Human Factors in Prolonged
Space Flight
AE 426, Lecture 4
Outline
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Physiological Issues
Psychological and Social Factors
Space Architecture and Habitability
Physiological Factors
See References 1-3
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Space is the harshest environment humans have been subjected to,
with many physiological challenges. But these can be overcome,
provided that…
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First priority: A sustainable rationale for human space exploration
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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
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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
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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
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Cardiovascular deconditioning poses serious issues both in-flight
and post-flight
Zero-g exposure is associated with:
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Astronauts have experienced significant problems readjusting to
Earth gravity
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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
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:
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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
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Unloading of both bones and muscles in zero-g causes
rapid deterioration of both
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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
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Muscle Loss
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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.
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Space Adaptation Syndrome (SAS) and Neurovestibular Response
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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 0g.
Physiological Factors – Radiation Exposure
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Radiation in space has 3 principal forms;
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Different types of radiation have different biological effects, even if the same dose rate is
absorbed
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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
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:
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Prompt (i.e., sudden) dosages – causing radiation sickness
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0.75 – 2 Sv radiation sickness in 5-50% of patients
>3 Svradiation sickness in all patients with 50% fatalities at 4.5 Sv
6 Sv80% fatalities
>10 Svessentially no survivers
Chronic dosages – causing malignant cancers
Physiological Factors – Immunological
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Immunological suppression have been observed in all human and
animal life exposed to 0-g for extended periods
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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
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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
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In-flight respiratory tract infections have occurred
Genitourinary infections are a well-documented problem (e.g.
urosepsis in an Apollo crewmember)
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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
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So far, exercise has proven to be the most effective means for
counteracting physical de-conditioning intrinsic to long term
spaceflight
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At least relative to the “sit tight and fall apart” method!
Exercise time (~2 hrs. per day) and equipment provide:
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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
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Typical apparatus:
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Disadvantages:
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Treadmills (elastic ties simulate the pull of gravity)
Rowing machines
Bicycles (stationary)
“space boots” (tested on Mir)
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
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Several drugs and hormonal treatments have been shown to
decrease both muscular atrophy and bone loss (in earthanalogue studies)
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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
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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
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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
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Rotating structures subject humans to both linear gravity-like forces and
Coriolis forces, which can prove disorienting at high spin rates
Countermeasures – Artificial Gravity
Onset of
motion
sickness
Comfort
zone
4 rpm
Artificial gravity
becomes more “normal”
with increasing radius
Psychological and Social Issues – Primate behavior under prolonged,
severe stress (see References 4,5)
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Illustrated most dramatically by African ape behavior studied
by anthropologists
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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.
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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.
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There are many examples of prolonged stress triggering apparently random or
unprovoked violence
Psychological and Social Issues – Human behavior under prolonged,
severe stress
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Destructive (and self-destructive) moods and behaviors tend to
emerge under very certain conditions:
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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.
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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
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This state of constant alarm resembles a milder version of posttraumatic 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:
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Depression,
Insomnia,
Attentional deficits,
Mood instabilities and, ultimately,
Immune system irregularities and physical illness.
Common side effects of long-term isolation and confinement include:
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Inattentiveness,
 Mood instabilities,
 Sleep disturbance,
 Perceptual distortions including fugue states
Psychological and Social Issues –Compatibility
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Biosphere 2 data:
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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.
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Russian experience in space:
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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
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Submariner experience: There are three stages that emerge during long -term
voyages:
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Stage 1: Excitement and anxiety,
Stage 2: Boredom and depression, and
Stage 3: Increased aggressiveness and emotional outbursts— “third quarter phenomenon”.
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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.
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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
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There is a wealth of psychological research regarding the evolution
and manifestation of maladaptive behavior stemming from
dysfunctional family relationships.
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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.
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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.
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In summary, managing stress on long-term flights involves:
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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
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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
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Radiation shielding, life support system integrity, and reliability
 Aesthetics, noise control, and efficient waste management are also major
considerations.
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Privacy is another important concern. People with different cultural
backgrounds may vary widely with respect to privacy needs.
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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 sixmonth journey.
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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.
2.
3.
4.
5.
G. Bonin, “Physiological issues in Human Space Flight: Review and Proposed
Countermeasures” MAAE 4906/Mech 5801: Biomedical Engineering and Biomechanics,
Dec. 2005
Wiley J. Larson and Linda K. Pranke, ed. “Human Spaceflight: Mission Analysis and
Design”,MacGraw-Hill Inc. 2005.
Lawrence J. Prinzel III, “Research on Hazardous States of Awareness and Physiological
Factors in Aerospace Operations”, NASA Technical Memorandum 2002-211444. 2002.
J. Putman, “Human factors and the new Vision for Space Exploration”. December 12, 2005
http://www.thespacereview.com/article/515/2
M.Ephimia Morphew, “Psychological and Human Factors in Long Duration Spaceflight”,
MJM 2001 6: 74-80, 2001