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# Artificial Gravity in Spacecraft

by Ron Kurtus (revised 19 January 2014)

** Artificial gravity** is a force that

*simulates*the effect of gravity in a spaceship. It is not caused by the attraction to the Earth but is instead caused by acceleration or centrifugal force. There is a need for artificial gravity in spacecraft to counter the effect of weightlessness on the astronauts.

A rotating circular space station can create artificial gravity for its passengers. The rate of rotation necessary to duplicate the Earth's gravity depends on the radius of the circle.

The major requirement for an astronaut to experience artificial gravity is that he is in contact with the rotating floor of the spaceship.

Questions you may have include:

- Why is artificial gravity needed?
- How can artificial gravity be created?
- What are special requirements for artificial gravity?

This lesson will answer those questions. Useful tool: Units Conversion

## Artificial gravity needed in spaceships

Artificial gravity is needed in spaceships that are in orbit around the Earth, as well as ones that are so far out that the effect of gravity or gravitation is negligible.

The International Space Station is in orbit around the Earth at approximately 350 km. Because the centrifugal force keeping the space station in orbit counters the force of gravity at that altitude, astronauts in the station do not feel the effect of gravity. Anything or anybody that is not tied down will float within the Space Station.

Astronauts in any spaceship that is far enough away from the Earth that the effect of gravity or gravitation is negligible will also feel the effects of weightlessness. The gravitation on a spaceship that is about 15,000 km from Earth is about 1/10 the gravity on the ground.

Thus, artificial gravity is needed to facilitate the tasks the astronauts must do, to make them more comfortable, and to avoid negative health effects from long-term weightlessness.

## Ways to create artificial gravity

Constant linear acceleration and centrifugal force are two ways to create artificial gravity.

### Using linear acceleration

One way to simulate a gravitational force is to accelerate a rocket or spaceship. This is similar to the effect you feel when you are in an accelerating elevator, where you can feel heavier when the elevator is moving upward.

In developing his General Theory of Relativity, Albert Einstein noted that you could not tell the difference between gravity and constant acceleration. He used this example to state his theory that gravity or gravitation was not a force but an action related to inertia on moving objects.

If the rocket accelerated at 9.8 m/s^{2} (32 ft/s^{2}), the inertia of your body would simulate the effect of gravity on you. The only problem is that the effect is short-lived, since the rocket can only accelerate until it approaches the speed of light.

Thus, creating artificial gravity through linear acceleration is impractical, since there is a limit to the velocity of a spaceship.

### Using centrifugal force

A better way to create artificial gravity is to use the effect of centrifugal force, which is an outward force caused by an object being made to follow a curved path instead of a straight line.

If the spaceship was in a large, circular or donut shape that was rotating at a certain rate, the crew on the inside could feel the centrifugal force as artificial gravity. The equation for the rate of rotation is:

Ω =9.55√(g/r)

where

**Ω**is the rate of rotation in revolutions per minute (rpm)**g**is the acceleration due to gravity (**9.8 m/s**or^{2}**32 ft/s**)^{2}**r**is the radius of the spaceship donut in meters or feet

(See Artificial Gravity Equations for more information.)

In the 1968 movie *2001: A Space Odyssey*, a rotating centrifuge in the* *spacecraft provided artificial gravity for the astronauts. A person could walk inside the circle with his feet toward the exterior and his head toward the center, the floor and ceiling would curve upwards.

In the United States, the *National Aeronautics and Space Administration (NASA)* has considered similar concepts for attaining artificial gravity in their spacecraft.

Proposed NASA artificial gravity spaceship

## Special conditions and problems

The major requirement for the astronaut to experience artificial gravity in a rotating spacecraft is that he is fixed to the floor. This means that he would be moving in a circular path along with the rotation of the spacecraft. The centrifugal force would be acting on the astronaut, creating the artificial gravity effect.

Astronaut must be fixed to floor in rotating spaceship

However, if he jumped up off the floor, he would only have a linear velocity in the direction of rotation and would fall to the floor not necessarily upright. (See *Dropping Something* below.)

If an astronaut was not initially in contact with the floor or walls, he would be floating within the area.

### Shoes or skates

Special shoes might be needed to keep the astronaut in contact with the floor. Velcro grip shoes or magnetic shoes are a few ideas being considered.

An interesting idea is for the astronaut to use magnetic roller skates to navigate along an iron floor.

### Direction of walking or skating

Walking or skating in the direction of rotation could slightly increase the feeling of gravity, while moving in the opposite direction would decrease that feeling. However, the effect would be negligible since the velocity would be small.

### Dropping something

If an object was not in contact with the floor, it would float about. If it had some initial velocity, it would move in a straight line.

Suppose the astronaut would drop or let go of a pencil he was holding. Since it was no longer forced to move in a curved path, the pencil would simply moved forward in a straight line, according its initial velocity, when released.

Dropped object would move in straight line but appear to fall

However, since the floor of the spacecraft was curved, the pencil would move forward until it hit the curved floor. Although it was not pulled to the floor by artificial gravity, it would appear to do so to the astronaut.

## Summary

Artificial gravity is a force that *simulates* Earth's gravity. There is a need for artificial gravity in spacecraft to counter the effect of weightlessness on the astronauts.

Acceleration and centrifugal force can duplicate the effects of gravity. A rotating circular space station can create artificial gravity for its passengers provided they are in contact with the rotating floor. The rate or rotation necessary to duplicate the Earth's gravity depends on the radius of the circle.

Think of ways to improve on nature

## Resources and references

### Websites

**Artificial gravity** - Wikipedia

**Simulating Gravity in Space** - From Batesville, Indiana HS Physics class

**Artificial Gravity and the Architecture of Orbital Habitats** - Theodore W. Hall - Space Future; detailed technical paper

**Artificial Gravity** - Technical resources from Theodore W. Hall -

**The Physics of Artificial Gravity** - Popular Science magazine

**Simulated Gravity with Centripetal Force** - Oswego City School District Exam Prep Center, New York

**Technologies in 2001: A Space Odyssey movie**

**Artificial Gravity in the Spinning Discovery One** - Wired Magazine

**The Physics of a Spinning Spacecraft in Interstellar** - Wired Magazine

### Books

**Top-rated books on Simple Gravity Science**

**Top-rated books on Advanced Gravity Physics**

## Questions and comments

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## Artificial Gravity in Spacecraft