Geostationary transfer orbit

A geostationary transfer orbit (GTO) is a Hohmann transfer orbit around the Earth in orbit low earth orbit (LEO) and geostationary orbit (GEO). It is an ellipse where the perigee is a point in a LEO and the apogee is the same distance from the earth as the GEO.

More generally, a geostationary transfer orbit is an intermediate orbit between a LEO and a geosynchronous orbit.

After a typical launch, the tilt of the OTB (the angle between the plane of the orbit and the plane of Ecuador is determined by the latitude of the launch site and the direction of the launch. The GTO inherits the same inclination. The inclination must be reduced to zero to obtain a geostationary orbit. This is done at the distance of the GEO as it requires less energy than in LEO. This is because of the necessary delta-v (Δ Δ v{displaystyle Delta v}) for a certain change of inclination Δ Δ i{displaystyle Delta i} is directly proportional to orbital velocity v{displaystyle v} which is less in his apogee. The delta-v necessary for a shift in inclination both in the node of ascent and in the decreasing orbit is defined as:

Δ Δ v=2vwithout Δ Δ i2{displaystyle Delta v=2vsin {frac {Delta i}{2}}}}}

In a GTO of an Ariane 5 with a semimajor axis of 24.582 km, the perigee speed of a GTO is 9.88 km/s while the apogee speed is 1.64 km/s.

A launch vehicle moves from LEO to GEO by firing a rocket at a tangent to LEO to increase its speed. Typically the last phase of the vehicle has this function. Once in GTO, it is normally the satellite that performs the conversion to geostationary orbit by firing a rocket at the tangent to the apogee. Therefore, the capacity of a rocket that can launch multiple satellites is usually shown in terms of mass at GTO rather than GEO. It may also be that the rocket has the option of inserting itself into GEO. This saves the satellite's fuel, but greatly reduces the payload.

For example, the capacity (separate ship mass) of the Delta IV:

• GTO 12 757 kg (185 km x 35,786 km to 27,0o inclination)
• GEO 6 276 kg

Normally, insertion into geostationary orbit is performed at the ascent node. This is because most of the cosmodromes from which GTO is launched are located in the northern hemisphere.

In most cases, the last stages of rockets are left in GTO (some are left in GEO, such as the Proton Block DM). If the perigee of the GTO is chosen to be low enough to have friction with the atmosphere, the apogee altitude will drop rapidly and will not be a danger to objects in the geostationary ring. Most late phases used to bring loads to GTO are designed with this requirement.