Analysis of On-Orbit Behavior of GPS Block II-R Time Keeping System

Abstract : This paper presents three phases of the Time Keeping System analysis (TKS) of the first on-orbit GPS IIR Satellite, SVN 43. The first phase is a comparison of the performance of the SVN 43 Rubidium Atomic Frequency Standard (RAFS) to other GPS satellite clocks. The results indicate that the SVN 43 RAFS is performing better than specification and ranks highly when compared to the other clocks in the constellation. The second phase was to analyze all available data to determine the causes of several transients seen in the SVN 43 TKS. This led to a concentration on the RAFS and associated inputs and outputs, as well as the utilization of TKS simulation tools. The third phase was to examine the entire system to determine how to improve our visibility into the TKS operation. This led to an SV software enhancement whose purpose is to buffer TKS related data in SV memory for subsequent dump and analysis. An example will be presented showing the value of this new TKS buffer capability in the investigation of some TKS events that occurred in August 1998.