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The Earth Station
Published in Jerry D. Gibson, The Communications Handbook, 2018
The term Earth station is generally used to refer to a ground based communications facility made up of the transmitters, receivers, and antennas used to relay signals to or from a communications satellite. By definition, the Earth station also includes the equipment required to interconnect the satellite signals to the end user, whether the user is located at the Earth station facility or at a remote location. Information may be transmitted or received in the form of analog or digital carriers for voice, data, or video transmission. The signal is transmitted, or uplinked, from the ground station to a satellite transponder (Fig. 58.1). The satellite transponder relays the signal back to Earth where it can be received, or downlinked, anywhere within the coverage area known as the footprint. The majority of commercial Earth stations are designed to operate with satellites in geosynchronous orbit operated by AT&T, GE, Hughes, and other domestic and international carriers. Geosynchronous satellites are positioned approximately 22,300 mi. above the equator and rotate at the same speed as the Earth. From a fixed point on the ground, a satellite in geosynchronous orbit appears stationary and can provide continuous service to the end user. Figure 58.2 is an aerial view of Teleport Chicago showing multiple earth station antennas used for video and audio transmission. There are approximately 35 commercial satellites that can be accessed by locations in North America, which provide domestic C- and Ku-band satellite service (not including the Direct Broadcast Satellites).
Satellite systems
Published in Geoff Lewis, Communications Technology Handbook, 2013
Communication satellites occupy either equatorial, elliptical, or polar orbits as shown in Fig. 31.1(a). Geosynchronous satellites are those whose period of rotation is synchronised to that of the earth or some multiple of it. The geostationary orbit is a unique geosynchronous one, located over the equator. The satellite has a height and velocity such that it appears stationary to earth-bound observation. It is the earth’s period of rotation relative to the fixed stars in space (the sidereal time) that is important. This is slightly less than the solar period and is approximately 23 h 56 min 4.1 s (23.9345 h). The height above the earth’s surface of 35 765 km and velocity of 3.073 km/s, can be calculated as follows:
The View from Space
Published in Dawna L. Rhoades, Evolution of International Aviation, 2016
In 1945, a true science fiction writer, Arthur C. Clarke, proposed the concept of geostationary satellite communications. There are three types of orbits: geostationary (or geosynchronous), asynchronous, and polar. A geosynchronous satellite is always positioned over the same area of land. Asynchronous orbits pass overhead multiple times in a day. Polar orbits are designed for low altitude and are commonly used for mapping and photography. In order to place a satellite in a given orbit, a precise launch window must be calculated to consider escape velocity and the Earth’s rotation around its own axis (Brown, 2000). Such issues will also affect the “ideal” location of a spaceport (Chapter 22).
Combined GPS+BDS instantaneous single- and dual-frequency RTK positioning: stochastic modelling and performance assessment
Published in Journal of Spatial Science, 2021
Pengyu Hou, Baocheng Zhang, Yunbin Yuan
In December 2012, the BeiDou (Regional) Navigation Satellite System (BDS-2) entered into official operation and declared the start of its regional service, covering latitudes 55°S to 55°N and longitudes 70°E to 150°E. The initial service was provided for single-frequency users in the B1 band, and dual-frequency (B1/B2) observables were made available in December 2013. The global system (BDS-3) will be completed by 2020, and the space constellation will consist of five geostationary earth orbit (GEO) satellites, as well as 27 medium earth orbit (MEO) satellites and three inclined geosynchronous satellite orbit (IGSO) satellites. The current satellites will be a part of the constellation that forms the BDS-3 (CSNO 2013, Yang et al. 2017).