For the constellation identifies nominal orbit slots

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Unformatted text preview: design for the GPS constellation is presented in Table 3-1. Slot assignments for the nominal constellation plan are specified in terms of the Right Ascension of the Ascending Node (RAAN) and the Argument of Latitude for a defined epoch. SLOT A1 A2 A3 A4 Table 3-1. Reference Orbit Slot Assignments as of the Defined Epoch RAAN Argument of SLOT RAAN Argument of Latitude Latitude D1 272.847° 268.126° 92.847° 135.226° D2 272.847° 161.786° 92.847° 265.446° D3 272.847° 11.676° 92.847° 35.156° D4 272.847° 41.806° 92.847° 167.356° B1 B2 B3 B4 332.847° 332.847° 332.847° 332.847° 80.956° 173.336° 309.976° 204.376° E1 E2 E3 E4 152.847° 152.847° 152.847° 152.847° 197.046° 302.596° 66.066° 333.686° C1 C2 C3 C4 32.847° 32.847° 32.847° 32.847° 111.876° 11.796° 339.666° 241.556° F1 F2 F3 F4 212.847° 212.847° 212.847° 212.847° 238.886° 345.226° 105.206° 135.346° EPOCH: 0000Z, 1 July 1993 h m s GREENWICH HOUR ANGLE: 18 36 14.4 REFERENCED TO FK5/J2000.00 COORDINATES The rest of the reference orbit values are presented below: • Groundtrack Equatorial Crossing: ± 2° • Eccentricity: 0.00 – 0.02 • Inclination: 55° ± 3° • Semi-major Axis: 26,559.7 kilometers ± 50 kilometers for Block IIR, ± 17 kilometers for Block II/IIA • Longitude of the Ascending Node: ± 2° • Argument of Perigee: ± 180° Note that actual constellation RAAN values will change over each satellite’s lifetime due to perturbation forces and variations in each unique orbit’s nodal regression rate. It is also possible for inclination to drift out of the nominal tolerance. Maintenance of the Groundtrack Equatorial Crossing (GEC) and relative spacing of the constellation are therefore the controls employed to compensate for constellation drift and sustain constellation geometry at acceptable levels. The semi-major axis and orbital period shall be periodically adjusted to maintain the relative spacing of the satellite GECs to within ±2° of the chosen values. GEC values are chosen such that the position solution geometry criterion is continuously sustained for the core 24-satellite constellation. Page 12 October, 2001 3.2 GPS SPS Performance Standard Service Availability Standard The U.S. Government commits to maintaining the Position Dilution of Precision (PDOP) in accordance with the following tolerances. Table 3-2. Position Dilution of Precision Availability Standard PDOP Availability Standard Conditions and Constraints • Defined for position solution meeting the ≥ 98% global Position Dilution of representative user conditions and operating Precision (PDOP) of 6 or less within the service volume over any 24-hour interval. ≥ 88% worst site PDOP of 6 or less • Based on using only satellites transmitting standard code and indicating “healthy” in the broadcast navigation message (sub-frame 1). In support of the service availability standard, 24 operational satellites must be available on orbit with 0.95 probability (averaged o...
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