k is not technically efficient it will not be commercially efficient. 16.19 Satellite Spectrum and Orbit Options The satellite systems of interest to us are deployed either into L Band between 1518 and 1675 MHz or S Band between 1.97 and 2.69 GHz and are either in geostationary geosyn- chronous (GSO) orbits at 35 000 km, in medium-earth (MEO) orbits between 10 000 and 20 000 km or in low-earth (LEO) orbits or 'high' low-earth orbits (HLEO) between 700 and 1400 km. For the sake of comparison, the US Space Shuttle orbits at 350 km. Some highly elliptical orbits such as the Molniya or low polar orbits provide optimised coverage for countries at extremely northern or extremely southern latitudes. 'Seeing' geo- stationary satellites from these latitudes can be problematic. The choice of orbit determines the number of satellites needed to provide a particular coverage footprint, the size and po- sition of the satellites determines their functionality. The spectrum into which the satellites are deployed and the proximity of this spectrum to other users also determines their func- tionality, particularly in terms of system interoperability with other terrestrial or satellite networks. LEOS have the advantage of low round-trip latency, about 20 milliseconds compared with 133 milliseconds for a MEO and 500 milliseconds for a GSO satellite. Geostationary satellites have the advantage that they stay in the same place when viewed from the earth. This simplifies handover and radio planning algorithms when servicing mobile users. Table 16.11 Present and proposed S band satellite and terrestrial (ATC) broadcast and two-way radio networks XM Sirius Broadcast 2332.5 192 audio channels 2345.00 12.5 MHz Mobaho Broadcast Japan 11 video channels including HDTV 25 audio channels 3 data channels S- DMB Similar to Mobaho Korea 25 MHz Terrestar and Broadcast and two way ICO US 20 MHz 20 MHz ICO Europe Broadcast and two way 1997.5 2187.5 12.5MHz 12.5 MHz Eutelsat Broadcast but potentially broadcast SES Astra and two way Potential integrati