President Clinton authorized the disabling of the Selective Availability feature of the GPS satellite effective at midnight May 1. Selective Availability involved dithering the L1 signal from the GPS Navstar satellites to degrade accuracy. With SA disabled, the civilian signal will now be ten times as accurate as before with no alteration required for receiving equipment. Typical civilian sets can now be accurate to within 10-30 meters. More expensive commercial units can be even more accurate down to centimeters, especially if Differential Correction GPS or combined GPS/GLONASS techniques are used (GLONASS is the Russian equivalent of GPS).
President Clinton cited civilian uses that drove the decision "including air, road, marine, and rail navigation, telecommunications, emergency response, oil exploration, mining", etc. He also noted that the security risks were minimal as SA effectiveness' has been reduced by commercial techniques and the United States has a demonstrated capability to reduce GPS accuracy in a specific region at will.
GPS has become truly crucial technology in the civilian arena. Ships, planes and recreational vehicles depend upon it for safe navigation and rescue, developers need it for engineering/construction projects in remote locations, and surveyors use it for land and resource mapping.
The current civilian uses pale before the projected uses for GPS. For instance, FAA Administrator Garvey testified before Congress that the FAA expects air passengers in the US to reach 1 billion per year in 2015, doubling the number of passengers from 1998 totals. The FAA's solution to burgeoning air traffic in a budget conscious political environment is to allow Free Flight; flight paths that maximize efficiency rather than forcing planes into specific routes for the benefit of ground-based radar. The network of ground radar would be passed on in favor of GPS-based navigation and traffic management (except for airspace around airports). The Wide Area Augmentation System is intended to orbit additional GPS satellites to assist with the Free Flight program, though Congress is reluctant to fund it.
GPS has prompted a revolution in military affairs. GPS allowed American forces to maneuver safely in featureless deserts even in severe weather during Desert Storm, materially contributing to the success and low casualty rate enjoyed by allied forces. Special Forces can now carry out operations with greater safety and accuracy, firepower can be called in more precisely, and SAR for downed pilots can be surer and faster.
The biggest change within the past three years has been weapon systems that incorporate GPS into their guidance packages. Bombs, cruise missiles, howitzer shells and reportedly even Iranian recon drones are using or will use GPS for navigation and precision attack. GPS-guided weapons have comparable accuracy to their laser-guided predecessors with the added advantages that cloud cover will not hinder their accuracy and attackers do not have to keep a laser designator on the target. These features mean greater safety for strike aircrews or FOs on the ground, and a true all-weather PGM capability. GPS airstrike weapons will allow for actual 24x7 airpower and further enhance air forces capable of intense sortie rates. Mating GPS with technologies such as glide bombs can increase engagement range at relatively little cost. The US is heavily committed to GPS weapons. The Joint Direct Attack Munition <GPS bombs> are the centerpiece of current US conventional strike weapon purchases, with 16,000+ units of an expected 87,000 ordered so far. Other allies and potential opponents are proceeding with GPS-based weapons as well.
GPS is not without it's troubles. The most immediate problem is that the GPS signal is relatively weak, leaving it prone to jamming. A Space Aggressor Squadron committed to testing open source technology recently demonstrated a $7000 jammer that works against satellite communications and could be used against GPS signals. Presumably an enemy could readily deploy a far more powerful jammer or hundreds of weaker, cheaper jammers.
Countermeasures to jamming have already been considered. The ultimate 'fix' is a newly upgraded second generation of GPS satellites by Boeing and Lockheed Martin with anti-jam features, with a third generation satellite becoming available in 2007. In the meantime, Boeing has equipped it's JDAM bomb kits with enhanced antennas and an inertial navigation system to take over if jammed and has tested it in a jamming environment. The Extended Range glide bomb version of JDAM is being tested with a manual guidance option- a control signal from an attacking aircraft would be far stronger than a satellite signal and thus defeat cheap jammers.
GPS does have the advantage of using up to 7 satellites at a time, each coming from a different direction, so any jammer must be powerful enough to block at least 3-5 of them at a time. This fact means that effective GPS jammers should be easy to spot and attack. The USAF may have to plan on a GPS suppression campaign similar to classic radar suppression in order to fully utilize GPS before the new satellites are deployed. The biggest victim of GPS jamming may be American troops used to navigating and calling artillery precisely by GPS. The US Army may end up having to fight an EW war for GPS spectrum in order to maneuver and fire effectively.
Another jamming target will be the sensor system that pilots will use to assign their weapons. SAR/GMTI systems (Synthetic Aperture Radar/Ground Motion Target Indicator) will be required to penetrate cloud cover, verify that the target is there, and feed targeting data to the GPS weapon at a safe range before weapons release. A jammer would not necessarily have to 'snow' an SAR/GMTI (APG-70, APG-73, APG-76, APQ-164, APQ-18), only cause enough doubt to abort an attack by pilots hamstrung by stringent ROE.
The second biggest problem involves an enemy potentially using GPS weapons against US forces. A 1995 RAND report on national GPS policy noted that GPS would not materially aid in ICBM accuracy, but could be very useful for cruise missiles that require constant accurate
navigational updates. The latent SA capability that President Clinton alluded to could be turned on to frustrate enemies foolish enough to rely on the L1 signal. Unfortunately civilian workarounds such as Differential GPS could still be applied if the US or EU used SA capabilities in a region. China for instance is mapping every point it can using DGPS. Reactivating SA or
moving the satellites would also have economic and political costs that the US may be unwilling to pay. The solution- the US deploys GPS jammers for it's forces.
Finally, a weak point in the system are the ground stations that track the satellites and feed correction data to keep the GPS system accurate. An opponent bold or desperate enough could potentially attack these stations on US soil and disrupt the system. The counter to this gambit is backup dark stations or dual-use civilian facilities.
Several press reports noted that the timing of President Clinton's announcement comes
one week before the International Telecommunications Union meets in Turkey for the World Administrative Radio Conference. The European Union's Global Navigation Satellite Service system and Mobile Satellite System are competitors for the same bandwidth that the US wants for implementation of two more civil GPS signals (including the FAA's WAAS). President Clinton had signed a Presidential Directive in 1996 to have SA disabled by 2006; disabling SA now probably was done for negotiating purposes at WARC. GNSS (also known as Galileo) is not only a competitor with GPS for frequencies for commercial and civil aviation use, but also for military
and political leverage. The US can degrade the L1 signal as desired while retaining accuracy on the encrypted P-code military frequencies, thus allowing American forces to use
GPS-based weapons while denying them to an enemy. Presumably Galileo will have the same capability, but would be under the control of the EU. If Galileo is built, the US would have to bargain with the EU to ensure GPS superiority in a given theater.
In addition, maintaining GPS constellations requires an extensive space infrastructure- an investment in Galileo could give EU members the kind of space industry that could seriously compete with the US and Russia. Combine these issues with the intended WAAS FAA frequency use, and the United States has an interest militarily and economically in hindering or eliminating Galileo before it is deployed. Russia's GLONASS (Global'naya Navigatsionnaya Sputnikovaya Sistema) is a player in the GPS world, but whether the Russians can keep their constellation operational in light of their financial woes is a very big question mark.
Galileo is due for a financing decision by the European Commission in December of this year. The cost is expected to be in the $2.9 to $3.5 billion dollar range. The EU intends to fund Galileo partially out of subscriptions to the higher quality signals. American GPS is unencrypted, free, is now very accurate and is deployed today. If the United States can convince other countries that the American GPS civilian L1 signal can do the job of GNSS at little cost to themselves, than the EU may not get the frequencies and cause Galileo funding problems. On the other hand, entrusting crucial economic operations such as air and sea transport navigation to a system
controlled by the US DoD may not be comforting to neutral nations. Certainly the potential foes of the US or Russia will want an alternate system so they could have GPS parity in the event of conflict. ITU delegates attending WARC will have to decide whether the US or EU is to be trusted and how much the EU choice will cost in terms of GNSS specific receivers and signal decryption fees. The stakes in disabling SA are high militarily, economically and politically- whether the US can win it's bet remains to be seen. -Robert Smith