would be difficult to bend down to tie one's shoes? Unfamiliar Motion Closely related to weightlessness are the various types of motion that can produce motion sickness (Kennedy, 1972~. Even astronauts who have had training intended to reduce the probability of motion sickness have experienced such sickness during space flight, usually during the first few days of a mission, although nausea has typically not precluded crew members from carrying cut ess Initial activities (Garriott, 19741. There is some indication that dizziness is more likely to be induced in situations that permit individuals to move around in large spans= than in those in which they are more confined (Berry, 1969, 1970~. When severe, motion sicknP== can be debilitating. Motion Restriction On the opposite end of the spectrum from the concern for unfamiliar motion is that for motion restriction. A variety of restrictive conditions on earth have been studied with a view to determining theta physiolcgi~1 and psychologist effects. These mclude immobilization from a plaster cast, bed rest, and prolonged confinement in submarines, space cabin simulators or other chambers (Fraser et al., 1972~. Among the most apparent physiological effects of long-term restriction of activity appear to be cardiovascular and mLscNloskelet=1 Reconditioning, including some bone decalcification. Other possible effects include electrolyte imbalances and hemolytic anemia. As measures that can be taken to prevent or oountPr the deconditioning effects of motion restriction, Fraser et al. (1972) list the following: adequate free living space (200-250 cubic feet per person at a minimum, up to 600-700 cubic feet per person as the "optimal, maximizing habitability in the light of other requirements"), adequate exercise, applied pressure (to control for fluid volume loss and orthostatic intolerance of deconditioning), artificial gravity (seen an expensive and therefore less practical than other approaches), and hormones and drugs (primarily to control fluid loss). Sensory and Perceptual Restriction What is known about the effects of sensory and perceptual deprivation or restriction on human performance has been summarized by Schultz (1965) and Zubek (1973~. Eason and Harter (1972) have also reviewed the literature on this topic through 1972 and attempted to extract from

60 it information that would be relevant to the prediction of human performance in prolonged space flight. (Sensory deprivation or restriction connotes an absence or marked attenuation of sensory input to one or more mcdalities; perceptual deprivation or restriction suggests reduction in patterned stimulation.) Eason and Harter noted that the studies available for their review did not include any in which the period of confinement or isolation exceeded a few weeks. Russian investigators have done studies on effects of confinement in which subjects spent as long as one year in relatively isolate] environments but details have not been available. The data from these studies are fragmentary at best and do not constitute a coherent set of findings. Results of individual studies are often mutually contradictory, same showing negative and same positive effects of deprivation on subsequent perception or performance. As they relate to long duration space missions, Eason and Harter (1972:101) Ace the findings as "rather heartening, for they suggest that the effects of severe sensory or perceptual restriction, isolation, and confinement are so minor, except in a few instances, that they a ~ difficult to demonstrate with any degree of consistency not only from one laboratory to another but often within the same laboratory". Eason and Harter caution against making predictions about an astronaut's sensory, perceptual and motor functions during long-range missions on the basis of experiments involving relatively short-term isolation. The results of such studies do provide a basis for raising questions and suggesting directions for research that can be relevant in the space flight context, and had they yielded solid evidence of large effects of isolation on sensory or motor functions, they would have raised some concerns about potential effects ~ the Space Station program. "As it turns out, the results of studies summarized in this paper suggest that only minimal and relatively insignificant change= in sensory and motor function are likely to occur during long-~uration missions" (Eason and Harber:103~. Eason and Harber point out that in extended space flight, boredom fern repetition of stimulation may turn out to be a more important determinant of performance than sensory deprivation as such. m ey note, however, that past studies have been too limited in various respects to provide a basis for confident predictions about possible effects of confinement and isolation in space flight and urge further study of these variables under conditions that will assure the applicability of the results. / Sleep Interference Sleep disturbances and irregularities take many forms. The most obvious departure from a typical sleep~wake cycle is total sleep deprivation--going for extended periods of time without any sleep. Other types of irregularity include unusual cycles (e.g. 4 hours of sleep, 4 hours of work), change in phase in the normal s~ccpJwake pattern (e.g. shifting from a work-in-the-day-sleep-at-night pattern to a sleep-~n-the-day-work-at-n~ght pattern), disruption of the quality of

61 sleep (fitful or shallaw sleep; decrease ~ stage-3 and stage-4 sleep) rating freon ~iro~n~cal Is, psychoic~ical sJcress or other unusual factors. Sties of shift workers have chain that nging freon day to night shift t57pically results in a reduction (1 to 2 incurs) in the duration of the main sleep period, an increase in average total amount of sleep per 24 hour period--~ue to naps taken outside the main sleep period and extra sleep on rest days and a change in the quality of sleep (Akerstedt and GilLberg, 1981; Tilley et al., 1981; Titchy et al., 19821. Indicants of quality include time to sleep onset, number of awakenings, number of body movements, and number of changes in sleep stage (Jchnson et al., 1972~. How situp disturbances affect performance is not under stood well. Data suggest that sleep loss is likely to have deleterious effects on tasks for which sensory stimulation tends to be low and the rate of data handling is not under the individuals control (e.g. monitoring or vigilance tasks) an] to have less effect on the performance of complex ntPllectNal tacks involving problem solving and logical analysis (Johnson et al., 1972~. Somewhat independent of the question of the effects of situp disturbance== on performance is that of their effect on moods and attitudes. insomnia is often linked to depression, tension, and irritability. Whether there is a cause-effect relationship and, if so, which way it goes, are not known for certain. Determ m ation of optima work-rest cycles will involve consideration of a variety of factors, technological, psychological and social. How often and how long people will near (or want) to sleep will depend in part on the demands of their jobs, and in part on the conditions of the sleeping environment. Requirements for sleep are likely to differ frog Person to person. With respect to social factors. there is some . _ _ _ , _ ~ _ ~ _ _ ~ ~ ~ _ . ~~ ~ . ~ ~ · evidence anal crews prefer co ne on one same wor~-rest cycle insofar as possible, and work and get along better when this is the case. The importance of rest periods interspersed among work tours has been kocwn at least since Taylor's (1947) early studies. Exactly how rest breaks should be scheduled, however, or ha' this should depend on the nature of the work being done, has not been ~st~hTished very precisely. It is not even clear that it is always optimal for work breaks to occur on a fixed periodic schedule. Any attempt to understand the relationship of sleep disturbances and stress will illustrate the problem of distinguishing cause Frau effect. S1^PP disturbanocs, such as those caused by unusual work-rest cycles or the need for prolonged wakefulness to deal with an emergency situation are seen as 50UrCe5 of both physiological and psychological stress. On the other hand, stress originating from other sources can be the cause of insomnia or other sleep-related difficulties. Boredom an] Other Motivational Problems It is somewhat paradox~a~ that one of the major concerns about such a risky venture as expended space flight should be a concern about boredom. However', boredom and various attendant complications could be among the most serious problems that have to be faced. although

62 surprisir~ly little er~p~ical work has been done on boredom (with, 19 ~ 1 ~ , it has }seen identi f fed as a s igni f icant probI en f or peop' e living in restrictive environments with monotonous schemes for weeks or months at a time. It is believed to have detrimental effects on motivation and morale and ~ lead too increased frequency of cants of hez~dhe arxI other physical problems. The tendency for motivation to decrease over a period of bed conferment is a con report fm m s ~ ies of stall go ~ s In isolated errviro ~ nts (Smirch, 1969~. Behavioral evidences of a loss in motivation include diminution of one's ability or willingness to engage An sustained purposeful activity. There is some evidence that declim ng motivation has a physiological correlate in a decreasing frequency of alpha rhythm in ~ he ~ r.~r~ ft7~1~1r ~1 =1 sac ~~- wave `=w_c~ ~- an./ 1969). This is an interesting finding because it suggests the possibility of using alpha rhythm as a means of man~toringindi~vi*uals' momentary cognitive state and of predicting how prc~uctive they are likely to be ~ specific work situations. cony studies have failed to find a decrement in ability to perform some Types of cognitive tasks and ~ some cases have even found an improvement in that ability as a consequence of spending substantial amounts of time ~ confined environments. However, Johnson et al. (1972) note the possibility that studies that measure performance under the circumstances in which motivation might be expected to be low often risk artifactual results by virtue of the possibility that the experim£nt=1 task itself, if unusual within the context, may be sufficiently arousing and ~ *ending to improve temporarily the subjects' motivational state. After reviewing the pert Went literature, Johnson, Williams and Stern oonclu de] that very little is known about how to reduce monotony and boredom *tiring long periods of group confinement. Social Isolation Isolation can mean a variety of things. Brownfield (1965) identifies four: spatial confinement; separation from persons, places, or things that one values highly; reduction or restriction of sensory stimulation; an] reduction in the variability and structure of stimulation. The first, third and fourth of these connotations have already been mentioned. Uhfcrtunately, effects of isolation often cannot be distinguished from those of confinement, motion restriction and social crawling, because chew= conditions typically occur together; nevertheless, it is believed that social isolation could prove to be among the mast important stressors in the context of prolonged space missions. Some concern has been expressed that it, combined with some of the other characteristics of the space environment such as weightl~ssn=mc, empty time, and distortion of the usual balances among sensory inputs, may lead to an increase frequency of daydreams and fantasizing arm a progressively more subjective orientation (l~renthal arm Wesley, 19721. Studies of Groups that have spent ex~ed , . _ e ~ e _ . e e _ . e ~ e ~ e e a, _ ~ peri—= (months) in relative isolation have shown bat individuals tab cover time ~ withdraw arxt dame more psychologically rob from other

63 members of the group (Haythorn et al., 1972). According to Sells and Gunderson (1972:204), extended isolation and conf mement of small groups on earth (e.g. at scientific stations in Antarctica) can increase the probability of "irritability and depression, sleep disturbances, boredom, social withdrawal, dissatisfaction, and deterioration in grcup organization and cohesion". Enriching the stimulus environment con counteract this tendency to some degree, but the stimuli must be meaningful and of interest to the people involved. There is some evidence that part of the withdrawal complex is a decreased tendency to avail oneself of whatever opportunities for stimulation the envircnment provides. Special problem; may rise when an individual especially close to a person on an extended mission became aridly ill (e.g. a child, ~use, or parent) and it is impossible for the person to return to earth, or if unanticipated events of major significance dour on earth *tiring a prolor~ed mission. The effects of such happenings on attires and morale card be substantive. Tt is easy to imagine other examples of events on earth Off calld prove to be stressors to people In spar. Thatch as fornication between earth arx] the station will pr ~ bly be primarily tbr w ~ gr~rx! control stations, at least for some time, information that could have a detriment=] effect on the morale of members of the Space Station crew could be withheld from them. Consideration of such a policy raises a serious ethical issue, however, an] woN1d probably not be tolerated in any case. mere me many reasons for maintaining frequent, if not constant, c~mn~ni~tion with earth. Not least ante these is the need for ir~abiJcants of Me station to car~nunicate fr~en~y with people other in themselves. Exam - ive Workload Exc~ssi~re track Canards can be a source of stress ark can lead to serious performance de ~ ts. When even moderate task demands are coupled with the constant pnC=ibility of catastrophic errors, long term exposure to the situation can produce a variety of stress-related symptoms. One inherently stress fin job that has keen the fores of considerable attention by researchers, and the general public as well, is err traffic control (Cobb and Rose, 1973: Cruma, 1979: Finkelman and ~;_~~~_~_ ~C~Q' · =~;1~ 1~Ql ~ , _ , . . . -~`c~/ =~/ ~~, _~-v'. m e stress in this case probably stems In large part fr ~ the facts that errors in performance can result in human fatalities and that most aircraft accidents are due to human error (Danaher, 1980~. Task demands in the Space Station are unlikely to be excessive for sustained periods of time, although they cculd be high at critical ssion junctures and could become excessive during emergencies. Perhaps more important is the ever-present possibility of human error having a catastrophic result. Every attempt will be made, of course, to ensure that the operating procedures are fail-safe and that any errors that can be anticipated are recoverable, but some degree of uncertainly in this regard is bound to remain, and with it some level of task-induced stress.

64 Acute M - Oman Problems With respect to the control of medical probers withy a spacecraft, the emphasis has to be first on prevention Chaser et al., 1972~. Hying taken all r~onabie preventive measures, however, the chance that medical problems will arise on any Conjuration mission is high. Within the Space Station there will be the possibility of many of the say types of physical injuries arising from accidents with equipment that might occur on earth. In addition there are c~aln by; of mishaps that are relatively unique to the space er~viro ~ nt; these include the aspiration of particles that float in the weightless environment of the station, effects of prolonged exposure to atypical mixes of atmospheric gases or pressures, exposure to high-, particles--high energy particles of high atomic number--or other forms of radiation, and heat disorders resulting from malfunctioning of a pressure suit during Eva. Fraser et al note also the possibility that some medical problems that would be very easy to treat on earth CCNId become significant in space, either because of inadequate treatment facilities (e.g. acute appendicitis) or because the medical problem has been complicated by virtue of various ways in which the body Hal adapted physiologically to the weightless environment (e.g. reduction ~ blood volume due to weightlessness). Other Sources of Stress Other features of space flight that card also be prdbl~tic include the a}=enc~e of normal terrestrial time references, I, i, magnetic fields (Fraser et al., 1972). Changes in 1mes of authority that cad prove necessary freon time to time could pose challenges for social stability of the spacecraft community. The need for privacy could be an especially important one ~ extended space flight; the ability to have some time and place wholly to oneself on a fa Ply regular basis may prove especially important in this environment. Sharing of sleeping quarters and other personal space over long periods of time can increase the frequency and ~ ricusness of interpersonal frictions. Habitability of the spacecraft will iDcrcase in importance with increases in the *orations of space missions. The Iffily of maintaining a habitable environment will also increase with mission *oration. It will be particularly important that inhabitants of the Space Station be able to resolve, quickly and expediticusly, any interpersonal conflicts that arise. Presumably selection procedures will disqualify If- participation in space missions individuals for whom the probability of interpersonal disputes or frictions is determined to be high. It will be important for those who do qualify to receive such trainer as is available r~ardi~ he to avoid varicus types of ~nte~racnal clispul:es, arm has to resolve thern when avoidance proves ~ be impossible. Irxlividua1s react differently to the same spoors, depending on arm noss=4v =~

65 motivation' familiarity with the situation, appropriateness of trainings degree of confidence in own ability to cope, degree of confidence in supporting colleagues and accessible resources, and other factors. There is some evidence that the magnitude of . . . · , · ~ ~ . ~ . . ~ · ~ physlologlcal reaction (e.g. 1ncreasea pit Use rare, do psyono~og~ca1 stress is likely to be less for individuals who are aerobically fit than for those who are not (Holmes and Roth, 1985). Tests that provide a reliable indication of how individuals will react to the types of stressors they are likely to encounter in the Space Station environment would be useful both for purposes of selection and for identifying specific Exalting needs. Development and validation of such tests are worthwhile goals. Similarly, development of more effective methods of ~ncr~ing tolerances to specific stressors and of improvir'3 the amid ity of individuals to function effectively in spite of them should be cont~nuir~ objectives. rufous et al. (1982:II-34) note that stress does not seem to have led to performance degradation so for in the spaceflight proven. They attribute failure to cove such degradation "to substantial o~rertrainir~ of flight crews for the tasks they ~ st perform, diverse and =~-resting stimuli present in the real environment contrasted with m m Imum stimulation environment in simulations, and stronger motivation in flight crews compared with test subjects". It would be unwise to extrapolate the relative unimportance of stress as a determinant of performance in the marry space program to the future, however; the much longer durations of the missions and the inclusion of participants who are not professional astronauts are two major differences that could make stress of various types much more consequential. QONclllSIONS AND RECOMMENDATIONS The Space-Station program is an ambitious undertaking. Establishing a permanently manned facility in space will be expensive and risky, but the long-range benefits for humankind that could result freon success in this endeavor are surely very great. Peeping the program moving forward without unpleasant surprises and major setbacks will rehire intensive planning, contin,~1 evaluation of plans, replanner based on the results of evaluations, and cursive attention to details of countless types. In the remainder of this paper, I shall identify hat appear to me to be same of the major needs, especially research nets, relating to productivity in the Space Station. At the beginning of this paper, it was noted that the term ~ro~uctivitv is used in a variety of ways and often without a very precise connotation, and that except in certain highly-structured situations, how to quantify productivity unambiguously is not clew'. If high productivity is to be an explicit objective of the space program, some consideration must be given to how it is to be measured or otherwise assessed in this context. Assessment will be desirable at various levels--that of the overall Space Station program, that of specific missions, that of specific crews during designated periods of time, and that of individuals performing specific

66 t=~:;kS . For present purls, it is assume that ~ncernents--~ncr=~es in the efficiency, accuracy, reliability--of the performance of humans or Imagine systems are very Silvery to improve productivity by nearly anyreasonab~e definition ar~asurement technique. The ~ ations that follow are predicated on that assumption. Research that is alluded to in some of these recommendations is already underway, in NASH laboratories an] elsewhere. I Am aware of some of these efforts, but there undoubtedly are many of which I am not. Inclusion in this list signifies only my opinion that the topic deserves attention; if it is getting it already, so much the better. While all of these recommendations are considered important to the Space Station program, they are not all uniquely applicable to it. Some of them are similar to reccm=£ndations that would apply to the design and develcpment of any complex system that will have people interacting with ccmputPr-based tools ~ non-trivial ways (Nickerson et al., 1984~. . . . . . There is a need to organize the information that has been obtained frum research on earth or friar data gathered in previous space flights that is relevant to human performance in space. This information should be organized and indexed so as to make it highly accessible to scientists and engineers in the space program. It would be useful also to commission the compilation of an encyclopedia of ignorance about productivity, an] performan~- more generally, in Apace. The priorly objective should be to identify as many as possible of the important unanswered q~estionsaba~t performance Respace. Questions should tee prioritized with rent to urgency, and classified in terms of the kirk of resort that cod lead to answers. at information will be r ~ Air ~ bar Specific me ~ rs of the Space Station team at specific times needs to be determined. This includes determining what information should be presented spontaneously, and in such a way as to capture the intended receiver's attention, what information should be available explicitly on some display all (or most) of the time, and what information shculd be available but presented only on request. Possible and most-likely patterns of communication or information flow both within the Space Station and between the station and earth need to be under stood better. More effective means of providing EVA ads to data-base information pertinent to EM tasks are needed. · An inventory of tacks that pile will be ~ to perform in the Space Station should be compiled.

67 . . . procedure descriptions should be evaluated for accuracy and claim. Criteria need to be established regarding what aspects of the Space Station's operation should be auto meted. The rule that anything that can be automated (effectively, safely) should be auto sated is not neces-C~'ily a good rule. m ere may be some functions that can be done acceptably by either people or machines that should be done by people. Issues of morale, perception of control, and skill maintenance must be considered as well as that of technical f=~ibility. More research is needed on the question of how much ''intelligences to build into teleoperator or telerobot systems, and how much to rely on remote control by humans. · The design of c~mputer-based aids for trouble shooting, problem solving and decision making, and of the protocols for interacting with them deserves considerable attention. . . Efforts to advance the state-of-the-art of aiding human operators through the use of "intelligent", or "expert-system" software should be supported: potential applications in the Space Station program include fault detection, identification, and repair; planning and plan revising; and crisis management. The knowledge of astronauts and space professionals must be codified to provide the basis for the development of expert systems and knowledge-based aids. The phasing of expert system technology into operational situations as its evolution warrants will represent an ongoing char lenge into the indefinite future. Possible problems involved in having crew members share responsibility of high-level cognitive tasks with "smart" software or expert systems need to be identified; policies should be established for deriding when to trust a svelter one when to override it. Design of the various mterfa~r== through which Spar= Station personnel will interact with the numerous systems and subsystems on boar] is among the most critical problems to be solved, from a human factors point of view. There is a body of literature relating to the design of workstations and displays that should be consulted; however, much remains to be learned about how best to represent and present information in various Space Station contexts. This topic deserves a continuing effort of research focused on the identification of display formats, information coding dimensions, and input techniques that are especially well suited to the Space Station enviror~t and the demarKis of specific tasks that are to be performed.

68 . . Proposed or planned displays and work stations should be evaluated in terms of conventional human factors criteria: lighting, glare, flicker, contrast, charact~r/symbol legibility/interpretability, functional -positional relationships, clutter, and so on. Display configurations and symbology must be designed and evaluated; this includes determination of content and format of specific-purpose displays. Display coding dimensions must be selected so as to munlmize confusion arising from multiple functions of a given display space. A better understanding is needed of when to use menus and when to use command languages as input methods. The menus and languages to be need must be designed, evaluated and refined. There is a need to identify situations in which voice could be used to advantage as an input or output medium, given the probable state-of-the-art of voice recognition and production technology Over the next decade or so. · Further work is needed on the design of control and feedback interfaces for remote manipulators, teleoperators, and semi-autonomous systems. The problem is complimented when the distance between the devices and their operators is great enough to cause significant communication delays. m e need for high resolution, stereo visual feedback from teleoperator systems should be studied and the f-~ibili~y of its use explored. More effective helmet-mounted displays for use in EM should be a continuing research objective. m e technology for tracking eye fixation and movement, and hand and finger position and movement could have applications in the Space Station, but near to be developed further. m e technology needed to make a virbual-~nterface approach to telecperator control a p~-actim=1 reality requires further exploration. Acquisition of antic, rEnge of motion, strer~h' and force and torque application data, with and without pressurized suits, should be continued. the ability to measure and monitor mental workload could be useful, especially for the est~hlishm==nt of crew responsibilities in the Station's day-to-day operation and in high-activi~y situations. But techniques that are to be used in operational contexts must be unlntrusive, and this rules out the

69 applim~iiity of many of those that have been wed to study mental workload in the laboratory. A catalog of possible human errors (of both cc~mnission arm emission) that card have non-trivial consequences In the Space Station should be developed; potential errors should be rated as to seriousness and probability of cocurrence, and the results need to develop safe ~ s and errc- detection and recovery Pro. . . . . . . A detailed study of human errors that are actually made in the Space Station environment will be very useful, as it has been in other' contexts (blister, 1966; Swain, 19~e, 1978~. Methods of assuring the maintenance of cri Scat skills that are typically used only in the event of a system Malfunction or failure must be developed. Effects of prolonged living in restricted] environments on work performance, social behavior arm stat state deserve further stuffer. More specifically, attempts should be made to identify ads of such er~virorunents that are the major deterTrinants of behavior, cognitive or emotional effects. Special attention should be given to the types of interpersonal tensions and conflicts that are likely to arise in the Space Station environment and the development of effective techniques for relieving or resolving them. m e question of how to occupy long periods of time during which the operational demands of the spacecraft are minima deserves considerable attention. The maintenance of motivation, alertness and social stability during extended stretches of being, in essence, passengers on an automatically piloted craft represents a significant challenge. Presumably, productivity in space can be enhanced by factor that contribute to the maintenance of high levels of alertness, motivation and general physical and mental well being. We need to understand better how these variables depend on such factors ~~ appropriate diet; regular physical exercise; the opportunity to engage in interesting and valued activities in free time; frequent communication with earth, not only regarding mission matters, but regarding those of personal interest; adequate variety in job responsibilities; adequate rest; and extensive use of error detection and failsafe procedure-= (especially those that can be automated). · We need also to learn more about the relationships among certain performance or psychological variables (attention, vigilance, perception, memory, learn Meg, thinking, and judgement) and

70 indicants of physiological state (EEG, evoked potential, contingent negative variation, heart rate, blood pressure, respiration, skin temperature, galvanic skin response). TO the extent that variables in the latter category can be shown to be reliable indicants of the quality of specific types of human performance, consideration should be given to the development of unintrusive ways of monitoring them, at least at critical times, and using the results of the mom taring to enhance performance in various ways (Johnson et al., 1972~. Althcugh techniques exist for doing such monitoring, they tend to be sufficiently intrusive to interfere with the monitored individuals' performance of their primary basks and to be less reliable than is desired. A cant Suing gang of research should be the development of less intrusive and more reliable techniques for may taring cognitive state. m e ability to mon~tor--and in particular to detect significant changes in- p ysiological and psychologist states could prove to be especially important in Jong-term space missions. State changes that could be important to detect include both temporary fluctuations in alertness and long-range changes in general physics condition, motivation and mood. Biofeedback technology is still In its infancy, however the evidence is clear that people can learn, within limits, to control certain p ysiological functions that had been thought to be completely automatic. Further study of biofeedback techniques is warranted with a view to their possible application in the Space Station for purposes of controlling tension, facilitat Meg good quality sleep, and otherwise tuning physiological states to enhance either performance or rest. SO Dues of the mental models that crew Embers or perspective crew members develop of the Space Station and its hardware and software components could help determine what kinds of ncd~ds are acceptable for conveyance to future participants in Space Station missions. There IS a need for better rapid prototyping capabilities especially for prototyping candidate interface resigns. Procedures and policies must be established for acquiring data in space that can be used to relate productivity and performance to the numerous variables that are believe] to affect them in significant ways. It is not likely that predictions about performance of humans in space can be very accurate very far into the future. A reasonable goal is the development of a predictive model, based on what Is currently known from data collected on earth an] from studies of performance in space to date, with the intent of

71 modifying that model contritely as further relevant data are obtained, esE^:ially from e~rien~ ~ apace. Conditions in space exploration will charge and the durations of says In Apace will Ink ~ se, so the mcdel will have to evolve to acocmrodate those changes. On the assumption that the changes that Drier will be evolutionary and relatively continue us, one can hope for a model that is highly predictive of the situation that is current at any given time and reasonably predictive of the situation as it is anticipated to be in the n-~r-term future. m;~;rIc:F~ AXerstedt, T., and Gillberg, M. 1981 Sleep disturbance and shift work. In A. Reinberg, N. Vieux, and P. Andlauer, eds., Night and Shift Work: Biological and Social Aspects. Oxford: Pergamon Press. Baily, M. N. 1986 What has happened to productivity growth. Science 234:443-451. Bechtold, S. E., Ganaro, R. E., and Sumners, D. L. 1984 Maximization of labor productivity through Optimal rest-break schedules. Management Science 30:1442-1458. Berry, C. A. 1969 Preli ~ clinical report of the medical aspects of Apollos VII and VIIT. Aerospace Medic me 40:245-254. 1970 Summary of medical experience in the Apollo 7 through 11 mart spaceflights. Aerospace Meclicme 41:500-519. Bawen, W. 1986 The pure payoff freon office Muters;. Fortune 5:20-24. advent, D. E. 1971 Decision art Stress. Near York: Academic Press. Backfield, C. A. 1965 Isolation, Clinical and E~riment~1 Approaches. New York: Barton House. Cameron, C. 1971 Fatigue problems in modern ir~ustry. Ergona~nics 14:713-720. 1973 A theory of fatigue. Ergonc~mics 16:633-648. Hi, J. G., and Wierwille, W. W. 1983 A Orison of rating scale, se~rx~ary task, physiological, and primary-task workload estimation ~hniqu~s in a simulated flight task Sizing ~nications load. Oman Factors 25 (6~: 623-641.

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78 Sc~hwab, E. C., N~amn, H. C., and Pisoni, D. B. 1985 Sew effects of training on Mae perception of synthetic Oh. Human Factors 27(4):395-408. Sells, S. B., arm G~l~;on, E. K. 1972 A social system approach to lore - oration missions. Oman Factors in Long-~ration Spaceflight. Wa~ir~ton, DC.: National Academy of Skiers;. Sheila, P., and Salably, G. 1985 ~ act of dep1:h of menu hierarchy on performance effectiveness In a supervisory Cask: Ccmputerized flexible manufacturing system. Human Factory 27~6~:713-722. Sharit, J., and Salvendy, G. 1982 Occupational stress: Review and reappraisal. Human Factors 24~2~:129-162. Sheridan, T .B., and Simpson, R. W. 1979 Tc ward the Definition and Measurement of the Mental Workload of Transport Pilots. Flight Transportation Man-~achine Laboratory, Technical Report No. DOr-06-70055. Cambridge, MA: MIT. Simon on, E., and Weiner, P. C., eds. 1976 Psychological Aspects and Physiological Correlate= of Work and Fatigue. Springfield, IL: Charles C. mamas. Singleton, W. T., Fox, J. G., and Whitfield, D., eds. 1971 Measurement of Man at Work. Lan don: Taylor and Francis. - Small, D. W., and Weldon, L. J. 1983 An experimental comparison of natural and structured query languages. Human Factors 25~3~:253-263. Smith, S. 1969 Studies of small gram In conf~nemnt. In J. P. Z0bek, ea., Sensory Deprivation: Fifteen Years; of Research. New York: Appleton Century~fts. Smith, R. P. 1981 Boredom: A rapier. Oman Factors 23(3):329-340. Sutermeister, A. 1976 People and Pr~cti~rity. 3rd. - ;tion, N - r York: M~;raw-Hill. Swain, A. D. 3970 Devel~nt of a Oman Ever Rate Data Bank. Sandia Corporation Report SC-R-70-4286, A~uq~e, Ha: Sarx~ia Corporation.

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