The System: GPS Health in Question

June 1, 2009 By: Alan Cameron GPS World

The U.S. Government Accountability Office (GAO) issued on May 7 an alarming report on GPS, characterizing ongoing modernization efforts as shaky. The agency appears to single out the Block IIF program as the weak link between current stability and ensured future capability, calling into doubt “whether the Air Force will be able to acquire new satellites in time to maintain current GPS service without interruption.” It asserts the very real possibility that “in 2010, as old satellites begin to fail, the overall GPS constellation will fall below the number of satellites required to provide the level of GPS service that the U.S. government commits to.”

The GAO report concludes that “some military operations and some civilian users could be adversely affected.

“Military users will experience a delay in utilizing new GPS capabilities, including improved resistance to jamming of GPS signals, because of poor synchronization of the acquisition and development of the satellites with the ground control and user equipment. Finally, there are challenges in ensuring civilian requirements for GPS can be met and that GPS is compatible with other new, potentially competing global space-based positioning, navigation, and timing systems.”

The report recommends that the Secretary of Defense appoint “a single authority to oversee the development of GPS, including space, ground control, and user-equipment assets, to ensure these assets are synchronized and well executed, and potential disruptions are minimized.”

The full report can be downloaded, and Congressional testimony from GPS providers, industry, and users is also online.

Gloomy Outcomes. Based on the most recent satellite reliability and launch schedule data from March of this year, the estimated long-term probability of maintaining a constellation of at least 24 operational satellites falls below 95 percent during fiscal year 2010 and remains below 95 percent until the end of fiscal year 2014, at times falling to about 80 percent.

The results of fewer than 24 operational satellites could include the following:

Intercontinental commercial air carriers may have to delay, cancel, or reroute flights.
Enhanced-911 response to emergency calls could lose accuracy.
Accuracy of precision-guided munitions could decrease, forcing the military to use larger munitions or use more munitions on the same target.
Both standard and precise positioning service could suffer, affecting civil users, both professional (for example, surveyors) and casual (users of location-based services via cell phones).

IIF at the Crux. Cristina T. Chaplain of the GAO presented the report to Congress, stating, “In recent years, the Air Force has struggled to successfully build GPS satellites within cost and schedule goals; it encountered significant technical problems that still threaten its delivery schedule; and it struggled with a different contractor. As a result, the current IIF satellite program has overrun its original cost estimate by about $870 million and the launch of its first satellite has been delayed to November 2009 — almost three years late.”

The GAO report cites specific problems with the IIF satellites contracted to Boeing. During the first phase of thermal vacuum testing in 2008, one of the test payload’s transmitters failed; consequently, the program suspended testing in August 2008 to identify the causes and take corrective action. Other hang-ups include maintaining the proper propellant fuel-line temperature, delaying final integration testing, and re-design of the satellite’s reaction wheels, used for pointing accuracy, because of on-orbit failures on similar reaction wheels on other satellite programs. $10 million in additional costs have accrued to the program, according to the GAO.

“While the Air Force is structuring the new GPS IIIA program to prevent mistakes made on the IIF program, the Air Force is aiming to deploy the next generation of GPS satellites three years faster than the IIF satellites. GAO’s analysis found that this schedule is optimistic, given the program’s late start, past trends in space acquisitions, and challenges facing the new contractor.”

Problems Aboard IIR(M)-20

Lt. Col. David Goldstein, chief engineer for the GPS Wing, told the European Navigation Conference in Naples, Italy, that the Wing is experiencing some “out of family” measurements from the recently launched IIR(M)-20 satellite. This corroborates rumors circulating about problems with “legacy signals” from the satellite, that is, L1 and L2. The April 10 broadcast of the first L5 signal secured that frequency for the U.S. GPS program; since that signal contains no navigation message at present, it presumably is not affected by these problems.

The Air Force will not launch any further satellites until this issue is resolved. IIR(M)-21, the last of the IIR(M) series, is scheduled to rise in August, with the first of the IIF generation to follow in late 2009 or early 2010.

Normally, a satellite is set healthy within 28 days of launch, after extensive testing, but this has not occurred with IIR(M)-20, launched March 24. The Air Force has formed a response team and is working “nearly round the clock” to resolve the problem, but according to Goldstein is not rushing the issue, seeking a thorough solution because the constellation is robust at 30.

“We are currently examining data from the satellite that is not consistent with data from the other IIR(M)s,” he stated, characterizing the variances as “measurements with larger than expected pseudorange errors that are elevation-dependent, and that we have not seen before. We have experimented with a few fixes and it looks very promising.”He described the response team’s approach as making a “fishbone diagram” of all potential failure mechanisms, and working through them methodically. “We think we have identified the failure but it may be several more months before the analysis is complete, and the situation is fully resolved.”

LORAN Report Sees Daylight

WITHHELD FOR TWO YEARS, the Independent Assessment Team (IAT) report has finally been released, just in time to counter recent efforts by the Obama administration, the Department of Homeland Security (DHS), and the U.S. Coast Guard to throttle the Loran program. The IAT “unanimously recommends that the U.S. government complete the eLoran upgrade and commit to eLoran as the national backup to GPS for 20 years.”

The IAT’s conclusion has long been informally known throughout the industry, but the report’s release adds considerable weight, expertise, and specifics to a sustained campaign to preserve the program. Compiled by the Institute for Defense Analyses, and presented to the Department of Transportation and Department of Homeland Security (DHS) Executive Committees in March 2007, its release now comes only after an extensive Freedom of Information Act battle waged by various interested parties.

Download the 32-page “IAT Summary of Initial Findings on eLoran.”

Only Effective Backup. The report asserts that “eLoran is the only cost-effective backup for national needs; it is completely interoperable with and independent of GPS, with different propagation and failure mechanisms...It is a seamless backup, and its use will deter threats to U.S. national and economic security by disrupting (jamming) GPS reception.”

The IAT, chaired by Bradford Parkinson, founding program director for GPS, evaluated all available or potential alternatives for a GPS backup. In particular, it examined the costs of the Loran system and a transition to a new, modernized enhanced or eLoran. It found eLoran’s infrastructure enhancements to be 70 percent complete, and the cost to complete its rollout less expensive than decommissioning the Loran system.

DHS has claimed that Loran termination will save $190 million over five years, but failed to specify or include decommissioning costs, or to explore operational savings available with modern eLoran transmitters. Senior DHS representatives have — unbelievably — also claimed that it is not clear a GPS backup is needed.

The report recommends that “eLoran be completed and retained as the national backup system for critical safety of life, national and economic security, and quality-of-life applications currently reliant on position, time, and/or frequency from GPS.” It emphasizes that “the U.S. government policy decision is needed to motivate users to equip.”Successive proposed annual federal budgets have regularly cut Loran/eLoran funds, which have just as regularly been restored by Congress. Such one-year reprieves, however, have not inspired industry to design and produce combined GPS/eLoran receivers in effective strength.