GPS Primer, anyone? : LUSENET : TimeBomb 2000 (Y2000) : One Thread

A co-worker just told me that she is making plans to go to Aruba on August 22nd. My jaw dropped. I tried to gently explain to her that that might be the worst day to make air travel plans. (she knows about my Y2K concerns) We started talking about the GPS, but she wsn't quite getting it. Then her phone rang and we said that we would talk about it later.

Anyway, can anyone point me to a real simple, not too technical primer on the GPS and why the rollover might cause problems, and why that might not be a good week to travel? It's tough finding stuff here, but I'm going to keep looking. Thanks in advance and don't knock yourself out...

-- pshannon (, February 22, 1999


Yardeni's is kinda slow & easy..... <--Chapter 8, Sect. 5

With links to more complicated descriptions.

-- Lisa (, February 22, 1999.

The GPS satelites send our precise time signals. By calculating the slight differences between 3-6 such signals from different GPS satelites, a receiving unit can calculate its exact position.

The time signal includes parts of the second, the second, the minute, the hour, and the day (of the week), and a week number.

It is the week number that is the source of the problem. There is a register of a sequential week number, going from 0 up to a maximum of 1023. When week 1023 is over, it flips back to week zero.

This happens every 20 years or so. Since the system was created around 1980, this is the first such flip.

It turns out that 20 years is so long that many programmers forget it will ever happen. Sort of like ever getting past 1999. Many receiving units are programmed to think that week 0 is in 1980. There are several million such bad receivers out there, including quite a few in the military.

There is a lot of speculation about deep problems with air travel, bank transfers, the stability of the electrical grid, and the efficiency of the web on August 22, 1999 when the GPS rollover happens. [The GPS signal is used as a precise time signal to "stamp" bank transfers, the co-ordinate the phasing of the electrical grid, and to run certain timing tests that fine-tune the efficiency of big trunk lines of the world wide web]

I hope this helps.

-- David Holladay (, February 22, 1999.

I've read that only the terminals produced prior to 1995 have the problem. David, I thought you would continue to discuss the problem but didn't. Here goes my response.

When a terminal requests a read for a position, the satellites compute the time the signal took for travel. At zero, they will assume the signal took some 18 years and provide an error message on the position. When the terminal requests an additional read, a millisecond will pass and delta t will now be a realistic positive number. The satellites will calculate a realistic position. Do you need an explanation of triangulation?

In additional planes have other navigation tools besides GPS. Pshannon what did you tell this co-worker? Hope it wasn't that the planes will fall out of the sky.

Troll Maria

-- Maria (, February 22, 1999.


I read something convincing about three months ago that the GPS rollover would be a non event. I beleive I accessed the information from a thread at this forum. Might check it out in the archives.

GODS Will Be Done


-- flierdude (, February 22, 1999.

Year 20000 (Y2K) and GPS End-of-Week (EOW) Rollovers

In the left hand vertical frame, a number of options are available. The first one, DEFINITIONS, lists these options: 1) Y2K/EOW Rollover Issues: Outlines Y2K issues as well as a GPS-unique rollover called the End of Week (EOW) rollover. 2) Air Force Five-Phased Approach: Summarizes a five-phased approach for Y2K/EOW compliance in accordance with DoD guidelines. 3) User Equipment (Civil Receivers): Provides a link to the US Coast Guard Y2K Page. The US Coast Guard is the government liaison to the civil sector for GPS. All information concerning civil receivers may be found on their web page. 4) User Equipment (Compliant DoD Receivers): Lists all DoD receivers that have been tested and found Y2K/EOW compliant. 5) Space Segment: Outlines Y2K/EOW status of the Space Segment. 6) Control Segment: Outlines Y2K/EOW status of the Control Segment. 7) USNDS: (Mil-only) Outlines Y2K/EOW status of the United States NUDET (Nuclear Detonation) Detection System

Obviously #7 is restricted. Some downloads are available. One is a Powerpoint presentation: Y2K Briefing.

-- Tom Carey (, February 22, 1999.

Good stuff, gang. Thanks. The yardeni thing is along the lines of what I'm looking for. No, I didn't tell her planes would fall from the sky, as I don't believe that will happen. I'm just worried about her making travel plans and having them screwed up.

I think it's likely that the days before the 22nd, there will be a big travel glut due to people trying to get to where they're going before the 22nd. This may likely cause unusualdelays, etc. Then, I think it may be tough to get a flight on the 22nd and maybe for a day or two after, as insurance companies try to limit the number of planes in the air. It's not the airliners, but the small planes that might cause that concern.

I just think it's dumb to plan a trip now to fly on Aug. 22nd. But not necessarily for safety reasons...

-- pshannon (, February 22, 1999.

Jim lord discussed it recently at the Westergaard site:

-- dave (, February 22, 1999.

The Week roll over is a dual issue. the navigation issue is probably going to be a true non-event. the problem will self correct, and teh positions will go back to correct.

the second issue is that of using the clocking time stamp function for certain types of transactions. these time stamps are used as keys in certain banking, and operations control functions. HERE is where we will have the non-zero probability of serious problems, as the keys will be SO OUT OF RANGE that the data may be lost, or filed as having an occurrence date in 1980.


-- Chuck, night driver (, February 22, 1999.

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