The word satellite is received from the Latin word satele which means servant, or someone who receives or serves another party. Meanwhile scientifically, a satellite is an object that moves around another object – usually larger – in a predictable path called an orbit, or briefly every celestial body that moves around a planet that forms a path or elliptical.
The satellite itself is divided into 2 types, namely:
Natural Satellite, Satellites that are derived from nature, a simple example is the moon which is a natural satellite for the earth. Earth and other planets in our solar system also become natural satellites of the sun.
Artificial Satellite. Satellites made by humans are placed in an orbit using a launch vehicle for certain functions, for communication, mapping, weather monitoring and so on. Examples such as the Palapa satellite, Telkom, Garuda, Indostar and many others.
Various Satellites & Uses
This man-made satellite consists of various forms and has its own uses. Artificial satellites can be divided into as follows:
Remote sensing satellites: specially designed to open the earth from an orbit that is suitable for non-military uses such as environmental surveillance, meteorology, maps and others.
Weather satellites: used for monitoring the weather and climate of the earth.
Communication satellites: are satellites used for long-distance communication systems, whether for telephone, data and the internet.
Navigation satellites: satellite systems that provide global independent geospatial positions commonly referred to as GPS satellites which are used for land, sea and air navigation.
Military satellites: used for military purposes such as intelligence gathering satellite-based intelligence, navigation and military communications.
Scientific satellites: satellites that provide meteorological information, land survey data, amateur radio and various other scientific research applications.
Satellite orbit is a path or path that is passed by the center of mass of the satellite. While the term satellite orbit slot has a specific location on the satellite orbit. In the world of satellites, each satellite in space will have its own orbital slot so as not to collide with each other. Satellites move in space moving (revolution) at high speed so as not to fall to the surface of the earth. Satellite also discusses the force, moon and sun. Based on the height of the orbit (orbit), satellites are divided into 3 types, including:
Geostationary Earth Orbit (GEO)
GEO is a satellite that orbits at an altitude of less than 36,000 kilometers above the earth. In this orbit the satellite moves at speeds of about 3 km / sec. Indirectly you could say that the satellite is moving at the same speed as the earth’s rotating speed, so that the satellite looks as if it is still when viewed from the surface of the earth.
Satellites orbiting GEO have the following characteristics:
– Satellites will change orbits within 23.9 hours equal to the rotation of the earth.
– Because its speed in orbit is the same as the speed of rotation of the earth, the satellites in GEO’s orbit seem to be stationary and always in position. So, satellites that are above Indonesia or other countries, these satellites will always be above those countries.
– Latency – the time required for wave propagation from earth to satellite and back to earth takes 250 ms to 1 second.
– Has a large area. Only need a few satellites to cover the whole earth.- Satellites in GEO orbit are in a single ring above the equator, so the slot for GEO satellites is very limited.
Medium Earth Orbit (MEO)
MEO is a satellite that orbits from an altitude of 2,000 – 35,000 kilometers from the earth, lower than GEO’s orbit. Because it is closer to the surface of the earth, the orbital period in the satellite will be higher. The satellite will be seen moving continuously.
Following are some of the characteristics of satellites orbiting at MEO:
– The satellite will finish circling the orbit faster than the rotation of the earth, in 5 – 12 hours per 1 turn. Because the satellite speed on the MEO orbit is around 19,000 km / hour.
– Because its orbital speed is faster than Earth’s rotation, satellites will appear to move when viewed from the earth.
– Lower latency than GEO.
– Has a smaller coverage area than GEO, so the number of satellites needed to cover the earth can be dozens of satellites.
– Satellites that are in MEO orbit can have different trajectories, do not have to be above the equator, can cross, or even pass through the north and south poles.
The MEO orbit is usually used for sensing satellites (image processing, weather and others) including the American GPS (Global Positioning Satellite) system at an altitude of 20,000 km or Russia’s GLONASS (Global Navigation Satellite System) located at an altitude of 19,000 km.
Low Earth Orbit (LEO)
LEO is a satellite orbit with the lowest altitude among others. The height of the satellites in this orbit is around 500 – 2000 kilometers (under the MEO orbit) of the earth. Has characteristics similar to MEO orbit, where the satellite period in orbit around faster than the rotation of the earth.
The orbiting satellites of LEO have the following characteristics:
– Satellites will finish circling the earth in 1.5 hours, or about 16 times a day. With a speed of 27,000 km / hour.
– With this speed, this satellite will appear to move when viewed from the earth.
– The lowest latency between GEO and MEO satellites
– The smallest coverage area compared to GEO and MEO. Requires more satellites for the same area as GEO satellites.
– Satellites that are in LEO orbit can also have different trajectories, not necessarily above the equator, can cross, or even pass through the north and south poles.
This LEO orbit is usually used for satellites with mobile telecommunications systems, such as the Iridium and Global Star satellite systems.
Satellite Frequency Spectrum
The use of the frequency spectrum is regulated globally by the ITU (International Telecommunication Union) – a body under the United Nations that works in the telecommunications sector -, its aim is to avoid interference from indiscriminate use.
Likewise with the satellite frequency spectrum, in addition to being differentiated based on its orbit, satellites can also be distinguished by the use of a frequency spectrum on its transponder.
What is a transponder? Transponders on satellites are devices used to send and receive signals. A satellite can have many transponders, depending on its design and intended use.
For example, the Palapa-D Satellite has 40 transponders consisting of 24 C-band transponders, 11 Ku-band transponders and 5 Extended C-band transponders. This number of transponders is intended to anticipate the increasing needs of customers. In the past, the first generation Palapa satellite (Palapa-A1) only carried 12 transponders (C-band) because at that time (Papala-A1 was launched in July 1976) the need for transponders was still very low.
L-band (1-2 GHz)
Used for satellite-based mobile telephone services, satellite radio, weather resistance, small bandwidth. This frequency has been used by Garuda-1 Satellite for BYRU and SURE satellite phone services.
S-band (2-4 GHz)
Used for radar systems and communications and broadcast systems, withstands weather with limited bandwidth. S-band in Indonesia is used by Indovision Satellite TV service from MNC.
C-band (4-8 GHz)
Usually used for communication systems, broadcast TV networks or data. Suitable for use in the tropics because it is resistant to changes in weather (rain), has a flexible bandwidth from small to large. This C-band has many satellites that are used in Indonesia and are applied to internet services or networks that require high reliability such as banks, the easiest example we find is the ATM service that is spread in several locations.
X-band (8-12 GHz)
Commonly used by the military for radar systems, defense and navigation systems both in the air, sea and land.
Ku-band (12-18 GHz)
Widely used as a communication and broadcast TV system, vulnerable to weather disturbances but has a large bandwidth. The current Ku-band frequency is a frequency that is quite popular in Indonesia, some satellite TV operators use this frequency. Likewise with some satellite internet services in Indonesia, this is because the Ku-band has greater bandwidth, smaller antennas and lower prices than C-band.
Ka-band (26-40 GHz)
Used as a communication and broadcast TV system, as well as a short-range radar system with high resolution in the military, it is very vulnerable to weather changes and has a large bandwidth above the Ku-band. Some satellite internet services in America and Europe already use this frequency so that the given bandwidth can compete with cable or GSM network bandwidth. From the several lists above, it can be explained that the higher the frequency used, the greater the bandwidth with the consequence the more vulnerable to weather disturbances.