Artemis mission astronaut underwater training

How do astronauts train for zero-gravity environments?

Last Updated: October 24, 2022

Going to and living in space allows us to test the boundaries of science, prep us for the future of space travel, and help us better understand ourselves and science here on Earth.

But how do astronauts train for space, particularly the zero gravity/ microgravity environment that is so different from the gravity we live in here on Earth?

While we can’t take away gravity here on Earth, there are ways that we can simulate reduced/ microgravity environments to ensure that they are prepared to live and work in space.

Brief Summary of Astronaut Training

Astronauts go through an extremely rigorous selection process. Once they pass the initial selection process, selected candidates undergo about two years of intensive training before beginning specialized mission training and officially becoming eligible for a flight assignment. During this intensive training “boot camp”, they are trained in a wide variety of fields necessary for living and working on a space station including space station systems, Earth sciences, meteorology, space science, engineering, land and water survival, aircraft operations, and scuba diving. Once this training is complete, they receive mission-specific training with experienced astronauts. 300 hours of simulator training on a variety of systems and activities and over 1,000 approaches in aircraft training are utilized to help prepare them. 

They practice on Earth-bound versions of equipment and instruments on the space station so they can do science experiments in space as well as perform maintenance on the space station itself. But knowing how to perform these functions on Earth in Earth gravity is very different than performing them in the microgravity environment of space. 

Here on Earth, we experience the pull of Earth’s gravity, due its mass, which keeps us from floating off into space. Humans and all other life on Earth have adapted specifically to Earth’s gravity. We can easily walk around, jump, do our work, and do other actions throughout the day without too much effort against gravity.

But in space, we don’t feel the same effects as we are not on Earth. Space is a vacuum and while technically you are still influenced by the impacts of gravity from the masses of other astronomical objects in the solar system on an atomic level, the effect is effectively nonexistent unless you are close enough to be pulled in by that body’s intense gravitational pull. 

Other planets and astronomical objects have different gravitational impacts based on their mass. Some have a stronger gravitational pull, meaning much more effort on our part to do anything while some have a weaker gravitational pull, meaning it requires less effort to perform actions. On the International Space Station which is in orbit around the Earth, the space station and all of its occupants are in freefall and therefore essentially weightless, floating. 

Astronauts train their bodies to work in gravitational environments different from Earth so that they are prepared to live and work in space. While microgravity provides some benefits like being able to work from any surface inside the pressurized space station (floor, walls, or even ceiling) since you float, a lot less effort is needed to move you and objects, which can be difficult to adapt to. There is no difference between up and down. Even something like eating their food can be something astronauts need to adjust for. Liquids will fly away in a bubble shape whilst crumbly food might fly off in every direction.

When you put something “down” it doesn’t stay there unless it’s attached to something. You float away if you are not attached to something. All of these differences can be weird enough in regular daily activities, but when you are working, such as doing science experiments or maintenance inside the space station, detail is crucial in ensuring success which is complicated by the new environment.

In addition, when maintenance is needed outside the space station, astronauts need space suits to protect them from radiation and the harsh environment of space. They have to work on very detailed systems with tools in space wearing heavy gloves and other equipment while making sure they and their tools don’t float away into the vastness of space. These spacewalks or Extravehicular Activities (EVAs) have many risks so adequate equipment and training are vital.

How do we simulate a microgravity environment here on Earth to prepare astronauts for their work in space on the International Space Station?

spacewalk astronaut spacesuit

An astronaut performing a spacewalk, also known as extravehicular activity (EVA).

The Beginning: NASA’s Reduced Gravity Program

In 1950, it was hypothesized that microgravity in space could be simulated in airplanes during a parabolic or wave-like flight path that featured a series of steep climbs and sharp dives since as the plane climbs up the “hump” of the climb, occupants achieve weightlessness. In 1957, the Air Force began training Mercury and Apollo astronauts in what would become the Reduced Gravity Program.

NASA operated the Reduced Gravity Training Program with a variety of planes including C-131s, KC-135 Stratotankers, and Navy C-9s from 1957 through 2008. Trips in these planes allow astronauts to experience weightlessness for about a minute at the hump of each climb. Changing the flight plan can result in different simulations of various levels of gravity such as Martian gravity at about a third of Earth’s or the moon’s gravity at about a sixth of Earth’s. Trips often include multiple crests so that they can increase the amount of time in weightless environments. While brief, these microgravity trips help astronauts learn how their bodies move in microgravity so that they are better prepared for daily life inside the space station.

In 2008, a private company called Zero Gravity Corp, took over the Reduced Gravity Training Program. Using a modified Boeing 747 called G Force One, they have trained astronauts for microgravity since then, but also offer luxury experiences for space tourists and celebrities starting at about $8,200 as of this publication.

However, the trips are not perfect. The rollercoaster-like movements often have an unsettling effect on people’s stomachs creating the nickname “the vomit comet” for the reduced gravity training plane. About a third of people training in the “vomit comet” become violently ill, another third become moderately ill, and the final third have no ill effects.

The “vomit comet” helps astronauts get a feel for living on the space station, moving around, interacting with objects, etc. but life inside the space station is not the only concern.

astronaut training inside reduced gravity aircraft

Astronauts training inside a reduced gravity aircraft. Image Credit: NASA.

Neutral Buoyancy Training

While the “vomit comet” helps acclimate astronauts to weightlessness inside the pressurized ISS, it doesn’t allow them to practice their duties in zero-g/ microgravity during EVAs. And so, in the 1980s, NASA began utilizing the concept of neutral buoyancy. Buoyancy refers to an object’s ability to either sink or float based on its density in comparison to the pressure of the water. Utilizing a combination of weights and flotation devices, you can make an object have an equal tendency to either sink or float, meaning a heavy object can appear to float underwater and easily be manipulated, similar to a microgravity environment.

Beginning in 1980, NASA began utilizing neutral buoyancy in astronaut training in their Weightless Environment Training Facility (WETF), located at Johnson Space Center (JSC) in Houston, Texas, a pool 24 meters (78 ft) by 10 meters (33 ft), with a depth of 7.6 meters (25 ft). Astronauts utilized adapted space suits with adequate weight and flotation to create neutral buoyancy and practice their maintenance duties on life-size mock-ups of space station components underwater with the help of divers. With the upcoming International Space Station, NASA knew that this training facility would not be big enough for adequate training.

Construction on the Neutral Buoyancy Lab (NBL), as part of the Sonny Carter Training Facility near JSC, began in 1995 with operations beginning in 1997. The NBL is 62 meters (202 ft) in length, 31 meters (102 ft) wide, and 12 meters (40 ft) deep, containing 23 million liters (6.2 million US gallons) of water. Readers of our previous article on the size of the ISS will note that this is not as big as the International Space Station, but provides enough space to adequately prepare astronauts on a life-size mock-up of the most important components and swap out components based on the training required.

Astronauts and divers use audio communications to ensure continual communication with supervisors in the control room who watch everything from closed-circuit TVs to ensure that the training is completed effectively and safely. Astronauts spend approximately 10 hours underwater for every hour they spend walking in space.

While the NBL provides a nearly weightless microgravity environment, it’s not perfect with two main detriments. They may be neutrally buoyant, but they feel their weight while inside the suits and the drag from the water hinders motion, making some tasks easier, and others more difficult, to perform in neutral buoyancy than in zero gravity. 

It’s also expected that it will take new astronauts a few days to adjust to living in microgravity on the International Space Station as they learn exactly how their body works in the new environment “24/7”. However, practicing their duties repeatedly in the NBL (under the guidance of experienced astronauts who have performed these duties in space) helps prepare them as best we can here on Earth for what they will experience on the space station. 

To get a sense of the NBL, try out this tour from NASA and/or this video from Jonathon Bird, a documentarian who specializes in underwater filming.

astronaut training underwater

Imagine what it would be like performing simple tasks whilst in a low gravity environment, whilst wearing such a bulky spacesuit. Image Credit: NASA


It’s not easy to prepare for a microgravity environment here on Earth. However, by utilizing training situations, with experienced astronauts who can guide trainees, in programs such as the Reduced Gravity Program/ “Vomit Comet” and the Neutral Buoyancy Lab, we are able to train astronauts for their missions in microgravity/ zero-gravity environments in space.

As preparations for the Artemis moon mission are ramping up, we know for certain that those Zero-G training facilities will be very busy over the next few years.

Sarah H.

Sarah Hoffschwelle is a freelance writer who covers a combination of topics including astronomy, general science and STEM, self-development, art, and societal commentary. In the past, Sarah worked in educational nonprofits providing free-choice learning experiences for audiences ages 2-99. As a lifelong space nerd, she loves sharing the universe with others through her words. She currently writes on Medium at and authors self-help and children’s books.

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