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Press Release

New Technologies: GPS-Guided Shells

By: John G. Roos
(Reprinted from Armed Forces Journal INTERNATIONAL, July 1999)

Tiny Keys Unlock US' Cannon-Launched, Precision Fire Programs.

Thanks to Sadam Hussein and Slobodan Milosevic, "smart" weapons have become the messengers of choice for Western politicians. The compelling need to keep allied casualties to a minimum, coupled with a desire to limit collateral damage on the receiving end of long-distance strikes, are the principal reasons why cruise missiles and laser-guided bombs have become weapons of first resort.

Despite the obvious advantages of today's smart weapons systems, their high cost and low stockage levels invariably begin to weigh on target-selection activities as conflicts wear on. This is particularly true for missiles guided by the Global Positioning System (GPS) ­ the long-range-strike weapons that receive guidance signals and targeting cues from a constellation of satellites. Navy Tomahawk Land-Attack Missiles (TLAM) (about $1 million a copy) and Air Force Conventional Air-Launched Cruise Missiles (CALCM) (some $2 million each) are among this category's crown jewels.

Although the Army Tactical Missile System (ATACMS) hasn't been called upon as frequently as the TLAM and CALCM, this highly accurate surface-to-surface weapon is also GPS-guided. Fired from the Multiple-Launch Rocket System, ATACMS missiles demonstrated their pinpoint accuracy in Operation Desert Storm. But, like their Navy and Air Force counterparts, ATACMS are also expensive ($900,000 for the latest Block 1A variant) and in relatively short supply.

The fiscal strains that today's high-priced GPS-guided missiles place on the services' procurement accounts prompted both the US Navy and US Army to seek lower-cost alternatives to TLAMs and ATACMS. The results are taking shape in the Navy's 5-inch, Extended-Range Guided Munition (ERGM) and in the Army's XM-982 howitzer projectile.

With a maximum range of just 63 nm, ERGM will be a short-range complement to the 1,000-nm TLAM. Fired from 5-inch naval guns, the GPS-guided projectile will provide the relatively close-range, precision-strike capability needed by shore-bound Marines and shore-based units. While it lacks TLAM's range, ERGM's relatively low cost (probably less than $20,000) and short time of flight, coupled with the high rate of fire that naval batteries can deliver, will make the smart projectile a valuable addition to the Navy's arsenal.

Similarly, the Army's XM-982 projectile's maximum range (about 30 miles) is well below that of the
180-miles Block 1A ATACMS. But with a price tag also in the neighborhood of $20,000 per round, a rapid response time, and the ability to obliterate distant enemy targets from any 155mm howitzer location, the XM-982 will give field artillery units the precision punch they've long desired. It will also give Army field commanders a responsive, precision-strike capability in future ground conflicts where collateral-damage considerations come into play.

HURDLES

The idea of developing precision, tube-fired projectiles isn't new; however, until recently technological barriers thwarted developmental efforts. The first challenge involves manufacturing a GPS guidance chip rugged enough to withstand forces of up to 15,500 g's (at a nine millisecond pulse duration) as a 100-pound shell is blasted from a cannon barrel. Next, there's the need to fit the projectile with a means for controlling its flight path once it leaves the barrel. The final challenge involves coping with enemy electronic countermeasures as the round makes its way to its target. The two latter challenges are being handled by ERGM and XM-982 developmental teams at Raytheon; the job of developing GPS chips for both systems falls to Interstate Electronics Corporation (IEC) of Anaheim, CA.

" . . . give Army field commanders a responsive, precision-strike capability in future ground conflicts . . . "

IEC is no newcomer to military weapons development programs: among its earlier achievements, the company provided guidance systems for Polaris missiles and is today the source of CALCM guidance systems. Still, challenges associated with developing a hardened GPS chip for an artillery projectile were considerable, Jim Grace, IEC's director of business development for military GPS systems, told AFJI.

"There are a variety of ways that we can 'package' the GPS units," Grace said. "The main issues are the mass of the device and the forces from the gun barrel that we have to overcome. It's not only the forces that are experienced as the round rotates and 'chatters' up the tube, but also those that the round encounters as it leaves the tube. They can be taken care of by reducing the sizes of the devices that are used in the packaging, as well as the attachments that are made to the electronic circuitry."

In order to overcome both the enemy's long-range electronic jamming activities and signals emitted by friendly forces, the GPS receivers will carry anti-jam electronics systems that will get them through the initial stages of their flights.

"A lot of the reduction in size is being taken care of by what's going on in the commercial industry right now," Grace continued. "There's cell phone technology that keeps getting smaller and smaller, and the integration of the signal processing that they use reduces the components into an electronics package that is much smaller than anything we've had in the past. That's why we have the ability to take something that we put into a CALCM missile and reduce its size to that of a fuze well in a 155mm shell - about a 9-cubic-inch space."

"In addition to being able to overcome the technological challenges of developing a hardened, miniaturized GPS, IEC also has the broad range of experience needed to give the projectile the ability to rapidly acquire the GPS signal and determine the flight path to the target," Grace said.

In order for the GPS to be able to influence the round's flight path, ERGM and XM-982 projectiles will need either fins or thrust-delivery nozzles controlled by the guidance system. "Some of the initial shells, which are being built from the ground up, will deploy fins to either roll-stabilize the platform or completely control its flight," Grace said. "To get the required stand-off distance, you need some kind of control surfaces to keep the projectile in the air longer. You can tell the projectile where it is and where it's supposed to be going, but unless it has some way of adjusting its flight path it's just another dumb round."

Even if a projectile can adjust its flight path, it still must contend with the prospect of enemy electronic jamming. This is a particular challenge for munitions used by ground forces.

WORST POSSIBLE ENVIRONMENT

"An Army artillery projectile begins its flight in the worst possible environment," Grace said. "It's on the battlefield - it's not flying over the battlefield after being launched from outside the area."

In order to overcome both the enemy's long-range electronic jamming activities and signals emitted by friendly forces, the GPS receivers will carry anti-jam electronics systems that will get them through the initial stages of their flights. Nonetheless, since many of the high-value targets for the projectiles will have electronic jamming capabilities either collocated with them or in close proximity, it's likely that the guidance systems will be defeated as they approach their targets.

"That's why we'll also put a small, inertial sensor in the package," Grace said. "We've adapted these from our automotive product line, and they'll help guide the rounds to their targets during the terminal phase of flight. They're pretty much a standard method of terminal guidance for smart weapons."

"The requirement for some type of inherent control in the projectile doesn't preclude retrofitting GPS to some existing shells," Grace said. "Program officials are looking at the only thing that currently gets added to a projectile - the fuze - and considering adding a small drogue that would deploy at a pre-set distance from the target in order to bring down the round on target."

"The spin-stabilized, fin-deployed system will probably be ready within the next two or three years," Grace concluded. "The fuze package is something that probably will come into play in three or four years. Thanks to data fusion, one microprocessor will do the navigation, guidance, and autopilot functions. The necessary technologies are being developed right now - the path is clear, and we're on that path."

For more information, contact:
Jim Grace
Director of Business Development
Phone: (714) 758-4216