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Unformatted text preview: d of mapping them through a position solution geometry.
Range Error (URE). Other ranging signal accuracy parameters of interest to the civil community
are range rate and range acceleration error. Previous documents established performance
standards for these two parameters to serve as bounding conditions for Selective Availability
(SA). With the removal of SA, these parameters are no longer explicitly provided as formal
standards. The U.S. Government has instead established its intent to impose no artificial range
rate or range acceleration errors. A description of current range rate and range acceleration error
behaviors is provided in Section A-5.6.
A-184.108.40.206 The Four Elements of GPS Performance Control Four core operational control mechanisms are used to manage GPS performance: Page A-3 October 2001 GPS SPS Performance Standard • Constellation slot definition and tolerances • Constellation slot availability • Constellation Signal-in-Space (SIS) User Range Error (URE) • GPS-UTC (USNO) time scale difference management Constellation slot management is the maintenance of each GPS satellite’s orbit to within a
specified tolerance, with tolerances established based on the satisfaction of a constellation
geometry optimization criterion. Satellite availability management is the process of ensuring each
satellite’s availability to users is maximized, while supporting required maintenance and repair
activities. Satellite URE management is the control of line-of-sight errors between each satellite
and users within view of the satellite. GPS-UTC (USNO) time scale difference management is the
process of monitoring and calibrating the bias between the GPS time scale and Coordinated
Universal Time (UTC) as defined by the United States Naval Observatory (USNO). Page A-4 October 2001 GPS SPS Performance Standard SECTION A-2 GPS Operations Overview
The purpose of this section is to describe how four core operational control mechanisms are
employed to sustain GPS performance in accordance with operational standards. GPS
performance management practices may evolve over time in response to changing system
behaviors or operating conditions.
The four core operational controls used to manage GPS performance are:
• Constellation slot definition and tolerances • Constellation slot availability • Signal-in-Space (SIS) User Range Error (URE) • GPS-UTC (USNO) time scale difference management The information provided in this section serves to provide users with background concerning the
operations of the GPS constellation. A-2.1 Constellation Slot Definition and Tolerances The GPS constellation is a dynamic entity that is designed to provide consistent position solution
geometry characteristics. The specific design goals of the GPS constellation were to:
1) Provide the maximum availability of optimum geometry on a global basis for a 24-satellite
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This document was uploaded on 09/26/2013.
- Fall '09