Flying in and out of Albuquerque, in New Mexico, the United States, one can catch a glimpse of a gigantic wooden trestle standing in the middle of an enormous pit in the desert. Built between 1972 and 1980, this wood and glue laminate structure called ATLAS-I (Air Force Weapons Lab Transmission-Line Aircraft Simulator) was used extensively during the waning days of the Cold War to test how well the United States’ strategic assets could withstand the effects of the electromagnetic pulse.
An electromagnetic pulse, or EMP in short, is an intense burst of electromagnetic energy that can be used as a weapon to inflict damage upon electrical and electronic systems by generating high levels of current and voltage surges to burn out sensitive components such as semi-conductors. Although not directly lethal, an electromagnetic bomb, or e-bomb, can devastate and render functionless any modern society that rely on electricity by knocking out their power grid and disrupting communication equipment.
ATLAS-I, also known as the Trestle, near Kirtland Air Force Base in Albuquerque, New Mexico.
The existence of powerful EMPs have been known since the early days of nuclear weapons testing. When the US Army was preparing for the first nuclear test, Trinity, in 1945, physicist Enrico Fermi advised the Army to shield their electronic equipment. The US Army shielded all their signal lines, in some cases twice. In spite of the protection, many records were lost because of spurious pickup at the time of the explosion that paralyzed the recording equipment.
In 1962, the US conducted a high-altitude nuclear test code-named “Starfish Prime”, where they detonated a 1.44 megaton bomb 400 kilometers above the mid-Pacific Ocean. 1,400 kilometers away in Hawaii, the EMP blast knocked off streetlights, set off burglar alarms and damaged a microwave link. In the months following the Starfish Prime test, at least six low earth orbit satellites failed due to radiation damage, including the one that was launched prior to the test to measure the distribution of radiation produced by the blast. It was only then the enormously devastating effects of EMP were realized.
In the Soviet Union too, similar research on EMP was being conducted. The same year Starfish Prime took place, Soviet scientists detonated a 300 kiloton bomb at an altitude of 290 km above Kazakhstan. To measure the effects of the EMP arising from the blast, they strung a 570 kilometer-long overhead telephone line and fitted them with fuses and gas-filled overvoltage protectors. The EMP from the test caused all the fuses to blow and all of the overvoltage protectors to fire along the entire length of the test-line. Furthermore, the EMP set on fire the electrical power plant in the city of Karaganda by inducing currents in a 1,000 km long shallow buried power cable. Despite the lower yield of the bomb, in comparison to that of Starfish Prime, the EMP damage caused by the Soviet bomb was much greater because the tests were done over a large populated land mass, and the earth’s greater magnetic filed at the location also assisted to concentrate the effects of the EMP.
From these tests it became apparent that EMPs were a threat, especially to military hardware, since modern militaries rely heavily on advanced electronics. Naval ships, aircraft, artillery pieces, armored vehicles, radars, military communication and data network, command and control centers, automated air defense weapon systems, etc., have substantial and critical electronic components that are vulnerable to EMP attacks. An e-bomb with a radius of a few kilometers could put out of action an entire battalion or a large number of airfields and naval vessels. And if an EMP is powerful enough, it can even disable an airplane in flight which could be potentially disastrous.
Hardening military hardware, primarily aircraft, became a major objective of the US Army. From the 1960s onwards, at least 18 separate EMP test facilities were built at air force bases across the country to test different parameters of an aircraft. All the tests followed the same basic principle—an aircraft was parked on the ground, and a short but powerful burst of electromagnetic radiation generated electrically was directed at it, and then its effects were studied. However, there was one basic flaw to the tests—the aircrafts were not flying and hence were subjected to almost twice the amount of radiation, one directly from the EMP generator and another reflected from the ground.
View of the Trestle on Google Earth.
ATLAS-1 was designed to minimize the effect of EMP being reflected from the ground, and to mimic as close as possible to an airplane flying while the test was being conducted. To do that, engineers at the Kirtland Air Force Base in Albuquerque built a huge wooden platform called the Trestle, inspired by those 19th-century railroad bridges, over a natural bowl-shaped arroyo. The platform was 200 feet square, with a 400-feet-long towpath and was 12 stories high—high enough to simulate an electrically neutral environment around the aircraft being tested, as if the plane was in flight.
The Trestle was strong enough to support a fully loaded B-52, then the largest and heaviest strategic bomber in the US inventory, yet it was built almost completely without metal to remove electrical interference. Even nuts and bolts were made out of wood. To provide better tensile strength, wooden boards were glued under heat and pressure to form massive elements. To date it is the world’s largest structure composed entirely of wood and glue laminate.
Wooden nuts and bolts.
While the Trestle is impressive to look, the most important component of ATLAS-1 was the generators. Two powerful Max generators, each capable of producing up to 5 megavolt of electrical potential was positioned on either side of the test platform. When fired simultaneously, it produced a short burst of energy 200 gigawatt in strength, comparable to the detonation of a nuclear bomb.
Strategic Air Command bombers were the primary objects tested at the Kirtland Air Force Base, but fighters, transport aircraft and even missiles were also tested for EMP hardness on the Trestle.
While EMP generation technology improved greatly over the years approaching energies in the terawatt range, the destructive EMP testing of aircraft was gradually replaced by far cheaper computer simulations, and in 1991, after the end of the Cold War, the ATLAS-I program was shut down.
The Trestle still stands in the arroyo, a few miles east of Albuquerque International Sunport. Efforts are on to preserve it as a national monument.
A B-52 bomber on top of the Trestle.
