Geostationary transfer orbit
A geostationary transfer orbit (also Geotransferorbit; . Abbr GTO Geostationary Transfer Orbit of engl ) is an orbit, are exposed on the satellites of missiles to (GEO) to be finally positioned shortly thereafter in a geostationary orbit.
The GTO is in the form of an elongated ellipse. A focus of the ellipse is the center of the earth. The farthest point from the earth - the apogee - often located in the vicinity of the geostationary orbit at 35,786 kilometers above the equator. However, the web speed there is still too low for the desired orbit and the orbital inclination ( | inclination ) are usually too big.
Normally uses a satellite rocket at (or near ) perigee point ( perigee ) of the elliptical orbit. The round trip time on a typical GTO (250 x 36,000 km ) is about 10.5 hours, so that the height of the geostationary orbit is first passed for more than 5 hours.
Special procedures of some launchers
Some launchers fly first to a low parking orbit and start from there usually a Hohmann transfer, the elliptic part is the geostationary transfer orbit.
Some launchers such as the Ariane satellite but take you to the geosynchronous transfer orbit, including a near-equatorial location, such as Kourou, one of nearly 9.8 km / s is also required.
Some launchers that start from very high latitudes from, for example, the proton control to a GTO ( "plus" ) or super -synchronous transfer orbit with very high apogee, where it can degrade the high inclination with less energy (bi - elliptic transfer).
Engines for the change in the Geostationary orbit
For the change from the elliptical GTO in the circular GEO one of nearly 1.5 km / s at apogee of the GTO is necessary. Some launchers do this with their grades. In this case, however, this remains in the vicinity of the GEO or must be "disposed of" a graveyard orbit.
Satellite that will bring about the change with a solid engine as apogee, often remain connected to it. The ignition can already after half orbit of the earth happen, or even after a few orbits of the GTO, eg the satellite to verify technically.
A liquid propellant apogee motor can ignite multiple times, each at apogee to raise perigee gradually. This has the advantage that the structural mass of the engine may be reduced in favor of the payload. A breakdown of the driving power for the higher grades and apogee would be technically possible, but is unusual.
Ion engines, which even lower drive power is supplied by the solar modules are particularly suitable for the path corrections always necessary during the life of the satellite. In order to use this engine for raising the perigee, are also used here the bi- elliptic transfer via a chemical propulsion reached GTO .