Jim Grace Director of Business Development for L-3/Interstate Electronics Corporation’s (L-3/IEC) military GPS receivers for weapon systems, tells how high-tech made its way to the head of a projectile		Smarter, cheaper and on target
				Projectile for the US Navy’s 5” MK45 gun Field artillery’s projectile just got smarter. For the first time in artillery history, high-tech has made its way to the head of a projectile. As a step towards the US Army’s goal, the US Navy recently received shipments of L-3/Interstate Electronics Corporation’s (L-3/IEC) projectile GPS receiver. The receiver operates after withstanding an incredible instantaneous, gravitational force 15,000 times that of the Earth’s gravity. Within seconds of leaving the gun’s barrel, the GPS receiver picks up satellite signals from the military’s global positioning system (GPS). This year L-3/IEC will deliver this same technology in an even smaller package that fits inside the fuse of a 155mm round for the army – about the size of a human fist. Propelling a projectile or missile to a greater range hasn’t proved to be a challenge. Artillery designers have developed shells with larger charges and extended barrel length while missile designers have developed more powerful motors and lighter, more devastating, warheads. In fact, designers have increased the stand-off distance with these upgrades, allowing the army to conduct effective counter-offensives from greater distances. But while the rudimentary guidance systems were sufficient for shorter range older weapons, flights beyond 13 miles increase environmental variables, significantly affecting the accuracy of new extended-range projectiles and missiles. The challenge The Mk45 deck mounted gun firing a 5” projectile In contrast to the successful fielding of weapon range extension, incorporating an on-board guidance system proved to be a big challenge. This ambitious programme had conflicting goals and required a dramatic shift and significant technological advancements. Many in the industry had the opinion that the Army was dreaming. Going ahead with the ERGM programme, the US Army would benefit through the ability to attack the enemy deeper, increasing stand-off distances while increasing weapon accuracy; increased accuracy secures the Army’s concern for hitting the target only; improved kill ratio in order to avoid counter fire, (shoot and move); reduced logistics to minimise the quantity of rounds brought to the front line to neutralise identified targets; increased mission options and depth of strategies. Simply stated, the US Army’s basic goal was to improve the range and accuracy of its existing artillery and tube-launched missiles. Obstacles But how could a GPS receiver survive the lower level of ground-to-ground missions? The demands of field artillery are very high. A guidance system must survive the high-G explosive shock of initial firing, quickly assess its location after leaving the gun barrel, immediately begin providing guidance to the projectile, and operate in a potentially high jamming environment. The system also must fit into the volume of the projectile’s fuse well, no bigger than the palm of a hand, and have a greater than 20-year shelf life. Considerations for the assembly, available space and design of a board were formidable obstacles as well as hardening of board components and anti-jam of the GPS signal under battlefield conditions. After meeting these demands, the guidance system must meet a much lower target cost than existing implementations. L-3/IEC recognised the opportunity. They realised the basic construction of all GPS/inertial measurement-unit (IMU)-based guidance systems are similar, whether developed for an expensive cruise missile or inexpensive projectile. They created breakthroughs for projectile guidance systems that give projectiles fast acquisition of the military GPS signal (less than six seconds), a much longer shelf life, and less field setup. Using a GPS-based integrated guidance system that allows the IMU to meet size/performance and cost requirements, designers developed a silicon-based micro-machine technology for the inertial sensor, high levels of processor integration and additional hardware function consolidation, making the guidance package inherently immune to the vibration and high-G shock (over 15,000) when fired from the 155mm gun. These consolidations meant the size and power were sufficiently reduced to fit the constraints of the fuse well. End-game accuracy For the potential of signal jamming, a GPS-only solution would probably never be able to guide the projectile all the way to the target. To resolve this limitation, an anti-jam (AJ) capability is incorporated into the GPS receiver with a miniature on-board IMU. As the projectile is fired, the GPS receiver, with an enhanced signal provided by the AJ sub-system, quickly acquires the visible satellite constellation immediately after it clears the gun barrel. The result is that the projectile needs only a couple of positional fixes to correct the miniature on-board IMU and meet its end-game accuracy. Projected location of the GPS receiver fitting inside the nose of the US Navy’s new 5” projectile Initial laboratory tests had already proven that this combined GPS/inertial guidance system, enhanced with a robust, low-cost AJ sub-system, consistently performed well under the simulated battlefield conditions defined by the army. As the design and development of the new projectile guidance system progresses and laboratory tests are being completed, upgrades are in process for the army’s multiple launch rocket system (MLRS) and tactical missile system (ATACMS). These mobile weapons were highly effective in destroying Iraq’s Republican Guard during the Gulf War. They are capable of delivering high-explosive warheads or sub-munitions with very high precision when used at less than 150km. But like artillery projectiles, the army intends to increase the effective range of the missile system while reducing the cost of the guidance system, both essential elements to the new design. The army is using the technologies developed for the low-cost projectile and the long-range missile guidance concepts to integrate new guidance systems for these two weapons. Prior to September 1998, there were three MLRS test launches using IEC supplied GPS receivers. The results proved that a fast acquisition GPS product and a tactical-grade inertial guidance system perform in the environment as expected and provide the required accuracy, and do so at a potentially lower cost than current guidance systems. What does all this mean? While other weapon systems have been able to integrate GPS-based IMUs, advances have only now allowed the army to incorporate this technology into their primary weapon systems – field artillery and rocket systems. Now, with increased accuracy and range obtained, targets become more specific, reducing the risk of collateral damage, evolving standard missions and strategies, providing more options, and reducing wasted munitions and over stockpiling. For the army, these advances will allow field commanders to improve the flexibility and job functions of the unit, while keeping the price to a minimum. More importantly, this technology provides the best alternative to hit specified selected targets without injury and unnecessary destruction to adjacent structures or people. © >>>>> www >>>>> L-3 Comms (Interstate Electronics)
	L3-IEC’s GPS projectile receiver shipped in May 1999