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This article was Originally Published on Nov 15, 2004 in Volume: 3  Issue: 3

Slamming the Jamming

New generation of Global Positioning Satellites will protect the vital navigation system against electronic interference.

By Harrison Donnelly

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After transforming the gamut of military operations, from combat munitions to logistics, the Global Positioning System (GPS) is heading for a long-term upgrade aimed at further strengthening its reliability and accuracy for all users.

GPS-guided weapons systems such as the Joint Direct Attack Munition (JDAM) performed with great success in Operation Iraqi Freedom (OIF), and military forces have become even more reliant on the space-based radio-positioning and time transfer system than the millions of civilian business and recreational users who have had full access, without Selective Availability, to the technology since 2000.

But OIF also provided some of the first real-world evidence of the potential vulnerability of GPS to electronic countermeasures. Although reported Iraqi efforts to jam GPS signals were unsuccessful, they only underscored the security concerns that led Congress in 2000 to call for GPS modernization.

The next-generation system, known as GPS III, is still in its early planning stages, and is not scheduled for deployment until at least 2012. Experts say, however, that the new system architecture needed to increase security will also make a host of other improvements possible for both military and civilian users.

The Navstar GPS Joint Program Office (JPO), a joint service effort directed by the Air Force and managed at the Space and Missile Systems Center (SMC) at Los Angeles Air Force Base, CA, is responsible for developing and acquiring GPS satellites, ground control stations and user equipment. The 50th Space Wing at Schriever Air Force Base, CO, which is also under the Air Force Space Command, operates the 24 or more satellites that make up the GPS constellation.

Earlier this year, the Air Force awarded two contracts worth about $20 million each to industry teams to carry out initial planning and development work on the project. The teams are led by Boeing and Lockheed Martin, each of which is currently involved in producing the latest upgrades of the current generation of satellites, known as GPS IIF and GPS IIR-M, respectively.

The Boeing team comprises Boeing Satellite Systems, Harris Corp., Lockheed Martin Management and Data Systems, ITT and Raytheon. Members of the Lockheed team include Spectrum Astro (recently acquired by General Dynamics C4 Systems), ITT, Raytheon and General Dynamics.

During this phase, known as Concept Definition, team members are focusing on translating Air Force needs into specific program elements and cost estimates. This phase will culminate with a corporate Department of Defense decision on how best to proceed with the program development effort.

“We’re staying fully engaged with each of the contractor teams,” said Colonel Allan Ballenger, system program director of the JPO. “We have a series of program reviews scheduled with each of them, as we monitor their thoughts, ideas and assessments. Ultimately, the output of both the contractors will result in a Systems Requirement Review, which is where we lock down what the real requirements are going to be, which we then put on the contract for the next phase of activity.

“We are working with AF Space Command, and they are the ones that give us the operational requirements. Here at the Joint Program Office, we are in charge of acquisition, so we look at those operational requirements and figure out how best to satisfy those operational requirements by translating them into system requirements.

“The contractors are looking at the operational requirements. Sometimes the operational requirements can be satisfied in several different ways, and you might have three different system alternatives. So we ask the contractors to look at those and give us some analysis and insight into the cost and benefits trade studies, so we can start to lock down what the real system requirements will ultimately be that go on contract. So what they’re really doing is helping us better understand how to translate the operational requirements into the system level requirements,” Ballenger said.

The SRR is scheduled for completion by June 2005, after which, Department of Defense officials will hold the next key round of decisions regarding the future of the program.

Despite the great success of the current system, GPS III has not been without controversy. The Air Force last year did not ask for additional funds for the project, which some observers interpreted as a sign of weakening support. But funds were subsequently found to enable the process to go forward and the fiscal 2005 defense appropriations bill contains full funding for the program.

The other factor roiling the GPS world, which will also play an important role in shaping GPS III, is the fact that the European Union (EU) is developing its own Global Navigation Satellite System (GNSS) system, known as Galileo. U.S. defense officials have repeatedly expressed concern that the new system could interfere with the military’s GPS operations. But an agreement reached at the U.S./EU summit in June cleared the way for interoperability between the two systems.

Jamming Threat

GPS signals are vulnerable to jamming because they are relatively weak, with less power in fact than the leftover background radiation generated by the Big Bang at the beginning of the universe. As a result, they can be blocked by simple, inexpensive radio transmitters operating at the proper frequencies. (For background on GPS jamming, see MAT, Volume 2, Issue 6, page 24.)

The military has long been aware of the potential risks of GPS jamming, conducting extensive research aimed both at protecting its own system against interference and blocking an enemy’s access to the information. This summer, for example, civilian GPS users in Alaska and in waters off the Eastern Seaboard had to contend with the loss of signal resulting from military exercises in the area.

Although Congress authorized GPS modernization well before OIF, the conflict focused renewed attention on the jamming issue. Iraqi forces loyal to Saddam Hussein deployed at least six jamming stations, and the topic generated tensions between the United States and Russia after Bush Administration officials faulted that country for selling GPS-jamming equipment to Iraq, a charge the Russians denied.

Coalition forces quickly destroyed the jamming stations, which are easily targeted. In one case, the jamming site was taken out by a GPS-guided munition.

As that history suggests, GPS jamming is by no means a “silver bullet” against sophisticated modern weaponry. Not only are jamming stations vulnerable, but also the latest “smart bombs” have effective countermeasures designed to ensure that they still find their targets. The JDAM, for example, also has an inertial navigation system that can guide it effectively even if the GPS signal is interfered with. Nevertheless, the need to provide assurance against jamming has been a driving force behind the development of GPS III.

While there are a number of ways to frustrate jamming, such as putting more powerful antennas on GPS receivers, researchers concluded that the most effective strategy was to develop an additional, more powerful signal, operating on a separate, military-only frequency in order to reduce disruption of civilian uses. Achieving that, however, requires moving away from the full-Earth coverage provided by the current system. Instead, planners want to transmit a focused signal down to an area that would be large enough to encompass much or all of a theater of operations.

“GPS III will have the ability to provide increased power and jam resistance in a specific military area of operations, while at the same time minimizing the impact to civil users. You’ll see that referred to in some places as a ‘spot beam.’ What that means is that we can provide a more tightly focused beam of higher power on a smaller area of the globe, so we can concentrate it there and minimize its impact outside that area of operations,” Ballenger explained.

To produce such a beam, a GPS satellite will need a larger antenna to direct the signal. To a great extent, that is where the next-generation system comes in, once engineers determined that the current GPS II models could not be modified sufficiently to handle the new technology.

“The anti-jamming really requires a pretty big re-architecture of the system,” explained Mike Rizzo, director of navigation systems for Boeing. “Presently the control segment does not have the capability to steer an antenna, and the satellites are not large enough to be able to put an antenna on there of the size that they’re talking about. It takes a lot of size and power, and when you start doing that, there are many other things that flow out of it.”

Enhanced Integrity

With that increased size and power, planners also are eyeing a number of other improvements in the system.

“Another thing that GPS III brings is improved accuracy, which we get through several different features,” Ballenger said. “It also brings integrity, which is a new concept. If a user is looking to those satellites to find their way around, and one of those satellites all of a sudden has a bad signal, what we want to do is notify that user very quickly to ignore the bad signal and use some of the other satellites. That way, the user will always have confidence that the GPS navigation solution they have isn’t corrupted by a bad satellite signal. In today’s architecture, it could take hours before we are aware of a satellite putting out a bad signal, and turning that satellite off. With a GPS III architecture, we could reduce that to minutes or seconds. Users would have much higher confidence when they’re using GPS for navigation or timing.

“That’s a very important feature to civil aviation, where users are very interested in having a very high confidence on any navigation system that they’re using. We’re working with them to understand what their aviation integrity requirements are, and ensuring that gets folded into the GPS III architecture,” he added.

As Ballenger’s comments suggest, the needs of civil GPS users are a major factor in planning improvements in the system. “GPS was originally conceived for military purposes, but once we began providing the signals to users worldwide, we have seen an explosion of innovative uses all around the world, from farming to recreation to many other different applications. Our office does not get involved in any of those, and we’re responsible just for the military user equipment. But the Department of Defense, by presidential policy, does make that signal available for all civil users as well.

“Even though the DoD and Air Force are charged with the acquisition and operation of the system, there is an interagency GPS board, which is co-chaired by the Departments of Defense and Transportation, which represents the civil interest. We have a senior Transportation Department civilian in the office, and he has direct input into all the things we do on the program,” Ballenger noted.

In the Pipeline

Because the units have a finite lifespan, maintaining a constellation of GPS satellites, which currently number 29, requires the launching of an average of three new satellites a year. With new spacecraft constantly moving through the pipeline, the Air Force is able to continually seek incremental improvements in the current generation, known as GPS II, even as it commissions long term work on more fundamental changes.

The majority of the current satellites on orbit are from an earlier stage of GPS II design, and have far exceeded their planned length of service. They are being gradually replaced by Lockheed Martin-built GPS IIR satellites, which offer upgrades that include an advanced antenna panel. The Air Force achieved the 11th successful launch of a GPS IIR unit in June.

Lockheed also is modernizing up to eight already-built GPS IIR craft, which will incorporate two new military signals and a second civilian signal. The first of these models, designated GPS IIR-M, is slated for launching early next year.

Boeing, meanwhile, is developing the GPS IIF, which will have all the capabilities of previous units plus the addition of a third civilian signal. By countering the effects of the ionosphere on the GPS signal, it will provide much more accurate location information for civilian users. Boeing is currently under contract to build 12 GPS IIF craft, and the government is considering increasing that order to 16, according to Boeing navigation systems director Mike Rizzo.

The first GPS IIF unit is scheduled for launch in 2006.

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