Geostationary transfer orbit

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. 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. GTO is a highly elliptical Earth orbit with an apogee(the point in the orbit of the moon or a satellite at which it is furthest from the earth) of , or a height of above sea level, which corresponds to the geostationary altitude. The period of a standard geosynchronous transfer orbit is about 10.5 hours. The argument of perigee is such that apogee occurs on or near the equator. Perigee can be anywhere above the atmosphere, but is usually restricted to a few hundred kilometers above the Earth's surface to reduce launcher delta-V () requirements and to limit the orbital lifetime of the spent booster so as to curtail space junk. If using low-thrust engines such as electrical propulsion to get from the transfer orbit to geostationary orbit, the transfer orbit can be supersynchronous (having an apogee above the final geosynchronous orbit).