CÓMO SE ENTRENA UN ASTRONAUTA PARA LA ISS

An extremely competitive selection process

Before ever setting foot on the ISS, every astronaut has already gone through a brutal filter. Each recruitment round at agencies like NASA, ESA, Roscosmos, JAXA, or CSA draws thousands of applicants for what, at best, amounts to a handful of open spots. Selection criteria combine strong technical or scientific credentials — engineering, medicine, physical or life sciences, experience as a military test pilot — with exhaustive medical exams, psychological testing, and evaluations of how well candidates work as a team under pressure. Being brilliant on paper isn't enough: agencies are looking for people who can stay calm and make sound decisions under stress, isolation, and confined quarters for months at a time.

Making it through selection doesn't mean flying right away. It's just the first step of a training program that, from becoming an astronaut candidate to an actual first flight, typically stretches out over several years.

Underwater training for spacewalks

One of the best-known parts of astronaut training happens, somewhat ironically, underwater. To prepare for extravehicular activities (EVAs) — spacewalks — astronauts train in giant neutral buoyancy pools, such as NASA's Neutral Buoyancy Laboratory in Houston, a facility large enough to hold full-scale replicas of ISS modules. By carefully balancing the weight of the suit against the astronaut's own buoyancy, they become neutrally buoyant in the water: neither floating up nor sinking down, a sensation that approximates real weightlessness reasonably well. There, session after session, astronauts rehearse the movements, tool handling, and emergency procedures they'll later have to execute in the vacuum of space, where mistakes are far harder to correct.

Simulators, technical systems, and emergency procedures

A large part of astronaut training is far less dramatic and looks a lot more like an intense engineering course. Astronauts spend years learning the ISS's technical systems: life support, electrical power, communications, thermal control, waste management, and a long list of emergency protocols for fires, depressurization, or critical system failures. Those who will pilot a spacecraft go through additional training in simulators specific to whichever capsule they'll fly — the Russian Soyuz, the American Crew Dragon, or the Chinese Shenzhou — repeating docking maneuvers and contingency procedures until they become almost automatic.

Languages and working as an international team

The ISS is a deeply international project, and that shows in the training. Since much of the Soyuz's systems and shared technical documentation are in Russian, nearly every astronaut preparing for the station, regardless of nationality, learns Russian as part of their training. In turn, Russian astronauts generally train in English, the station's everyday working language. That language crossover is no small detail: future crew members spend long stretches training at different centers across Russia, the United States, Europe, and Japan, living alongside colleagues from other agencies and cultures — which, in practice, doubles as training in communication and teamwork under demanding conditions.

From selection to first launch: a long-distance race

Adding up selection, basic training, technical specialization, and, where applicable, spacecraft-specific training, the full journey to a first ISS flight usually takes several years. It isn't a quick or linear process: it blends theory, hands-on practice, drills, periodic evaluations, and a great deal of physical preparation to keep the body in shape even before leaving Earth. By the time launch day finally arrives, that astronaut has already spent years training for exactly that moment.

Frequently asked questions

How long does astronaut training take?

From selection to first flight usually takes several years, combining general technical training, specialization in ISS systems, and, where applicable, training specific to the spacecraft that will be used.

Why do astronauts train underwater?

Because neutral buoyancy in a giant pool reasonably approximates the feeling of weightlessness, letting astronauts rehearse spacewalk procedures using full-scale replicas of ISS modules before doing them in the vacuum of space.

Do all astronauts have to learn Russian?

Yes, in general every astronaut preparing for the ISS learns Russian, since it's the language of the Soyuz's systems and much of the technical documentation and procedures shared with Roscosmos.

What kind of professional background do space agencies look for?

They typically look for advanced training in engineering, medicine, science, or military aviation, along with strong physical and psychological fitness, teamwork skills, and the ability to adapt to demanding, multicultural environments.