Parking orbit

When the craft crosses the equator, the upper stage is fired to raise the spacecraft's apogee to geostationary altitude (and often reduce the inclination of the transfer orbit, as well).

Finally, a circularization burn is required to raise the perigee to the same altitude and remove any remaining inclination.

Using a preliminary parking orbit before final injection can widen this window from seconds or minutes, to several hours.

For example, during the development Centaur upper stage, the following problems were noted and had to be addressed:[4] The Centaur and Agena families of upper stages were designed for restarts and have often been used in missions using parking orbits.

The Briz-M is also capable of coasts and restarts, and often performs the same role for Russian rockets.