Electronic Systems Vulnerable to High-Altitude A-Blasts : Military Anxious to Protect Sensitive Equipment Against Damage From Electromagnetic Pulses

Microchips, those sensitive Computer Age workhorses for everything from communications to defense, were in their infancy the night Starfish Prime lit the sky.

A rocket carried the nuclear device 280 miles into the atmosphere over tiny Johnston Atoll in the Pacific Ocean, about 925 miles southwest of Hawaii.

The 1.4-megaton nuclear detonation on July 9, 1962, was one of the last of its kind before the United States agreed to ban above-ground nuclear tests.

It also was one of the last times scientists had a chance to study a full-scale electromagnetic pulse triggered by a high-altitude atomic blast.

Effects Felt in Hawaii

The EMP surge drove detection meters off their scales in Hawaii, where strings of street lights flicked out.

“Ever since that time, people have been studying the effects of high-altitude EMPs,” said Conrad Longmire, who has been investigating the pulses since about 1960.

“It affects telephone lines, the U.S. power grid, U.S. military equipment in general. This problem seems worse than it was in 1962 because electronics these days are more sensitive.”

The military is keenly interested in EMP effects. Key studies are being conducted at Kirtland Air Force Base in Albuquerque, where scientists are trying to find ways to shield--or harden--electronics from the mighty pulses.

Has Potential as Key Weapon

An EMP could be a keystone in a wartime scenario. An enemy nuclear device could be triggered over the U.S. heartland, generating an EMP of perhaps 50,000 volts per meter, which could hit sensitive electronics within line of sight.

A blast at 250 miles can be seen as far away as about 1,350 miles, said Longmire, a former Los Alamos National Laboratory researcher who now is chairman of the board of Mission Research Corp. in Santa Barbara, Calif.

“The total amount of energy in an EMP itself is not very great,” Longmire said. “Quite often, however, equipment fails because the EMP puts that equipment into the state in which its own internal power produces the damage.”

Army Lt. Col. Richard M. Smith, chief of the EMP effects division at the Defense Nuclear Agency in Washington, said the need for shielding is much more critical today because the increased use of integrated electronics makes sensitive equipment more susceptible to EMPs.

Transistors More Vulnerable

Longmire said old electronic circuits based on vacuum tubes were much harder to damage than “these little transistor components that people have these days.”

Scientists have a pretty good handle on the makings of an EMP.

Albert Griffin, chief of the test operations branch at the Air Force Weapons Laboratory at Kirtland, said the main constituents of a high-altitude nuclear detonation are X-rays and gamma rays. The high-energy radiation interacts with air molecules in the upper atmosphere and knocks off electrons from the molecules.

The electrons, called Compton recoil electrons, are knocked forward like billiard balls and get trapped by the Earth’s magnetic field, Longmire said.

“They tend to spiral in unison in a given direction,” Griffin said. “It’s that flow of electrons, which basically is a current, which is the EMP.”

Can Induce Currents

The Compton electrons radiate out like a wave from a radio transmitting antenna, Longmire said, and that wave is the EMP. All this happens in a fraction of a microsecond.

Anything metal can pick up an EMP.

“When the pulse falls on wires, such as a telephone line, it can induce currents in the wires in the order of thousands of amperes,” Longmire said.

“Unless the electrical systems have been designed to keep out such currents, they can be damaged by it. Very large-scale integrated circuits are exceedingly sensitive.”

Immunizing electronics against EMPs is not impossible, but it can be expensive, he said.

Smith said the skin of an airplane offers good protection against EMPs, but openings like rivet joints, windows and hatches must be sealed.

Must Cover Small Openings

“A small opening becomes a very large opening electronically,” he said.

But it’s tough to seal those openings for permanent protection.

“One thing we know quite well is how to protect things,” Smith said. “The difficulty is when the system needs protection over time.”

The nation’s underground command centers are completely sealed and scientists are looking into hardening the nation’s communications systems and its power grid against EMPs.

Griffin said fiber optics, which do not respond to EMPs, could be coupled between subsystems, doing away with solid wire connectors.

Built Giant Simulator

The Air Force Weapons Laboratory operates five EMP simulators at Kirtland. One, aptly named Trestle, looks like someone went wild with a giant wooden Erector set.

Trestle is 12 stories of Douglas fir and larch girders bound together by 250,000 wooden and fiber glass bolts. More than 6 million board feet of lumber were used, enough to build 4,000 frame houses. The Air Force said it is the largest glued-laminated wooden structure in the world,

Trestle, which cost about $58 million, enables scientists and engineers to simulate in-flight EMP effects on aircraft electrical equipment. It mimics an EMP by using two 5-million-volt pulsers that discharge into a wire antenna mesh surrounding an airplane, which rests on a 200-foot-square laminated wood deck 118 feet above ground.

Planes can fly into nearby Albuquerque International Airport and taxi directly to the deck via a 400-foot-long, 50-foot-wide ramp.

Began Tests in 1980

Trestle can handle an aircraft the size of a C-5 Galaxy, which weighs at least 550,000 pounds.