Here’s why USAF put B-52 and B-1B Strategic Bombers on a Giant Trestle

Due to their higher flight altitude and nuclear payload, SAC bombers were the primary object of the tests, but fighters, transport aircraft and even missiles were also tested for EMP hardness on Trestle.

The Kirtland AFB Trestle Facility is arguably one of the largest all wood structures in the world, an engineering marvel and a landmark of the Cold War.

The reason for the Trestle and its all wood design was to test the effects of electromagnetic pulse, generated during a nuclear explosion, on operational aircraft.

The Trestle was built from 1972 to 1980 and the designer and structural engineer on the project was Robert Krause.

Developments in the field of atomic weapons during the 1940s helped lay the foundations for the Cold War, and it was under this perceived threat of a potential nuclear attack on American soil that Sandia National Laboratories devised their own playground for testing the latest advancements in weapon design. Scientists here were not primarily concerned with the issue of radioactive fallout; their concern was to develop technology that wouldn’t be affected by a different aspect of a nuclear explosion.

According to the article ATLAS-I – Top secret EMP testing site appeared on Abandoned Spaces, to test this kind of technology a top-secret testing facility, code-named Trestle, was built close to Kirtland Air Force Base (AFB), on the southeast of the city of Albuquerque in New Mexico. The facility formal name is rather long, though clearly depicts its use: Air Force Weapons Lab Transmission-Line Aircraft Simulator (ATLAS-I).

ATLAS-I was a matchless testing contraption for the effects of electromagnetic pulses (EMPs) of damaging radiation. It was devised during the 1970s and was the most advanced non-nuclear electromagnetic pulse generator in the world. The idea behind this contraption is as follows; upon entering outer space, during high altitude flight, or around particle accelerators and nuclear reactors, a certain amount of high energy electromagnetic and particle radiation is present. And, crucially during the Cold War, EMPs of these types are generated by a nuclear explosions. This amount of radiation causes malfunctioning in electronic components, thus the components need to be ‘radiation-hardened’ in order to remain functioning. This can be through manufacturing processes, for example using non-standard electronic chips based on insulating materials; by physically shielding electronic components; and through software programming. ATLAS-I was designed to test the radiation-tolerance of different component designs and materials.

According to Wikipedia, the facility was built at a cost of $60 million and was composed of two parts: a pair of powerful Marx generators capable of simulating the electromagnetic pulse effects of a high-altitude nuclear explosion (HANE) of the type expected during a nuclear war, and a giant wooden trestle built in a bowl-shaped arroyo, designed to elevate the test aircraft above ground interference and orient it below the pulse in a similar manner to what would be seen in mid-air.

Trestle is the world’s largest structure composed entirely of wood and glue laminate.

The primary wooden structure of Trestle was 1,000 feet long, 125 feet (about 12 stories) tall, and constructed of 6.5 million board-feet of lumber, sufficient to support a fully loaded B-52 (then the largest and heaviest strategic bomber in the US inventory) while also minimizing any chance of interference from the ground or the structure itself, creating a reasonable simulation of airborne conditions. A mix of Douglas Fir and Southern Yellow Pine were used for the timbers, as both showed excellent EMP transparency with the former having the best tensile strength and the latter the best weather resistance. By using an all glued laminated timber structure and woodworking joints to mate the giant timbers, with the joints being held together with wooden bolts and nuts, measurements from the EMP tests would not be skewed by large amounts of ferrous material in the structure. Some metal was used in the construction as critically loaded joints incorporated a circular steel sheer ring that surrounded the wooden bolt clamping the joint. Even the fire escape along one side of the trestle and the whole of the extensive fire suppression piping were constructed of fiberglass.

Due to their higher flight altitude and nuclear payload, Strategic Air Command (SAC) bombers [such as the B-1B] were the primary object of the tests, but fighters, transport aircraft and even missiles were also tested for EMP hardness on Trestle. In addition to electronics survivability tests, numerous sensors located inside, beneath and to the sides of the aircraft would gather additional data on the airframe’s EMP permeability to be used in design considerations for future Cold War aircraft and to identify areas which needed additional EM hardening.

The ATLAS-I program was shut down after the end of the Cold War in 1991, which brought an end to destructive EMP testing of aircraft, being replaced by far cheaper computer simulations as technology improved. Today the wooden trestle structures are all still standing and it remains the biggest metal-free wood laminate structure in the world. The trestle has, however, become a significant fire hazard since the creosote-soaked wood has dried considerably in the desert conditions and the automatic fire sprinkler system was deactivated in 1991. Efforts are underway to secure the funding necessary to have the structure protected as a national historic landmark, although efforts are complicated by the top secret nature of the Sandia/Kirtland facility it is situated on.

The trestle structure is still easily visible from commercial aircraft landing and taking off from Albuquerque International Sunport, lying about one mile to the southeast of the threshold of Runway 26.

Photo credit: U.S. Air Force