ICE environments are often in remote locations with extreme weather conditions, such as Antarctic Stations (e.g., South Pole, Palmer), which limit travel, accessibility, and the possibility of emergency evacuation of crewmembers. Scientists and other professionals living and working in these ICE environments primarily focus on conducting specialized field research or training, therefore, human research endeavors are incorporated as a secondary objective. Crewmembers can enroll in research studies that assess the effects of isolation and stress on individuals while they carry out their primary research or training objectives (Cromwell and Neigut, 2020).

Research conducted in ICE environments has provided insights into changes in behavior and performance that could occur on the International Space Station (ISS) or during future extended duration missions beyond low Earth orbit (LEO). For example, Antarctica winter-over crewmembers have experienced disruption of circadian rhythms, as has been shown in astronauts on the ISS (Flynn-Evans et al., 2016). Studies have shown that crewmembers overwintering in Antarctica often experience disruptions in their sleep-wake cycles, leading to fatigue and cognitive impairments (Palinkas and Suedfeld, 2008); on the ISS, astronauts are often subject to schedule shifting, which can severely disrupt their body’s internal clock. Both the ISS and Antarctic environments therefore pose challenges to maintaining a regular day-night cycle, which is crucial for protecting sleep duration and sleep architecture (Nasrini et al., 2020).

Antarctic research has demonstrated that most individuals do not experience clinically significant changes, but rather, that prolonged isolation and confinement can be associated with decreases in positive emotions and increases in physical symptoms for some individuals (Alfano et al., 2021). Whether these declines in wellbeing are indicators of a later adverse behavioral condition is unknown, given that most winter-over expeditions conclude within a year. Evaluating the effectiveness of countermeasures to support behavioral health in an environment such as Antarctica may help determine future methods for testing and implementing targeted mitigation strategies during long-duration exploration missions. ICE environments generally offer a high level of psychological fidelity to distant exploration spaceflight missions, however, the operational nature of these platforms often limits research opportunities. For example, it is often not feasible to assign individuals who winter-over to highly controlled conditions to assess systematic measurements of effects. Crewmembers at these facilities have field work to conduct, limiting their availability to participate in research studies. Additionally, the number of crewmembers can fluctuate throughout the mission duration (roughly around a year), and team sizes are often much larger than typical astronaut crews on a long-duration space mission (Cromwell et al., 2021). Additionally, because crews of stations such as McMurdo no longer undergo psychological selection or screening, selection criteria will vary substantially between Antarctic station crewmembers and astronauts.

ICC environments are settings where isolation and confinement are maintained under regulated conditions. Unlike remote ICE facilities, ICC locations tend to be physically more accessible. Participants of research studies conducted in ICC environments perform as crewmembers of a simulated space mission and are typically isolated and confined to habitats that replicate exploration transit vehicles or extraterrestrial habitats.

ICC platforms provide a realistic simulation of certain aspects of space missions, particularly isolation and confinement, which are critical for studying outcomes related to behavioral health, team dynamics, and operationally relevant task performance. Similar to the limitations of ICE environments, ICC platforms do not replicate the full range of spaceflight hazards encountered in actual space exploration environments, such as microgravity, which impacts physiological functions such as fluid distribution and muscle usage. Microgravity cannot be effectively simulated in ICC settings unless the study is conducted in a bed rest isolation and confinement facility.

Additionally, although ICC platforms can simulate delayed communication with Earth to some extent, they may not fully capture the impacts of prolonged communication delays that astronauts experience during deep-space missions. The simulation aspect of ICC platforms can lower the psychological fidelity of communication delays owing to “distance from Earth”. The physical environment of exploration vehicles, including spatial limitations and equipment, can also be challenging to replicate precisely in ICC habitats.

ICC platforms can be designed to immerse participants in realistic spaceflight activities and scenarios, enabling future systems, interfaces, and tasks to be evaluated and tested. Spaceflight-relevant stressors including increased social isolation, confinement, altered sleep patterns, and elevated stress levels, can affect cognitive abilities, including visuo-spatial orientation skills and their underlying neural mechanisms (Lukavský, 2014). ICC platforms can, therefore, be used to elicit stress responses, and then effectiveness of specific countermeasures can be tested. Future missions will include intelligent onboard technologies to support the crew responding to an anomaly, and technologies that assist the crew by providing relevant knowledge to help them make informed decisions in the absence of immediate ground support. Although human-in-the-loop testing in a laboratory setting is an extremely valuable step when developing and validating such countermeasures, assessing these systems in an exploration-like analog allows for a fuller assessment in a realistic mission-like environment. ICC environments are particularly helpful for assessing changes in crew performance over extended durations because these facilities allow crews to live and conduct simulated mission operations over periods spanning many weeks or months.

The Human Exploration Research Analog (HERA) at NASA Johnson Space Center (Figures 1, 2) and the Scientific International Research in a Unique terrestrial Station (SIRIUS) at the Nazemnyy Eksperimental’nyy Kompleks (NEK) (Figures 3, 4) are examples of ICC facilities. NASA’s HERA is a 2-tiered module attached to a hygiene module and a simulated airlock (see Figure 2). NASA conducted its first HERA Campaign in 2014, which included a complement of studies on a team of four astronaut-like individuals in the HERA facility over a 7-day mission. These missions were repeated 4 times, each with a new set of four crewmembers, over a period of 1 year. In more recent years, HERA campaigns have included a complement of studies repeated 4 times a year in missions lasting around 45 days. Each 1-year campaign typically ‘sets’ a standard operational scenario with a consistent tempo and series of stressors, i.e., severe sleep restriction schedule throughout HERA Campaign 4 (2017–2018). More information on HERA can be found in Appendix A.

Research in ICC environments has helped to characterize both individual and team behavioral health and performance outcomes. Similar to spaceflight and ICE experiences, most findings and reports from ICC environments highlight positive experiences without adverse outcomes. Specific challenges in some individuals however can arise.

As an example, in their assessment of performance changes over 45-days under the HERA Campaign 4 sleep restriction protocol (5 nights of 5 h in bed, followed by a two nights of 8-h sleep opportunity, repeated throughout each 45-day mission), Flynn-Evans and colleagues (2023) found a significant worsening of performance from the beginning to the end of the mission for mean reaction time, response speed, and fastest 10% reaction time. Researchers have also shown that individuals performing a spaceflight-like task in HERA can demonstrate performance impairments over time, even under nominal conditions (Stankovic et al., 2023), suggesting such isolation and confinement analogs can impact performance of complex tasks. Additionally, at a team level, creativity and conceptual performance has been shown to decrease later in the mission when compared to performance early in the mission (Larson et al., 2019). Other performance measures in HERA however, such as performance on the Cognition test battery, have been reported to be mostly steady or improved over time under nominal schedules (Dev et al., 2024).

Studies in the NEK facility in Moscow have further characterized the potential psychological effects of prolonged exposure to confinement and isolation. For example, three crewmembers who participated in the 520-day simulated mission to Mars in the NEK reported increasing levels of stress, physical exhaustion, and workload throughout the mission, with one of these individuals reporting increasing symptoms of depression (Basner et al., 2014). A more recent international analog campaign included six participants in an 8-month simulated spaceflight mission in the NEK. Lungeanu and colleagues (2023) found that these isolated participants developed and maintained more motivating relationships than non-isolated teams, but also faced fewer viable relationships and sustained fragmentation.

In summary, both ICE and ICC environments contribute uniquely to our understanding of isolation and confinement. ICE settings offer realism and ecological validity, whereas ICC environments provide control and replicability, allowing researchers to balance the advantages and limitations of each approach based on their specific research objectives.

The second category of spaceflight analogs induce physiological adaptations without simulating all spaceflight conditions. Long-duration (60 days or more) of head-down tilt bed rest is a prime example of this category (Sundblad et al., 2016). Bed-rest analogs simulate the effects of microgravity on the body, impacting musculoskeletal, cardiovascular, and sensorimotor systems, while also allowing researchers to measure the psychological responses to prolonged inactivity and confinement. This dual focus on both physiological and psychological functions may enhance the relevance of ICC platforms for studying the multifaceted challenges of space exploration.

Lying in a bed for extended periods with the head tilted slightly downward, simulates the effects of microgravity. This position induces fluid shifts towards the upper body, emulating the bodily fluid redistribution astronauts experience during spaceflight (Lee et al., 2019). This change of gravity loading affects multiple physiological systems, notably the musculoskeletal, cardiovascular, sensorimotor systems, and potentially behavioral health systems, as summarized in Table 1 (Basner et al., 2021; Scott et al., 2020; Richter et al., 2017; Scott et al., 2011). Muscle atrophy and bone loss are induced during bed rest as a direct consequence of prolonged inactivity (Sundblad et al., 2016). Additionally, recent studies have determined that bed rest impacts the sensorimotor system (Mulavara et al., 2018).

Assessments of behavioral data collected during 60 days of bed rest show an increasing tendency over time towards negative valence, as noted by Basner et al. (2021). Subjective ratings of sickness, physical exhaustion, mental fatigue, and stress increased over time throughout the duration of bed rest, and additional deterioration occurred during the post bed-rest recovery phase (Basner et al., 2021). Likewise, a study by Brauns et al. (2021) showed that participants in a 60-day bed-rest study experienced mood decrements, emotion recognition challenges, and other behavioral changes. Vestibular and emotional dysregulation can occur together because the vestibular and emotional systems share neural pathways in regions such as the insular and anterior cingulate cortex (Preuss et al., 2014a; Preuss et al., 2014b; Clément et al., 2020). This shared functionality is evident in these brain areas, where vestibular and emotional networks overlap, suggesting that vestibular signals play a role in affective control and decision-making outcomes (Carmona et al., 2009; Preuss et al., 2014a; Preuss et al., 2014b).

These findings may be related to the inherent isolation of bed-rest participants; unlike spaceflight missions, where astronauts work in teams towards a common goal, current bed-rest study participants are typically isolated, therefore, bed-rest participants have less social and team interactions than astronauts during a space mission. The experience of bed rest can therefore feel even more isolating than spaceflight, presenting an intriguing interplay between physiology and psychology. Bed rest can be used to study the interaction of multiple factors, including fluid shifts, variations in CO₂ concentrations, glymphatic changes, and sleep, but in its current common design, bed rest does not fully capture important social and team aspects of behavioral health and performance.

Flight-based analogs of spaceflight conditions currently include parabolic flights, which induce short-term bouts of microgravity (multiple exposures each lasting an average of 20 s over the course of approximately 120 min), enabling researchers to study the acute effects of microgravity on a range of human performance outcomes. Relevant outcomes measured encompass physiology, fluid shifts, and sensorimotor function. Such studies have furthered the understanding of how the human body reacts to microgravity, even for a brief or transitional period (Kermorgant et al., 2020). Parabolic flights can also be used to ensure equipment intended for use on the ISS functions optimally in the real conditions of the spaceflight environment. Although, in certain circumstances data obtained in parabolic flight is very translatable to spaceflight, the short-term exposure to microgravity limits translating outcomes for long-duration space missions, and minimal behavioral health and performance focused research has been conducted on this platform to date.

Flight-based studies provide a direct exposure to microgravity and the spaceflight environment, but they also come with limitations relative to future exploration missions, in addition to logistical and cost challenges. Researchers can use the ISS to study the physiological, neurological, and psychological effects that occur with long-duration exposure to microgravity in LEO (Kermorgant et al., 2020), and studies on the ISS have provided insights into some of the challenges astronauts will encounter on extended missions, such as prolonged exposures to weightlessness and radiation. Radiation exposure levels on the ISS however, are relatively low compared to radiation exposures anticipated during long-term interplanetary missions.

Much has been learned from the ISS in preparation for future missions regarding protecting sleep and circadian rhythms, particularly through the scheduling of tasks and through habitat design (Flynn-Evans et al., 2023). High tempo lunar missions in vehicles and habitats that will be much smaller than the ISS will require alternate mitigation strategies. Additionally, communication challenges and changes in the roles of personnel in the mission control center (MCC) and ISS astronauts during exploration missions are expected to impact scheduling, extravehicular activity (EVA), and MCC support. The relatively close proximity of the ISS to Earth and the real-time communication between MCC and the crew limits the ability to simulate the delayed MCC communications and support that will occur during future exploration missions—conditions that will require crews to function more autonomously with interfaces and processes that are developed accordingly (Gore et al., 2021).

The increasing presence of commercial vehicles in LEO offers another potential platform for conducting spaceflight research. Depending on the provider and the nature of the missions, such endeavors offer unique opportunities for human spaceflight research that will prepare for exploration missions. Recent commercial missions include the Inspiration-4 SpaceX mission, during which 4 civilian SpaceX astronauts embarked on a 3-day mission at a peak altitude of 364 miles. Human research studies facilitated by SpaceX, the Translational Research Institute for Space Health, and other partners, addressed key aspects such as biological and behavioral changes. Presently, the duration of these commercial missions spans minutes to several days, and planning is underway for future extended commercial missions in LEO. These commercial spaceflight platforms may provide more comprehensive opportunities for conducting research on behavioral health and performance in preparation for future exploration missions.

As noted by Clément and colleagues (2020), radiation exposure will be a crucial factor during future lunar and martian missions due to its potential long-term health impacts on astronauts. Missions beyond Earth’s magnetosphere expose astronauts to significantly higher levels of cosmic radiation, which can affect various physiological systems and is associated with increased cancer risk, central nervous system effects, and cognitive impacts. As noted by Sishc and colleagues (2022), targeted mitigations are needed for risks associated with space radiation exposure to ensure astronauts are safe during and after missions to Mars.

Although it is not ethical to incorporate radiation exposures when studying humans in analogs of spaceflight, radiation is an underlying hazard that could impact the long-term health of crewmembers, which highlights the complexities of maintaining crew health and safety in deep space (Miller et al., 2022). Understanding the impacts of exposure to cosmic radiation is essential for developing comprehensive countermeasures to ensure crewmembers’ wellbeing on future lunar and martian missions. Terrestrial rodent studies are used to assess the effects of the radiation exposure crewmembers are anticipated to receive beyond LEO (Dev et al., 2025; Mao et al., 2024; Alaghband et al., 2023; Miller et al., 2022; Mhatre et al., 2021; Willey et al., 2021), which are much higher than the exposures incurred by astronauts on the ISS. A description of these studies is beyond the scope of this paper; however, it is important to note that efforts are being conducted to translate the anticipated radiation exposure during lunar and martian missions to human health and performance outcomes (Alwood et al., 2023).

Efforts critical for designing habitats and implementing protective measures for Moon and Mars exploration include direct measurements of the space radiation environment around the Moon (George et al., 2024), developing and validating models to simulate radiation exposure at the lunar surface and subsurface that help to quantify the potential exposure astronauts would receive during lunar missions (Dobynde and Guo, 2021), and efforts to inform risk mitigation strategies for astronauts during Mars missions by analyzing data from the Mars Science Laboratory’s Radiation Assessment Detector to determine the radiation environment on the surface of Mars (Guo et al., 2021).

EVAs on the lunar and martian surfaces will substantially differ from those conducted on the ISS. Whereas EVA on the ISS is primarily focused on vehicle maintenance and occur in microgravity, lunar and martian EVA will require astronauts to navigate the planet surface in reduced gravity, which will affect mobility and will require new techniques and EVA equipment (León et al., 2021). Furthermore, the lunar and the martian regolith, which is composed of fine, abrasive dust, may pose significant challenges to the health of astronauts and the durability of equipment (see Figures 5, 6).

Analogs of lunar and martian EVA should account for the technical and environmental complexities of the specific mission. Scenarios should cover both routine and off-nominal surface EVA, including habitat maintenance or assembly, geological sampling, and navigation. Innovations such as detachable rover modules and flexible modules for habitat-system assembly and repair activities will enhance the realism of these simulations and allow for a closer approximation of the physical and technical aspects of conducting EVA.

EVA on the initial lunar missions is anticipated to include two crewmembers on the surface. Simulations should include the low-light and/or low-angle lighting conditions that are expected near the poles or permanently shadowed regions to prepare astronauts for EVA in environments with minimal sunlight. Training with limited visibility, using lighting equipment on spacesuits and rovers, and conducting scientific operations in minimal lighting are essential for adapting to these conditions. Off-nominal scenarios, such as medical conditions, technical malfunctions, or communication latency, should also be simulated (Walton et al., 2023).

Simulations of EVA on Mars should include extended, multi-day EVA durations and variable surface and weather conditions (Coan et al., 2020). Scenarios should focus on crew autonomy, particularly when managing critical incidents such as equipment malfunctions or environmental hazards or prioritizing and managing limited resources, all while contending with the psychological stresses of increased isolation and confinement.

The volume and structure of lunar and martian surface habitats will differ dramatically from the ISS (see Figure 7). Surface habitats need to ensure adequate minimal volume for logistics, storage, systems, and crew living and work functions (Whitmire et al., 2014; Burke et al., 2022; Howard, 2021). Analogs of these habitats and modules should accurately reflect the logistical constraints and limited volume anticipated for these DRMs to mimic the specific activities and challenges of living and working in confined spaces (see Figures 7–10). Other factors that will contribute to creating a realistic living and working environment include noise levels, temperature regulation, task scheduling, and internal lighting conditions. If these elements are carefully controlled to simulate the actual conditions of space habitats, researchers can align these environmental factors with anticipated conditions of the internal habitat and the EVA environment. Research should reference the habitat-specific challenges, characteristics and requirements of Artemis, Gateway, and Mars habitats listed in Table 4.

Because crews of exploration missions will be required to perform more autonomously, their workload will increase and operational processes may become more complex, especially when crewmembers are required to work in dispersed locations. It is critical that the composition of analog teams reflect the intricate social dynamics of real spaceflight crews including both sexes, and multiple nationalities, technical, and organizational backgrounds. Spaceflight analogs should support assessment of different team structures that focus on defining clear roles, responsibilities, and the importance of managing cultural and interpersonal differences. Behavior should be monitored continuously both at the team and individual levels to evaluate performance in autonomous decision-making scenarios and help determine ways through which safety and performance can be supported. Example Crew Health and Performance Characteristics and Analog Recommendations for Artemis, Gateway, and Mars habitats are listed in Table 5.