Astronaut candidates need a strong science or technical education. NASA asks for a master's degree in a STEM field. Candidates must also be able to pass the astronaut physical. As of November 2026, NASA astronaut applicants must be U.S. citizens and have at least three years of related work experience after their degree. ESA astronauts are chosen only from countries that are ESA Member States and Associated Member States. New NASA astronauts spend about two years learning basic astronaut skills at Johnson Space Center, and astronaut training is long and intensive.

Astronauts practice spacewalks in a huge pool of water, the closest you can get to microgravity on Earth. In water, a neutrally buoyant object neither floats nor sinks, which is how a pool imitates weightlessness. A centrifuge is a spinning machine that presses on astronauts with the same g-forces they feel during launch. In one centrifuge session ESA candidates were pushed from chest to back with up to 6G, while talking to medical staff. Centrifuge training teaches astronauts to work while the high forces of launch press on their bodies.

Astronauts wear spacesuits for spacewalks, outside the station, because space is airless and dangerous without one. A spacesuit backpack holds oxygen for astronauts to breathe and removes the carbon dioxide they breathe out. In the near vacuum of space there is no air to carry heat away, so suits cool astronauts with water in tubes. The flexible parts of a spacewalk suit are made from as many as 16 layers, with about 300 feet of cooling tubes closest to the skin. Spacewalk gloves must let astronauts pick up objects, and fingers are the part of the body that gets coldest in space.

Without gravity pressing down on them, astronauts' bones lose about 1 to 1.5 percent of their mineral density each month. Astronauts also lose muscle mass in space faster than they would on Earth. The loss of bone and muscle in space is called atrophy. Astronauts exercise to keep their muscles and bones strong. As of November 2026, crews on the space station exercise about two hours a day, and NASA schedules two and a half hours.

Apollo 11 carried Neil Armstrong, Michael Collins and Buzz Aldrin, and launched on July 16, 1969. On July 20, 1969, Armstrong became the first person to walk on the Moon, and Aldrin joined him. As he stepped onto the Moon, Armstrong said, "That's one small step for man, one giant leap for mankind." While they were on the Moon, Collins stayed in orbit in the command module Columbia. Armstrong and Aldrin spent about 21 hours on the Moon's surface, with about two and a half hours of it outside. The three astronauts splashed down in Hawaii on July 24, 1969. Apollo missions brought back more than 800 pounds of Moon rock and soil.

On April 12, 1961, Yuri Gagarin became the first person to orbit Earth, in Vostok 1. Alan Shepard became the first American in space on May 5, 1961, in a 15-minute flight that did not go all the way around Earth. On March 18, 1965, Alexei Leonov became the first person to float in open space. The first American spacewalk, by Ed White, came about three months later.

Valentina Tereshkova became the first woman in space on June 16, 1963. Her Vostok 6 flight lasted 70.8 hours and made 48 orbits of Earth. Sally Ride became the first American woman in space on June 18, 1983. She studied physics and English literature at Stanford University. Ride and five other women were chosen in 1978 for NASA's Astronaut Group 8.

As of November 2026, NASA says Mars remains its horizon goal for human exploration, and its goal is to send humans there as early as the 2030s. As of November 2026, getting to Mars could take up to 6 to 9 months, and a round trip with a long wait for the planets to line up could take 3 to 3.5 years. Radio signals take roughly 3 to 25 minutes to travel between Earth and Mars, depending on where the planets are. Nothing can travel faster than light, so a Mars crew's messages will always arrive late. Because help and supplies would be far away, a Mars crew has to plan for self-sufficiency.

Artemis II launched on April 1, 2026, from Kennedy Space Center in Florida. It carried NASA astronauts Reid Wiseman, Victor Glover and Christina Koch. As of November 2026, NASA plans Artemis III for 2027: four astronauts in the Orion spacecraft on a test flight in low Earth orbit, not to the Moon. As of November 2026, NASA plans for its first crewed Moon landing under the Artemis program to take place in 2028.

Words to know

• atrophy: wasting away
• centrifuge: spinning machine
• vacuum: space without air
• buoyant: able to float
• splashed: landed in water