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Press Release

GPS Processor to Increase Accuracy of Shells

Michael O. Lavitt
(Reprinted from Aviation Week 12/07/98 issue. pp. 86-87)

Anaheim, CA - Interstate Electronics Corp. has developed a miniaturized system that can integrate GPS and inertial guidance technology to increase the accuracy of U.S. Army and Navy artillery shells.

The system is on a circuit board small enough to fit into the nose of an artillery shell. Initially, the board will process only GPS data, but Interstate's concept is to use a single processor to handle GPS data and inertial data from a silicon-based micro-electromechanical system (MEMS) that could eventually be placed on the board, said Jim Grace, the company's director of business development for GPS systems. It also could function as the navigation computer. The MEMS is like the sensor that triggers the release of automotive air bags.

Interstate's GPS will be used in both the Navy's Extended Range Guided Munition (ERGM) and Army's XM-982. Interstate developed the integrated GPS/IMU concept under a subcontract to Raytheon, the prime contractor for ERGM and XM-982.

The board also had to be ruggedized to withstand being fired from a gun and be able to acquire a GPS signal quickly in a high-jamming environment. In the case of ERGM, a 5-in. projectile with a rocket assist will receive 12,500g as it is fired and has a range of 63 mi. (100 km). The Army XM-982 is fired from a howitzer and has a range 12.4-15.5 mi. (20-25 km). But since it lacks a rocket booster to augment its range, the 155-mm. shell receives 15,500g when it is fired. The XM-982 spins at 20 rev./sec., but the GPS takes position samples 12 times per revolution.

Interstate has demonstrated acquisition of the more-precise, harder-to-jam GPS Y code in 7 sec., Grace said. Usually, military GPS receivers first acquire the less-precise CA code, then search for the Y signal. "IEC can go direct to the Y code," Grace said.

The GPS will be activated after launch and then pass on position data as the inertial navigation system (INS) becomes more stable. If the GPS is jammed, the navigation computer will rely solely on the INS. Other precision-guided weapons are fed inertial data before launch, then use GPS to update the INS in flight.

The GPS is ruggedized by using specialized glues and coatings and more potting material. "All of those things make up the technology that's needed to shoot a shell out of a gun," said program manager Dennis Schumann. The components were tested at more than 30,000g.

The phase stability of the GPS receiver's oscillator also had to be high in order to acquire the satellites and accurately track a shell's velocity. This was a challenge, Grace said, because the units will have to sit for years.

Before firing, the GPS in a shell will be programmed with its position within 5 mi. as well as with its prelaunch velocity and the correct GPS time.

A substantial challenge will be reducing the cost. "When you're talking about shells that cost a couple of thousand dollars, you can't have electronics that cost more than that," Interstate's Schumann said. The goal is to get the price of an integrated GPS/IMU below $1,000.

The next step will be to further miniaturize the GPS/IMU board so it can be inserted into a 9-cu.-in. NATO fuze well, Grace said. Tiny canards in the fuze would deploy after launch to guide a shell.

Interstate Electronics Corp., 602 E. Vermont Street, Anaheim, Calif. 92803.

Caption: Interstate Electronics' GPS receiver for the Navy ERGM and Army XM-982 is tapered to fit into shells' nose. Extra Adhesives and potting material ruggedize it for high g loads.

For more information, contact:
Greg Martz
Marketing Manager, Communications
Phone: (714) 758-4158