Design philosophy for the ELLIPSO satellite system (1998)

The ELLIPSOTM Global Mobile Personal Communications System (GMPCS) is being designed to provide the lowest possible telephonic cost-per-minute communications service to worldwide customers. This system received an FCC license on July 1, 1997, to operate in the U.S. in the 1610 to 1621 MHz frequency band, using broadband CDMA. Virtually every facet of the system and subsystem design of the ELLIPSOTM system is being optimized to provide the greatest possible performance at the lowest possible cost. The satellite constellation itself consists of unique, patented, and highly sophisticated elliptical plus circular orbital combinations. The resulting coverage matches both the world's population distribution and man's night versus day activity patterns. Thus, ELLIPSOTM is the only Big-LEO system whose capacity closely matches real-world requirements. At the same time, it uses far fewer satellites than competing all-circular orbit GMPCS systems. The use of inclined, sun synchronous, elliptic orbits, as well as circular and/or elliptical equatorial orbits, greatly simplifies satellite design. ELLIPSOTM satellites have a design lifetime of five years. This allows for a simpler design with a lesser degree of design redundancy than present ten to fifteen year lifetime GEO satellites require. The highly automated Ground Control Stations (GCS), (or gateways) are sites optimally located to serve customers in a particular country or region. Hand-held ELLIPSOTM user terminals are dual-mode; i.e., they will communicate through available terrestrial cellular sites where available and less expensive, or, alternatively into ELLIPSOTM system satellites, by default. Copyright ©1998 by the American Institute of Aeronautics and Astronautics. All rights reserved. Introduction/System Overview The ELLIPSOTM System is one of the socalled Big-LEO satellite communications systems. It is intended to provide worldwide satellite cellular telephone services to regions not adequately served by terrestrial cellular systems. Although MCHI was the first of several companies to file for an FCC license for GMPCS (on November 5, 1990), it was one of the last to receive one(on July 1, 1997). The FCC awarded three licenses in November 1995 to Iridium, Globalstar and Odyssey. MCHI's vision for ELLIPSOTM has always been as a supplement to (and not a replacement for) cellular terrestrial telephone service. Continuing market analyses by MCHI have shown that highly developed urban areas are not the prime target for our satellite system. Rather, the more attractive targets are the relatively thinly populated, undeveloped or underdeveloped countries (with inadequate existing telephone service and infrastructure), plus a growing global roaming (business, tourist, and personal) market. The first priority for satisfaction is going to be voice telephony (or POTS 'plain old telephone service'). Other needs will be addressed in addition, such as low data rate, paging, fax, etc., but these extras should not be allowed to either increase the cost of the basic service, or to excessively delay the time frame for first introduction of the service. It is anticipated that initial service will be established in the low latitude regions, using the equatorial plane satellites, in the last quarter of the year 2000. Full operational capability is planned by the year 2002. There will be three types of user terminals in the ELLIPSOTM System; the handheld (cellular) type, the mobile (vehicular, marine, or aircraft) type and the fixed ('village phone') type. *Vice President, Constellations & Launch Vehicles Copyright© 1998, American Institute of Aeronautics and Astronautics, Inc. The ELLIPSOTM System functional layout is shown in Figure 1. The major segments or components are shown schematically. The satellites employ relatively simple bent-pipe transponders to relay CDMA signals. The frequencies of the user (or service links) are: 1610-1625.5 MHz (up-customer to satellite); and, 2483.5-2500 MHz (down-satellite to customer). The feeder links use C-Band (7 GHz) for the down-link (space to earth) and Ku Band (15 GHz) for the up-Iink (earth to space). The gateways (Ground Control Stations, or GCSs) service the feeder links, and connect with the ELLIPSOTM Switching Offices (ESOs), which then route the signals to the Public Switched Telephone Network, a private network, or an international/longdistance carrier. The ELLIPSOTM Constellation The ELLIPSOTM constellation, with its unique elliptic orbits, characterizes the system and accounts for the major reductions claimed for both overall system costs, as well as costs to the customer (as measured by the parameter billable cost per minute). This patented2'3 array is able to closely match the satellite coverage and capacity with the actual market requirements. Extra capacity is provided at those latitudes where there exists a greater population density. Also, more capacity is provided for the daylight hours, when more of the world's people are awake and communicating for business or pleasure, than at nighttime when they are asleep (or watching TV). The development and optimization of the ELLIPSOTM constellation has been described in a succession of published technical papers''' so only the elements will be presented here. The total constellation of the ELLIPSOTM System is made up of two sub-constellationsBOREALISTM and CONCORDIATM . The former, as its name implies, has as its primary goal the coverage of Northern hemisphere customers. It consists of two elliptic, sunsynchronous, repeating ground-track planes with five satellites per plane. Both planes are nearly edge-on to the sun (and remain so throughout their lifetime). Since the satellites are in stable elliptic orbits, their apogees can be made to lean towards the sun and therefor provide extra coverage during daylight hours. (The satellites gain altitude, lose speed, and tend to bunch together at and near their apogees.) The CONCORDIATM satellites (six, plus one spare) are in orbit in the equatorial plane. They are primarily intended to cover the equatorial region of the Northern hemisphere, plus the totality of the Southern hemisphere (down to about 50° South latitude). These equatorial satellites can be placed in either circular or elliptic orbits. If they are in circular orbits, the night versus day coverage will be approximately equal. However, it is possible, using the Apogee Pointing to the Sun (APTS) type orbit, to use elliptic orbits with the apogee points of these orbits pointing towards the sun. This provides a coverage that is somewhat similar to the BOREALISTM satellites, in that the apogees remain on the sunward side of the earth, providing augmented daytime coverage, year-in year-out. It should be noted, however, that since the equatorial plane of the earth is inclined approximately 23.5° from the plane of the ecliptic (the plane of the earth's orbit around the sun), these equatorial CONCORDIATM satellites do vary from being edge-on to the sun. In the Northern hemisphere summer and winter solstice their plane is 23.5° away from being edge-on. At spring and autumn equinox, however, the orbit plane is exactly edge-on. A view of the ELLIPSOTM constellation is seen