GPS Control Segment Upgrade Goes Operational - Enhanced Phased Operations Transition Details

摘要

This paper introduces the concepts, progress, results, and lessons learned from the phased transition of the Legacy GPS Master Control Station (MCS), which has operated the command and control of the GPS constellation for the past 22 years, to the Architecture Evolution Plan (AEP) Control Segment, which became operational in September 2007. The Schriever Air Force Base -led transition of the MCS, known as the Enhanced Phase Operations Transition (EPOT), consisted of a multi-year effort between operations, development, and sustainment organizations to achieve a seamless navigation service transition to GPS users. EPOT consisted of a three-step process consisting of (1) initializing the AEP Kalman filter with a snapshot (checkpoint) of the Legacy MCS filter, (2) continuous monitoring of the two system navigation services over a 48 hour period against key performance metrics, including Kalman filter estimations, predictions, and broadcast messages, and (3) transfer of the MCS monitoring stations (MS) and ground antennas(GA) to AEP before the new system began controlling the GPS satellite constellation. The primary objective of the EPOT transition approach was to validate navigation performance before sending or broadcasting any data to the GPS user community. Only after meeting tight performance comparison criteria between the Legacy and AEP control segments did EPOT proceed to the next transition step.This paper discusses EPOT performance results from one year of Rehearsal and Transition practice activities, culminating in a transition approach demonstrating continuation of GPS performance at levels nearly invisible to users during the actual transition. A brief overview of the Legacy and AEP control segment will be presented, along with some significant events, which improved the GPS mission performance. A trend plot of the Navigation performance, as reflected in constellation signal-in-space estimated range deviation (SIS-ERD), will be presented showing performance improving by a factor of three from the early 1990s to current levels. The EPOT approach permitted iterative improvements to the new system enabling successful and repeatable demonstrations of Kalman filter synchronization to sub-decimeter User Range Error (URE) agreement. The details associated with the various improvements applied to the AEP system to achieve such agreement will be discussed. Analysis will include performance measures of the MCS Zero Age-of-Data (ZAOD), predictions, and the signal-in-space URE. The paper will conclude with insights of lessons learned during the AEP development and transition process.