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# Mean Motion (revs/day)

MichaelBartmess.Mean Motion (revs/day)

The **Mean Motion (revs/day)** calculator computes the mean motion based on the number of revolutions (e.g. orbits) in a a period of time.

**INSTRUCTIONS:** Choose units and enter the following:

- (
**R**) Amount of rotation - (
**P**) Period of time associated with the amount of rotation.

**Mean Motion (rpd):** The calculator returns the revolutions per day. However, this angular velocity can be automatically converted to compatible units via the pull-down menu.

#### The Math / Science

This vCalc equation computes the angular speed required for a body to complete one orbit, which is called the ** Mean Motion**.

Mean motion is expressed as number of revolutions or orbits per unit time.

A unit revolution may be a revolution, 360 degrees, or 2`pi` radians.

Period can be expressed in any units of time but more typically is in minutes, hours or days.

Note: the two line element set used to represent an oribital trajectory of an Earth oribiting object represent mean motion in units of `"revs"/"day"`.

## Orbit Classifications by Mean Motion or Period

In many Earth orbital analysis systems, classification of orbits are defined by Near Earth Orbits (NEOs -- sometimes called Low Earth Orbits or LEOs) , Medium Earth Orbits (MEOs), Geosynchronous orbits (GEOs), or Deep Space Orbits. These classes of orbits have arbitrary boundaries defined by their orbital period or mean motion. Often for instance a NEO is defined as any orbit with a period less than 225 minutes (a mean motion of 6.4 revs/day).