Artificial gravity

Space can feel very light.

Astronauts can spin to feel heavy. This is called artificial gravity.

It helps our bodies stay strong. Being weightless can hurt our muscles. It can also hurt our eyes.

Spinning makes us feel like we are on Earth. This could help people travel to Mars. It is a clever way to stay healthy in space.

In space, astronauts feel weightless. This can hurt their bodies. It can change their blood and muscles. It can even affect their eyes.

To fix this, scientists think about artificial gravity. This is a way to make people feel heavy again.

One way to do this is by spinning. If a spacecraft spins, it creates a centrifugal force. This force pushes objects toward the outer walls. To a person inside, it feels like gravity pulls them down.

But spinning has some tricky parts. In a small spinning ship, the force changes. A person's feet might feel heavier than their head. This can cause dizziness. This happens because of the Coriolis effect. This is a force that acts on things that move inside a spinning room.

It can make people feel sick.

To stay safe, ships should be very large. A big ship can spin slowly. This makes the force feel more like Earth.

Scientists have many ideas for these ships. Some want to use a ring shape. Others want to tie two parts together with a long cord.

Artificial gravity is a way to make people feel weight in space. In space, everything is weightless, which can be hard on the human body. Scientists want to create a force that mimics the pull of Earth. This is often done through rotation, or spinning. This spinning creates a force that pushes things outward. To a person inside, this feels like gravity pulling them down toward the floor.

This way of working uses a thing called centrifugal force. When a spacecraft spins, the walls push inward on everything inside. This inward push is called centripetal force. Because of this, objects feel like they are being pushed toward the outer hull. This force acts like a floor for anyone standing inside. However, the force is not the same everywhere. It gets stronger as you move further from the center of the spin. This means a person's feet might feel heavier than their head.

People have tested these ideas for a long time. In 1966, the Gemini 11 mission tried to make artificial gravity. The capsule was tied to a vehicle with a 36-meter tether. They used thrusters to spin the two parts together. The gravity they made was very small, only 0.00015 g. It was not enough for astronauts to feel, but objects moved toward the floor. Later, in 1975 and 1977, satellites named Bion 3 and Bion 4 used centrifuges. These machines put small specimens in an artificial gravity environment.

There are many reasons why we need this technology. Long trips in weightlessness can cause health problems. In 1991, a Spacelab experiment showed that muscles and white blood cells can decrease. Blood volume also drops by 10% in the first day. Artificial gravity could help prevent these issues on long trips to Mars. Many designs have been proposed to solve this. The 2011 NASA MMSEV proposal included a spinning habitat for up to six people. Another idea, the Nautilus-X, was a concept for a spinning station.

Designing these ships is a very hard job. If a ship is too small, it must spin very fast. Fast spinning can cause the Coriolis effect. This effect makes moving objects curve and can cause dizziness or nausea. This happens because the force affects the inner ear. To avoid this, ships should be very large so they can spin slowly. A slow spin of 2 rpm or less might prevent these bad feelings. Some scientists even suggested using water as a weight to keep the ship from wobbling.

Artificial gravity is the creation of an inertial force that mimics the effects of gravity. In the vacuum of space, astronauts experience weightlessness, which can be very difficult for the human body to endure. Scientists can simulate gravity through rotation or through linear acceleration, such as the push from a rocket engine. Because of the equivalence principle, the feeling of linear acceleration is indistinguishable from the feeling of gravity. However, most research focuses on rotational gravity. This method uses a rotating frame of reference to create the appearance of a downward pull.

To understand how rotational gravity works, we must look at the relationship between two forces. When a spacecraft rotates, its hull provides a centripetal force. This is a force that pulls or pushes toward the center of the rotation to keep objects moving in a circle. In a rotating station, the hull pushes inward on the occupants. According to Newton's third law, this creates an equal and opposite force called centrifugal force. To the person inside the rotating station, this centrifugal force feels like it is pulling them "downward" toward the outer hull.

There are several physical differences between artificial gravity and the gravity we feel on Earth. First, centrifugal force is not constant; it varies based on your distance from the center. The force is directly proportional to the distance from the axis of rotation. This means if a spacecraft has a small radius, a person's feet might feel much heavier than their head. Second, moving objects inside the station experience the Coriolis effect. This is an apparent force that acts at right angles to the motion and the rotation axis. It tends to curve the motion of objects in the opposite direction of the station's spin.

These physical forces can cause significant health issues for astronauts. The Coriolis effect acts on the semicircular canals of the inner ear. This can lead to severe nausea, dizziness, and disorientation. To minimize these effects, engineers suggest a low spin rate. It is generally believed that a rotation of 2 rpm (revolutions per minute) or less will prevent these adverse effects. However, humans have shown the ability to adapt to much higher rates, as high as 23 rpm. Additionally, any movement of mass inside the station could cause a dangerous wobble. Engineers might use a liquid water supply as ballast to stabilize the axis of rotation.

History shows that we have been testing these concepts for decades. In 1966, the Gemini 11 mission attempted to create artificial gravity. The capsule was attached to an Agena Target Vehicle by a 36-meter tether. By using side thrusters, they rotated the two crafts together like a pair of bolas. The resulting gravity was only 0.00015 g, which was too small for astronauts to feel. However, researchers observed objects moving toward the floor of the capsule.

Later, in 1975 and 1977, the Bion 3 and Bion 4 satellites used on-board centrifuges to study specimens in artificial gravity.

The need for this technology is driven by the biological risks of weightlessness. In 1964, Soviet scientists feared humans could not survive more than 14 days in space. While we now know humans can stay in space for over 437 days, weightlessness still causes damage. A 1991 Spacelab experiment showed that muscle mass and white blood cell responses decrease in zero gravity. Furthermore, blood volume can drop by 10% within the first 24 hours. Long-term exposure can also cause brain swelling and eyesight problems. Artificial gravity could solve these issues by removing weightlessness entirely during long journeys, such as a six-month trip to Mars.

Many specific designs have been proposed to solve these engineering challenges. The 1989 NASA concept for a rotating Mars spacecraft is a well-known example. In 2011, NASA proposed the Multi-Mission Space Exploration Vehicle (MMSEV). This design included a torus-ring centrifuge that could provide between 0.11 and 0.69 g. Another concept, the Nautilus-X, was proposed as a centrifuge demonstration for the International Space Station.

Even the Mars Gravity Biosatellite was proposed to study the effects of 0.38 g on mice, though it was canceled in 2009 due to a lack of funding.

Ultimately, artificial gravity is a bridge to deep space exploration. While current spacecraft are too small or too expensive to provide useful gravity, the technology remains a major goal. Companies like Vast Space are even proposing the construction of the first artificial gravity space station. By mastering rotation and centripetal force, humans may one day travel to distant planets like Mars or Jupiter without the physical toll of weightlessness.