GPS & Y2K - Nautical Know How

The GPS Joint Program Office has determined that all generations of GPS satellites are unaffected by the Year 2000 (Y2K) and GPS End-of-Week (EOW) Rollover Issues. However, the Civilian GPS users may need to verify that their receivers and applications will work properly through these events.

GPS has two “rollover” issues

The Year 2000 “Millennium” problem with computer implementations, and;

The GPS End of Week (EOW) Rollover at 0000 hrs UTC,
22 August 1999

GPS as a total system must account for both cases by design and operate through successfully

Y2K Issue: The Year 2000 rollover issue, commonly referred to as the Y2K problem, stems from the fact that many computer programs are using a two digit date field and assume the year is 19xx. When the year 2000 arrives, a two digit date becomes '00' and could be interpreted as an invalid date.

EOW Rollover Issue: The EOW rollover problem is really a problem that occurs every 20 years. GPS system time, which counts weeks, started counting on midnight January 5/6, 1980, in modulo 1024 (0-1023). GPS System Time will roll over at midnight August 21-22, 1999, 132 days before the Year 2000.

On August 22, 1999, unless repaired, many GPS receivers will claim that it is January 6, 1980, August 23 will become January 7, and so on. Accuracy of navigation may also be severely affected. Although it appears that GPS broadcasts do contain sufficient data to ensure that navigation need not be affected by rollover in 1999, it is not proven that the firmware in all receivers will handle the rollovers in stride; some receivers may claim wrong locations in addition to incorrect dates.

Some manufacturers have already solved the problem, but some have not.

This is how the precise rollover date is computed: The timescale origin (time zero) of GPS System Time, 00:00:00 UTC 6 January 1980, is Julian Day 2,444,244.500. A GPS Cycle is 1,024 weeks, or 7,168 days, so the first GPS rollover will occur at Julian Day (2444244.5+7168)= 2,451,412.5, which is 00:00:00 UTC 22 August 1999 AD, which is the midnight between Saturday night the 21st of August, and Sunday morning the 22nd of August, 1999.

The NIS has compiled a list of GPS receiver manufacturers and associated Points of Contact (POC) to address your questions. We also encourage you to revisit this site from time to time as we will continue to update this list.

The firmware in all affected (mostly older) receivers will have to be replaced. This will involve replacement of PROMs; some are socketed, some are soldered. As a technical matter, the solution is quite simple. It's the logistics that will take some effort.

Without a GPS Simulator, there is no way for users to test a GPS receiver for this problem. Users are encouraged to contact their receiver manufacturer to determine if their receiver will be affected, in particular if a failure of navigation could put lives or property at risk."

In light of the pending potential problems, the entire GPS system is being modernized through an initiative announced by Vice President Al Gore in January of 1999. In essense, the initiative will make the Global Positioning System more accessible to civilian users.

For more than you ever wanted to know about GPS, we have included a Glossary of GPS Terms.

Related Articles:
An Overview of GPS
GPS Update

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Will Y2K Effect Your GPS and When? At the Millinium Or Sooner!

Will Y2K Effect Your GPS and When?
At the Millinium Or Sooner!