Tolerances the gps constellation is a dynamic entity

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: the global four-satellite Position Dilution of Precision (PDOP) at a five-degree mask angle as the optimization criterion. 2) Maintain consistent ground tracks. 3) Minimize the effects on availability of removing any single satellite from service. 4) Define slot position tolerances such that no satellite requires more than one maneuver over any one-year interval to remain within its slot. Obviously a satellite constellation is not a fixed entity in space and exhibits a range of dynamic behavior over its lifetime. This dynamic behavior begins with launch dispersions unique to each satellite and continues with satellite-unique orbit precession over the lifetime of the satellite. Stationkeeping maneuvers are conducted to compensate for orbit precession effects and maintain Groundtrack Equatorial Crossings (GECs), but orbit plane divergence from the nominal is unavoidable. To this end, two different sets of ephemeredes are presented in this section. The first set is the nominal constellation plan, illustrating the intent of the constellation design and the ground rules for maintaining the constellation. This set is representative of the nominal constellation slot assignments presented in the SPS Performance Standard, Section 3.1. The second set is an example of the current operational nominal constellation, with GECs adjusted to compensate for orbit plane dispersion. Orbital element sets are presented for the nominal constellation plan and the current nominal constellation in almanac form for ease of use. For comparison purposes, both sets are defined at the same epoch time. Page A-5 October 2001 A-2.1.1 GPS SPS Performance Standard Nominal Constellation Plan The current architecture for the constellation identifies nominal orbit slots for a 24-satellite constellation and tolerances for establishing and maintaining satellites within the slots. Table A2-1 identifies values for an almanac that is representative of the system nominal constellation plan defined in the SPS Performance Standard. The listed Mean Anomaly values (Mo) place the satellites at GECs consistent with the intent of the nominal constellation plan. Table A-2-1. Nominal Constellation Plan, Time of Almanac: 9/24/2000 17:04:00.00 Mo A (km) Orbit e ω Ωo (2) δi (1) ΩdotJ2 Slot (degrees) (degrees) (degrees) (deg/sec) (degrees) 0.000 1.000 -4.4874E-07 26559.7 162.374 0.000 82.826 A1 0.000 1.000 -4.4874E-07 26559.7 162.374 0.000 -23.514 A2 0.000 1.000 -4.4874E-07 26559.7 162.374 0.000 186.376 A3 0.000 1.000 -4.4874E-07 26559.7 162.374 0.000 -143.494 A4 B1 B2 B3 B4 0.000 0.000 0.000 0.000 1.000 1.000 1.000 1.000 -4.4874E-07 -4.4874E-07 -4.4874E-07 -4.4874E-07 26559.7 26559.7 26559.7 26559.7 -137.626 -137.626 -137.626 -137.626 0.000 0.000 0.000 0.000 -104.344 -11.964 -235.324 19.076 C1 C2 C3 C4 0.000 0.000 0.000 0.000 1.000 1.000 1.000 1.000 -4.4874E-07 -4.4874E-07 -4.4874E-07 -4.4874E-07 26559.7 26559.7 26559.7 26559.7 -77.626 -77.626 -77.626 -77.626 0.000 0.000 0.000 0.000 -73.424 186.496 154.366 56.256 D1 D2 D3 D4 0.000 0.000 0.000 0.000 1.000 1.000 1.000 1.000 -4.4874E-07 -4.4874E-07 -4.4874E-07 -4.4874E-07 26559.7 26559.7 26559.7 26559.7 -17.626 -17.626 -17.626 -17.626 0.000 0.00...
View Full Document

This document was uploaded on 09/26/2013.

Ask a homework question - tutors are online