In astrodynamics or celestial mechanics a **circular orbit** is an elliptic orbit with the eccentricity equal to 0.

## Velocity

Under standard assumptions the orbital velocity () of a body traveling along **circular orbit** can be computed as:

where:

Conclusion:

- Velocity is constant along the path.

## Orbital period

Under standard assumptions the orbital period () of a body traveling along **circular orbit** can be computed as:

where:

Conclusions:

## Energy

Under standard assumptions, specific orbital energy () is negative and the orbital energy conservation equation for this orbit takes the form:

where:

The virial theorem applies even without taking a time-average:

- the potential energy of the system is equal to twice the total energy
- the kinetic energy of the system is equal to minus the total energy

Thus the escape velocity from any distance is √2 times the speed in a circular orbit at that distance: the kinetic energy is twice as much, hence the total energy is zero.

## Equation of motion

Under standard assumptions, the orbital equation becomes:

where:

## Delta-v to reach a circular orbit

Maneuvering into a large circular orbit, e.g. a geostationary orbit, requires a larger delta-v than an escape orbit, although the latter implies getting arbitrarily far away and having more energy than needed for the orbital speed of the circular orbit. It is also a matter of maneuvering into the orbit. See also Hohmann transfer orbit.

## See also

Last updated: 06-01-2005 23:08:28