[LEAPSECS] Problems with GPS?

Matsakis, Demetrios matsakis.demetrios at usno.navy.mil
Wed Feb 10 16:25:28 EST 2010

I have no privileged information and GPS receiver programming is not what I do, but I also have never known the ICD200 to be incorrect. Perhaps ten years ago, two timing experts separately informed me of great frustration they had writing their own GPS receiver software, but it turned out they were following an incorrect unofficial summary of the ICD. If anyone is aware of ambiguous wording in the ICD, as claimed below, they should notify those groups also listed at the very bottom of this email.

In contrast, this listserve has passed along many stories about dumb programming involving leap seconds, including both GPS receiver and NTP software. Hopefully the manufacturers fix those too, but I'm beginning to think Pasteur was not entirely correct. That is, for some kinds of bugs spontaneous generation appears to be a valid process.


From: Rob Seaman
Sent: Wed 2/10/2010 1:48 PM
To: Leap Second Discussion List
Subject: [LEAPSECS] Problems with GPS?


Any comments on this email exchange between our Deputy Director and an observatory engineer? (I would presume the issue is not directly pertinent to leap seconds.)

Systems at the observatory also rely on NTP, of course, but certainly GPS is widely deployed throughout our infrastructure at remote locations.


Rob Seaman
National Optical Astronomy Observatory

Begin forwarded message:

Subject: RE: Problems with GPS


We are an institution that heavily relies on accurate time, and GPS is the preferred if not the only way of synchronizing our clocks. In our facilities we use a large number of GPS time receivers for a "mission critical" function. Those units are made by different manufacturers over different periods of time. As the article states, the GPS team does not control what manufacturers do, and on this opportunity an ICD was issued for manufacturers to provide updates for their equipment.

Given that there are incompatibility issues with the new GPS standards I would recommend for the person in charge of each GPS time receiver to contact the manufacturer and inquire about the status of the particular model in use and update the firmware if necessary. Case the manufacturer no longer exists or the unit is not upgradable it would be prudent to check the unit against a certified unit. At this time also seems appropriate conducting a deeper investigation regarding the future of the GPS standards and compatibility issues so nobody gets hit without advice.

I hope this helps,


Subject: Re: Problems with GPS
Thanks for the heads up Oliver. Can you tell us what it means?
Problems with GPS Ground Control Software Update: AEP 5.5C
February 8, 2010


The GPS Wing and 2SOPS (2nd Space Operations Squadron) initiated a software update of the ground command and control (C2) system for GPS on January 11, 2010. The update has not gone as smoothly <http://www.gpsworld.com/gnss-system/out-front-rocky-road-robustness-9424> as planned.

There appear to be two core problems with the software update, one affecting military selective availability anti-spoofing module (SAASM) receivers, and the other affecting timing receivers. The problems have reached such an extent that the GPS Wing has issued a unique Notice Advisory to NAVSTAR User (NANU) for civilian and commercial GPS users and for military users, asking for user comments.

See here <http://www.gpsworld.com/gnss-system/news/gps-control-software-glitch-nanu-issued-9414> for the first NANU, issued January 24.

The Air Force has now issued a second NANU through the GPS Operations Center (GPSOC), for military users, again asking for user comments: "Attention military users with SAASM receivers. For information about an anomaly on a limited number of these receivers, please go to . . . " and so on. "Also reference previous NANUs 2010002, 2010011, 2010016, 2010018."

History of Problems. The Architecture Evolution Plan (AEP) software provided to the Air Force by Boeing (designated single prime integrator for AEP in 2001, with Lockheed Martin subcontracted to continue the development) has generated at least two previous major SNAFUs, one involving the inability to upload nav data to seven satellites, and one involving non-compliant international receivers.

In September 2007, when the phased transition of the 22-year-old Legacy GPS Master Control Station (MCS) to the AEP control segment became operational, the Air Force described its implementation "like changing the engine on a car while it's speeding down the freeway going 65 miles per hour." Apparently either some dropped parts now litter that freeway, or some gears, somewhere, are not meshing properly.

The following comments are drawn from Don Jewell's Defense newsletter, to appear later this week. For a free subscription, visit GPS World's newsletter subscriber page <http://www.gpsworld.com/gps/subscribe-e-newsletters-8410> ,

"The GPS is so ubiquitous and there are so many global receiver manufacturers, with so many different receivers on the market today that, not surprisingly, the GPS Wing has been unable to keep track.

"This is such a Herculean task, and therefore instead of checking and certifying every GPS receiver manufactured, prior to activating the software update, the GPS Wing issued an updateable ICD or Interface Control Document that all receiver manufacturers use as a voluntary guide to determine compliance.

"However, even the ICD leaves room for interpretation and is more ambiguous than the GPS Wing intended, so it should come as no surprise that there were and are still receiver issues following the latest AEP update. The GPS Wing is currently receiving more help than they think they need, but this too shall pass; it will just take time. The GPS Wing did not revert to AEP 5.4 (the previous version) because of the upcoming IIF-SV1 launch. The scheduled sequential AEP 5.5C and AEP 5.5D updates are required before the ground control segment can adequately control the more advanced capabilities of the IIF satellites.

"The actionable aspect of this update and NANU is that if you are experiencing any problems or glitches with your GPS receiver that occurred after the 11 January update, then you should notify the 2SOPS if it is a military receiver and the NAVCEN if it is a civilian or commercial receiver. The original deadline as 29 January 2010, but I have it on good authority that reports are still being received. So, if you have a GPS receiver issue, please report it.

"Military users can find additional information on the GPSOC SIPRNet (classified) website at http://gpsoc.afspc.af.smil.mil/. If you don't have access to this classified military site, then access the unclassified and unsecured military website at http://gps.afspc.af.mil/gpsoc or the secure but unclassified military website at https://gps.afspc.af.mil/. You may also call the GPSOC at (military switch) DSN 560-2541, or commercial 719-567-2541. You can also communicate using their email address:gps_support at schriever.af.mil. As an alternate contact the Joint Space Operations Center at (military switch) DSN 276-3514 or commercial 805-606-3514. Email the JSpOC at jspoccombatops at vandenberg.af.mil.

"For civil and commercial users the U.S. Coast Guard Navigation Center's address is NAVCEN MS7310, 7323 Telegraph Road, Alexandria, VA 20598-7310 and you can contact them by telephone at (703) 313-5900 or go to their comprehensive website at http://www.navcen.uscg.gov/."

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