Apogee kick motor
Encyclopedia
An apogee kick motor refers to a rocket motor that is regularly employed on artificial satellites destined for a geostationary orbit
. As the vast majority of geostationary satellite launches are carried out from spaceport
s at a significant distance away from Earth's equator
, the carrier rocket would only be able to launch the satellite into an elliptical orbit of maximum apogee 35,784-kilometres and with a non-zero inclination approximately equal to the latitude
of the launch site. This orbit is commonly known as a "geostationary transfer orbit
" or a "geosynchronous transfer orbit
". The satellite must then provide thrust to bring forth the needed delta v to reach a geostationary orbit. This is typically done with a fixed onboard apogee kick motor. When the satellite reaches its orbit's apogee position, the AKM is ignited, transforming the elliptical orbit into a circular orbit, while at the same time bringing the inclination to around zero degrees, thereby accomplishing the insertion into a geostationary orbit. This process is called an "apogee kick".
Apogee kick motors often employ either a bipropellant engine, with a solid fuel and a liquid oxidiser, or a monopropellant engine with both the fuel and the oxidiser in a solid state. Less frequently are reverse-hybrid propellant systems with a liquid fuel (injectant) and a solid oxidiser.
The amount of fuel carried on board a satellite directly affects its lifetime, therefore it is imperative to make the apogee kick maneuver as efficient as possible. The mass of most geostationary satellites at the beginning of its operational life in geostationary orbit is roughly half that when it separated from its vehicle in geostationary transfer orbit, with the other half having been expended in the apogee kick maneuver.
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
. As the vast majority of geostationary satellite launches are carried out from spaceport
Spaceport
A spaceport or cosmodrome is a site for launching spacecraft, by analogy with seaport for ships or airport for aircraft. The word spaceport, and even more so cosmodrome, has traditionally been used for sites capable of launching spacecraft into orbit around Earth or on interplanetary trajectories...
s at a significant distance away from Earth's equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
, the carrier rocket would only be able to launch the satellite into an elliptical orbit of maximum apogee 35,784-kilometres and with a non-zero inclination approximately equal to the latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
of the launch site. This orbit is commonly known as a "geostationary transfer orbit
Geostationary transfer orbit
A geosynchronous transfer orbit or geostationary transfer orbit is a Hohmann transfer orbit used to reach geosynchronous or geostationary orbit....
" or a "geosynchronous transfer orbit
Geostationary transfer orbit
A geosynchronous transfer orbit or geostationary transfer orbit is a Hohmann transfer orbit used to reach geosynchronous or geostationary orbit....
". The satellite must then provide thrust to bring forth the needed delta v to reach a geostationary orbit. This is typically done with a fixed onboard apogee kick motor. When the satellite reaches its orbit's apogee position, the AKM is ignited, transforming the elliptical orbit into a circular orbit, while at the same time bringing the inclination to around zero degrees, thereby accomplishing the insertion into a geostationary orbit. This process is called an "apogee kick".
Apogee kick motors often employ either a bipropellant engine, with a solid fuel and a liquid oxidiser, or a monopropellant engine with both the fuel and the oxidiser in a solid state. Less frequently are reverse-hybrid propellant systems with a liquid fuel (injectant) and a solid oxidiser.
The amount of fuel carried on board a satellite directly affects its lifetime, therefore it is imperative to make the apogee kick maneuver as efficient as possible. The mass of most geostationary satellites at the beginning of its operational life in geostationary orbit is roughly half that when it separated from its vehicle in geostationary transfer orbit, with the other half having been expended in the apogee kick maneuver.