Weightlessness

Weightlessness is when you feel like you have no weight at all, almost like floating in water or air. It is also called zero g-force, zero-g, or microgravity. Normally, we feel weight because the ground or chairs push up against us, but in space, this feeling disappears.

On Earth, weight is the force we feel because of gravity pulling us down. But when we are moving freely, like astronauts in orbit, there is no push against us, so we feel weightless. This happens in orbiting spacecraft where gravity is still present but everything is moving together.

Even though gravity is still acting on objects in space, the way they move makes us feel like there is no gravity. This is called a microgravity environment. It is very important for astronauts to understand weightlessness because it affects how they move and work while they are in space.

Weightlessness in Newtonian mechanics

In simple terms, astronauts feel weightless not because there is no gravity in space, but because they are constantly falling towards Earth while moving forward very fast. This makes them float inside their spacecraft.

Gravity is still present and keeps satellites in orbit around Earth. They stay in space because they move sideways so quickly that they keep "missing" the Earth as they fall. This is why we call it weightlessness — there is no solid surface pushing back against them to make them feel their weight.

Weightless and reduced weight environments

Airplanes have been used since 1959 to create a nearly weightless environment for training astronauts, doing research, and making movies. These airplanes are often called "Vomit Comet".

To make weightlessness, the airplane flies in a 10 km curved path, first going up, then diving down. During this path, the airplane’s controls are adjusted to balance out air resistance, making it feel like it is falling freely in space.

NASA has used versions of these airplanes since 1973. Their current airplane, called "Weightless Wonder VI", is based at Ellington Field near Lyndon B. Johnson Space Center. NASA also offers chances for students to design and test experiments in weightlessness on these flights.

The European Space Agency uses a special Airbus A310-300 airplane to do research in weightlessness. They fly from Bordeaux-Mérignac Airport in France, with each flight giving about 10 minutes of weightlessness. These flights help scientists learn more about space conditions.

People can also experience weightlessness on special commercial flights. These flights, operated from Bordeaux-Merignac, France, let passengers feel weightless for a short time. After the flight, an ESA astronaut talks about space travel. Other companies also offer similar weightless flights using different airplanes.

Ground facilities can also create weightless conditions for research. These are called drop towers or drop tubes. For example, NASA has a tall tower where experiments can fall freely for about 5 seconds. Other places around the world also have drop towers for short periods of weightlessness.

On the International Space Station, there are tiny forces that make it not perfectly weightless, but very close. These forces come from the Sun, other objects, and movements by astronauts.

Objects in orbit around Earth are in a kind of constant free fall, which creates weightlessness. However, there are small effects that make it not perfect weightlessness, like air friction, pressure from sunlight, and movements inside the spacecraft.

If an object could travel to the very center of a planet without stopping, it would feel weightless. This is because the gravity from the planet pulls equally in all directions at the center, canceling out any single direction of pull.

Absence of gravity

To feel like there is almost no gravity, you would need to travel very far away from Earth. For example, to make Earth’s gravity a million times weaker, you would have to go 6 million kilometres away. This is very far and has only been done by special space probes like Voyager 1 and Voyager 2.

When objects orbit Earth, they are still being pulled toward it, but they move so fast sideways that they keep missing the Earth. From their point of view, other objects seem to float because everything is moving together. These objects are in a state called free fall, not true zero gravity.

Health effects

Main articles: Effect of spaceflight on the human body and Space medicine

Living in space without feeling the pull of gravity can change how our bodies work. Our bodies are used to the normal pull of gravity we feel on Earth. When we are in space for a long time, our bodies can start to change.

One common problem people notice right away when they first feel weightlessness is feeling sick. This is called space sickness. Symptoms can include feeling nauseated, vomiting, dizzy, having headaches, feeling tired, and just not feeling well. This was first noticed in 1961. Most people who go to space feel some of these symptoms, but they usually go away after a few days as the body gets used to space.

Longer times in space can cause more changes. Muscles can get weaker, and bones can lose strength. These changes can be helped by exercising, like cycling. Astronauts also wear special pants to help keep their leg bones strong. Other changes can include fluid shifting in the body, changes in how the heart works, and a decrease in the number of red blood cells. These changes usually go back to normal after returning to Earth.

After long trips in space, astronauts can also notice changes in their vision. There are also concerns about how space travel might affect the brain and increase the risk of certain diseases. Scientists are studying these effects to help keep astronauts healthy on future trips to places like Mars.

Space motion sickness

See also: Space adaptation syndrome

Space motion sickness is a type of sickness that affects many astronauts when they first enter space. It feels similar to motion sickness on Earth, with symptoms like feeling disoriented, nauseous, vomiting, tired, and having headaches. It was first noticed in 1961 and can make it hard for astronauts to do their jobs. Sometimes it is so strong that astronauts cannot do important tasks like spacewalks.

Even experienced astronauts can feel this sickness. The symptoms usually last from one to three days but can come back when returning to Earth. Scientists think it happens because of confusion between what the eyes see and what the inner ear feels. There is no perfect fix yet, but some medicines can help, though they may make people feel drowsy.

Musculoskeletal effects

In space, where there is very little gravity, muscles and bones can weaken. Muscles start to shrink after just a few days without the need to support weight. This can lead to weaker muscles and less strength. To fight this, astronauts exercise and use special equipment like elastic bands in their suits to keep muscles active.

Bones also lose density in space, which can increase the risk of fractures. Exercises like cycling help, but other methods such as using vibration devices or special suits are also used. These help keep bones stronger even in the absence of normal gravity.

Cardiovascular effects

Without gravity, the heart and blood vessels change how they work. Fluids in the body shift toward the upper body, which can overload the circulatory system. This can lead to changes in blood pressure and heart function. When astronauts return to Earth, their bodies must adjust again to gravity, which can cause problems like feeling faint or dizzy.

Studies using special flights that mimic weightlessness have helped scientists understand these changes. To help astronauts, measures such as drinking salt solutions or using certain medicines are used to support blood pressure and heart function during and after space travel.

Effects on non-human organisms

Main articles: Effect of spaceflight on the human body, Infection, Medical treatment during spaceflight, and Space medicine

Scientists have studied how space affects other living things. They found that some animals, like cockroaches born in space, grew faster and were tougher. Chicken eggs behaved differently depending on when they were placed in space during their development.

Bacteria, such as a type that can cause food poisoning, became more active in space. Some microbes can even survive in the vacuum of space. These studies help scientists understand how life might behave in space and on other planets.

Commercial applications

See also: Commercial use of space, Scientific research on the International Space Station, and ESA Scientific Research on the International Space Station

High-quality crystals

Scientists are interested in growing special structures called crystals in places with very little gravity, like space stations or satellites. This might help create crystals without flaws, which could be useful for tiny electronic parts. In 2017, an experiment on the International Space Station showed that crystals made there were more uniform than those made on Earth. This could help create medicines in smaller amounts that are easier to use.

History

Isaac Newton explained ideas in the 1600s that help us understand weightlessness.

Later, Konstantin Tsiolkovsky talked about weightlessness in space orbits. In the 1950s, brothers Fritz Haber and Heinz Haber suggested using special parabolic flights to feel like there is no weight.