Omnipresent GPS coverage takes another hit

Despite some improvements, future GPS coverage may not be as good as it is today

The idea that GPS coverage will be pervasive all of the time in the future just might not pan out.  That's because while some improvements in delivering components of the system have occurred, the US Air Force, which is responsible for the GPS system, faces numerous challenges in getting new satellite and support systems off the ground, according to a report out this week from the Government Accountability Office.

Six Long-awaited satellite projects eye the sky

If that warning sounds familiar that's because the GAO warned of satellite problems in 2009, but says that some issues have gotten worse since then.  And because GPS has become an essential element in military and many civilian operations, keeping it fully functional has become essential.

From the GAO:  "Conditions have improved for the near-term size and availability of the GPS constellation. While Department of Defense has strengthened acquisition practices for GPS and made concerted efforts to maximize the life of GPS satellites, it still faces many of the same challenges we identified last year, as well as new ones we identified this year. For example, the GPS IIIA satellite program has complex and difficult work ahead as it undertakes assembly, integration, and test efforts, and its schedule may leave little margin to address challenges that may arise. Such issues could affect the Air Force's ability to launch satellites on time, which in turn may affect future GPS satellite constellation availability."

The GAO went on to say that continued delays with ground control systems and the challenges the Air Force is encountering with enabling quicker procurement of military GPS user equipment, new capabilities may not be delivered when the DOD needs them. For example, the contract for the newest ground system development effort,  operational control segment-known as OCX-was awarded in February 2010, about 10 months later than the original contract award date. To account for the delay the Air Force extended the OCX delivery schedule by adding 16 months of development time. As a result, key OCX capabilities associated with the IIIA satellites will not be operational until September 2016 -over 2 years after the first IIIA satellite launch, the GAO stated.

The Air Force is working on a mitigation strategy that calls for development of a separate effort to launch and control the first IIIA satellite, the GAO stated. However, GPS Wing officials told the GAO such a system will not support new capabilities offered by IIIA, including a signal known as Military Code (M-code), which is designed to boost resistance to jamming, and three civil signals related to signal accuracy, aviation and international global space-based Position, Navigation and Timing systems, the GAO found.

Because there are currently 31 operational GPS satellites of various blocks, the near-term probability of maintaining a constellation of at least 24 operational satellites remains well above 95%. However, the DOD predicts that over the next several years many of the older satellites in the constellation will reach the end of their operational life faster than they will be replaced, and that the constellation will, in all likelihood, decrease in size, the GAO stated in 2009.

In the new report the GAO looked at what GPS meant to a number of key users of GPS systems.  From the GAO report:

  • Civilian agencies: Civilian agency officials stated that if the satellite constellation performance fell below the committed level of service, their operations would be affected; however, the effects vary by agency. For instance, Federal Aviation Administration officials stated that a constellation smaller than the committed 24 satellites could result in flight delays and increased reliance on legacy ground-based navigation and surveillance systems. Likewise, US Coast Guard officials stated that they could revert back to older methods of navigation if GPS service were diminished, but there would be a loss of efficiency. On the other hand, the National Institute of Standards and Technology, within the Department of Commerce, relies on GPS for timing data rather than navigation data and may be less sensitive to decreases in the number of GPS satellites. Furthermore, some civil agencies rely on both GPS and augmentation systems. For example, FAA augmentation systems increase the integrity of GPS for aviation purposes. However, officials from a few civil agencies explained that the augmentation systems cannot compensate for a drop in the size of the GPS constellation below the committed level.
  • Air Force. The Air Force user representative stated that the Air Force has "a healthy concern for the ready viability, integrity, and availability of this system. Specific data points, analysis, and vulnerabilities would be classified." Any system that would possibly function without its full designed or optimized capability would naturally have some operational degradation.
  • Army. The Army user representative stated that effects largely depend on which satellites would remain available. If there is a decline just below 24 satellites, the effect would probably be minimal, but with each additional space vehicle lost the operational impact would increase.
  • Marine Corps. The Marine Corps user representative stated that Marines are accustomed to using GPS for PNT; therefore the loss of GPS would severely affect Marines' ability to navigate. Effects would vary depending on the situation in which a user operates. The most severely affected Marines would be those who use GPS in marginal but currently acceptable conditions, such as under foliage, in mountains, and in urban settings, where a smaller constellation is more likely to result in diminished or no service.
  • Navy. The Navy user representative stated that there is no "one-size-fits-all" answer, that information regarding the effects would be classified, and that the Navy would continue to operate even if it could not use GPS, although missions might take longer to accomplish and require additional assets.

In the end of its report the GAO again called for the Secretary of Defense to appoint a single authority to oversee development of GPS space, ground control, and user equipment, to ensure they are synchronized, well executed, and potential disruptions are minimized.

Follow Michael Cooney on Twitter: nwwlayer8  

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