Archive for May 3rd, 2009

SVN 49, PRN 1 URE too high

May 03rd, 2009 | Category: General Navigation,Launch

After the last Nog, someone pointed me to the following picture, published by the GPS Operations Center from this site:, (pick the Position Errors By Satellite value in the drop down box)


This shows that PRN 1, on April 30, 2009, had a very large User Range Error (URE), larger than any other satellite in the entire GPS constellation. If you've been following the Nog for awhile, you know that a URE this big can lead to large navigation errors.  This is certainly the reason PRN 1 is not healthy yet.  URE's are calculated using ephemeris and clock errors.  Ephemeris errors are rarely a problem, so it's likely that this satellite has a clock problem.