## Synthetic Gravity in Space Habitats

Human bodies have evolved inside a gravitational field that provides a constant downward pressure as long as we stand on the surface of the planet. Healthy operation of the body depends on this state. In the zero-gravity environment of space, we will need to synthetically reproduce this condition.

The term, “centrifugal force” describes the inertial tendency of objects to fly away from a center of rotation. The inertia of a moving object wants it to keep moving in a straight line, but if the object is to remain in contact with the center of rotation, it must curve around with the rotation. Placing an object on the inside of a rotating surface provides the same “downward” (or outward) pressure that duplicates the result of gravity.

Building space habitats that are essentially large rotating wheels creates an environment for healthy living. The occupants will live inside the wheels with an upright position of heads oriented inward or “upward” toward the center of the wheel and feet oriented outward or “downward” against the inner surface of the wheel.

Data on how much synthetic gravity is needed for healthy living is minimal, but what there is suggests that about 1/3 of normal Earth gravity will be a minimum. Full Earth gravity is described as 1G. The size of the habitat wheel and speed of rotation will determine the amount of gravity that is produced. A wheel that has many floors (layers) will have variable gravity on different floors depending on the radius distance from the center of the rotating wheel.

The formula to calculate the amount of gravity produced is: gravity = radius((2pi/time)(2pi/time)) or G=r(2pi/t)sq, where radius = the radius of the wheel in meters, pi = 3.14159…, time = the time of one full rotation of the wheel in seconds. This will give the outward acceleration in meters per second. This result can be divided by 9.81 meters per second to give the result in terms of “G”.

Here is how these principles might be used in space habitat wheel design:

A wheel with an outer radius of 500 meters, that turns at a speed of 1.32 rotations per minute, will produce 0.97 G at the outer edge. For the same wheel, if inner floors are built at a radius of 200 meters, the gravity will be 0.39 G at that level. This gives us a range of gravity from nearly full Earth normal to just above the 1/3 G minimum we have suggested. And it provides a building range from a radius of 200 meters out to 500 meters. If we postulate a floor height of 5 meters, this provides a potential of sixty floors of building within the desirable range of gravity.

If we use the same optimal gravity range of 1G maximum to 0.3G minimum, we can adjust the size and speed of rotation to calculate building ranges. Here is a preliminary list: