GEO satellites

Main applications for GEO satellites are telecommunications (TV broadcasting, internet, voice and telephones) and meteorology. MEO/HEO (elliptical orbits) satellites are mainly dedicated to global positioning systems. LEO satellites applications include Earth observations, communications (mobile satellite constellations), scientific/techno-logical demonstrations and early warning systems. 

Due to their main characteristics (fixed position over one point on the Earth), these satellites are mainly used for telecommunications hy operators that have assembled fleets covering the Earth (direct home TV broadcasting, voice and internet Intelsat, Eutelsat, Astra satellites, etc.). It is also important to remember that GEO satellites are used for Earth observation purposes (remote sensing) in addition to communication applications meteorological satellites are also positioned in geostationary orbits (Meteosat and National Oceanic and Atmospheric Administration satellites). 

Until recently, GEO satellites were repositioned (to compensate the Coriolis force, the moon attraction and solar flux impacts which make the satellite drift around its orbit to... 

The GEO satellite size increased since the beginning from few 100 kg to more than 6 tons today. In parallel, the electrical power raised from a few tens of watt to more than 20 kW for the more powerful satellites. 

Reminder the battery weight is less of a key factor compared to the GEO satellites as the launch price of 1 kg is less for LEO due to the lower altitude. Volume and performance tend to be key design drivers with batteries specifically tailored to each individual mission requirements. 

Mitsubishi Electric Corporation (MELCO), Japan, has started to develop large-scale Li-ion batteries for satellite systems since 1998, using large formatted cells. After the first flight in 2003 of an experimental satellite, named Sends-1 , over 100 battery modules have been provided not only to the MELCO standard satellite platform DS2000 series but also to the US companies, middle Asian and European countries, and had been launched successfully in LEO and GEO satellites and space transportation vehicles for the International Space Station (ISS). 

Standard GEO battery characteristics are shown in Figure 14.8. The first flight was in 2008 for a GEO satellite with a 15-year expected life. 

Figure 16.66 depicts several kinds of satellite links and orbits. The geostationary Earth orbit (GEO) is in the equatorial plane at an altitude of 35,786 km with a period of one sidereal day (23 h 56 min 4.09 sec). GEO satellites appear to be almost stationary from the ground (subject to small perturbations) and the... 

Links between LEO satellites (or the NASA Shuttle) and GEO satellites are used for data relay, for example, via the NASA tracking and data relay satellite system (TDRSS). Some systems wiU use intersateUite Unks (ISL) to improve the interconnectivity of a wide-area network. ISL systems would typically operate at frequencies such as 23 GHz, 60 GHz, or even use optical links. 

Attitude The angular orientation of a satellite in its orbit, characterized by roll (R), pitch (P), and yaw (Y). The roll axis points in the direction of flight, the yaw axis points toward the Earth s center, and pitch axis is perpendicular to the orbit plane such that R x P —> Y. For a GEO satellite, roll motion causes north-south beam pointing errors, pitch motion causes east-west pointing errors, and yaw causes a rotation about the subsatellite axis. 

This type of cell is widely used for GEO satellites and LEO satellites. These cells are manufactured by Eagle-Pitcher Technology Corp. in the United States. In both cases, primary power is supplied by solar panels. When orbit brings the satellite into the earth s shadow, which represents an eclipse, the battery starts to deliver electrical energy to various electrical components and electronic and electro-optic sensors. The solar panels will subsequently recharge the secondary batteries during the sunlit periods. 

Nickel-hydrogen Long cycle life under shallow discharge, long fife Primarily for aerospace applications such as LEiO tmd GEO satellites... 

The BeiDou navigation (NAV) messages are formatted in D1 and D2 based on their rate and structure in superframe, frame and snhfirame. The first format is transmitted by all 35 satelhtes, the second by GEO satellites only. The rate of these messages is 50 bps and 500 bps respectively (www.beidou.gov.cn). 

Whereas the constellation of 27 MEO satelhtes will provide global coverage at any moment, the constellation of 3 IGSO and 5 GEO satellites will can be used in limited area only. It means that the advantages of D2 NAV message, integrity information in particular will be accessible to users in China and the Asia-Pacific region only. 

As the augmentation service information is and will be transmitted by 5 GEO satellites only, at the moment of BeiDou Full Operational Capability FOC (space segment with 35 satellites) for all users without the possibility of the reception this information China system will be another SNS for positioning only. 

The GEO satellites are mostly telecom orbits. In this case, the external equipment is subjected to a thermal environment of [—200°C, -l-200°C] depending on the Sun exposure, under a secondary vacuum 10 Torr for 15 years. The main source of radiation to consider is from the UVs. 

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