The Space Reviewin association with SpaceNews

ISS crew
The ISS provides a platform for researchers to understand and mitigate the physiological and psychological effects of long-duration spaceflight. (credit: NASA)

Human factors and the new Vision for Space Exploration

It may seem a little ignominious to begin a discussion on human spaceflight by examining the behavior of apes. But then, all things in nature tend to be hierarchical in that highly organized living creatures tend to include previously tried and true physiological architectures. The brain, for example, is a hierarchical structure: The brainstem and the reptilian complex make up the earliest structures, followed by the limbic system (also called the mammalian brain) and, finally, the “neo” cortex (or modern brain). In other words, even if certain psycho-physiological systems appear to have outlived their usefulness, they remain “online” or, at the very least, leave behind some remnant to remind us of what we once were. And so our friend the ape serves as an apt introduction to the subject of human behavior in isolated groups.

Anthropologists studying apes in Africa have found many interesting parallels between human behavior and the behavior of apes. Apes generally live in the forest where they are relatively safe from predators due to the sanctuary provided for them by the trees. However, in periods of food scarcity they must migrate to other forested areas, which sometimes involves long periods of travel across the African open plains. During these long migrations they are extremely vulnerable to attack by predators. After several days without an attack a rather curious behavior begins to emerge: the apes begin to attack and kill each other. It is theorized that the long periods of physiological mobilization due to fear of attack ultimately overrides the apes’ inherently altruistic nature, resulting in violence towards each other. (This mobilization is often referred to as the “fight or flight” response). In human beings, when a threatening situation is prolonged and never resolved, the sympathetic nervous system essentially remains engaged, or at least never completely disengages. The sympathetic nervous system is responsible for mobilizing the body for action in the face of a threat to survival (fighting or fleeing).

Probably the most important issue of long-term spaceflight with respect to the human element is that of compatibility.

We have seen many examples in the human domain of this same sort of violence resulting from exposure to prolonged threat. The more obvious ones are inner-city gang violence and wartime atrocities where young men who, under ordinary circumstances wouldn’t consider stealing the neighbor’s newspaper, end up killing innocent civilians by the hundreds. These, of course, are extreme examples. But they shed light on an important aspect of human behavior: that destructive (and self-destructive) moods and behaviors tend to emerge under very certain conditions—namely a pervasive, unrelenting threatening situation from which there is no escape, coupled with long periods of boredom. Adding the condition of isolation only amplifies the perception of inescapability, as studies of Arctic expeditions have revealed. Although very few of these situations ever result in violence, it has been demonstrated in virtually every arena of medicine that prolonged periods of exposure to a threatening situation for which there is no resolution will ultimately take a substantial toll, both physically and psychologically, on the individual and, consequently, on all persons in the proximal group.

Experiences aboard the Mir space station indicate that long-term space missions are potentially fertile environments for the emergence of such conditions. When human beings are placed in a strange environment where the workload is extreme and the threat of destruction is omnipresent, the level of arousal in the human nervous system tends to remain above a certain threshold. It is something like a milder version of what happens with post-traumatic stress disorder, where traumatic situational events have reset the physiological set point for the alarm response in the brain. This leads, ultimately, to a state of exhaustion in the brain that has distinct features in the EEG (or brainwave activity). Typical symptoms that accompany this state of cortical exhaustion are: depression, insomnia, attentional deficits, mood instabilities and, ultimately, immune system irregularities and physical illness.


Probably the most important issue of long-term spaceflight with respect to the human element is that of compatibility. Biosphere 2 gives us a high profile example. Despite the compromised scientific integrity of the experiment (and some rather negative press), it was a noble and courageous undertaking and yielded some useful information. One of the more interesting pieces of “data” was in the human factors domain. In 1991 the six members of the Biosphere 2 crew entered the habitat aglow with high team spirit and expectation. By the end of the two-year rotation crewmembers weren’t even speaking with one another. Such examples of deteriorating interpersonal relationships are not uncommon among isolated groups, whether they be scientific groups in the high Arctic or company canoe trips down the Colorado River.

In the book Spacefaring: The Human Dimension, Albert Harrison surveys the literature on the experiences of crews from under the sea, space, and polar outposts. Common side effects of long-term isolation and confinement include inattentiveness, mood instabilities, sleep disturbance, and perceptual distortions. In one case 40% of the participants in an Antarctic expedition suffered from “wandering attention” and absent-mindedness. In a few cases a person entered a fugue state where he would “come to” far from his quarters with no memory of how he got there.

The Russians have a great deal of experience in long-term spaceflight and have been fairly forthcoming about their findings. According to Bryan Burrough, on three occasions over a 20-year period a spaceflight had to be terminated due to psychological reasons (deteriorating mood, poor performance, or interpersonal problems). In general, on long flights, initial excitement gives way to exhaustion, insomnia, and irritability. Cosmonauts may tend to withdraw and speak in a monotone, giving brusque answers to questions from each other and ground control.

In submariners, Rohrer found that there are three stages that emerge over time during long -term undersea voyages. The first is characterized by excitement and anxiety, the second by boredom and depression, and the third by increased aggressiveness and emotional outbursts—something Harrison refers to as “third quarter phenomenon”. What is interesting is that these three stages seem to occur regardless of the total length of a tour of duty or rotation—whether three weeks, three months, or a year.

Crew compatibility will certainly be of primary importance as the quality of social interaction and communication between members will be critical.

Even television’s recent obsession with real-life scenarios (“reality” TV) gives us a fly-on-the-wall vantage point on human group dynamics in isolated environments. Granted, many of the persons chosen for reality TV scenarios aren’t picked because of their emotional stability and rational demeanor (that makes for boring TV and poor ratings). Still, the tendency to form different splits and coalitions within an isolated group seems to be common and is often quite destructive, particularly when the group is under some form of situational threat or stress. Reality TV takes full advantage of this human behavioral characteristic with highly profitable results.

Interestingly, the discipline that offers the most insight into the prediction of the nature of social interactions within a specific group is that of family system dynamics. There is a wealth of psychological research regarding the evolution and manifestation of maladaptive behavior stemming from dysfunctional family relationships. Very simply, a person acquires specific coping strategies in childhood that were tailored to suit his or her immediate environment. And so, that which has served so well in the past (i.e. was conducive to survival) will tend to be employed in any situation that “resembles” a family unit in the present. In other words, there is a strong tendency (in all of us) to recreate that which is “familiar”, whether good or not so good. Thus, you probably wouldn’t want a crew comprised of persons raised in violent or intemperate family environments. On the other hand, those raised in dangerous environments may have certain desirable characteristics such as tolerance and patience. Thus the selection process for a mission to Mars will undoubtedly be multi-layered and highly individualized.

A basic approach to managing stress on long-term flights involves some fairly obvious considerations. Crew compatibility will certainly be of primary importance as the quality of social interaction and communication between members will be critical. Desirable individual skill sets will also serve to increase harmony and interdependence of the crewmembers. In addition, supportive countermeasures (both on board and on the ground) will also be needed.

Environmental design

Another major consideration on the human factors front is that of environmental design. Designing the most efficient and appealing architecture for long-term spaceflight involves several factors. The primary consideration is functionality, while another is aesthetics. The goal in any spacecraft or habitat construction is to maximize working/living space while minimizing the amount of construction material (and hence reducing mass and weight), and do both these things while not compromising structural integrity. This is why variations on a spherical shape (such as cylinders, domes, etc.) are often used in space architecture.

Beyond that, obviously the most important consideration is that the structure must protect against the harsh environment of space. Radiation shielding, life support system integrity, and reliability will be of paramount importance. Aesthetics, noise control, and efficient waste management are also major considerations.

Depending on your orientation the same corridor on the space station can appear completely different depending on your choice of the “floor”. It is not too difficult to imagine getting lost while not straying too far.

Privacy is another important concern. People with different cultural backgrounds may vary widely with respect to privacy needs. Asian and Middle Eastern persons tend to tolerate higher-density living better than most North Americans. Within the North American culture, men tend to need more privacy than women. Harrison states that cultures that emphasize meditation are more able to tolerate crowded situations since they have developed an ability to create a form of inner privacy. “Habitability volume,” as Harrison terms it, increases as a function of the duration of the mission. Habitable volume refers to the usable living space. According to NASA research, 17 cubic meters/person is optimal for a six-month journey. Thus for a six-person crew the total volume would be 102 cubic meters.

Disorientation is also a consideration. For instance, traveling down a tunnel in the ISS is not the same as walking down a corridor. For one thing your visual frame of reference has no meaning. On terra firma the floor is always under you chin. In microgravity you can choose your own floor. Thus, depending on your orientation the same corridor on the space station can appear completely different depending on your choice of the “floor”. It is not too difficult to imagine getting lost while not straying too far. Interior designs may therefore need to counter the natural disorientation that tends to occur in microgravity. This can prove particularly important in emergency situations. Coloring the walls or providing visual cues that suggest a gravity field orientation can be helpful.

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