adminCOMMUNICATION SATELLITE
A communication satellite is an artificial satellite. Its main function is to receive, amplify and transmit telecommunication signals from one place to another. Thus a system of communication by satellite consists of three segments, the space segment which is the satellite itself. The transmission segment which is the transmission medium and the earth segment which is the earth or ground station.
A typical communication satellite system comprises of a payload and a bus or platform.
The payload is the equipment used to provide the service for which the satellite has been designed for a given mission. The payload components include the following; transponders, antennas, signal amplifiers and frequency converters.
The bus or platform components is made up of the power system, propulsion and fuel system, thermal control system, altitude control system and telemetry, tracking and command (TT&C) system.
The payload transponder is communication equipment that receives, amplify, and retransmit signals. The transponder provides the connecting link between the satellite transmitter and the receiver’s antennas. Typically satellites have between 24 and 72 transponders. A single transponder is capable of handling up to 155 million bits of information per second (155mbps).
The antennas are used to transmit and receive signals to and from the earth station.
The frequency converters are used to convert the frequencies of the received signals to a different frequency for retransmission.
The bus or platform components include among others the power system which also includes the solar panels, batteries and power conditioning equipment. The main function of the power system is to generate and supply power to the whole satellite.
The propulsion system includes power thrusters and fuel system. The main function of this unit is to keep the desired or predetermined satellite trajectory, perform orbital maintenance and maneuvers.
The thermal control system regulates the satellites temperature using radiators, heaters and insulation.
The altitude and orbital control (AOCS) maintains the satellites, orientation and position in orbit.
The telemetry, tracking and command (TT&C) system enables communication between the satellite and ground station.
The communication satellite earth station is responsible for transmitting and receiving telecommunication signals from a satellite which in turn is relayed to other earth stations or users equipped with satellite receivers.
The components of a communication satellite earth station includes; antenna systems, low noise amplifier (LNA), frequency converter, modem, baseband equipment, power amplifier and tracking system.
The transmission of signals from the earth station to the satellite is called the uplink. Similarly the transmission of signals from the satellite to the earth station is called the downlink.
In the uplink process, the earth station generates a signal which can be voice, data or video transmission. The signal is modulated onto a carrier wave, which is a high frequency signal that can be transmitted over long distances. The modulated signal is converted to a higher frequency typically in the range of 5 to 14 GHz, to match the frequency band of the satellite transponder. The signal is amplified to increase its power and ensure reliable transmission. The amplified signal is transmitted to the satellite through a high gain antenna, which is typically a parabolic dish antenna. The signal is received by the satellites antenna and processed by the transponder.
In the downlink process, the process signal is transmitted back to the earth station through the satellites antenna. The signal is converted to a lower frequency, typically in the range of 3 to 6 GHz, to match the frequency band of the earth station receiver. The signal is received by the earth station antenna which is typically a parabolic dish antenna. The received signal is amplified by the low noise amplifier (LNA) to increase its strength and improve its signal quality. The amplified signal is converted to a lower frequency, typically in the range of 70 to 140 MHz, to match the frequency band of the receiver. The signal is demodulated to extract the original information, which can be voice, data or video. The demodulated signal is processed to improve its quality and remove any errors or noise.
The advantages of satellite communications are obvious since they facilitate the global communication services. Satellites offer high-band width communication, enabling fast data transfer and high quality video transmission. Above all they are reliable, offers secure communication and are mobile, hence support the maritime, aeronautical and land communication on the move.
Despite these advantages, they are prone to high latency due to the distance between the earth and the satellite, interference from other satellites, solar radiation and other terrestrial sources and weather conditions. Also the cost of deploying and maintaining satellite communication systems is quite enormous. Satellites have limited capacity which can lead to congestion and reduced service quality.
The application of communication satellites covers a wide range of industries including; telecommunication, broadcasting, navigation, weather forecasting, earth observation, military communication and disaster response.
There are approximately 11,780 satellites in orbit around the earth today. Approximately 8110 of these satellites are in the low earth (LEO) orbit, with 6,050 of these belonging to space X. There are around 199 satellite in medium earth (MEO) orbit, which is suitable for navigation satellite constellations like GPS, GALILEO, and GLONASS.
LEO satellites are ideal for remote sensing, earth observation and scientific research due to their short orbital periods and high resolution imaging capabilities.
About 552 satellites are in geostationary earth (GEO) orbit. This orbit is often used for communications and weather forecasting satellites.
The future of communication satellites is bright and follows trends and developments in communication technologies; it is expected that in the future that the next generation satellites will offer higher capacity and faster data rates and longer service life which is currently between 15 and 20 years by producing rocket fuel in space. Also the deployment of more networks of smaller satellites particularly in LEO orbit is anticipated.
Satellite communication integration with terrestrial 5G and 6G networks and in orbit service, repair and maintence of satellites and the recovery of spent satellites will go a long way in creating an efficient and sustainable space based satellite networks.
SOURCES:
- Satellite communications by Dennis Roddy.
- Satellite communication systems by Gerard Maral and Michel Bousquet.
- Mobile satellite communications by Shingo Ohmort, Hiromitsu wakana and Seiichiro Kawase.
- Communication satellite system technology by Joseph N. Pelton,et al.
- Satellite communications in the 21st century by Takashilida, et al.
