Who Goes to Mars — and How They Are Chosen
Selecting the crew for a human Mars mission will be one of the most consequential decisions in the history of space exploration. The people chosen won't just represent their agencies or nations — they will be the first humans to live and work on another planet, likely for 18 to 24 months without any possibility of emergency return. The recruitment and selection process reflects that weight entirely.
How Many Crew Members?
Current mission architecture concepts, including NASA's Moon to Mars framework and studies conducted under the Artemis program, generally converge on a crew size of four to six astronauts for a Mars surface mission. Four is often considered the practical minimum for safety redundancy and workload distribution. Six allows greater task specialization and resilience if a crew member is incapacitated, but adds complexity to life support, consumables, and habitat volume.
The crew must cover an enormous range of competencies. NASA's Human Research Program identifies the ideal crew as having overlapping skills rather than single-function specialists — a recognition that on Mars, there are no backup teams on the ground who can step in physically.
The Candidate Pool
Unlike the early Apollo era, when astronauts were drawn almost exclusively from military test pilots, a Mars mission crew would likely include a broader range of expertise. Mission planners at NASA and ESA have outlined core competencies that any serious candidate would need to demonstrate:
- Medical and surgical training: The crew will be more than 20 light-minutes from Earth at maximum distance, making real-time telemedicine impossible. At least two crew members are expected to hold advanced medical qualifications, with one capable of performing surgical procedures.
- Geology and field science: A primary goal of any Mars mission is scientific investigation of the surface. Crew members trained in planetary geology, astrobiology, or geochemistry will be essential for sample collection and in-field analysis.
- Systems engineering and EVA operations: Operating and repairing life-critical systems — pressure suits, habitats, power generation, ISRU (In-Situ Resource Utilization) equipment — will be a daily reality. Engineering competency is not optional.
- Piloting and navigation: For landing, surface vehicle operations, and potential ascent vehicle operations, at least one or two crew members will require advanced piloting skills.
- Psychological resilience and interpersonal skills: NASA's behavioral health research, including studies from Antarctic analog missions and the Mars-500 isolation study conducted in Moscow between 2010 and 2011, consistently identifies interpersonal conflict and psychological isolation as mission-critical risks.
Physical and Medical Standards
Candidates will face some of the most rigorous medical screening in any professional context. The journey to Mars involves approximately six to nine months of microgravity transit each way, exposing the body to bone density loss (typically 1–2% per month without countermeasures), muscle atrophy, fluid shifts toward the upper body, and vision changes associated with spaceflight-associated neuro-ocular syndrome (SANS). Cardiac function, immune response, and gut microbiome composition are all affected by long-duration spaceflight.
Radiation exposure is a defining constraint. Outside Earth's protective magnetosphere, astronauts face galactic cosmic rays (GCR) and solar particle events (SPEs). NASA's current career radiation limit is 600 millisieverts for astronauts, a threshold a Mars mission could approach or exceed depending on shielding and solar activity. Candidates with certain genetic predispositions to cancer or cardiovascular disease may face additional scrutiny.
Candidates must also demonstrate sustained physical fitness, with particular attention to bone density baselines, cardiovascular health, and ophthalmological status — SANS has been documented in approximately 40–50% of long-duration ISS crew members.
Psychological Profiling and Team Compatibility
Perhaps no aspect of selection is more nuanced — or more critical — than psychological screening. The Mars-500 study, which simulated a 520-day Mars mission in an isolation facility, revealed that sedentary behavior, sleep disruption, and shifting group dynamics were among the most persistent challenges. One crew member became almost entirely inactive over the simulated mission duration.
Agencies use structured psychological assessments, scenario-based evaluations, and extended analog mission deployments — such as NASA's HERA (Human Exploration Research Analog) campaigns at Johnson Space Center, or HI-SEAS habitat studies in Hawaii — to evaluate how candidates perform under isolation, ambiguity, and interpersonal stress. The ability to manage conflict constructively, maintain motivation during repetitive operations, and communicate effectively under time-delay conditions are weighted heavily.
"The psychological demands of a Mars mission may ultimately be more challenging than the physiological ones. Crew cohesion over 30 months — including transit and surface time — is one of the least solved problems in human spaceflight." — Summarizing conclusions from NASA's Human Research Program behavioral health research
International Composition and Agency Coordination
A human Mars mission is unlikely to be a unilateral national effort. NASA's current Moon to Mars strategy explicitly frames international partnership — already demonstrated through the Artemis Accords, signed by over 40 nations as of 2024 — as central to deep space exploration. ESA, JAXA, and other partner agencies would likely contribute both personnel and hardware.
International crew composition introduces additional considerations: language proficiency, cultural dynamics under stress, differing national standards for medical and psychological screening, and legal frameworks governing authority and decision-making on the Martian surface, which currently falls into uncharted territory under the Outer Space Treaty of 1967.
Training Timeline
Once selected, crew members would enter a training pipeline lasting an estimated five to seven years before a Mars departure date. This pipeline would include ISS long-duration missions (as physiological and operational preparation), lunar surface operations under Artemis, geology field training in Mars analog environments such as the Atacama Desert or Devon Island in the Canadian Arctic, EVA suit training for the specific Mars pressure suit architecture, and extensive simulation of the communication time-delay that will characterize all ground interactions during the mission.
Selection itself, in a realistic scenario tied to a late 2030s or early 2040s launch window, would likely begin a decade or more in advance — meaning the next generation of Mars candidates may already be in university classrooms today.