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Orbits and trajectories
Published in Jonathan Allday, Apollo in Perspective, 2019
This is known as a geostationary orbit and it is the orbit of choice for communications satellites. From our perspective, the satellite remains floating in the sky at the same place relative to the ground so we have no need to ‘track’ a communications aerial across the sky as the satellite passes. This is why satellite television dishes can be pointed in one direction and left in that position. In essence, they are ‘talking’ to a satellite in a geostationary orbit over the equator.
Satellite Systems
Published in Jerry D. Gibson, The Communications Handbook, 2018
A communication satellite, often called a COMSAT, is a spacecraft that receives electrical signals from a transmitter on the Earth, amplifies these signals, changes the carrier frequencies, and then retransmits the amplified signals back to receivers on the Earth [Douglas, 1988]. Since communication satellites simply amplify and retransmit signals, they are often called repeaters or relays. Communication satellites are usually placed in geostationary Earth orbits, which allows the satellites to appear stationary to the transmitters and receivers on the Earth. Placing communication satellites in this special orbit prevents problems caused by the Doppler shift. One Earth station transmitter and one satellite can provide signals to receivers in an area that covers almost one-third of the Earth's surface. Satellites have revolutionized electronic communications since the first commercial satellite was launched in 1965. There are now more than 200 communication satellites in orbit around the world, and new satellites are launched regularly. Communication satellites have made it possible to routinely receive live television coverage of important news and sporting events from anywhere in the world. Satellites have also improved worldwide telephone communications, navigation, and weather information.
Satellites
Published in Mohammad Razani, Commercial Space Technologies and Applications, 2018
Communication Satellite is a satellite that provides voice, video, and data services. In a more general term, a communications satellite is an artificial satellite that relays and amplifies radio communications signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, Internet, and military applications. There are over 2,000 communications satellites in Earth’s orbit, used by both private and government organizations.10
Stochastic model predictive control-based countermeasure methodology for satellites against indirect kinetic cyber-attacks
Published in International Journal of Control, 2023
M. Amin Alandihallaj, Nima Assadian, Khashayar Khorasani
The objective of this section is to demonstrate and illustrate the effectiveness of our proposed collision avoidance methodology as applied to the accidentally occurred collision between the Iridium-33 and the Cosmos-2251 on February 10, 2009. Cosmos-2251 was an inactive Russian communications satellite, while Iridium-33 was an active commercial communications satellite operated by the U.S.-based Iridium Satellite LLC. The Iridium-33 collided with the Cosmos-2251 at a relative speed of nearly 10 km/s. The nominal orbits of these two spacecrafts are shown in Figure 4, where the intersection of the orbits is evident above the Northern Hemisphere. The projected trajectory of each orbit is plotted on each fundamental plane. The last achieved TLE sets of both satellites before the collision are also reported in Table 1.
Clock synchronisation: the establishment of Coordinated Universal Time (UTC) through the work of Louis Essen
Published in The International Journal for the History of Engineering & Technology, 2023
Clarke’s dream of communicating by satellite came a step nearer with the dawn of the Space Age on 4 October 1957 when the Soviet Union launched Sputnik-1 into earth orbit. The successful launch shocked and embarrassed the American public, who were convinced that Russian technology lagged well behind that of America. It forced President Eisenhower to bring forward the planned launch of the first United States satellite but it took almost four months before Explorer-1 was put into orbit. The satellite’s shape was a cylinder 1.8 metre long and 15 centimetre in diameter which made it a poor candidate for a microwave reflector but, on 12 August 1960, America launched a communications satellite, Echo-1, and with it came the possibility for an entirely new approach to clock synchronisation.
Understanding Redundancy Requirements in the Design of Non-Serviceable Systems
Published in Engineering Management Journal, 2022
Alejandro Salado, Aditya U. Kulkarni
Given that incorporating redundancies in space system design is a costly and time-consuming exercise, a significant question is whether redundancy requirements positively affect the solution space even when a reliability target at EOL for the space system has already been specified. While there are multiple research works on statistical analysis and modeling of space system reliability (Castet & Saleh, 2009; Guo et al., 2014), to the best of our knowledge, only J. Saleh et al. (2005) and J. H. Saleh and Marais (2006) have previously explored a research problem similar to ours. In their work, J. Saleh et al. (2005) and J. H. Saleh and Marais (2006) analyzed the impact of different redundancy configurations for transponders on a communications satellite on the revenue generated by the satellite. The results of their model showed that redundant transponders often do not justify their costs on communications satellites. Furthermore, J. H. Saleh and Marais (2006) suggest that perhaps there are other drivers in space system design that motivate redundancy requirements.