e, or intersatellite linked networks. The International Telecommunications Union (ITU) designation of Mobile Satellite Service (MSS) classifies radio communications among mobile subscribers and between mobile subscribers and Public Switched Telephone Network (PSTN). Classes of service within MSS include Aeronautical Mobile Satellite Service (AMSS), Maritime Mobile Satellite Service (MMSS), and Land Mobile Satellite Service (LMSS). Subscribers in MSS systems may gain access to the communications network from anywhere in the antenna footprint of the satellite or constellation. Fixed Satellite Service (FSS) is defined as radio communication between subscribers at specified fixed locations. Subscribers in FSS systems may gain access to the communications network only from their registered earth terminal location. The operational characteristic of a satellite system refers to the method or means in which subscriber information is propagated through the communications network. In messaging systems where concurrent contact between the sender and receiver of a message is not necessary, store-and-forward systems provide lower cost solutions. These systems support two-way data communications and messaging (but not telephony) and data gathering such as asset tracking, environmental assessment reporting, and remote data acquisition and reporting are specific markets of these systems. Figure 2-1 indicates the situation in which the satellite is not capable of simultaneous contact with both the originator and receiver of the message. In store-and- forward systems, the satellite receives a message from the originator while in direct contact with their location, stores the message in payload memory, and transmits the message to the recipient when the satellite is in view. Systems which operate according to the same principle, but with minimal delay, are referred to as Near-Real-Time systems. Orbcomm, Gonets, and Leo One are near-real-time systems requiring 28, 45, and 48 satellite constellations respectively. Faisat, Safir, E-Sa