In late January, there was a short note in GPS World reporting problems associated with a GPS AEP Command and Control operational software update on 11 January that was meant to provide additional features to GPS-enabled military systems.
The GPS World story said that, "Some of the new features that are incorporated only work with authorized military receivers that have successfully passed security tests. However the live introduction of the new functions is causing problems wherein some of these receivers are intermittently not tracking Y-code, and non-compliant civilian receivers are also reporting continuing problems."
The "GPS glitch" story then basically went quiet until last month, when there were several news stories like these (here and here) by the AP, which said that the US Air Force had fixed the problem. The US Air Force also said that it had not performed any advanced testing on the GPS receivers that apparently had the lock-on problems (the makers of the problematic receivers, Trimble Advanced and Military Systems, said that it did run advance tests and found no problems).
The US Air Force declined to say how much the fix cost or how many military systems were ultimately affected, only saying that the Navy's unmanned X-47B jet program had to temporarily halt its development work.
Yesterday, the AP published a follow-on story that said that some 8,000 to 10,000 US military GPS receivers (out of an estimate 800,000) were unable to lock on during the January glitch. The AP also reported that "the Air Force initially blamed a contractor for defective software in the affected receivers but later said it was a compatibility issue rather than a defect. The Air Force didn't immediately respond to a request for clarification."
The story quotes Space and Missile Systems Center spokesman Joe Davidson as saying that, "We are extremely confident in the safety and security of the GPS system from enemy attack.... Since GPS' inception, there has never been a breach of GPS."
This caught my eye because in January, there was an item at the DoD Buzz, the online defense and acquisition journal, that reported Gen. Norton Schwartz, Air Force Chief of Staff, saying that the US military must lessen its dependence on GPS in the face of jamming threats and potential attacks on the GPS satellites.
The DoD Buzz story also says that, "Schwartz’s call is driven by serious threats to GPS, according to officials familiar with the issue who would not discuss current threats in detail but confirmed that GPS has been jammed or interfered with recently."
The US is currently spending $8 billion dollars to upgrade the GPS system from the ground up, with a promised capability to pinpoint a person's location to within a few feet as compared to 20 feet today. You can read more about the upgrade here and here.