Near the end of the Cold War, the United States military grew concerned about the capability of its equipment to withstand the effects of an electromagnetic pulse. So, in the middle of a vast pit in the desert outside Albuquerque, New Mexico, the government built a giant wooden structure named ATLAS-I. Standing for Air Force Weapons Lab Transmission-Line Aircraft Simulator, this massive and ominous structure was built between 1972 and 1980, to validate the United States' security measures in the event of an EMP attack.
What are EMPs?
Electromagnet pulses, or EMPs, are intense bursts of electromagnetic energy which can result from a high-altitude nuclear explosion. In the event of war, such blasts could be used to inflict damage on electrical and electronic systems of opposing countries. EMPs affect electronic systems with both high and low amplitude surges created through the initial blast.
When a nuclear device explodes at high altitude, somewhere between 25 miles (40 kilometers) and 250 miles above the Earth, it produces powerful gamma rays. When these collide with molecules in the Earth’s atmosphere, a powerful electromagnetic energy field is created. This EMP doesn’t hurt humans directly, but it produces a surge of high-voltage current.
The EMP arrives in three phases. The initial pulse high-amplitude pulse which burns out electrical conductors by inducing a voltage beyond what they can handle. A subsequent pulse is less powerful, but can also cause damage. In addition, the fireball from a large detonation briefly warps the Earth’s magnetic field and can knick out long electrical conductors, such as power and telecommunications lines over a wide area, for between several seconds and several minutes.
Back in the 1980s, this would have been bad news for the US, or any country for that matter – but in 2019, this would practically bring the modern world to a standstill. Communication would be nearly impossible, cars and planes wouldn't work, phones wouldn't work. Nothing about our modern life would work.
It's this fear that led the US government to build the ATLAS-I testing center.
Also known as the Trestle, this center was specifically designed for testing electronic machines against EMP blasts, but to understand a little more about why such a center was built, we need to step a little further back into the heat of the Cold War.
EMPs have been known and understood since early nuclear tests in the 1940s. In 1945, when the US was getting ready for their series of Trinity tests, physicists advised the Army to take precautions to protect their electronic equipment. Even so, many recordings of those tests were fried from the blast.
1962 marked the most prominent EMP test for the US, using a high-altitude nuclear explosion. Named "Starfish Prime", this test involved the detonation, at an altitutde of around 400 kilometers over the Pacific Ocean, of a bomb weighing 1.44 megatons. The resulting EMP blast knocked out streetlights more than 1400 kilometers away, set off alarms, and damaged other electronics. In the following days and months, several low-earth satellites actually failed due to radiation damage. It was after these unplanned effects from the EMP that the US government and military became acutely aware of just how damaging an EMP blast could be.
Over in the Soviet Union, EMP tests were also being conducted – after all, it was the heat of the Cold War. In 1962, the same year as the Starfish Prime test, the Soviets detonated a 300 kiloton bomb, roughly 4 times smaller than the US bomb, over Kazakhstan. The Soviets set up a 570-kilometer long telephone line fitted with sensors and overvoltage protectors at a regular interval. The EMP blast caused every sensor to trip.
It also set an electrical power plant many miles away on fire, thanks to induction that occurred in a 1,000 km long-buried transmission cable. While the Soviet bomb was much smaller than the Starship Prime test, it caused much more damage, due to its positioning over land.
The growing fear of attack
Both the US and the Soviet Union now grew increasingly fearful of EMP attacks, as they were more aware than ever of just what such an attack could do. An EMP could knock out an entire Navy fleet; it could disable an airbase; it could cause an immeasurable amount of damage.
The US Army became obsessed with hardening all of its military hardware, making sure that it could withstand EMP blasts. They built 18 different test facilities at Air Force bases all over the US. Each testing center focused on the same principles: aircraft were parked on the ground and a short burst of electromagnetic radiation was blasted right at them. After that, engineers studied the aftermath.
The problem was that this EMP, generated from high energy transmission, reflected off of the ground under the aircraft, causing the vehicles to be exposed to twice the amount of radiation they would absorb if they were flying. This is where the ATLAS-I testing center came into play.
The engineering of the Trestle
ATLAS-I was specifically designed to mitigate this radiation reflection from the ground. Engineers built a giant wooden platform over a bowl-shaped indention on the desert floor. This platform made up the bulk of the ATLAS-I test structure and it was made of wood and fiberglass so that it didn't interfere with the electromagnetic pulse.
Measuring 200 feet by 200 feet, it also had a 400-foot long towpath and came in at the height of a 12-story building. All of this careful design and placement meant that it could simulate an EMP blast on an airplane while stopping any radiation reflection from the ground. It was the perfect test site for military aircraft.
Planes would be towed onto the platform to wait for an EMP blast. A pair of MAX 5 megavolt generators, one mounted on each side of the platform, were used to produce the short-range EMP burst. When combined, they could produce a 200-gigawatt electromagnetic pulse. At short range, this was equivalent to the pulse from a thermonuclear explosion.
Over the years of ATLAS-I's operation, from 1980 to 1991, the Trestle was used to test massive bombers, fighters, and even missiles against EMP attacks.
In 1991, at the end of the Cold War, the ATLAS-I test site was finally shut down, but the structure still stands and can be seen today.