Directions 2015: What It Takes to Make a Gold Standard

December 1, 2014  - By
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GPS-directions-CooleyBy Colonel William T. “Bill” Cooley, U.S. Air Force, Director, Global Positioning System

Last year in my “Directions” article, I emphasized the commitment made by the U.S. government to ensure GPS signals are available to all users, and I shared some of our excitement in the GPS Directorate regarding the modernized capabilities we are developing and fielding. This year I’d like to share with you progress we’ve made in the past 12 months, provide an update on the modernization initiatives, and challenge civil users and receiver companies to innovate and accelerate these modernized capabilities for users worldwide.

This past year has been productive for the GPS program. The most visible progress was the addition of four new Boeing-built GPS IIF satellites to the GPS constellation, bringing the total number of available satellites from 36 to 39 (SVN-33 was safely disposed in October 2014, or the number would be 40). These additions also reduced the average age of the satellites on orbit from 11.1 to 10.3 years. This year’s GPS launch tempo had not been matched since the early 1990s! Table 1 lists the current satellites in the constellation by block.

GPS-table-Directions

TABLE 1. GPS constellation as of October 31, 2014.

Perhaps the most exciting aspect of the GPS satellite constellation is the ever-improving performance. As I mentioned last year, the 2008 Standard Positioning Service (SPS) Performance Standard, issued by the Office of the Secretary of Defense, codifies our commitment to civil users. Among other attributes that make GPS the “gold standard” for positioning, navigation, and timing (PNT), the SPS requires a signal-in-space (SIS) user range error (URE) of 4.0 meters or less for every healthy satellite. The SIS URE is the difference between a GPS satellite’s navigation message (for example, ephemeris data and satellite clock correction data) versus the truth (for example, satellite transmit antenna location and satellite clock offset from GPS time). While the commitment of the U.S. government is four meters or less, the actual average performance over the past year has been 0.68 meters and in the past quarter has been an impressive 0.63 meters!

While this is admirable, continued modernization efforts will allow us even better performance. A significant contributor to the errors experienced by GPS receivers are ionospheric delays that can be eliminated only with knowing the characteristics of the ionosphere (free electron density in the region roughly 100-1,000 kilometers above the Earth’s surface) or by using two signals at different known frequencies. While systems like Federal Aviation Administration Wide Area Augmentation System (WAAS) and the U.S. Coast Guard National Differential GPS (NDGPS) provide a modeled approximation of the ionosphere, the new L2C and L5 civil signals on the GPS IIR-M, GPS IIF, and soon-to-launch GPS III satellites enable GPS receivers to directly measure and eliminate the ionospheric delays altogether — thereby delivering on the GPS modernization program first announced in 1999. These new signals began pre-operational Civil Navigation (CNAV) message broadcast on 28 April 2014 (with the L2C signal set “healthy” and L5 set “unhealthy” until sufficient monitoring capability is established).

With CNAV now on the air, civil users should take advantage of it. My challenge to commercial receiver companies and innovators is to incorporate the modernized signals in future receivers and continue to improve user experience and GPS performance. Currently 14 L2C-broadcasting satellites are in the constellation, and by early 2016 we expect to have 19 on-orbit and transmitting L2C (7 GPS IIR-Ms and 12 GPS IIFs). GPS modernization is well on its way from a signal-in-space perspective; receiver manufacturers and innovators must bring new, improved products and solutions to users.

Less visible but real progress modernizing the GPS Enterprise is underway with the next generation of GPS satellites, ground control, and user equipment segments. The first GPS III satellite and the newly developed navigation payload have been delayed approximately two years from the original planned delivery of the completed GPS III satellite of October 2014. But in September of this year, the GPS III navigation payload was shipped from Exelis (the payload subcontractor) in Clifton, New Jersey, to Lockheed Martin’s (GPS III prime contractor) facility in Waterton, Colorado. There, it completed the payload-level thermal vacuum testing at the end of October, a key step toward payload and eventually satellite vehicle delivery. The first GPS III satellite is now 87% complete and the program is making solid progress.

The GPS Next-Generation Operational Control System (OCX), with Raytheon as the prime contractor, experienced significant challenges in development but can also claim measurable progress this year. Complex cyber-security requirements and their implementation drove a significant number of these challenges, but are essential to provide civil and military GPS users with a secure and resilient command and control system. These and other challenges resulted in significant cost and schedule overruns and a two-year delay to the program, which drove an update to the development plan. The revised OCX plan reflects the complexity of implementing these unique cyber requirements and accounts for planned improvements to Raytheon’s systems engineering and software development approach. The plan establishes a schedule meeting GPS III’s projected first-launch date.

Despite its challenges, OCX development completed four end-to-end space-to-ground launch readiness exercises with GPS III, as well as entered the formal integration and test phase. The new monitoring station receivers are entering qualification test, and the first production receiver is on track to be delivered in spring of 2015. OCX is on track to provide robust PNT services, improvements in URE accuracy, enable access to new military and civil signals, and provide cyber security for the GPS ground control.

Our development of Military GPS User Equipment (MGUE) is another area where we have made important strides this past year. We started the year by developing a commercial market-based acquisition approach that will accelerate delivery of MGUE systems by years. In this effort, we want to establish a race to a certified marketplace where the U.S. government serves as the race official while our industry partners set their own pace to deliver capability. Our goal is to increase speed of delivery to the warfighter while capitalizing on industry’s ability to innovate.

Our MGUE team of government and industry partners (Rockwell Collins, Raytheon, and L3) successfully completed major system design reviews demonstrating a readiness to define the process of security and compatibility certification. Additionally, the team participated in the GYPSY Juliett multi-service, multi-nation PNT demonstration hosted by the U.S. Strategic Command this past summer. While we battled the elements through two hurricanes, the team successfully demonstrated the capability of M-Code receiver cards in an operational demonstration. Our goal is to enable full operational testing with four lead platforms in summer 2016.

While many risks and challenges to GPS modernization still lie ahead of us, the persistent effort by the GPS team has produced important progress in 2014 across the space, ground, and user equipment segments.

A civilian GPS user recently thanked me for providing the incredibly useful utility free to everyone around the globe. Although my impulsive response was to say simply, “You’re welcome,” I’d like to provide a more thoughtful and thorough reply that recognizes those responsible for GPS.

There are two key groups to thank for GPS: the first is the men and women across the United States government and industry who develop, field, and operate the GPS Enterprise. Among this group are satellite factory technicians, software engineers improving the ground segment, receiver designers, program office engineers, and satellite operators continuously monitoring the constellation, updating each GPS satellite’s clock correction and ephemeris data 24/7. This team works with an unwavering passion for this mission that inspires me every day.

The second group responsible for GPS is the American taxpayer who, through Congress, funds the GPS Enterprise every year.  The U.S. financial commitment to GPS is not just for U.S. security or the well documented positive impact GPS has on the American economy, but for the benefit of the entire world as a global utility. GPS is the gold standard for PNT because American taxpayers continuously provide fiscal support so the GPS Enterprise’s men and women can design, produce, field, and maintain the global utility that we all have come to depend on. 

Thank you for supporting this enterprise, and know that the GPS team works hard to ensure those resources are spent wisely to provide continuously improving, predictable, and dependable performance from the Global Positioning System.


Colonel William T. Cooley is director, Global Positioning Systems (GPS) Directorate, Space and Missile Systems Center, Air Force Space Command, Los Angeles Air Force Base, California.

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