Astronaut Selection in the Modern Era: Criteria, Procedures, and Comparative Practices at NASA and ESA

Astronaut selection is a foundational process for ensuring the safety, performance, and sustainability of human spaceflight missions. As exploration objectives expand beyond low-Earth orbit toward sustained lunar operations and future Mars missions, selection frameworks must identify individuals with advanced technical competence, physical robustness, psychological resilience, and strong team performance capabilities. This paper examines contemporary astronaut selection practices with a focus on the criteria, procedural stages, and comparative approaches employed by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). Recent se-lection campaigns associated with NASA’s Artemis program and ESA’s astronaut re-cruitment initiatives are discussed. Particular emphasis is placed on the increasing in-tegration of quantitative human-factor metrics into selection decisions. The analysis highlights shared selection philosophies, institutional differences, and implications for long-duration exploration missions.