Growing up, many children dream of becoming astronauts and going to the moon.

In order to get that elusive job, would-be astronauts must make it through a competition. The space agency chose 10 candidates from more than 12,000 applicants.

US citizenship and a master's degree are included in NASA's basic requirements. In order to pass NASA's physical exams, astronauts need to be in top shape.

More than 350 people have become astronauts since NASA's first class of astronauts in 1959.

(1961) Astronaut nurse Delores B. O'Hara, R.N., in the Aeromedical Laboratory at Cape Canaveral, Florida, takes a blood sample from Mercury astronaut John H. Glenn Jr.
An astronaut nurse takes a blood sample from NASA astronaut John Glenn in 1961.
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Military men were the first to become astronauts during the space race between the US and the Soviet Union. The people who have walked on the moon are all white. NASA wants to land the first woman and person of color on the moon during its long-awaited Artemis mission, which will take place in the year 2024.

A two-year training course is required for astronauts to become fully qualified. Massive pools and hot deserts are some of the places where astronauts are trained to test their skills.

Using mockups of the Gemini and Agena spacecraft in the pool at the McDonogh School in Owings Mills, Maryland, astronaut Edwin E. “Buzz” Aldrin trains for his Gemini XII spacewalks in October 1966.
Buzz Aldrin trains underwater for a spacewalk in October 1966.
NASA

Astronauts float in a massive indoor pool with a submerged spacecraft to practice spacewalks

In order to prepare for travel beyond the confines of a spaceship, astronauts train underwater. They will experience microgravity while working in space.

When astronauts leave the spaceship to work in the vacuum of space, they use a mock-up of it in the pool.

Astronaut Carl J Meade, STS-64 mission specialist, is being submerged prior to an underwater simulation of a space walk scheduled for his September mission, 10th August 1994.
NASA astronaut Carl J. Meade practices an underwater spacewalk on August 10, 1994.
Space Frontiers/Archive Photos/Getty Images

Most modern spacewalk training takes place at the neutral buoyancy laboratory at the Johnson Space Center. A partial mock-up of the International Space Station can be found in the massive pool, which contains over 6 million gallons of water.

Divers at NASA’s Neutral Buoyancy Laboratory turned off the lights to simulate what an Artemis astronaut might experience at the lunar south pole in February 2022.
Divers at NASA's Neutral Buoyancy Laboratory turned off the lights to simulate what an Artemis astronaut might experience at the lunar south pole in February.
NASA / Johnson Space Center

Astronauts experience weightlessness by riding a plane nicknamed the 'vomit comet'

Project Mercury astronauts on board a C-131 Samaritan flying as the
Project Mercury astronauts on board a C-131, one of the first planes affectionately nicknamed the "vomit comet," in November 1958.
NASA

NASA's reduced gravity research began in 1959 A zero gravity airplane called the "vomit comet" is used as a training tool for astronauts.

The plane's passengers achieve about 25 seconds of zero gravity once they reach the top of the wave through a series of steep climbs and dives.

NASA's KC-135A aircraft, which was part of the program, was retired in 2004.

US astronaut Buzz Aldrin wearing his space suit practices to move in weightlessness aboard a plane on July 9, 1969 seven days before Apollo XI space mission launch to the moon.
Buzz Aldrin floats in a moment of weightlessness aboard a plane on July 9, 1969.
NASA

A floating lab can be found on the plane. Medical studies and motion sickness experiments are performed on these flights because the plane's roller-coaster-like maneuvers make passengers feel unwell.

The plane has been used for film shoots. The zero gravity scenes in "Apollo 13" were filmed by actors Tom Hanks, Kevin Bacon, and Bill Paxton.

American astronaut Anna Lee Fisher services a 'damaged' tile during a simulation of repair work during EVA (Extravehicular Activity) in the weightless environment of a Boeing KC-135 Stratotanker (aka the 'Vomit Comet'), 3rd July 1980. The aircraft flies in a series of parabolic curves in order to simulate microgravity for short periods. The tool she is using is part of the thermal protection system (TPS) repair kit supplied in case of issues prior to re-entry.
Astronaut Anna Lee Fisher practices doing repair work in the "vomit comet" on July 3, 1980.
Space Frontiers/Archive Photos/Getty Images

Astronauts endure grueling desert survival training in case of an emergency landing

NASA astronauts have learned survival techniques in case they have to make an emergency landing.

Frank Borman, Neil Armstrong, John Young and Deke Slayton during desert survival training in Nevada on Aug. 13, 1964.
Frank Borman, Neil Armstrong, John Young, and Deke Slayton during desert survival training in Nevada on August 13, 1964.
NASA

Apollo 11 astronauts traveled to Nevada in 1964 to practice their survival skills in the desert. They are wearing clothes made from parachutes to stay cool in the heat.

Astronaut Franklin Story Musgrave at a water still made during desert survival training near Pasco, Washington, US, 5th August 1969.
Astronaut Franklin Story Musgrave gathering and purifying water during desert survival training near Pasco, Washington, on August 5, 1969.
Space Frontiers/Getty Images

The environment of the desert is similar to an alien planet. The space agency will conduct two field trainings in the Arizona desert that are similar to the moon.

An astronaut candidate starts a fire as part of NASA's wilderness survival training, near Rangeley, Maine in 2013.
An astronaut candidate starts a fire as part of NASA's wilderness survival training, near Rangeley, Maine in 2013.
NASA

Early astronauts trained on a disorienting contraption that mimicked a spacecraft spinning out of control

Training
The gimbal rig, seen here in 1959, was developed to train astronauts to gain control of a spinning spacecraft.
NASA

During the space race, astronauts trained on a multi-axis trainer, which twirled them around in a wild combination of spins. The idea was to get astronauts used to the rides in a spaceship.

"That was one of the more demanding tests or training exercises we went through anywhere in the whole training floor for spaceflight," John Glenn said in a NASA Glenn Research Center video. We hated that rig.

Pilot Jerrie Cobb trains in the Multi-axis Space Test Intertia Facility in 1960.
Pilot Jerrie Cobb trains in the gimbal rig, or the Multi-axis Space Test Inertia Facility, in 1960.
NASA

In 1960, the seven original Project Mercury astronauts and 13 women of Mercury 13 were trained. The rig is in motion.

The spinning contraption is no longer used by NASA since they don't need spacefarers to control their spin.

Astronauts test their tolerance for intense gravitational force on a whirling machine

Astronaut Walter M. Schirra Jr. prepares to enter the Johnsville Centrifuge in 1960.
Walter Schirra Jr., an astronaut, enters the Johnsville Centrifuge in 1960.
NASA

NASA used a machine called a human Centrifuge to test the effects of gravity on astronauts preparing to go to the moon.

A human can be held at the end of a human Centrifuge with a capsule. The astronauts test their tolerance for the force of gravity.

View of a centrifuge with fifty-foot arm used in astronaut training at NASA's Manned Space Center (later renamed the Lyndon B Johnson Space Center), Houston, Texas, 1960s.
A human centrifuge with a 50-foot arm for astronaut training at NASA's Manned Space Center, in the 1960s.
NASA/Interim Archives/Getty Images

Glenn said in his 2000 memoir that he was acting as a "guinea pig" for what a human being might experience being launched into space or reentering the atmosphere.

Keeping in touch with psychologists while in space helps astronauts adjust to the highly stressful environment

Mercury astronaut M. Scott Carpenter lies on a bed with biosensors attached to his head during astronaut training activities at Cape Canaveral in 1962.
M. Scott Carpenter, an astronaut, lies on a bed with biosensors attached to his head during astronaut training at Cape Canaveral in 1962.
HUM Images/Universal Images Group via Getty Images

People who aren't fit for space travel are screened for psychological and psychiatric problems.

The mental burden of space travel was understood by NASA as more humans ventured into space. There was a person that became obsessed with the hatch. All I have to do is turn the handle and the hatch will open. In a 2001 interview, Henry Hartsfield said that one of his earlier missions was frightening. The hatch was locked.

Scott Kelly peers out one of the International Space Station’s windows during his year in orbit in 2015.
Scott Kelly peers out one of the International Space Station’s windows during his year in orbit in 2015.
NASA

Going to space is a lot of work. NASA's human research program found that crew members endure sleep changes, radiation exposure, and long bouts of isolation. Crew members on the International Space Station talk with medical staff through private video conferences after they become astronauts.

NASA's goal of sending humans to the moon and Mars in the not-so- distant future will pose a challenge to the mental well-being of astronauts.