This mission architecture is useful because it minimizes the mass that the spacecraft must push to GEO, allows for maximally efficient circularization burns taking advantage of the Oberth effect, and allows the spent launch vehicle to deorbit primarily through aerobraking due to its low perigee, minimizing its orbital lifetime.
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 42,164 km (26,199 mi),[3] or a height of 35,786 km (22,236 mi) above sea level, which corresponds to the geostationary altitude.
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 (
However, this method takes much longer to achieve due to the low thrust injected into the orbit.
The thrust direction and magnitude are usually determined to optimize the transfer time and/or duration while satisfying the mission constraints.
The out-of-plane component of thrust is used to reduce the initial inclination set by the initial transfer orbit, while the in-plane component simultaneously raises the perigee and lowers the apogee of the intermediate geostationary transfer orbit.
By using low-thrust engines or electrical propulsion, months are required until the satellite reaches its final orbit.
for an inclination change at either the ascending or descending node of the orbit is calculated as follows:[7] For a typical GTO with a semi-major axis of 24,582 km, perigee velocity is 9.88 km/s and apogee velocity is 1.64 km/s, clearly making the inclination change far less costly at apogee.
In practice, the inclination change is combined with the orbital circularization (or "apogee kick") burn to reduce the total
Even at apogee, the fuel needed to reduce inclination to zero can be significant, giving equatorial launch sites a substantial advantage over those at higher latitudes.
Guiana Space Centre, the European Ariane and European-operated Russian Soyuz launch facility, is at 5° north.
Also, many launchers now carry several satellites in each launch to reduce overall costs, and this practice simplifies the mission when the payloads may be destined for different orbital positions.
Because of this practice, launcher capacity is usually quoted as spacecraft mass to GTO, and this number will be higher than the payload that could be delivered directly into GEO.
For example, the Proton-M uses a set of three intermediate orbits, requiring five upper-stage rocket firings, to place a satellite into GEO from the high-inclination site of Baikonur Cosmodrome, in Kazakhstan.
This means that the satellite appears to remain stationary relative to a fixed point on the Earth's surface.
The geostationary orbit is located at an altitude of approximately 35,786 kilometers (22,236 miles) above the Earth's equator.