WAAS PRN 135 User Information
In April 2010, WAAS satellite PRN 135 lost control of its navigation computer – the system that keeps the satellite stationary over the equator. Normally PRN 135 is at longitude 133º West. With no navigation computer, the satellite drifted slowly to the East. In December 2010, it had drifted to 93ºW, when finally the navigation computer was back online. In January 2011, work began to bring the satellite back online and move it back to 133ºW.
While on the move back to 133ºW, PRN 135 will be in test mode. Receivers on the ground may be selecting PRN 135 as the primary WAAS satellite to use, based on where it is in the sky. If only test messages are available on the receiver’s primary WAAS satellite, the receivers wait to see if full messages will be coming. Unfortunately this prevents the receiver from using the valid signals that are currently transmitting from PRN 133 and 138. To ensure uninterrupted WAAS performance, users should manually tune their receivers to use PRN’s 133 and 138 until PRN 135 arrives back at its home at 133ºW, later in 2011.
To monitor the status of the WAAS satellites, users can monitor these sites:NTSB FAA
While SBAS operators worldwide strive to prevent situations like this from happening, the potential exists that something similar could occur somewhere else in the future. The information in this workflow may help configure systems in such cases.This information courtesy of Hemisphere GPS Hemisphere GPS WAAS Info