GPS service is in danger of severe erosion, according to a report from the Government Accountability Office (GAO). A Congressional “watchdog” of programs and spending of government departments, the GAO warns that the satellite navigation service could slowly worsen after 2010, and not recover to acceptable aviation levels before 2022.

Normally, the GPS constellation has 24 satellites to provide worldwide, 24/365 navigation. Today, 31 satellites are in orbit, and the system has never been better. However, many satellites are “legacy” units in which the original triple- or quadruple- redundant elements of one or more critical systems are now down to or approaching “single thread” operation, with total failure of individual satellites expected to occur at any time over the next few years.

Although replacement satellites are routinely launched, the GAO’s analysis indicates that there may be insufficient satellites in storage to replace the number of potential failures before launches of the next-generation GPS III satellites begin.

The GAO bases its concern on the Department of Defense’s space program record, marked by overspending, late delivery, poor oversight of contractors, “requirements creep” and a lack of firm management direction. As an example, 12 of the 13 replacement satellites currently in storage were contracted to Boeing for $729 million, but ended up costing more than twice that amount at $1.6 billion, and their delivery was three years late. Among other things, the GAO faulted the DoD for having no single top decision maker in the department, and pointed to a number of poorly coordinated offices with sometimes conflicting requirements.

Nevertheless, the DoD will not build additional replacement units, because it is confident that the first GPS III satellite will go aloft in 2014 to pick up the slack. However, while the GPS III satellites now under development are much more complex than the Boeing units, the DoD insists they can be built three years more quickly. The GAO is skeptical, and stated that if the GPS III’s first launch should be delayed for two years, today’s constellation could steadily deteriorate after 2010 to as few as 18 satellites by around 2017, with a slow recovery to 24 by 2022.

An 18-satellite constellation could create outage periods of several hours duration, along with much lower accuracy. At an international satnav conference last year, United Airlines stated that even a reduction to 23 satellites would negate several GPS-based procedures.

The GAO noted that the DoD’s difficulties also extend to the GPS ground control segment and to user equipment. Several control segment enhancements are many years late and, while advanced encrypted military signals are potentially available to warfighters, it will be a further 10 years before they will receive the avionics to use them.

For civil operators, some amelioration could be provided by the FAA’s two Waas satellites, each of which provides a single GPS “look alike” signal. Also, Europe’s GPS-compatible Galileo is forecast to commence operations around 2016, and
the GAO cautioned that GPS difficulties could erode its leadership position in
the face of competing foreign systems. Unquestionably, significant reductions in GPS satellites could have a serious impact on mandated ADS-B operations in 2020.
The non-technical GAO report can be found online at www.gao.gov/new.items/d09325.pdf.