Astronaut selection processes, such as those used by the National Aeronautics and Space Administration (NASA), the Canadian Space Agency (CSA), the European Space Agency, Roscosmos, and South Korea’s astronaut program, share several common elements despite variations across countries and organizations [8-11]. In addition to academic qualifications, these programs collect basic medical information and exclude candidates with physical or mental health conditions that could disqualify them from spaceflight. Initial assessments are conducted to identify any previously undetected physical or psychological risks, ensuring that only healthy candidates are advanced forward. This is followed by comprehensive medical evaluations, psychological assessments, and in-depth interviews. Through this rigorous selection process, the most qualified candidates, equipped with the necessary capabilities for mission success, are selected [12].

NASA’s medical selection process, in place since the Mercury program, has evolved with changing mission profiles and advances in medical knowledge and capabilities [10,12]. Major revisions to this process occur every 5-10 years and are agreed upon by all international partners. It applies to all international partner astronauts and cosmonauts participating in specific missions, such as those aboard the International Space Station or Artemis. The criteria are closely aligned with those of the U.S. military, with strict definitions of disqualifying medical conditions. However, exceptions may be granted to experienced astronauts if they can demonstrate that their disqualifying condition has been treated, mitigated, or proven not to impair their performance. The selection process consists of multiple stages. First, a call for applications is announced via USA JOBS, followed by a review of applications and evaluation by a rating panel. Approximately 100-120 candidates are selected for Round 1 interviews, conducted over 4-6 weeks. From this group, 30-50 candidates advance to Round 2 interviews, held over 3-5 weeks. The final astronaut candidate class is then selected. Post-selection medical testing is a key component of the final stage. Medical evaluations begin in Round 1 with low-cost, in-house assessments, such as basic vision and audiometry tests. High-cost tests, including magnetic resonance imaging and exercise stress tests, are conducted during Round 2 and after selection. Ultimately, each candidate is classified as either “medically qualified” or “not medically qualified.”

CSA began its astronaut recruitment in 1983 after NASA invited it to participate in a Space Shuttle mission. This was followed by recruitment campaigns in 1992, 2008-2009, and 2016-2017 [13,14]. The first two campaigns, in 1983 and 1992, focused on selecting payload specialists with scientific and technical expertise, aligned with the criteria of NASA and the Russian Space Agency. Psychological evaluations were minimal during these early campaigns, consisting of basic mental health questions included in the general medical screening, with no specific assessments of personality traits or interpersonal skills. However, the 2008-2009 and 2016-2017 campaigns marked a shift toward a more comprehensive approach, integrating internationally agreed-upon standards for long-duration missions to the International Space Station. These later campaigns placed greater emphasis on psychological and behavioral assessments, reflecting a growing recognition of the importance of human factors in mission success. The selection process evolved to include thorough physical, medical, and psychological evaluations. By 2008, human behavior and performance criteria for long-duration missions were well established, and the CSA adopted this framework for astronaut selection. The CSA partnered with the Department of National Defense to conduct behavioral evaluations in military training settings and collaborated with psychologists and psychiatrists for indepth psychological interviews, informed by psychological testing results. The selection process emphasized key traits such as adaptability, resilience, and cross-cultural competence—essential for astronauts living and working abroad for extended periods. In the 2016-2017 campaign, the CSA further refined its medical and psychological assessment procedures, working closely with NASA to ensure compatibility of their selection criteria and integrating comprehensive medical and psychological evaluations throughout the process.

The astronaut selection process at the European Space Agency is closely aligned with that of NASA, particularly in terms of medical evaluations, while also incorporating psychiatric and psychological assessments [15]. The psychiatric evaluation is aimed at excluding candidates who may be at risk of developing mental health issues during space missions, while the psychological assessment focuses on identifying individuals with the personality traits and cognitive abilities required for successful spaceflight, especially for long-duration missions. This phase includes personality testing, performance evaluations, behavioral observations during group activities, and structured interviews. Additionally, stress resilience is tested through experiments such as isolation chamber tests, ensuring candidates can cope with extreme environments. The psychological selection process consists of two phases. In Phase 1, candidates undergo online cognitive tests and basic aptitude assessments, with only those meeting specific criteria advancing to the next stage. Phase 2 takes place at the European Astronaut Centre in Cologne, Germany, where the focus shifts to evaluating teamwork and interpersonal skills. During this phase, candidates participate in group exercises, projective tests, and indepth interviews to assess their psychological suitability. This comprehensive selection process ensures that chosen astronauts possess the social and psychological competencies essential for the challenges of long-duration space missions.

In late 1959, the Soviets initiated a program to select cosmonauts for spaceflight [16]. Initially, the selection process was adapted from pilot selection procedures, but as the U.S. developed its own astronaut selection process, the Soviets expanded their approach. Early selection consisted of three phases: first, an initial selection based on recommendations and family medical history; second, a comprehensive medical examination; and third, physical and psychological stress testing. Over time, this process evolved [9]. The modern cosmonaut medical selection process is now comprised of three main stages. In the first stage, candidates undergo outpatient evaluations by specialists from various medical fields, including internal medicine, neurology, and ophthalmology. The second stage involves more in-depth clinical evaluations to identify hereditary or recurring health conditions, particularly those affecting vital organs like the circulatory and respiratory systems. Advanced diagnostic techniques, such as roentgenography and endoscopy, are employed, along with psychological tests and stress resistance assessments. The final stage, conducted at the Gagarin Cosmonaut Training Center, evaluates the candidates’ overall physical and psychological results. Based on these assessments, candidates are either selected for training, deferred for treatment of specific conditions, or rejected if their medical or psychological issues are deemed unresolvable.

In South Korea, technology development was guided by the Space Development Medium and Long-Term Basic Plan (1996-2015), which supported the industrial utilization of space in areas such as Earth and space science, telecommunications, and space exploration. Astronaut training was aligned with these objectives. The criteria for astronaut selection encompass general, behavioral, and medical suitability, as well as language proficiency [11]. The evaluation framework consists of several key areas: general suitability, which reviews basic qualifications and applies exclusion criteria; behavioral suitability, which uses quantitative tests, interviews, and other methods to identify candidates with desirable characteristics; and medical fitness, which assesses physical health and adaptability to specialized work environments. Mental health is evaluated across all of these categories.

Overall, physical standards for astronaut selection are relatively consistent across countries. However, specific details regarding psychological assessments are typically not disclosed to the public due to privacy concerns. Despite this, factors such as stress tolerance and the ability to contribute effectively to teamwork are widely recognized as critical. To address these requirements, some selection processes include peer assessments or evaluations by team leaders to assess team performance and cohesion during separate training periods [17,18].

The selection process for becoming a submariner in the United States Navy entails meeting several stringent requirements [19]. Applicants must first satisfy the general enlistment criteria for the Navy, followed by a comprehensive medical examination to confirm their physical suitability for submarine duty and their ability to endure the demanding conditions of a submarine environment. Candidates also undergo psychological evaluations designed to assess their capacity to cope with the isolated, confined, and high-stress nature of submarine life. These evaluations include assessments of stress tolerance, teamwork capabilities, and adaptability to working in confined spaces for extended periods. Additionally, physical standards, such as vision and hearing, play a crucial role in determining eligibility.

The study examining the impact of cognitive abilities and personality traits on the performance and adaptation of military divers in underwater environments confirmed that emotional control, intelligence, and stress resilience are essential for successfully adapting to the demanding conditions of the underwater environment [20]. This research specifically highlighted the importance of psychological assessments in the selection process for military divers, demonstrating that these traits are critical for predicting performance and adaptation under extreme conditions.

In accordance with the Korean Navy’s special operations regulations, candidates undergo physical examinations, along with routine and ad hoc medical assessments, to evaluate their fitness for underwater tasks, including working in confined underwater spaces and conducting diving operations [21]. This process ensures that individuals medically suited for such demanding underwater duties are selected, and their health is regularly monitored.

Antarctica is becoming increasingly accessible, and international scientific collaborations are growing each year [22]. While technological advances have enabled safer and more comfortable living conditions, Antarctica remains an undeniably extreme environment [23]. Therefore, it is essential to identify applicants capable of handling the unique mental and physical demands of life in Antarctica through a rigorous selection process. This process varies across Antarctic programs [24]. For example, Australia operates a 24-hour assessment center, whereas the New Zealand Antarctic Program employs a web-based recruitment system that includes face-to-face interviews and online personality questionnaires. The use of psychologists in the selection process was discontinued in the mid-1990s [25]. Although factors such as interpersonal chemistry, group dynamics, and the unpredictability of the natural environment are beyond the control of the selection committee, contextual factors are still considered during the evaluation of applicants. At the individual level, applicants are assessed based on three main criteria: task fitness, physical (or medical) fitness, and mental (or psychological) fitness [26].

Water UK is a trade association representing water companies in the UK and operates its own Occasional Guidance Note, The Classification & Management of Confined Space Entries [27]. It has developed medical standards to ensure that workers possess an appropriate level of cardiovascular, respiratory, musculoskeletal, and neurological function to perform tasks related to confined spaces. In the water industry, confined spaces range from open trenches to sewers and underground areas, and the medical standards for workers in these environments vary depending on the specific conditions and nature of the work.

At this stage, the self-reported medical history forms submitted by applicants are reviewed to screen out individuals with conditions that may pose significant risks during the mission. The medical history form covers various systems, including respiratory, cardiac, neurological, and auditory systems, allowing for the identification of both acute and chronic illnesses. Additionally, it includes a section for disclosing any history of major psychiatric disorders.

Screening is conducted based on absolute and relative contraindications, focusing on conditions likely to worsen in highpressure environments, such as tympanic membrane perforation, spontaneous pneumothorax, and unrepaired abdominal wall hernias. Infectious or contagious diseases that may disrupt group living, as well as conditions like a history of cardiac surgery or cerebrovascular disease, which could lead to severe functional impairment or mortality, are also considered during this phase.

At this stage, a basic physical examination is conducted to identify any disqualifying conditions that were not detected in the self-reported records from the first stage and to confirm that the basic physical criteria are met. The examination includes simple and cost-effective essential tests, such as measurements of height and weight, vision and hearing assessments, and otoscopy. Blood tests—including fasting blood sugar, blood urea nitrogen, creatinine, and liver function tests—are conducted, along with urine tests, an electrocardiogram, and a chest X-ray. Additionally, the physician performs a brief assessment of the head and neck, musculoskeletal system, and nervous system.

In the previous stage, basic physical evaluations were conducted; the third stage is focused on a fundamental psychological assessment. This assessment consists of self-report items designed to evaluate personality traits and the presence of any undiagnosed major psychiatric disorders. By administering the Minnesota Multiphasic Personality Inventory and the Sentence Completion Test, applicants are comprehensively evaluated for personality characteristics and potential psychopathologies [33,34]. Additionally, the Symptom Checklist 90 Revised, Beck Depression Inventory, State-Trait Anxiety Inventory, and Alcohol Use Disorders Identification Test are used to screen for depression, anxiety, problematic drinking, and alcohol use disorders [35-38]. Applicants who exhibit severe depression, anxiety, a high risk of suicide, or problematic drinking behaviors are excluded from further participation in the selection process.

This stage is focused on confirming whether the candidates possess the physical condition necessary to maintain their health and perform their tasks efficiently in the underwater environment. Compared to the physical examinations conducted in the second stage, this phase involves higher-cost, time-intensive tests. To ensure that candidates can safely perform highlevel tasks, an exercise stress test is conducted to assess cardiac function, and a pulmonary function test is performed to evaluate lung capacity and respiratory function. Even minor physical discomforts experienced during the selection procedure are closely monitored to enhance safety and ensure that no potential risks are overlooked.

This stage is focused on selecting candidates who demonstrate superior mental fitness for the mission and involves a comprehensive battery of assessments, including intelligence tests, neuropsychological evaluations, and projective tests. Following these assessments, a semi-structured interview is conducted to evaluate the candidate’s motivation, mission performance abilities, problem-solving skills, and overall mental state.

The semi-structured interview is conducted by two mental health professionals: one interviews the candidate while the other observes and evaluates the assessment simultaneously, ensuring greater reliability. The primary goal of this interview was to gain a comprehensive understanding of the candidate’s suitability for the mission. Questions regarding the candidate’s past experiences—such as academic performance, interpersonal relationships, and childhood trauma—provide important contextual information. Additionally, inquiries into their lifestyle, including sleep patterns, diet, and daily functioning, help identify any potential risk factors for maladaptation.

This stage involves the final selection of candidates deemed most suitable for missions conducted in a group setting. Alongside individual characteristics, factors such as teamwork and the ability to perform team-based tasks are carefully evaluated in the decision-making process. The Aquanaut selection committee will conduct a final interview with each candidate and, if necessary, interviews involving multiple candidates and the committee may also take place.