y other mission types have utilized LEO orbits, until recently few telecommunications satellites have utilized this orbit altitude, primarily due to the large number of satellites necessary to achieve adequate earth coverage. The main advantage of LEO satellites is the reduced distance between the subscriber and satellite, resulting in reduced RF propagation path loss and reduced delay time for signal propagation. Reduced RF propagation path loss results in the need for less subscriber unit radiated power and smaller satellite uplink antenna aperture. Achieving small subscriber unit size and weight necessitates the reduced radiated power and small antenna configuration enabled by the LEO signal propagation distances. The reduced signal propagation delay time is important in telephony applications where the several hundred millisecond delay associated geostationary links is uncomfortable for most telephone users. The main disadvantage of a LEO constellation is the movement of the satellite with respect to both mobile and fixed station users. This results in the limited visibility that a single satellite presents to a subscriber. Movement of the satellite requires the use of an omnidirectional antenna on subscriber equipment and a tracking antenna for other ground segments requiring communication with the satellite. The limited duration of contact between an individual satellite and a subscriber results in the need for numerous satellites to provide continuous communications services to the subscriber. The elevation angle is the angle between a line connecting the subscriber to the satellite and the subscriber's horizon plane. Operation at low elevation angles results in additional path loss due to increased distance and atmospheric loss factors, highly distorted antenna patterns, the opportunity for obscuration by local geographic features and terrain, and ITU regulations limiting power flux density to prevent interference with other terrestrial and space systems. Figure 2-5 indicates the required number of satell