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9.1 Introduction

The images of the Apollo landing on the Moon are one of the most iconic of the twentieth century. Neil Armstrong’s “one small step for man, one giant leap for mankind” inspired millions of people around the world, helped boost the U.S geopolitical image around the globe and was the winning aspect of the US-Soviet “Space Race”. Understandably, the Apollo program (11 total missions, 6 Moon landings and 12 astronauts walking on the Moon) was and still is the crowning achievement of human space flight. However, the program ended in 1972, and since then, humans in space have remained very close to Earth indeed. Operating in Low Earth Orbit (LEO), mostly within space stations such as Skylab (US), Mir (Soviet Union and then Russia), the International Space Station (US/Russia/EU/Japan/Canada) and the Tiangong-1, 2 and 3 (China). These stations circle the Earth at orbits between 350 and 450 km.

However, we are entering once again an era of space exploration beyond Earth, with the Moon as a steppingstone and Mars as the ultimate destination. Plans for these kinds of missions have always existed but it seems that the 2020–2030 decade will once again see humans on the Moon, or soon within the decades after. These plans for the Moon have gone now beyond the planning phase and are now being “operationalized”, with NASA having signed the “Artemis Accords”Footnote 1 and other space agencies adapting their own space programs or parts thereof for operations in the lunar vicinity and/or surface, in partnership with NASA or concurrently, as is the Chinese/Russian plan for an International Lunar Research Station on the Moon, as announced at the Global Space Exploration conference on June 16, 2021.

Obviously, there is a plethora of questions to be answered regarding the “how?”, encompassing the myriad of technical issues to be solved and worked out in order to make a Moon or Mars landing feasible. There are also several questions regarding “why?”, that have to do with the purpose of landing humans on an extra-terrestrial surface, being either scientific or political in nature.

However, this case study will not delve into these aspects, but rather focus on the issue of whether sending humans to another celestial body is an ethical thing to do, and how space agencies currently deal with the ethical issue that the mere presence of humans in space puts them in harm’s way.

9.2 Space Exploration and Effects on Humans

“Space is hard” is a common saying amongst people working in the space industry. It signifies the complicated issues surrounding space travel, an issue that is also reflected on the cost of space missions. Space travel beyond LEO is even more so, given the distances involved. Apart from the danger of relying on complicated machinery for transferring the crew to its destination, the space environment itself is extremely harmful to human beings. Many of the problems encountered in human space travel deal with keeping the crew alive. Interplanetary space as well as the lunar and Martian surfaces are extremely hostile environments, including hard vacuum, extreme temperatures, space debris, zero or reduced gravity, as well as harmful radiation. It is this later aspect, the harmful radiation, that this case study will focus on as it constitutes the greatest uncertainty in respect to effects and mitigation. Mitigation efforts regarding vacuum, temperatures and debris are possible, based on proper spaceship and astronaut suit construction as well as effective operational design. The effects of reduced gravity have been extensively studied and countermeasures are in existence (Blaber et al. 2010). These countermeasures cannot eliminate the side effects of long duration space travel but can reduce them to the point that the crew remains operational for the duration of the mission. The issue of harmful radiation is rather more complex. There are currently no effective strategies for complete shielding from space radiation. Any human in space thus will be exposed, with exposure being relative to the duration and type of each mission.

9.2.1 Space Radiation Physics

The main sources of radiation in space are galactic cosmic rays (GCRs) and solar particle events (SPEs). GCR are very energetic and thus highly penetrating. They are very difficult to attenuate and essentially cannot be stopped by shielding, since shield mass in space is limited. Spacecrafts cannot carry a heavy amount of shielding material (putting mass in orbit is very expensive), and a “weak” shield might in fact be worse than no shield at all, since a GCR will create a cascade of secondary particles of shield material that will saturate the insides of the spacecraft. It is thus preferable to let GCRs just pass through the human body.

SPEs include particles such as helium ions and other ions. SPEs originate at the Sun. These events occur sporadically with varying frequency. Frequency and intensity of SPEs are unpredictable, although they are related to the Solar 11-year cycle (solar minimum/maximum). Low energy SPE protons cannot penetrate spacecrafts or astronaut suits, but the high energy particles can, and thus contribute to astronaut radiation exposure. However, shielding (especially within a spacecraft) is effective against SPEs. Issues arise with astronauts outside the spacecraft (extravehicular activities) or exposed on the lunar or Martian surface, since when an SPE occurs, astronauts may not have time to seek protective shelter.

GCR flux can be modelled and expected exposure calculated. SPEs can be shielded against based on assumptions about intensity and frequency and planning of activities. Prediction of SPEs is not possible but advanced warning once one has occurred is feasible, albeit with a very small reaction timeframe.

9.2.2 Current Practises

Currently, space agencies have regulations that define radiation exposure standards that astronauts should not exceed. For example, NASA defines space permissible exposure limits (SPELs) for their astronauts which indicate that “astronauts shall not exceed 3% risk of exposure-induced death (REID) from cancer”. The current NASA standard is adjusted for age and sex, which is not the case for all space agencies. The SPEL indicates an upper 95% confidence limit that the individual will die from cancer associated with the radiation exposure that the individual received while in space. In essence, out of 100 astronauts that have travelled in space, 3 might die from radiation related cancer. This is calculated for each astronaut, based on sex and age.

Radiation exposure dose equivalent unit in dosimetry is measured (in SI units) in sieverts (Sv). For exposure to small doses of ionising radiation, it is easier to use the millisievert (mSv). The current standards of the international space station partners can be seen in Table 9.1.

Table 9.1 Radiation exposure career limits for astronauts. ISS partner agencies. Adopted from NAS (2021)
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To get an indication of how mission profiles affect radiation exposure, Table 9.2 summarises the radiation dose (average) for various mission types. Despite the difference in the type of radiation, 1 mSv of space radiation is roughly equivalent to receiving three chest X-rays.

Table 9.2 Mission profile and duration with observed radiation dose (averaged). Adapted from NASA’s space radiation FAQFootnote

https://srag.jsc.nasa.gov/spaceradiation/faq/faq.cfm.

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Radiation doses are cumulative. Thus, under the current standards, a 30-year-old female NASA astronaut might be able to fly once or twice to the ISS before reaching her career limit, whereas a male astronaut can probably fly more times. For Russian, European or Canadian astronauts, longer or more missions can be undertaken. Note that older astronauts have higher exposure limits, as the overall impact on the rest of their lives is less than the impact on a younger astronaut.

9.2.3 Effects of Space Radiation on Human Health

Exposure to large doses of harmful radiation can signify increase risk for the development of cancer and non-cancer anomalies, such as leukaemia, circulatory diseases, vision impairing cataracts, cognitive and memory problems, potential heritable effects and infertility (Cucinotta and Durante 2006; Chylack et al. 2009; NRC 2006). The great degree of uncertainty about whether an astronaut will develop any of these health problems, especially cancer, makes it challenging to communicate these risks to astronauts, the public and policy makers. There are several sources of uncertainty.

As mentioned in the previous section, the average flux of GCR and solar activity can be simulated and modelled. However, SPEs are stochastic events, as there is no way to know exactly when and where an SPE will take place. Thus, it can be treated as a random occurrence, and therefore there is always a risk for a high energy event that exceeds the modelling parameters.

Another source of uncertainty is the actual effects of radiation on the human body. This might be surprising at first, given that radiation sources have been available for decades on Earth. Considering the effects of long-term exposure to radiation (rather than acute radiation exposure), however, showcases the difficulty of gathering data over a long period of time (decades) for large groups of exposed humans in order to conduct statistical studies and infer accurate risk rates.

Risk projections for cancer specific illnesses have largely been based on data from the Life Span Study (LSS) of the Japanese atomic bomb survivors. Additional data sources are being made available, such as studies of occupational radiation. Nevertheless, uncertainties remain regarding potential long-term effects (Chylack et al. 2009; NRC 2006).

9.2.4 Leaving Earth

The current space radiation exposure standards (see Table 9.1) were developed with short space missions in mind, planning for repeated missions (i.e. multiple stays in the ISS), where it was possible to return to Earth (and have access to health care there) within days. In venturing outside the Earth, to travel to the Moon and Mars, this will no longer be the case. In the case of travel to Mars, the round trip can take more than two years with the projected technology (for 2030+). The mission profile calls for a 6-month cruise, 18 months surface stay (waiting for Mars and Earth to re-align in their orbits and reduce necessary travel time) and 6 months travel back. Thus, once the mission has begun, an astronaut cannot decide that he or she no longer wants to be part of it. This is quite different from what is typically found in terrestrial occupations that include radiation exposure. Terrestrial workers can choose to leave their job and thus end their exposure. Furthermore, the radiation environment outside Low Earth Orbit changes.

The most important factors that contribute to the heightened risk of radiation exposure for astronauts in Lunar or Mars exploration missions can thus be inferred from the above. Once outside the Earth’s protective global magnetic field, which the Moon and Mars do not have (there are localised but not global magnetic fields), the flux of radiation (both GCR and SPEs in origin) increases. Additionally, the response window for energetic SPEs diminishes, as Solar observatories have to observe the event and a signal communicated to the astronauts needs to happen for them to take shelter. The further they are from Earth, the longer it will take for the message to be transmitted to them. In addition, the expected mission durations increase quite substantially, essentially placing future astronauts in a more hostile environment than they operate now, for much longer periods. Contrast Table 9.2 with expected radiation doses for future extra-terrestrial exploration missions (Table 9.3).

Table 9.3 Mission profiles for future space exploration scenarios and expected radiation doses. Adopted from (Cucinotta and Durante 2006). Risk calculations can be found therein
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9.3 Ethical Space Exploration

The previous section highlights several issues regarding future space exploration destinations.

  1. 1.

    The effects of radiation will probably not have a technological mitigation measure in the envisaged timeframe for these countermeasures to be available. Thus, exposure to harmful radiation is a given for any mission.

  2. 2.

    Uncertainty still remains about the types of adverse effects that astronauts will incur due to long duration spaceflight. This makes it hard to accurately inform the crew on the impact of each mission on the participant’s long-term health and quality of life.

  3. 3.

    For missions to Mars, termination of participation might not be an option. If the astronaut so chooses, he cannot just stop participating in the mission. The physical distances and planetary alignment might make it impossible to return to Earth, outside the planned window.

  4. 4.

    Given that exposure is cumulative, Lunar and Mars missions might necessitate inexperienced astronauts as crew (no previous exposure).

  5. 5.

    The current standards for astronaut lifetime radiation exposure do not actually allow participation in missions to Mars, as the nominal mission scenarios would exceed the allowable limits.

The points above ultimately create the situation that a future Mars mission will put the crew in harm’s way, regarding career-received radiation, with increased risk of adverse health effects. This section will now describe the official (space agency) response and efforts to deal with this situation.

Spaceflight is an endeavour that brings benefits to many (society, scientists, future astronauts, etc.) but the risks are shared by a few (astronauts and their families), especially health risks. The astronaut corps can be considered an elite group of people, selected from a wide pool of willing candidates. Given the formation and training that the astronaut candidates receive once selected, it is difficult to claim that they are not aware of the risks for space flight and that they are not consenting to them.

The approach of NASA and other space agencies to address Mars as an exploration destination for astronauts is to offer a mission specific waiver for astronauts in such missions. Thus, explicitly informed consent will be needed for each member of a potential crew. As of today, only NASA allows for such a process, although other space agencies seem to agree with this approach.Footnote 4 It is highly probable that NASA will lead the way on this issue as the US has more mature plans for future space exploration. Thus, the US response to the problem will most probably define the responses of other agencies.

NASA has asked a committee of experts, brought together by the National Academies of Sciences, Engineering and Medicine (NAS), to review the current process for assessment and management of long-term risk with respect to cancer for crews (NAS 2021). The committee, which was comprised of experts in several related fields, such as radiation dosimetry, clinical oncology, biostatistics, physics, risk communication and management as well as former astronauts, offered recommendations to the agency. The full report also discusses NASA’s plan to move to a different exposure limit standard, which will increase allowable career exposure limit that is common for all astronauts (male and female). The standard in question still remains more conservative that other space agencies with a unified approach (600 mSv for all, as opposed to 1000 mSv that is the standard for other agencies, as seen in Table 9.1). However, even with the new proposed standard, Mars missions will still require a waiver, and thus the situation as seen in the previous sections, remains similar.

It is of interest to note some of the recommendations made to NASA by the NAS committee (2021), regarding ethical issues.

Recommendation 2: “In the near future, NASA should re-examine whether to use risk of exposure-induced death (REID) or other metrics, or a combination of metrics, in setting the dose-based space radiation health standard. NASA should conduct an independent analysis of the validity of 3% REID and make explicit the agency’s justification for the metrics they choose.”

The key element in the above recommendation is the need to make explicit the justification for the metrics to be used, regardless of the standards. This is sage advice and the foundation for creating trust in the standards. The main issue in the case of astronauts is that the current standards differentiate between male and female astronauts, but the proposed future standard is a common standard (based on a 35-year-old female) that, given the physiological differences, will allow more exposure to young, female astronauts but less exposure to older, male astronauts (which they could have been allowed with the older standard). As such, there is a trade-off between equality of opportunity for all versus restrictions imposed on a subgroup. Thus, the need for disclosure on the justification of choice, which will make explicit the argumentation for the change and present the ethical arguments that were evaluated against each other, which will help reassure the subgroup that might feel that their opportunity is being unfairly diminished, and that their position has been considered.

For missions regarding a waiver, it was recommended to follow the previous recommendations of a work on Health standards for spaceflight (IoM 2014), and to “Adopt an Ethics-Based Decision Framework, NASA should apply the relevant ethics principles and fulfil the concomitant responsibilities through a three-level, ethics-based decision framework that examines (i) decisions about allowing risk to astronaut health and safety in excess of that permitted by health standards, (ii) decisions about undertaking specific missions, and (iii) decisions concerning individual astronaut participation and crew composition” (IoM 2014, Recommendation 4).

It is understood that current exposure standards cannot apply for future missions to Mars (and some Moon missions). Thus, a waiver is the only way forward. The proposed, ethics-based decision framework, will then be used to decide who can join which mission. The three proposed levels of decision in the framework concern:

  1. (i)

    the decision that a waiver is indeed ethically acceptable, for which kind of missions and the criteria for the mission objectives and parameters for a waiver to be a possible option. This is necessary to minimise the use of a waiver and avoid a situation where all missions are indeed possible, given that a waiver can be granted.

  2. (ii)

    The second decision level concerns each individual mission and whether it meets the criteria established in the previous level and thus a waiver is ethically acceptable. Finally,

  3. (iii)

    the third decision level, which includes the crew composition for the selected mission. The objective here is to acquire informed consent and thus, it is necessary to provide as complete information as possible on flight risks, risk management plans and also the state of research knowledge that has informed the risks. The complete framework and decision points can be seen in the IoM report (2014, 145–150).

The way to communicate such risks to astronauts was also a main consideration in the more recent report (NAS 2021). The current paradigm is to use REID (Sect. 9.2.2) and distribution statistics based on age and gender. As an example (NAS, figure S-2), the risk associated with an effective dose of >600 mSv and thus above the NASA allowable limits, is indicated, highlighted red, as: High Risk—requires Agency Waiver—REID >2.27% mean (0.6, 7.8%) 95% CI for a 35-year-old female.

Even though astronauts are highly trained individuals, with advanced knowledge of risk statistics, it seems that even amongst astronauts the above type of communication is still confusing; effective dose as the main communicating tool would be preferred (NAS 2021, 14). It is interesting to note that it seems (based on discussions between active astronauts and the committee) that communication regarding reproductive health and possible issues from exposure might influence decisions in context for astronauts. The recommendations regarding risk communication to NASA were to:

  • Assess and communicate risk at an individual level (rather than generic) for all astronauts

  • Follow up the statistical presentation of risks with individualised discussion and answers to possible questions, in order to address questions from individual astronauts.

  • Provide access to addition information as needed.

  • Develop risk-based communication that is based on what astronauts want, how they process risk information and identify who and what are the most effective sources of information for them.

9.4 Conclusions

Transparency and full informed consent are critical in decision making regarding future exploration missions, even in the context of highly motivated individuals, such as the astronaut corps. It is highly unlikely that there will be no volunteers for a mission to Mars; the opposite is more likely. That, however, does not alleviate the ethical requirement of volunteers to have consented to be placed in such a situation.

There is another concern regarding future space exploration that has to do with the nascent era of commercial space flight. The year 2020 saw the first commercial crewed flight to the ISS, with the Space-X Demo 2 mission.Footnote 5 In early 2021, the same spacecraft, Dragon from SpaceX, carried, in addition to the US astronauts, one European and one Japanese astronaut to the ISS.Footnote 6 2021 also saw the first suborbital flights from Virgin Galactic and Blue Origin, which were highly publicised as the respective CEOs were on board. However, both these flights were suborbital, as they did not achieve orbit, but rather flew close to the “edge of space”, the Kármán line, an altitude of 100 km that defines the boundary between the beginning of space and Earth’s atmosphere (this is an artificial boundary and does differ between nations. Blue Origin’s New Shepherd vehicle flew above 100 km and Virgin Galactic’s Unity 22 flew below it).Footnote 7 Given the brevity of the suborbital flights (4–5 min of microgravity), the issues with exposure discussed in this article do not apply and thus suborbital space tourism is not considered at present.

Commercial spaceflight, and in future commercial space exploration, do need to be considered. There are discussions for commercial crew missions to the Moon and Mars as well, although currently, it is difficult to gauge their preparedness level. SpaceX does indicate future missions on its website to Moon and Mars with their Starship design (see for example: https://www.spacex.com/human-spaceflight/) but as of August 2021, there are not many details about these missions. Nevertheless, one can imagine that given the effects of radiation on the human body and that ill effects can manifest after several years or decades of someone exposed to radiation in space, it might be difficult for commercial companies to offer comprehensive informed consent information to potential astronauts, as they may not have the necessary data. Currently, only the national space agencies can dedicate resources to investigate the uncertainty regarding space radiation effects. Thus, space agency astronaut guidelines, standards and procedures may be adopted by potential commercial endeavours or at least be available as the “industry standard”.

The conclusion from this case study is an extrapolation from the very specific group of people that constitute the astronaut corps. If candidates to be the first human to reach Mars or to walk on the Moon once again, still prefer fully informed consent procedures to be put in place, it is therefore evident that such a process should follow any decision regarding any group that is tasked with performing an action that will inherit some sort of risk. Policy makers, as representatives of society in such situations, need to ensure that society demonstrates its appreciation and support to the ones it asks to put themselves in harm’s way, by ensuring that they do it knowing the full reasons and consequences of doing so. Thus, public agencies need to be constantly mindful of the ethical implications of their work, incorporate ethical decision making where relevant and ensure a continuous discursive engagement regarding the societal state of what is considered ethical.