Human Factors in Prolonged Space Flight

AE 426, Lecture 4

Outline

Physiological Issues Psychological and Social Factors Space Architecture and Habitability

Physiological FactorsSee References 1-3

Space is the harshest environment humans have been subjected to, with many physiological challenges. But these can be overcome, provided that…

First priority: A sustainable rationale for human space exploration It is fundamentally about reaffirming the pioneering character of our society The vast majority of the rights and freedoms that western civilization enjoys were

conceived of and cemented behind the line of human expansion. New destinations have offered proving ground for new and better values and

ways of living, with benefits to the societies pushing the frontier. To deny exploration is to deny the better instincts of humanity. Besides the social

consequences of a closed frontier, in the final analysis, humanity will either become spacefaring or extinct.

Physiological Factors

No human being has ever traveled into interplanetary space

In 5 decades of manned spaceflight, our understanding of physiological change during long duration missions remains limited

Physiological impacts are significant and varied During the course of a mission: 0-g effects, radiation exposure and

immunological depression Return to Earth: cardiovascular de-conditioning and orthostatic

intolerance* Both in-flight and post-flight physiological issues must be countered

*Orthostatic intolerance (OI) is a disorder of the autonomic nervous system occurring when an individual stands up. OI occurs in humans because standing upright is a fundamental stressor and requires rapid and

effective circulatory and neurologic compensations to maintain blood pressure, cerebral blood flow, and consciousness. When a human stands, approximately 750 mL of thoracic blood is abruptly translocated

downward. People who suffer from OI lack the basic mechanisms to compensate for this deficit.

Primary Stressors in Long Duration Spaceflight

Physiological Factors – Cardiovascular Alterations

Cardiovascular deconditioning poses serious issues both in-flight and post-flight

Zero-g exposure is associated with: Changes in both function and structure of the cardio system Movement of fluid from the lower extremities to the thorax and head Decreases in intravascular volume and arterial pressure Synergistic effects on the heart due to changes in lymphatic, neural and

hormonal control systems Astronauts have experienced significant problems readjusting to

Earth gravity Reconditioning problems tend to grow with increased duration of spaceflight For missions approaching 1.5 years, the implications of cardio deconditioning are

largely unknown Specific effects:

Orthostatic intolerance (hypotension, inability to stand up upon landing) Cardiac Dysrhythmias (long-term zero-g may decrease heart electrical stability,

with possibility of sudden death) Diminished cardiac function (reduction in cardiac mass, along with other aspects

of musculature) Manifestation of previously asymptomatic cardiovascular disease

Physiological Factors – Bone Loss

Normal bone structure Osteoporotic structure

Physiological Factors – Bone Loss

Unloading of both bones and muscles in zero-g causes rapid deterioration of both Average rate ~1.2% by mass per month Rates between 0 and 24% have been observed in Russian

cosmonauts Weight-bearing bones (hips and spine) are most

susceptible Post-flight symptoms in astronauts are comparable to

patients who experience extended periods of bed rest Impaired bone strength in astronauts means increased

risk of fracture, both in-flight and post-flight There is the additional possibility of improper and/or

prolonged healing Osteoporosis associated with age-related bone loss may

also occur at an earlier age

Physiological Factors

Muscle Loss As expected, musculoskeletal unloading also reduces muscle mass Reductions in both mass and performance are manifested – but

deterioration in strength has frequently exceeded mass reduction – suggesting complicated factors

Reduced strength also results in increased fatigability. This becomes very important when sustained level of high performance - such as EVAs – are required.

Space Adaptation Syndrome (SAS) and Neurovestibular Response SAS is the most pronounced effect when going from 1-g to zero-g It is the vestibular system’s lack of ability to distinguish direction SAS prompts the body to act as if it were being poisoned, attempting to

reject toxins (“space sickness”) Onset can be life-threatening if it occurs during critical mission events,

such as EVAs. Typically, most major symptoms abate after ~72 hours of exposure to 0-

g.

Physiological Factors – Radiation Exposure Radiation in space has 3 principal forms;

Galactic Cosmic Rays (GCRs) – high energy protons, alpha particles and heavy nuclei Solar Particle Events (SPEs, called “Solar Flares”) - protons, alpha particles and heavy nuclei Particles trapped in the Earth’s magnetic field (Van Allen belts) – mostly protons and electrons Neutron radiation is also generated when any of the above interacts with metallic walls/shielding

Different types of radiation have different biological effects, even if the same dose rate is absorbed

The International Commission of Radiological Protection developed a set of weighting factors (Relative Biological Effectiveness, REB) for the different kinds of radiation.

The standard units are the Radiation Equivalent Man (rem), or the Sievert (Sv) where 1 sv = 100 rem Radiation exposure can cause damage to human tissue in two ways:

Prompt (i.e., sudden) dosages – causing radiation sickness 0.75 – 2 Sv radiation sickness in 5-50% of patients >3 Svradiation sickness in all patients with 50% fatalities at 4.5 Sv 6 Sv80% fatalities >10 Svessentially no survivers

Chronic dosages – causing malignant cancers

Physiological Factors – Immunological

Immunological suppression have been observed in all human and animal life exposed to 0-g for extended periods Symptoms exhibited by astronauts are similar to those of

Immunosuppressed patients on earth Possible mechanism: Without gravity, viruses and bacteria are more

likely to be carried in air (aerosolization) and to collect on body surfaces Consistent with observed 10-fold increase in flora of the throat and skin

of astronauts Although great efforts are made to clear the air of microflora, the

decrease in the variety of bacteria is accompanied by an increase in number

In-flight respiratory tract infections have occurred Genitourinary infections are a well-documented problem (e.g.

urosepsis in an Apollo crewmember) Without gravity to assist proper urine flow and renal filtration (and

reduction in personal hygene) such infections have a high risk in prolonged 0-g.

Physiological Factors – Summary

Physiological Factors – Summary, continued

Countermeasures – Exercise and Body Loading

So far, exercise has proven to be the most effective means for counteracting physical de-conditioning intrinsic to long term spaceflight At least relative to the “sit tight and fall apart” method!

Exercise time (~2 hrs. per day) and equipment provide: Low-resistance, high-frequency exercise of large muscle groups for cardio

conditioning (aerobic ergometers, treadmills, lower-body negative pressure enclosures

High-resistance, low-frequency exercise for skeletal and muscle loading Psychomotor exercises and active games for neuromuscular coordination

Typical apparatus: Treadmills (elastic ties simulate the pull of gravity) Rowing machines Bicycles (stationary) “space boots” (tested on Mir)

Disadvantages: Mass, volume and power Noise and vibration

However, no amount of exercise has yet been able to counteract the progressive de-conditioning of the human body in zero-gravity!

Countermeasures – Pharmaceutical

Several drugs and hormonal treatments have been shown to decrease both muscular atrophy and bone loss (in earth-analogue studies) Osteoprotegerin (OPG) has been shown to inhibit bone loss due to

both osteoporosis and metastatic bone cancer Other drugs, such as bisphosphates have been shown to increase

bone mass in oseoporotic patients by 10-15% over 3 years – but these also cause severe gastrointestinal distress – thus are problematic for spaceflight conditions

The use of pharmaceuticals in spaceflight is potentially problematic. Significant interactive physiological changes occur during long-duration spaceflight – and consequently, astronauts cannot necessarily be expected to respond as expected to drugs used in treatment of similar conditions on Earth

Countermeasures – Artificial Gravity

Artificial gravity is perhaps the most promising – and paradoxically the least studied – method for countering the physiological issues of human spaceflight. The impact of many issues can be reduced or even eliminated by creating artificial accelerations that simulate gravitational forces.

The most realistic method of generating artificial gravity is by rotating space habitats, in whole or part.

The centripital acceleration , c, is related to the angular velocity, , and the radius of spin, r, by:

c = 2r

Rotating structures subject humans to both linear gravity-like forces and Coriolis forces, which can prove disorienting at high spin rates

Countermeasures – Artificial Gravity

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Artificial gravity becomes more “normal” with increasing radius

Psychological and Social Issues – Primate behavior under prolonged, severe stress (see References 4,5)

Illustrated most dramatically by African ape behavior studied by anthropologists Usually live in trees where they are well protected But in times of scarcity, they migrate to other forested areas. This involves

extended treks across open savanna where they are extremely vulnerable to predators.

After several days without an attack the apes begin to attack and kill each other. It is theorized that the long periods of physiological mobilization (“fight or flight” response) due to fear of attack ultimately overrides the apes’ inherently altruistic nature.

In human beings, as in most primates, the sympathetic nervous system is responsible for mobilizing the body for action in the face of a threat to survival (fighting or fleeing). When a threatening situation is prolonged and never resolved, the human sympathetic nervous system remains essentially engaged. There are many examples of prolonged stress triggering apparently random or

unprovoked violence

Psychological and Social Issues – Human behavior under prolonged, severe stress

Destructive (and self-destructive) moods and behaviors tend to emerge under very certain conditions: Pervasive, unrelenting threatening situation from which there is no escape, Combined with with long periods of boredom The condition of isolation only amplifies the perception of inescapability (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 ultimately takes a substantial toll on all concerned

Experiences aboard the Mir: 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…..

Psychological and Social Issues – Human behavior under prolonged, severe stress and isolation

This state of constant alarm resembles a milder version of 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.

Common side effects of long-term isolation and confinement include: Inattentiveness, Mood instabilities, Sleep disturbance, Perceptual distortions including fugue states

Psychological and Social Issues –Compatibility

Biosphere 2 data: 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. Russian experience in space:

On three occasions over a 20-year period a spaceflight had to be terminated due to psychological reasons

On long flights, initial excitement gives way to exhaustion, insomnia, and irritability. Cosmonauts may tend to withdraw and speak in a monotone

Submariner experience: There are three stages that emerge during long -term voyages:

Stage 1: Excitement and anxiety, Stage 2: Boredom and depression, and Stage 3: Increased aggressiveness and emotional outbursts— “third quarter phenomenon”.

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.

Psychological and Social Issues – Crew Composition

There is a wealth of psychological research regarding the evolution and manifestation of maladaptive behavior stemming from dysfunctional family relationships. A person acquires specific coping strategies in childhood that were tailored to

suit his or her immediate environment. Behaviors that served 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.

In summary, managing stress on long-term flights involves: Crew compatibility since 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. Supportive countermeasures (both on board and on the ground)

Psychological and Social Issues –Space Architecture

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.

The structure must protect against the space environment Radiation shielding, life support system integrity, and reliability Aesthetics, noise control, and efficient waste management are also major

considerations. Privacy is another important concern. People with different cultural

backgrounds may vary widely with respect to privacy needs. 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” increases as a function of the duration of the mission.

Habitable volume refers to the usable living space. According to NASA, 17 cubic meters/person (a 2.6m cube!) is optimal for a six-

month journey. Disorientation: The same corridor on the space station can appear

completely different depending on your choice of the “floor”. Coloring the walls or providing visual cues that suggest a gravity field orientation can be helpful.

References

1. G. Bonin, “Physiological issues in Human Space Flight: Review and Proposed Countermeasures” MAAE 4906/Mech 5801: Biomedical Engineering and Biomechanics, Dec. 2005

2. Wiley J. Larson and Linda K. Pranke, ed. “Human Spaceflight: Mission Analysis and Design”,MacGraw-Hill Inc. 2005.

3. Lawrence J. Prinzel III, “Research on Hazardous States of Awareness and Physiological Factors in Aerospace Operations”, NASA Technical Memorandum 2002-211444. 2002.

4. J. Putman, “Human factors and the new Vision for Space Exploration”. December 12, 2005 http://www.thespacereview.com/article/515/2

5. M.Ephimia Morphew, “Psychological and Human Factors in Long Duration Spaceflight”, MJM 2001 6: 74-80, 2001