O'Neill Cylinder Artificial Gravity Calculator

Calculate the spin rate and rim velocity needed to simulate gravity inside a rotating space habitat.

meters
O'Neill Island Three: 3,200 m
m/s²
Earth = 9.81, Moon = 1.62, Mars = 3.72
Rotation Rate
—
Angular Velocity (ω)
—
Rim Velocity
—
Rotation Period
—
Rim Speed (km/h)
—

Artificial Gravity Through Rotation

In the absence of gravitational fields, the only practical way to create a sense of gravity for inhabitants of a space habitat is centripetal acceleration from rotation. A spinning cylinder pushes everything on its inner surface outward, creating a force indistinguishable from gravity for the inhabitants standing on the inside of the rim.

The Spin Gravity Formula

The centripetal acceleration at the rim of a rotating cylinder is:

g = ω² × r

Solving for the angular velocity needed to achieve a target gravity:

ω = √(g / r)

Converting to RPM: RPM = ω × 30 / π

The O'Neill Cylinder Design

Gerard K. O'Neill proposed his cylinder habitat concept in 1976. The "Island Three" design features two counter-rotating cylinders, each 3.2 km in radius and 32 km long. At this size, only 0.53 RPM is needed for Earth-normal gravity, well within human comfort limits. The interior would have alternating strips of land and glass windows, with mirrors controlling the day-night cycle.

Comfort Limits

Human tolerance for rotation is limited by the Coriolis effect and gravity gradient. Most research suggests that untrained humans can tolerate about 2 RPM without significant discomfort. Trained astronauts might handle up to 6 RPM. This sets a practical minimum radius of about 224 meters for 1g gravity at 2 RPM. See the Coriolis Deflection Calculator for gravity gradient analysis.

Engineering Challenges

The primary engineering challenge is the immense structural stress from rotation. The rim of an O'Neill Cylinder at 1g experiences centripetal stress equivalent to supporting a column of material extending to the axis. Materials like high-strength steel, carbon fiber composites, or carbon nanotubes would be required. The total mass of an Island Three cylinder would be on the order of billions of tonnes, requiring extensive space-based mining and manufacturing.

Frequently Asked Questions

An O'Neill Cylinder is a space habitat design proposed by physicist Gerard K. O'Neill in 1976. It consists of a pair of counter-rotating cylinders, each several kilometers in radius and tens of kilometers long, simulating gravity through rotation on the inner surface.
When a cylinder rotates, objects on its inner surface experience centripetal acceleration pushing them outward, which feels like gravity. The acceleration equals omega squared times the radius (a = ω²r). By choosing the right spin rate, any desired gravity can be achieved.
Smaller radii require faster rotation for the same gravity, which causes stronger Coriolis effects. Dropped objects curve, and there is a noticeable gravity difference between head and feet. Most studies suggest a minimum radius of ~500 meters for comfortable habitation.
Research suggests most people can adapt to about 2 RPM without significant discomfort. Trained individuals may tolerate up to 6 RPM. Above these rates, the Coriolis effect causes severe vestibular disorientation and nausea.
O'Neill proposed three designs. Island One was a 500m-radius Bernal sphere. Island Two was about 1.8 km radius. Island Three, the classic O'Neill Cylinder, was 3.2 km radius and 32 km long, housing millions of inhabitants at a comfortable 0.53 RPM.