Quote of the Day
There is something to be said for cold, calculating competence.
— Morning Joe TV program gave this review of the movie Vice and its portrayal of Dick Cheney.
Figure 1: GPS-III-A satellite. (Source: US Government)
I have been working since May 2018 as a contractor for various companies on resolving specific issues – I am a troubleshooter. This role has provided me with a number of interesting challenges. One of my recent challenges is helping folks deal with the GPS Week Number Rollover (WNRO) issue. This issue involves a 10-bit week counter that has been counting up from 0 every week since 21-August-1999. This counter can will count up to 1023 and then it will rollover to 0 on 7-April-19. Not everyone is prepared for this rollover. This issue shares many similarities with the Y2K problem. See this presentation for a good overview of the rollover issue.
These 1024 week intervals are referred to as epochs. Each epoch lasts 19 years, 7 months, and 15 days. GPS went live on 6 - Jan-1980 and the first epoch ended on 20-Aug-1999. We are now in the second GPS epoch and the 3rd epoch begins 7-April-2019.
Going forward, GPS implementations will be using 13-bit counters, which will reduce the frequency of these events.
We can easily use Excel to show that the next rollover date is 7-April-2019.
I swear that I deal with these counter rollover issues at least once a year (earlier example).
And there is the upcoming Unix epoch roll-over in 2038.