Astronaut

An astronaut is a person who is trained, equipped, and sent into space by a human spaceflight program. Astronauts serve as the commander or a crew member of a spacecraft. The word comes from the Ancient Greek words astron, meaning "star," and nautes, meaning "sailor." The word is usually used for people who travel to space as their job. Sometimes it is also used for anyone who goes into space, such as scientists, politicians, journalists, and space tourists.

In the United States, "astronaut" is an official title used by three groups: NASA, the FAA, and the military. The word is also used for people who finish certain training courses and are ready to fly in a spacecraft, even if they have never been to space.

In general, the word "astronaut" can be used for any person who travels to space, from any country. However, people from Russia or the Soviet Union are usually called cosmonauts. This word comes from the Russian word "kosmos," which means "space." Recent successes of the China Manned Space Program have led to the informal word taikonaut. This word comes from the Mandarin word "tàikōng," which also means "space."

As of April 2026, 781 people have flown in space, and many of them have visited space stations. More than 290 people have visited the International Space Station, and 105 people have visited the Mir station. Until 2002, only governments sent and trained astronauts, either through the military or through civilian space agencies. In 2004, the SpaceShipOne flew a short trip into space. It was paid for by private money, and this started a new kind of astronaut called the commercial astronaut.

Some people use the word "astronaut" in a strict way. In the United States, three groups use the term: NASA, the Federal Aviation Administration, and the military. Each group has slightly different rules. NASA and the military use it only for their own workers who meet certain standards. In Europe, the European Astronaut Corps calls graduates of its training "ESA astronauts." The Collins and Cambridge English Dictionaries describe astronauts as people trained to fly in a spacecraft. What counts as human spaceflight also differs from place to place. Some rules focus on the height where the air is very thin, and centrifugal force rather than aerodynamic force holds up most of the flying object. The Fédération Aéronautique Internationale (FAI) only counts flights that pass the Kármán line, which is about 100 kilometers (62 mi) high. In the United States, astronauts who go above 80 kilometres (50 mi) receive astronaut wings.

As of 22 May 2026^[update], 781 people from 55 countries have reached 100 km (62 mi) or higher. Of these, 28 people have traveled beyond low Earth orbit. Everyone except Canadian Jeremy Hansen is from the United States. Jim Lovell, John Young, and Eugene Cernan have each done it twice. Ten crewed missions have gone beyond low Earth orbit. Apollo 8 and Apollo 10 orbited the Moon without landing. Apollos 11–12 and 14–17 landed on it, and Apollo 13 and Artemis II flew around it. The American astronaut Wally Schirra wrote in his 1988 autobiography that only people who control the spacecraft should be called astronauts. He applied this idea to membership in the Society of Experimental Test Pilots.

Terminology

See also: Astronaut ranks and positions

In 1959, before either the United States or the Soviet Union had sent people into space, NASA leaders T. Keith Glennan and Hugh Dryden talked about whether space crew members should be called astronauts or cosmonauts. Dryden liked "cosmonaut" because flights would go out into the wider cosmos. "Astro" suggested travel to the stars. Most members of the Space Task Group liked "astronaut" better, and that word became the common American term. In 1961, the Soviet Union sent the first person into space, Yuri Gagarin. The Soviet word for this kind of traveler anglicizes to "cosmonaut."

A professional space traveler is called an astronaut. The first known use of the word in its modern sense was by Neil R. Jones in a 1930 short story. NASA uses the term for any crew member on its spacecraft that goes into Earth orbit or beyond. The European Space Agency uses it in a similar way.

Main article: Soviet space program

An astronaut who works for the Russian Federal Space Agency or the Soviet space program is called a cosmonaut. The first cosmonaut was Yuri Gagarin. Valentina Tereshkova was the first woman to fly in space. In 1995, Norman Thagard became the first American to ride to space on a Russian launch vehicle.

In Chinese, astronauts from China are called hángtiān yuán. Some news organizations use the English word taikonaut. Other words, such as spationaut for French space travelers, have also been used. As space tourism grew, NASA and the Russian Federal Space Agency agreed to use the term "spaceflight participant" for space travelers who are not professional astronauts. In the United States, the Federal Aviation Administration has its own definitions, such as commercial astronaut. A 2021 order changed the rules for who counts as an astronaut.

Space travel milestones

See also: Spaceflight records and Timeline of space travel by nationality

Many people have reached firsts in space. Yuri Gagarin of the Soviet Union was the first person in space, in 1961. Valentina Tereshkova was the first woman in space, in 1963. Alan Shepard was the first American in space. John Glenn was the first American to orbit the Earth. Sally Ride became the first American woman in space in 1983. Alexei Leonov made the first spacewalk in 1965. In 1968, William Anders became the first Asian-born astronaut. He was born in Hong Kong. Over the years, the Soviet Union and the United States also brought people from other countries into space. Pham Tuan of Vietnam became the first Asian person in space in 1980. Marc Garneau was the first of eight Canadian astronauts to fly in space. In 1991, Helen Sharman became the first Briton to fly in space. In 2003, Yang Liwei became China's first astronaut to fly on its own spacecraft, the Shenzhou 5.

Some records are about age, time, and distance. The youngest person to reach space is Oliver Daemen, who was 18 years old. The oldest person to reach space is William Shatner, who was 90 years old. Valeri Polyakov spent the longest time in space, 438 days. In 2026, Artemis II flew around the Moon. It set the record for the farthest distance from Earth that an astronaut has traveled. The first civilian in space was Valentina Tereshkova again. In 2001, Dennis Tito became the first space tourist who paid for his own trip. Jared Isaacman was the first person to pay for a mission to orbit. He commanded Inspiration4 in 2021.

Further information: Space tourism

Training

See also: Astronaut ranks and positions

Main article: Educator Astronaut Project

The first NASA astronauts were chosen for training in 1959. Early on, people often needed military jet test pilot or engineering training to be chosen. John Glenn and Scott Carpenter of the Mercury Seven did not have a university degree when they were chosen, though. At first, only military pilots could be picked. The first astronauts of both the US and the USSR were often jet fighter test pilots. After being chosen, NASA astronauts train for twenty months in many areas. This includes extravehicular activity practice in a place like NASA's Neutral Buoyancy Laboratory. Astronaut candidates may also feel short periods of weightlessness (microgravity) in the "Vomit Comet," which is a pair of modified KC-135s that fly parabolic flights. Those planes were retired in 2000 and 2004, and a C-9 replaced them in 2005. Astronauts also need flight hours in fast jets, mostly in T-38 jet aircraft from Ellington Field, which is close to the Johnson Space Center. The Shuttle Training Aircraft is also kept there, although most of its flights take off from Edwards Air Force Base. Astronauts must learn to fly the Space Shuttle and know the International Space Station well.

NASA candidates must be United States citizens and have a master's degree in a STEM field, such as engineering, biological science, physical science, computer science or mathematics. They also need at least two years of related work after their degree, or at least 1,000 hours of pilot-in-command time in jets. They must also pass the NASA long-duration flight physical. Leadership, teamwork and communication skills are also important. The master's requirement can be met in other ways too. For example, two years of doctoral study in a related field, a Doctor of Medicine or Doctor of Osteopathic Medicine degree, or a nationally recognized test pilot school program can count. Mission Specialist Educators, or "Educator Astronauts," need a bachelor's degree and teaching experience from kindergarten through twelfth grade. An advanced degree is strongly wanted but not required. Educator astronauts were first chosen in 2004. As of 2007, there are three: Joseph M. Acaba, Richard R. Arnold, and Dorothy Metcalf-Lindenburger. The media considers Barbara Morgan, who was chosen as back-up teacher to Christa McAuliffe in 1985, the first Educator astronaut, although she trained as a mission specialist. The Educator Astronaut program follows the Teacher in Space program from the 1980s.

Health risks of space travel

See also: Effect of spaceflight on the human body and Space medicine

Astronauts can face many health problems. These include decompression sickness, barotrauma, immunodeficiencies, loss of bone and muscle, loss of eyesight, orthostatic intolerance, sleep disturbances, and radiation injury. The National Space Biomedical Research Institute (NSBRI) is running large medical studies in space to look into these problems. In one of them, the Advanced Diagnostic Ultrasound in Microgravity Study, astronauts, including former International Space Station (ISS) commanders Leroy Chiao and Gennady Padalka, use ultrasound scans while experts on the ground guide them. These methods are now also used for sports injuries and in rural care, where a trained doctor is often hard to reach. In a 2006 Space Shuttle experiment, Salmonella typhimurium, a bacterium that can cause food poisoning, became more harmful when grown in space. In 2017, bacteria were found to resist antibiotics better and to grow well in the almost no-gravity conditions of space. Microorganisms have also been seen to survive the vacuum of outer space.

In December 2012, a NASA-supported study reported that human spaceflight may harm the brain and speed up the start of Alzheimer's disease. In October 2015, the NASA Office of Inspector General issued a health hazards report about space exploration, including a human mission to Mars. Over the past decade, doctors and scientists at NASA have seen vision problems in astronauts on long missions. This is known as visual impairment intracranial pressure (VIIP), and many space explorers have reported it after long stays on the ISS. On 2 November 2017, scientists reported that the position and structure of the brain had changed in astronauts who took trips in space, based on MRI studies. Longer trips were linked to bigger brain changes. Being in space can weaken the body, affecting the otolith organs and the adaptive abilities of the central nervous system. Zero gravity and cosmic rays can have many effects on astronauts. In October 2018, NASA-funded researchers found that long journeys into outer space, including travel to the planet Mars, may greatly damage the gastrointestinal tissues of astronauts and age them early. Also in 2018, researchers found five Enterobacter bugandensis bacterial strains on the ISS. None were pathogenic to humans, but the researchers said that microorganisms there should be carefully monitored. A study by Russian scientists published in April 2019 found that space radiation could temporarily slow the making of new cells in the brain's memory centers, without affecting intellectual abilities. Finally, a 2020 study of the brains of eight male Russian cosmonauts, after they returned from long stays on the ISS, showed many physiological adaptations, including microstructural changes. The study found that spaceflight can lead to new motor skills (dexterity), but also slightly weaker vision. It was the first to give clear evidence of sensorimotor neuroplasticity, the brain's ability to change through growth and reorganization.

Food and drink

Main article: Space food

An astronaut on the International Space Station needs about 830 g (29 oz) of food for each meal every day. This includes about 120 g (4.2 oz) of packaging for each meal.

Space Shuttle astronauts worked with nutritionists to choose menus they liked. Five months before a flight, the shuttle dietitian picked menus and checked their nutrition. Foods are tested to see how they will behave in low gravity. The average American uses about 35 US gallons (130 L) of water every day on Earth. On the ISS, astronauts keep their water use to about three US gallons (11 L) per day.

Insignia

In Russia, cosmonauts who finish their missions are often given the title Pilot-Cosmonaut of the Russian Federation. They may also receive Hero of the Russian Federation. This follows the practice in the USSR, where cosmonauts were usually given the title Hero of the Soviet Union.

At NASA, people who finish astronaut training receive a silver lapel pin. After they have flown in space, they receive a gold pin. U.S. astronauts who are also in the military can earn a special badge called the Astronaut Badge after a trip to space. The United States Air Force also gives an Astronaut Badge to its pilots who fly higher than 50 miles (80 km).

Deaths

For a more comprehensive list, see List of spaceflight-related accidents and incidents § Astronaut fatalities.

Astronaut David Scott left a memorial on the Moon during his 1971 Apollo 15 mission. It was a small statuette called Fallen Astronaut. A list of names of astronauts and cosmonauts who had died in service was placed with it.

The Space Mirror Memorial stands on the grounds of the Kennedy Space Center Visitor Complex. The Astronauts Memorial Foundation looks after it. It honors men and women who died during spaceflight and training in the United States space programs. The names include NASA astronauts, an X-15 test pilot, a U.S. Air Force officer, and a civilian spaceflight participant.