Satellite Orbits: Types and Definitions
In these times, humanity uses several different orbits to place satellites. Most attention is focused on the geostationary orbit, which can be used for “stationary” placement of the satellite over a particular point of the Earth. The orbit chosen for the operation of the satellite depends on its purpose. For example, satellites used for direct broadcasting of television programs are placed in geostationary orbit. Many communication satellites are also in geostationary orbit. Other satellite systems, in particular those used for communication between satellite phones, rotate in low Earth orbit.
Similarly, satellite systems used for navigation systems such as Navstar or the Global Positioning System (GPS) are also in relatively low Earth orbits. There are countless other satellites – meteorological, research, and so on. And each of them, depending on its purpose, receives a “residence permit” in a certain orbit.
Earth’s gravity and satellite orbits
As the satellites orbit around the Earth, they slowly move away from it due to the Earth’s gravity. If the satellites were not orbiting, they would gradually fall to Earth and burn up in the upper atmosphere. However, the very rotation of satellites around the Earth creates a force that pushes them away from our planet. Each of the orbits has its own calculated speed, which allows you to balance the force of gravity of the Earth and the centrifugal force, keeping the device in a constant orbit and not allowing it to gain or lose altitude.
It is quite clear that the lower the orbit of the satellite, the more it is affected by the attraction of the earth and the greater the speed required to overcome this force. The greater the distance from the Earth’s surface to the satellite, the lower the speed required for it to stay in a constant orbit. For a spacecraft orbiting at a distance of about 160 km above the Earth’s surface, a speed of about 28,164 km/h is required, which means that such a satellite orbits the Earth in about 90 minutes. At a distance of 36,000 km above the Earth’s surface, a satellite requires a speed of just under 11,266 km / h to stay in a constant orbit, which makes it possible for such a satellite to orbit the Earth in about 24 hours.
Definitions of circular and elliptical orbits
All satellites orbit the Earth using one of two basic types of orbits.
Circular satellite orbit: When a spacecraft orbits the Earth in a circular orbit, its distance above the Earth’s surface remains always the same.
Elliptical satellite orbit: The rotation of a satellite in an elliptical orbit means a change in the distance to the Earth’s surface at different times during a single orbit.
Satellite orbits
There are many different definitions associated with different types of satellite orbits:
Center of the Earth: When a satellite orbits the Earth-in a circular or elliptical orbit – the satellite’s orbit forms a plane that passes through the center of gravity or the center of the Earth.
Direction of motion around the Earth: The ways in which a satellite orbits our planet can be divided into two categories according to the direction of this rotation:
- Prograde orbit: The orbit of a satellite around the Earth is called an acceleration orbit if the satellite rotates in the same direction as the earth rotates;
- Retrograde orbit: The orbit of a satellite around the Earth is called retrograde if the satellite rotates in the direction opposite to the direction of rotation of the Earth.
The track of the orbit: A satellite’s orbit path is a point on the Earth’s surface where the satellite is directly overhead during its orbit around the Earth. The track forms a circle in the center of which is the Center of the Earth. It should be noted that geostationary satellites are a special case because they are constantly above the same point above the Earth’s surface. This means that their orbital path consists of a single point located on the Earth’s equator. You can also add that the orbit of satellites orbiting strictly above the equator stretches along this very equator.
For these orbits, as a rule, the displacement of the orbit path of each satellite in the west direction is characteristic, since the Earth under the satellite turns in the east direction.
Orbital nodes
Orbital nodes are the points at which the path of the orbit passes from one hemisphere to the other. For nonequatorial orbits, there are two such nodes:
- Ascending node: This is the node where the path of the orbit passes from the Southern hemisphere to the Northern hemisphere.
- Descending node: This is the node where the path of the orbit passes from the Northern hemisphere to the Southern hemisphere.
Conclusion
Humanity has not yet exhausted the possibilities of using near space to build communication systems for various purposes.
It is expected that promising low-orbit communication systems will absorb new types of services such as remote sensing of the Earth, monitoring, etc., which will optimally balance satellite capabilities and bring low-orbit systems to a level of profitability that is not inferior to geostationary systems. The same applies to systems with highly elliptical satellites.
