Geostationary transfer orbit

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An example of a transition from GTO to GSO.
  EchoStar XVII ·   Earth.

A geostationary transfer orbit (GTO) or geosynchronous transfer orbit is a type of geocentric orbit. Satellites that are destined for geosynchronous (GSO) or geostationary orbit (GEO) are (almost) always put into a GTO as an intermediate step for reaching their final orbit.

A GTO is highly elliptic. Its perigee (closest point to Earth) is typically as high as low Earth orbit (LEO), while its apogee (furthest point from Earth) is as high as geostationary (or equally, a geosynchronous) orbit. That makes it a Hohmann transfer orbit between LEO and GSO.^[1]

While some GEO satellites are launched directly to that orbit, often times the launch vehicle lacks the power to put both the rocket and the satellite into the particular orbit. So, extra fuel is added to the satellite, the launch vehicle launches to a geostationary transfer orbit; then the satellite circularises its orbit at geostationary altitude. This benefits from staging: the launch vehicles and the mass of its structure and engines do not need to be lifted up to a circular geostationary altitude.

Manufacturers of launch vehicles often advertise the amount of payload the vehicle can put into GTO.^[2]