Anaheim Firm Ships Weapon Guidance Units

Now, if the government can just find the right maps. . . .

Anaheim’s Interstate Electronics Corp., a major manufacturer of satellite-based navigation devices, has shipped the first batch of GPS receivers designed for use with the U.S. Navy’s 5-inch shells. The rocket-assisted shells, fired from deck guns, are used to bombard land targets.

GPS shells--the initials stand for Global Positioning System--use a high-tech receiver that locks onto a signal from a military navigation satellite within seconds of clearing the end of the gun barrel. The receivers, packed in special shock-resistant cases in the nose of the shell, then decode the signals and use them to guide the shell--via its rocket booster--to its target.

The challenge in building the system, said an Interstate Electronics spokesman, is that the delicate electronic components have to withstand the shock of being fired from the big guns. The initial explosion of the powder that propels the shells from the deck guns subjects the GPS receivers to an acceleration force of 12,500 gravities, or “Gs.” Simply put, a “G” is equivalent to the force, or pull, of gravity. A really nasty roller coaster hits about 4.5 Gs in its worst turns. An object the size and weight of a U.S. quarter at normal gravity would weigh almost a ton when subjected to 12,500 Gs.

Interstate, which first demonstrated its capability to build a GPS system that could withstand such force in 1996, also is developing a satellite guidance system for shells for the Army’s 155-millimeter cannon, said Jim Grace, business development chief for Interstate’s military GPS unit.

The Navy contract is an initial development contract with future renewal options, said Grace, who declined for competitive reasons to disclose the value of the deal to the company.