GNSS Markets and Applications - Understanding GPS: Principles and Applications - page 656

symbiotic as technology allowed for faster processors, smaller receivers, and lower
cost, strapped-down inertial measurement units. The age of GPS guided missiles and
other smart weapons had dawned.

12.9.2 Autonomous Receivers—Smart Weapons
Modern warfare attempts to minimize civilian casualties while maximizing the
effectiveness of destroying intended targets. This requires pinpoint accuracy, on the
order of a few feet in some cases. A December 2004 test of a 155-mm artillery shell
guided by GPS landed 3m from its intended target. GPS is once again the enabling
technology. By combining GPS measurements with those of an on-board inertial
sensor, a weapon can provide the required probability of kill with a smaller warhead
than would otherwise be necessary. It is no longer a question of how many sorties
will be necessary to kill a target, as was the case in World War II. Today, military
planners speak in terms of how many targets can be killed in a single sortie using
GPS-equipped weapons. GPS receivers have found their way into ballistic missiles,
guided missiles like the Tomahawk, smart bombs like the Joint Attack Direct Muni-
tions (JDAM), artillery shells, and autonomous air, land, and sea vehicles. Recent
applications include guiding unmanned combat air vehicles and reconnaissance
drones. Use of GPS in combat, however, begs the question about jamming vulnera-
bility. For these applications, antijam techniques are employed, such as nulling
antennas and ultratight coupling of the GPS and the inertial sensors. In the future,
higher military signal power from the satellites will further mitigate the possibility of
disruption due to enemy jamming.
GPS-equipped precision guided munitions quantities will total over 300,000 in
the U.S. Air Force alone. JDAM accounts for about 80% of these [21]. The Army
and Navy will buy even more units as artillery and naval gun shells become
GPS-guided. Figure 12.5 shows a typical munitions GPS receiver with its SAASM.

Figure 12.5 L-3 Communications munitions GPS receiver. (Courtesy of L-3 Communications.)