ites to provide global coverage as a function of 1,000 satellite altitude for several Min. Elevation Angle minimum elevation angles. 10 degrees 20 degrees Figure 2-6 describes the 30 degrees number of orbit planes into 45 degrees which the satellites must be deployed in order to assure ODYSSEY IRIDIUM operation at the minimum h = 10,400 km h = 780 km elevation angle in the equatorial regions. In GLOBALSTAR assessing the number of h If 1,400 km satellites required for a constellation, consideration is GEO Satellite h = 35,780 also given to the benefits of n = 3 providing diversity by having more than one satellite in view 1,000 10,000 100,000 of a subscriber. In addition to Altitude of Satellites (km) determining the number of Figure 2-5. Number of Satellites for Global Coverage satellites which are necessary [Jamalipour98] to provide coverage, the relationship of the satellites within Min. Elevation Angle the constellation must be considered. 10 degrees 20 degrees The Walker-star configuration uses 30 degrees adjoining planes traveling in the 45 degrees same north-south direction, resulting in two seam segments. Walker-delta and Ballard-rosette configurations result in adjoining planes not IRIDIUM ODYSSEY h = 780 km h= 10,400 km traveling in the same direction, So = 3 hence no defined seam region. Figure 2-7 provides comparison between star-seamed GLOBALSTAR configuration and the delta or rosette h = 1,400 km seamless configuration. 1,000 10.000 Altitude of Satellites (km) Figure 2-6. Number of Orbit Planes (S) for Equatorial Coverage [Jamalipour98] orbital seam (coverage overlaps even more) no orbital seam; ascending satellites descending satellites ascending and descending satellites overlap (moving towards north pole) (moving away from north pole) Walker Delta or Ballard rosette Walker seamed polar star Figure 2-7. Walker Star-Seamed and Walker-Delta (Ballard Rosette) Orbit Planes [Wood98] Historically, the orbit used for most telecommunications satellites has been geostationary, in which the orbital period eq