3

Health Risks

In considering the ethics issues that will emerge when making decisions about sending humans into harm’s way on long duration and exploration spaceflights, the committee decided to examine some of the health risks that illustrate key ethical challenges and tensions in risk and decision making. It is important to note that the stressors and health risks may vary from mission to mission, depending on the remoteness of the destination and many other factors. For example, missions to locations that will require months to years to return to Earth can have fundamentally different stressors than destinations that are closer but may involve being in space for long periods of time. Although the phrase “long duration and exploration spaceflights” is used throughout the report, the committee acknowledges that the health risks may vary widely between missions.

These examples are meant to illustrate the diversity of risks and, therefore, highlight some of the ethics quandaries arising in decisions regarding uncertain risks, unknowns about the extent of individual variations, and long-term health implications for astronauts. In addition, the examples also demonstrate the range of risk management strategies that are being employed by or considered by the National Aeronautics and Space Administration (NASA), international partners, and commercial companies to prevent, mitigate, or treat these risks to human health. The following sections are brief overviews of the complex issues relevant to:

  • the risk of loss of life due to mission operations,
  • vision impairment risks,
  • behavioral health and performance risks,


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3 Health Risks In considering the ethics issues that will emerge when making deci- sions about sending humans into harm’s way on long duration and explo- ration spaceflights, the committee decided to examine some of the health risks that illustrate key ethical challenges and tensions in risk and deci- sion making. It is important to note that the stressors and health risks may vary from mission to mission, depending on the remoteness of the destination and many other factors. For example, missions to locations that will require months to years to return to Earth can have fundamental- ly different stressors than destinations that are closer but may involve being in space for long periods of time. Although the phrase “long dura- tion and exploration spaceflights” is used throughout the report, the committee acknowledges that the health risks may vary widely between missions. These examples are meant to illustrate the diversity of risks and, therefore, highlight some of the ethics quandaries arising in decisions regarding uncertain risks, unknowns about the extent of individual varia- tions, and long-term health implications for astronauts. In addition, the examples also demonstrate the range of risk management strategies that are being employed by or considered by the National Aeronautics and Space Administration (NASA), international partners, and commercial companies to prevent, mitigate, or treat these risks to human health. The following sections are brief overviews of the complex issues relevant to: • the risk of loss of life due to mission operations, • vision impairment risks, • behavioral health and performance risks, 45

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46 LONG DURATION AND EXPLORATION SPACEFLIGHT • bone demineralization, and • radiation exposure. MISSION OPERATIONS RISKS Although there have been many successful space missions over the past 50 years, the substantial risks undertaken by astronauts are most ev- ident in documented “near misses” and tragic losses of life. During the Apollo 11 mission, Neil Armstrong piloted a lunar module to the Moon’s surface, landing with less than 30 seconds worth of fuel remaining (Garber and Launius, 2005). Apollo 12 was struck by lightning at ap- proximately 36 and 52 seconds after launch, momentarily shutting down the electrical power (Molloy and Petrone, 2013). During the Apollo 13 mission, an oxygen tank exploded while en route to the Moon, and ground crews and astronauts had to improvise to safely return the crew to Earth (Garber and Launius, 2005). The 1997 collision of a resupply vehi- cle, as well as a fire, jeopardized the lives of crew members aboard the Mir Space Station (NASA, 2014b). In 1967, a cabin fire in an Apollo capsule during a launch pad test in Cape Canaveral, Florida, killed three astronauts.1 Over the course of the NASA space program, 24 crew mem- bers have lost their lives in the line of duty, including the 14 individuals aboard the space shuttles Challenger and Columbia, the Apollo 1 astro- nauts, and 5 individuals who died in training-jet crashes (NASA, 2014a). Due to the nature of the propulsion systems needed to launch, the dis- tance from Earth, the immediacy of some inflight catastrophes and the challenges of landing, options for rescue operations are limited. The probability of loss of crew due to a catastrophic vehicle accident is generally higher and accompanied by greater uncertainty in early expe- rience with new crew delivery vehicles. As experience is gained through effective use of continuous risk management systems, the expected re- sults are decreased risk and less uncertainty, although risks remain high. Thus, for example, the probabilistic risk assessment for loss of crew and vehicle on the first shuttle flight was 1/10 versus 1/90 on the 135th shut- 1 On January 27, 1967, the crew of Roger B. Chaffee, Virgil “Gus” Grissom, and Edward H, White, Jr., were killed in a fire that spread quickly in a pure oxygen environ- ment; the astronauts had no opportunity to open the hatch (Garber and Launius, 2005; Williams, 2011).

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HEALTH RISKS 47 tle flight (Behnken et al., 2013). The shuttle mission aggregate risk of loss of crew and vehicle was approximately 1/46 (Behnken et al., 2013). The risks of the loss of the crew and vehicle during a spaceflight mission are calculated to allow comparisons of different approaches and platforms using probabilistic risk assessments. NASA provides detailed briefings for astronaut candidates on mission risks. Comparisons are made in this briefing to the risk of death in other high-risk occupations and to catastrophic events and combat. Astronauts who provided infor- mation to the committee emphasized the thorough and ongoing nature of communication throughout their careers regarding risks. VISION IMPAIRMENT Vision impairment represents a newly identified health risk and ex- emplifies how NASA approaches a new risk in the current risk manage- ment framework. The potential for vision changes has both acute and long-term implications for the astronaut and for current and future missions. Overview and Risk Identification Although astronauts have reported vision changes during spaceflight for more than 40 years (Alexander et al., 2012), these were assumed to be transient and isolated. With the Mir Space Station and the Internation- al Space Station (ISS), longer tours of duty became possible. A Mir tech- nical report from 2008 described disc edema in 8 of 16 cosmonauts on landing, with one magnetic resonance imaging (MRI) report showing signs suggestive of intracranial hypertension (as cited in Alexander et al., 2012). The spaceflight environment on Mir was noted to be similar to the ISS. More significant and lasting visual changes have occurred in astro- nauts on the ISS and have been documented in published case reports (Mader et al., 2011). These changes were primarily a shift toward hyper- opia (far-sightedness). Scotomas (blind spots in the visual field) were also reported. One astronaut reported that he needed to shift his head to compensate for scotoma when reading instruments during the mission (Alexander et al., 2012). In a group of astronauts examined pre- and postflight, clinicians observed flattening of the eyeball globe using ultra- sound and MRI, supporting the hyperopic shift, edema of the optic nerve, and changes of the optic fundus noted on examination (Mader et al., 2011). In this discussion of the detailed findings on seven astronauts after

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48 LONG DURATION AND EXPLORATION SPACEFLIGHT spaceflight, the results are presented in an “unattributable” manner and do not include dates or missions to preserve privacy and confidentiality (Mader et al., 2011). Refractive changes have persisted after return to Earth for these astronauts. Upon identifying the vision-related issues, NASA rapidly imple- mented pre- and postflight ocular testing protocols and convened a Papilledema Summit in July 2009 to bring together experts in space med- icine and terrestrial analogs and to suggest avenues for research (Watkins and Barr, 2010). The summit examined potential physiological causes of the vision alterations and suggested changes in preflight, inflight, and postflight testing. Because the optic changes bore a striking similarity to those seen with elevated intracranial pressure (i.e., papilledema), this hypothesis was the first to be extensively explored (Alexander et al., 2012). Lumbar puncture has been performed on four U.S. astronauts (at single intervals ranging from 12 to 60 days after flight), and opening pressures were found to be elevated in two individuals and borderline in the other two (Alexander et al., 2012). Other hypotheses regarding causes of vision alterations include elevated carbon dioxide in the ISS atmosphere, in- creased sodium content of the astronaut diet, fluid shifts due to increases in resistance exercises, radiation exposure, and individual susceptibility (Alexander et al., 2012). Since 1989, as part of postflight eye examinations, U.S. astronauts have been asked about improvements or degradations in their distant or near vision. Compilation of that information on 300 U.S. astronauts who had flown in space found that approximately 29 percent of shuttle astro- nauts and 60 percent of ISS astronauts noted a degradation in distant and near visual acuity, and some of these changes remained unresolved years after flight (Mader et al., 2011). With the exception of the report from Mir previously cited, data from international partners are lacking. Risk Management: Clinical Practice Guidelines, Surveillance, and Research NASA is monitoring vision changes and intracranial pressure, and research efforts in this area are fully under way. NASA has developed clinical practice guidelines for treatment of astronauts with postflight refrac- tive changes, which include a classification system from class 0 (least severe) through class 4 (most severe) based on the results of imaging studies

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HEALTH RISKS 49 and indicating the follow-up testing and monitoring that are required (Alexander et al., 2012). In 2012, the NASA Human Research Program released the evidence report Risk of Spaceflight-Induced Intracranial Hypertension and Vision Alterations, which summarizes research evidence and raises questions for future study (Alexander et al., 2012). Current research efforts are ex- ploring ground-based analogs and include studies of normal individuals in supine and head-down bed rest, hind-limb-suspended rodent models, and various pathologic situations in which elevated intracranial hyperten- sion and papilledema occur. The evidence report details four major gaps requiring future research: • Etiological mechanisms and contributing risk factors for ocular structural and functional changes seen inflight and postflight; • Validated and minimally obtrusive diagnostic tools to measure and monitor changes in intracranial pressure, ocular structure, and ocular function; • Ground-based analogs and/or models to simulate the spaceflight- associated visual impairment and increased intracranial pres- sures; and • Preventive and treatment measures to mitigate changes in ocular structure and function and intracranial pressure during space- flight (Alexander et al., 2012). Individual Variation Issues As with many health risks, individual factors (including, but not lim- ited to, age and sex) may account for some of the variability in manifes- tation of vision and ocular alterations. The evidence report on this risk concludes with this statement, “In summary, 15 long-duration male as- tronauts ranging in age from 45 to 55 years have experienced confirmed inflight and postflight visual and anatomical changes” (Alexander et al., 2012, p. 87). Health Standards and Risk Profile A NASA health standard has not yet been developed for vision im- pairment and increased intracranial pressure and the extent, if any, to which these are linked is not fully known (IOM, 2014). At present, this

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50 LONG DURATION AND EXPLORATION SPACEFLIGHT risk is listed as “unacceptable” on the Human Research Roadmap (see Table 2-2) for missions to the ISS for 12 months, to a near-Earth aster- oid, or to Mars, and “insufficient data” for a lunar mission (NASA, 2013). Issues for Long Duration and Exploration Spaceflights In 2013, Mader and colleagues reported on a single astronaut who was carefully studied after two long-duration missions, documenting progressive vision changes associated with repeat spaceflight, raising concerns that changes occurring during the first flight “may have set the stage for recurrent or additional changes when the astronaut was subject- ed to physiological stress of repeat space flight” (Mader et al., 2013, p. 249). The prevalence and severity of the observed visual changes raised significant concerns about the ability of an affected pilot to successfully land a spacecraft. This is an active area of research with many remaining unknowns that could affect future crew selection, mission success, and astronaut health. Ethics issues raised by this example focus on how best to address uncertainty and unknowns including determinations of long-term respon- sibilities for monitoring, preventing, and treating the health condition moving forward. Issues of individual susceptibility are still being deter- mined, but this example points to the importance of diverse participation, including women, to obtain population-based information (as all exam- ples to date of vision problems have occurred in men). BEHAVIORAL HEALTH AND PERFORMANCE RISKS NASA has identified three categories of behavioral health and perfor- mance risks associated with long duration and exploration spaceflight: (1) adverse behavioral conditions and psychiatric disorders; (2) performance errors due to fatigue resulting from sleep loss, circadian desynchronization, extended wakefulness, and work overload; and (3) performance decre- ments due to inadequate cooperation, coordination, communication, and psychosocial adaptation within a Team Gap (Schmidt et al., 2009; Slack et al., 2009; Whitmire et al., 2009).

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HEALTH RISKS 51 Overview and Risk Identification Much of the evidence regarding behavioral health risks associated with long duration spaceflight is derived from anecdotal evidence (Aldrin, 1973; Lebedev, 1988; Burrough, 1998; Linenger, 2000), archiv- al and observational data collected during spaceflight (Kanas et al., 2007; Stuster, 2010), and observational and experimental studies conducted in analog settings, such as polar expeditions (Gunderson, 1974; Sandal et al., 1996; Palinkas and Suedfeld, 2008), submarines (Tansey et al., 1979; Sandal et al., 1999; Thomas et al., 2000), and space simulations (Gushin et al., 1996; Sandal, 2001; Basner et al., 2013). The Mars 500 study, with participants from four nations, was a 17-month isolation experiment in preparation for a mission to Mars (ESA, 2011). While the reported incidence of behavioral health problems encoun- tered during spaceflight has been quite low, the actual incidence may be underestimated due to a reluctance of astronauts to report them (IOM, 2001; Shepanek, 2005). Billica (2000) reported a 2.86 per person-year incidence of such problems among the 508 crew members who flew on 89 space shuttle missions between 1981 and 1989. The most common behavioral symptoms reported by crew members were anxiety and irrita- bility. Data collected for 28.84 person-years of NASA spaceflight identi- fied 24 cases of anxiety, for an incidence rate of 0.832 cases per person- year (Slack et al., 2009). No behavioral emergencies have been reported to date (Slack et al., 2009). Studies in analog settings have reported much higher rates of behav- ioral health problems, reflecting longer periods of isolation and confine- ment and differences in crew member characteristics. For example, the incidence of behavioral health problems after extended stays in Antarcti- ca was estimated in one study at 5.2 percent (Palinkas et al., 2004). A number of factors may contribute to the risk of behavioral health and sleep problems in space, including mission duration (Slack et al., 2009), disruption of sleep and circadian rhythms (Czeisler et al., 1986; Dinges et al., 1997), physiological changes that occur in microgravity, workload, lack of social and environmental stimulation, cultural and organizational factors, family issues, and personality characteristics (Gunderson, 1974; McFadden et al., 1994; Rose et al., 1994; NRC, 1998; Rosnet et al., 2000). For the ISS, both observational (i.e., Stuster, 2010) and anecdotal evidence indicate that the crew has been successful at thriving.

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52 LONG DURATION AND EXPLORATION SPACEFLIGHT Risk Management: Countermeasures and Research Analog and other types of studies have identified measures that can prevent or mitigate behavioral health, sleep impairment, and cognition risks. Countermeasures that have been successfully implemented for ISS operations include working with ground control regarding scheduling, support services from operational psychology personnel, multiple layers of accountability when conducting critical tasks, and education for ground crews (Flynn, 2005; Slack et al., 2009). Existing techniques for monitoring crew behavioral health and providing social and psychologi- cal support also have proved effective on the ISS. However, it is un- known whether the effectiveness of these countermeasures can be maintained over longer periods and at greater distances from Earth where delays in communication, delivery of services, and implementation of countermeasures will occur. Policies designed to minimize fatigue, indi- vidual stress, and interpersonal tension, such as allocated “time off,” will be critical to preserving and promoting the behavioral health of astronaut personnel. Astronauts also train in analog environments (including Antarctica, the underwater NASA Extreme Environment Mission Operations [NEEMO], and winter and mountain survival programs). The training environments include both physical capabilities and problem resolution involving group dynamics. The National Research Council (NRC) Committee for the Decadal Survey on Biological and Physical Sciences in Space noted that “contin- ued research is required to identify individual, interpersonal, cultural, and environmental determinants of crew cohesion, crew performance, and ground-crew interaction” (NRC, 2011, p. 89). Such research may lead to greater specificity of behavioral health standards. The NASA Human Research Program is working on addressing research gaps in this area (see Box 3-1). BOX 3-1 NASA Human Research Program’s Research Gaps Behavioral Health and Performance Risks BMed 1: What are the most effective methods to enhance behavioral health and prevent decrements before, during, and after spaceflight missions?

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HEALTH RISKS 53 BMed 2: What are the most effective methods to predict, detect, and as- sess decrements in behavioral health (which may negatively affect per- formance) before, during, and after spaceflight missions? BMed 3: What aspects, if any, of cognitive performance change in-flight? If there are changes, do they persist post mission? If so, for how long? BMed 4: What are the most effective methods for detecting and assessing cognitive performance during exploration missions? BMed 5: What individual characteristics predict successful adaptation and performance in an isolated, confined, and extreme environment, espe- cially for long-duration missions? BMed 6: What are the most effective methods for treating the individual to remedy behavioral health problems during spaceflight missions (includ- ing behavioral health meds)? BMed 7: What are the most effective methods for modifying the environ- ment to prevent and remedy behavioral health problems during space- flight missions? BMed 8: How do family, friends, and colleagues affect astronauts’ behav- ioral health and performance before, during, and after spaceflight? Team Gap Risks Team Gap 1: We need to understand the key threats, indicators, and life cycle of the team for autonomous, long duration, and/or distance explo- ration missions. Team Gap 2: We need to identify a set of validated measures, based on the key indicators of team function, to effectively monitor and measure team health and performance fluctuations during autonomous, long du- ration, and/or distance exploration missions. Team Gap 3: We need to identify a set of countermeasures to support team function for all phases of autonomous, long duration, and/or dis- tance exploration missions. Team Gap 4: We need to identify psychological measures that can be used to select individuals most likely to maintain team function for au- tonomous, long duration, and/or distance exploration missions. Team Gap 5: We need to identify validated ground-based training meth- ods that can be both preparatory and continuing to maintain team func- tion in autonomous, long duration, and/or distance exploration missions. Team Gap 6: We need to identify methods to support and enable multiple distributed teams to manage shifting levels of autonomy during long du- ration, and/or distance exploration missions. Team Gap 8: We need to identify psychological and psychosocial factors, measures, and combinations thereof that can be used to compose high- ly effective crews for autonomous, long duration, and/or distance explo- ration missions. Team Gap 9: We need to identify spaceflight acceptable thresholds (or ranges) of team function, based on key indicators, for autonomous, long duration, and/or distance exploration missions.

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54 LONG DURATION AND EXPLORATION SPACEFLIGHT Sleep and Cognition Risks Sleep Gap 1: We need to identify a set of validated and minimally obtru- sive tools to monitor and measure sleep-wake activity and associated performance changes for spaceflight. Sleep Gap 2: We need to understand the contribution of sleep loss, circa- dian desynchronization, extended wakefulness and work overload, on individual and team behavioral health and performance (including oper- ational performance), for spaceflight. Sleep Gap 4: We need to identify indicators of individual vulnerabilities and resiliencies to sleep loss and circadian rhythm disruption, to aid with individualized countermeasure regimens, for autonomous, long du- ration, and/or distance exploration missions. Sleep Gap 5: We need to identify environmental specifications and opera- tional regimens for using light to prevent and mitigate health and per- formance decrements due to sleep, circadian, and neurobehavioral disruption, for flight, surface and ground crews, during all phases of spaceflight operations. Sleep Gap 6: We need to identify how individual crew members can most ef- fectively and safely use medications to promote sleep, alertness, and circa- dian entrainment, as needed during all phases of spaceflight operations. Sleep Gap 8: We need to develop individualized scheduling tools that predict the effects of sleep-wake cycles, light and other countermeas- ures on performance, and can be used to identify optimal (and vulnera- ble) performance periods during spaceflight. Sleep Gap 9: We need to identify an integrated, individualized suite of countermeasures and protocols for implementing these countermeas- ures to prevent and/or treat chronic partial sleep loss, work overload, and/or circadian shifting, in spaceflight. Sleep Gap 10: We need to identify the spaceflight environmental and mis- sion factors that contribute to sleep decrements and circadian misa- lignment, and their acceptable levels of risk. NOTE: Team Gap 7 merged with Team Gap 3. Sleep Gap 3 is closed. Sleep Gap 7 merged with Sleep Gap 2. SOURCE: NASA, 2014c. Individual Variation Issues Several studies have pointed to phenotypic and genotypic variations to sleep disruption and its behavioral consequences (Van Dongen et al., 2004; Landholt, 2008; Kuna et al., 2012), suggesting the identification of predictive biomarkers (Czeisler, 2011) that could prove useful in identi- fying astronauts likely to experience sleep-related performance decre- ments and for managing sleep-wake regulation during exploration spaceflight (Goel and Dinges, 2012).

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HEALTH RISKS 55 Individual characteristics identified as predictors of social compati- bility in analog studies and surveys of astronaut personnel include low extraversion and high introversion (Palinkas and Suedfeld, 2008), high positive instrumentality (goal oriented, active, self-confident) and ex- pressiveness (kind, aware of others’ feelings), and low negative instru- mentality (arrogant, hostile, boastful, egotistical) and communion (self- subordinating, subservient, unassertive) (McFadden et al., 1994; Rose et al., 1994). Crew heterogeneity with respect to social (e.g., age, sex, cultural background), psychological (need for achievement, aggressiveness, au- tonomy), and other characteristics (e.g., interest in leisure activities) also predicts crew cohesion and conflict, Team Gap decision making, and re- sponse to crisis (NRC, 1998, 2011; Kanas and Manzey, 2008; Kanas et al., 2009). Health Standards and Risk Profile According to NASA’s Human Research Roadmap, the research rat- ings for risk of adverse behavioral conditions and psychiatric disorders has been determined to be “Controlled” for the ISS and lunar missions, “Acceptable” for near-Earth asteroid missions, and “Unacceptable” for the Mars design reference mission (see Table 2-2) (NASA, 2013). The risk of fatigue-related performance errors is considered “Controlled” for all four design reference missions. The research rating for the third risk related to Team Gap issues is currently listed as “Controlled” for the lu- nar design reference mission and “Acceptable” for the ISS, near-Earth asteroid, and Mars missions. For a mission to a near-Earth asteroid or Mars, mission duration and distance from Earth are among the major stressors. A NASA health standard for behavioral health and perfor- mance has been developed that addresses all of these risks (see Box 2-1). Cognitive and psychiatric assessments and screening criteria are used in the initial astronaut selection process and in the annual astronaut re- certification medical examinations. Furthermore, processes have been developed by the ISS partner agencies that detail neurocognitive and be- havioral health baseline assessments and follow-up. Issues for Long Duration and Exploration Spaceflights Few established policies regarding limits to long-duration isolation and confinement exist. The National Science Foundation’s Division of

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64 LONG DURATION AND EXPLORATION SPACEFLIGHT ginally effective at reasonable thicknesses; increasing the thickness of the shielding adds substantial mass with minimal additional reduction in exposure (NRC, 2008). Innovative approaches to reduce the risks also are being investigated, including pharmacological countermeasures. To date, these methods have not been shown to be effective. Thirty-day exposure limits have been established to limit the poten- tial for acute health outcomes due to radiation exposure, and operational processes and procedures are implemented to ensure that astronauts do not approach these limits. The greatest likely source of acute exposure is solar storms. Providing access to modest shielding and a system for time- ly warning of a pending or ongoing storm are critical elements of a risk management strategy to mitigate this risk (NRC, 2008). Pre-mission planning includes estimates of the radiation exposure to minimize the risk that the crew will exceed the career limits (with consideration of the crew member’s prior exposure). Radiation exposures also may include risks of chronic, degenerative effects that could affect health during a lengthy mission. Only recently has quantitative progress been made in understanding these risks, par- ticularly those affecting the central nervous and circulatory systems (Cucinotta et al., 2013b). An ongoing research effort is under way to im- prove this understanding. Health Standards and Risk Profile NASA has long recognized the threat of radiation, and has estab- lished space permissible exposure limits to protect its astronauts (see Box 2-1). The three tiers of radiation exposure limits in the NASA standards address: career limits, designed to limit the lifetime risk of exposure- induced death from cancer; short-term limits, designed to limit the risk of acute affects; and operational processes and procedures which emphasize that “in-flight radiation exposures shall be maintained using the ‘as low as reasonably achievable’ (ALARA) principle” (see Box 2-1; NASA, 2007, p. 20). Radiation limits are significant in planning for long duration and ex- ploration missions. Existing radiation standards, developed for the Space Shuttle and the ISS, would limit missions to durations of 150 to 250 days (Cucinotta et al., 2013a). The radiation standards are written to apply to all NASA human spaceflight missions and are not developed for any specific program (NASA, 2007). However, while some of the existing programs, such as the Space Shuttle and the ISS programs, can be con-

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HEALTH RISKS 65 ducted within the standards, these standards impose potential limitations on long-duration missions (e.g., a 1-year stay on the ISS) or missions with architectures and objectives outside of LEO. The standards are based on recommendations to NASA from NCRP in a report that focused on LEO missions (NCRP, 2000). The NCRP report noted, “In this Re- port, the guidance is also only intended to be applied for radiation expo- sures incurred during missions in LEO” (NCRP, 2000, pp. 2-3). Individual Variation Issues A specific individual’s cancer risks vary by age, sex, and race, as well as genetic factors and life-style choices. National databases allow calculation by age, sex, and other factors, emphasizing the role of indi- vidual variability. NASA’s standards limit the additional risk of cancer posed by radiation exposure, not the total risk of dying from cancer. If one assumes a generic baseline lifetime risk of 23 percent for males and 19 percent for females (ACS, 2013), and leaves aside any differences in individual susceptibility, then male astronauts exposed to the 3 percent radiation exposure limit would have an estimated lifetime risk of death from cancer of 26 percent, while female astronauts would have an esti- mated risk of 22 percent. In general, for females the effective-dose radiation exposure is about three quarters that of males before reaching career limits (NASA, 2007). Females, on average, are more susceptible to radiation-induced cancer, in part because of the baseline higher risk of breast cancer in females; body size also is a factor as individuals with smaller builds have less body self-shielding. However, an individual’s risk of cancer is dominated by a number of factors (including genetic susceptibility, lifestyle choices, and prior exposures, both natural and medical), most of which may be highly individualized or unknown and, therefore, not currently possible to factor in calculations of cancer risk. Issues for Long Duration and Exploration Spaceflights As noted above, the number of days that astronauts could be exposed and stay within the current permissible exposure limits (safe days) will depend on assumptions about shielding and the radiation environment. The exposure varies with the 11-year solar cycle and with the number and intensity of solar storms (Cucinotta et al., 2013a). The existing radia- tion exposure limits would limit long duration or exploration missions to

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66 LONG DURATION AND EXPLORATION SPACEFLIGHT 150 to 250 days (Cucinotta et al., 2013a). The estimated time in the zero- g interplanetary environment (“deep space”)4 for a Mars mission with current propulsion systems is estimated at 400 to 600 days (NASA, 2009). The design reference missions to Mars that are being considered include those that would include a long stay on the Martian surface (500 or more days) with a shorter stay in deep space, as well as those that would have a longer deep space duration and shorter Mars surface stays, nominally 30 to 90 days (NASA, 2009). Technology research into alter- native propulsion systems could significantly reduce the Mars transit time (NRC, 2012b). Other factors also could affect the number of safe days in space with regard to radiation exposure. For example, noting that astronauts, in gen- eral, are healthier than the average U.S. population, NASA recently cal- culated the number of safe days in space using the data on cancer risks for non-smoking, normal weight Americans (see Table 3-1). This change in the population data increases the estimates of safe days in space by 30 to 90 percent, depending on an astronaut’s age and sex (Cucinotta et al., 2013a). The NASA current precautionary decision to set exposure limits to protect astronauts with 95 percent probability (given the level of uncer- tainty) itself limits the number of safe days in space. If a less precaution- ary approach were taken by NASA using a lower confidence interval, the number of allowable days in space would be greater; alternatively, if greater precaution were exercised by using a higher confidence interval, fewer days would be permissible. More precise information about the dose of radiation-inducing fatal cancers could also change the number of permissible days in space that would not exceed the health standard. Ethics issues raised in the consideration of radiation exposure in- clude informed decision making by astronauts, individual variation and other factors that might impact crew selection, and assessing and balanc- ing the unknown risks of radiation exposure with other risks and benefits of the mission. While NASA has analyzed health risks of radiation based on age and sex (see Table 3-1), other factors influencing individual varia- tion and radiation risk must also be considered. Existing data on such variation should be factored into analyses, and new data should be col- lected to better predict individual risk from exposure to radiation. 4 Calculations regarding radiation exposure factor in the higher exposures to radiation in interplanetary space outside Earth’s magnetosphere and the relatively lower exposure levels on a planetary or lunar surface.

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HEALTH RISKS 67 TABLE 3-1 Estimates of Safe Days in Deep Spacea Average solar maximum GCR and one significant solar storm (similar to that which occurred Average solar minimum GCR in August 1972) Age at NASA 2012 NASA 2012 NASA 2012 Exposure U.S. Average NASA 2012 U.S. Average Never- (years) Population Never-smokers Population smokers Males 35 209 (205) 271 (256) 306 (357) 395 (458) 45 232 (227) 308 (291) 344 (397) 456 (526) 55 274 (256) 351 (335) 367 (460) 500 (615) Females 35 106 (95) 187 (180) 144 (187) 276 (325) 45 139 (125) 227 (212) 187 (232) 319 (394) 55 161 (159) 277 (246) 227 (282) 383 (472) NOTE: Solar minimum is a 2- to 3-year period of low solar activity in the 10- to 11-year solar cycle. Solar maximum is a corresponding 5- to 7-year period of enhanced solar activity. Galactic cosmic radiation is at a peak during solar minimum and somewhat reduced during solar maximum. Values in parentheses for solar minimum are for the deep solar minimum of 2009. Values in paren- theses for solar maximum are for the case where a storm shelter is available to reduce the solar storm exposure to a negligible amount. GCR = galactic cosmic radiation; REID = risk of exposure-induced death. a Safe days in deep space (zero-g interplanetary environment) is a concept de- fined as the maximum number of days with 95 percent confidence interval to be below the NASA 3 percent REID limit, assuming nominal shielding of 20 g/cm2 aluminum. SOURCE: Adapted from Cucinotta et al., 2013a. DISCUSSION: Because the highly penetrating GCR dominates the effective dose, and because GCR is at a peak at solar minimum, the safe days are lowest at solar minimum. The deep solar minimum of 2009 had a significantly higher GCR than previously experienced, thus further reducing the safe days. There are more safe days near solar maximum because the GCR is reduced relative to solar minimum, and because solar storm radiation is significantly attenuated by nominal shielding. If a storm shelter (a smaller volume within the vehicle with additional shielding) is available to the astronauts, the exposure from a solar storm can be reduced to a negligible amount, so the total exposure would be from the GCR alone. This could further increase the number of safe days at solar maximum, assuming adequate solar storm warning.

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68 LONG DURATION AND EXPLORATION SPACEFLIGHT SUMMARY The examples provided in this chapter illustrate the range of issues that are faced as NASA makes decisions about health standards for long duration and exploration spaceflights. The potential short- and long-term health impacts encompass many systems of the human body as well as behavior and performance issues. Decisions about health standards are complicated by the depth of uncertainty regarding what will happen with extended stays in space, high exposures to galactic cosmic radiation, and other risks and challenges. Additionally, data are minimal or non-existent for variations in individual susceptibility based on factors such as eth- nicity, sex, age, etc. A major challenge is the lack of information about the interaction of risks and the extent to which these interactions alter the overall level of risk. The following chapter outlines the ethics principles and responsibilities that can be brought to bear on decisions regarding health risks. REFERENCES ACS (American Cancer Society). 2013. Lifetime risk of developing or dying from cancer. http://www.cancer.org/cancer/cancerbasics/lifetime-probability-of- developing-or-dying-from-cancer (accessed January 15, 2014). Aldrin, B. 1973. Return to Earth. New York: Random House. Alexander, D. J., C. R. Gibson, D. R. Hamilton, S. M. C. Lee, T. H. Mader, C. Otto, C. M. Oubre, A. F. Pass, S. H. Platts, J. M. Scott, S. M. Smith, M. B. Stenger, C. M. Westby, and S. B. Zanello. 2012. Evidence report: Risk of spaceflight-induced intracranial hypertension and vision alterations. http://humanresearchroadmap.nasa.gov/Evidence/reports/VIIP.pdf (accessed November 8, 2013). Basner, M., D. F. Dinges, D. Mollicone, A. Ecker, C. W. Jones, E. C. Hyder, A. D. Antonio, I. Savelev, K. Kan, N. Goel, B. V. Morukov, and J. P. Sutton. 2013. Mars 320-d mission simulation reveals protracted crew hypokinesis and alterations of sleep duration and timing. Proceedings of the National Academy of Sciences of the United States of America 110(7):2635-2640.

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