The Global Positioning System (GPS) is an incredible technology. It can provide location data to within a horizontal accuracy of 36 meters for civilian users and to within 15 meters for military users. During Operation Desert Storm, the world witnessed the stunning capabilities of the GPS in real time as U.S. forces swiftly and accurately moved across featureless desert terrain while simultaneously targeting aircraft, troops, and ordnance against Saddam Hussein's forces. And surely no one will soon forget the extraordinary 1995 rescue of U.S. Air Force Captain Scott O'Grady from behind enemy Serb lines, which owed much to GPS technology. Now, ten years after Desert Storm, the Taliban and al Qaeda have experienced the system's dead-aim accuracy.
The GPS has become intertwined in the civilian economy as well. Its satellites provide data to civilian emergency rescue services, commercial shipping and fishing, commercial and general aviation, earth mapping and surveying, and pleasure boating. (There is even a GPS dog collar so that Fido will never be lost again.) Some estimates put GPS-related jobs at about 100,000, with a worldwide market of $2 billion per year and growth potential to $30 billion.
With its capability to provide instantaneous locating information to virtually every square meter on the globe, the GPS is on the verge of explosive growth both in military and civilian applications. Therein lies the rub. With the U.S. armed forces relying solely on the GPS for critical navigation and locating information, is the military in general—and the Navy in particular—setting itself up for spectacular failures in future conflicts? What if it fails? Could the results be lost ships and aircraft, and missed targets? Would the civilian economy suffer grievously if the GPS is not reliable? But the critical question is: what are the backups? The short answer is: there are not many.
A Brief Tutorial
The GPS consists of a constellation of 24 satellites plus spares that circle the earth every 12 hours in 11,000-mile-high orbits. The satellites are spaced so that every point on the earth always has at least four satellites in view. Each satellite continuously broadcasts a digital signal of its position and the time (using an atomic clock accurate to one-billionth of a second).
A GPS receiver takes the information from the four satellites, compares its own time and pseudoranges with the time and pseudorandom codes sent by the satellites, and uses the time and range differences to calculate distances to each satellite. For example, if a satellite's time is one-thousandth of a second behind the receiver's time, then the receiver would be an additional 186 miles from that particular satellite (186,000 miles/sec x 0.001 secs = 186 miles). By capturing all four signals, a GPS receiver can use a relatively simple quartz crystal clock as its time standard—rather than another atomic clock—and compute its position instantaneously.
Is There A Threat?
Almost every weapon system in the U.S. inventory depends on the GPS—at least those systems that require navigation, time, or locating data. Many weapons must use it to achieve their design effectiveness: for example, Tomahawk and air-launched cruise missiles, Joint Direct Attack Munitions, GBU-15 precision-guided bombs, certain Army ballistic missiles, and all types of unmanned aerial vehicles (UAVs). Even systems with a low probability of interception, such as the Joint Tactical Information Distribution System, use the GPS. Its availability often is an unstated assumption regarding weapon system performance and operational employment.
What if the GPS is not available for a few minutes? Is there any credible evidence that the GPS has ever been jammed or that the satellites are threatened? In fact, the system is quite vulnerable. We could live with a brief loss of GPS signals. Inertial navigators and other navigational systems certainly are good enough—at least during the end game of weapon delivery. The much greater concern is loss of the system for days, weeks, or months. Unfortunately, the Central Intelligence Agency (CIA) and the President's 1996 Commission on Critical Infrastructure do not think this is a farfetched scenario. A CIA study presents some chilling prospects for information operations and access to space over the next decade:
Adversaries will seek to attack the U.S. military capabilities through electronic warfare, psychological operations, denial and deception, and the use of new technologies such as directed energy weapons or electromagnetic pulse weapons. The primary purpose would be to deny U.S. forces information superiority, to prevent U.S. weapons from working.... adversaries realize the degree to which access to space is critical to U.S. military power, and ... they will have made strides in countering U.S. space dominance. By 2015, several countries will have such counterspace technologies as improved space-object tracking, signal jamming, and directed-energy weapons such as lowpower lasers.
There are numerous examples of how the GPS is threatened and what can happen when it is disrupted:
- At the Paris Air Show in 1999, the Russians offered an eight-watt GPS jammer for sale at a cost of $40,000. Touted as an "information weapon," the sales flier referenced the use of U.S. GPS-guided weapons against Iraqi and Serbian forces and claimed the jammer could thwart such attacks.
- In 1997, during a GPS transmitter test at Griffis Air Force Base, the transmitter was left on inadvertently; over a twoweek period this caused complete loss of GPS signals to 16 commercial airliners and partial loss of signals to almost all aircraft operating within a 300-nautical-mile radius. As a result, the Coast Guard concluded that GPS jamming poses a "serious threat to aviation safety."
- During hearings before the Senate Intelligence Committee last February, CIA Director George Tenet and Director of the Defense Intelligence Agency Vice Admiral Thomas Wilson testified that China is developing ground-based laser weapons and electronic pulse weapons capable of blinding or destroying U.S. satellites. Director Tenet added, "Our adversaries well understand U.S. strategic dependence on access to space. Operations to disrupt, degrade, or defeat U.S. space assets will be attractive options for those seeking to counter U.S. strategic military superiority."
Limiting GPS Vulnerabilities
While there apparently is no evidence—at least in the public domain—that hostile jamming or other electronic attacks have been made on the GPS, we cannot bury our heads in the sand and conclude there is no threat. The United States relies on the GPS and discounts system upgrades and other technologies at its peril. Here are practical suggestions for protecting access to critical navigation data:
- Expand and improve intelligence collection efforts. Ensure understanding of current threats to the GPS as well as threats on the drawing boards. If this requires revision of current intelligence collection policies, then so be it.
- Increase funding for initiatives to acquire antijamming technologies. Incorporate these devices in weapon systems and future GPS system components, such as satellites and ground stations.
- Speed deployment of next-generation GPS satellites. Ensure they have improved self-protection capabilities against electronic warfare and other attacks; where feasible, include collision-avoidance technologies.
- Initiate a program to build and acquire more modern ground-based navigation systems. They should be rapidly deployable by ship, aircraft, and truck, and capable of assembly by a small team. This kind of system would be a mobile, updated version of the Loran-C and Omega navigation systems.
- Accelerate development and deployment of pseudosatellites, both airborne (UAVs) and ground-based stations. The GPS pseudosatellites provide robust navigation capability when GPS signals are jammed. This technology is especially important now, before the introduction of new satellites that will provide additional signal strength to the ground. (Current estimates do not have new satellite capabilities in place until 2016.)
- Outline and fund projects suitable for the Defense Advanced Research Projects Agency to investigate. Focus on emerging technologies that can be incorporated rapidly into the GPS to enhance system performance and protect against a variety of attacks.
- Continue joint GPS combat effectiveness test and evaluation group efforts. Evaluate and test the GPS for vulnerabilities and recommend improvements; include upgrades to make the its interference and navigation tool a better system for evaluating shortcomings.
- Evaluate current tactics, techniques, and procedures. It is essential to determine how and where to make improvements in the GPS to minimize loss of information today, even as new hardware and systems are being developed for the future.
- Study and implement improved testing regimes. This would overcome the interference that often results from testing technologies that enhance the military capabilities of the GPS but degrade civilian uses during the testing period.
The Global Positioning System provides the United States and its allies a substantial strategic military advantage. In addition, civilian uses have expanded greatly over the past decade and are having a measurably positive effect on the nation's economy. However, the central reason for the GPS is to give war fighters—on the deck, in the cockpit, and on the battlefield—up-to-date, accurate locating information so that our enemies die, not them. We are not interested in a fair fight.
Almost every operational U.S. weapon system and those envisioned for the future cannot live up to expectations without timely and accurate GPS information. Thus, protecting the GPS, improving its capabilities, and providing alternatives and backups are of paramount importance to the nation and the service members who are sent in harm's way.
Dr. Hancock is a senior project engineer at Emergent Technology Services, Incorporated, in Arlington, Virginia. Mr. Pettit is a member of Emergent’s technical staff.