ATLAS-I

ATLAS-I (Air Force Weapons Lab Transmission-Line Aircraft Simulator), better known as Trestle, was the codename for a unique electromagnetic pulse (EMP) generation and testing apparatus built between 1972 and 1980 during the Cold War at Sandia National Laboratories near Kirtland Air Force Base in Albuquerque, New Mexico.

ATLAS-I was the largest NNEMP (Non-Nuclear Electromagnetic Pulse) generator in the world, designed to test the radiation hardening of strategic aircraft systems against EMP pulses from nuclear warfare. Built at a cost of $60 million, it was composed of two parts: a powerful Marx generator 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.

EMP generator
The Marx generator providing the EMP pulse generated 200 gigawatts of electromagnetic flux at an electrical potential of 10 megavolts, powerful enough to reliably reproduce (at short range) the deleterious effects of a thermonuclear detonation on electronic circuitry as created by such examples as the HARDTACK I, ARGUS and DOMINIC I (Operation Fishbowl) high altitude nuclear tests. The generator itself was mounted at the end of a long, diagonal wooden scaffold structure, located above and to one side of the aircraft platform, with the primary receiving tower located at equal elevation on the other side of the arroyo.

Due to their higher flight altitude and nuclear payload, Strategic Air Command bombers 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 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.

The advances made in EMP generation technology by Sandia during the operation of Trestle greatly assisted in the construction of the much more powerful 40 megavolt, 50 terawatt (50,000 gigawatt) Z Machine at Sandia during the 1990s. Technological advances during the 2000s have since boosted this output to 290 terawatts (290,000 gigawatts), high enough to actually study nuclear fusion at the point of detonation.

Trestle structure
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 nail-free woodworking joints to hold the giant timbers together, measurements from the EMP tests would not be skewed by ferrous nails or braces in the structure. Even the fire escape along one side of the trestle and the massive lag bolts holding the load-bearing beams in place were entirely composed of wood and fiberglass.

Current status
The ATLAS-I program was shut down in 1991 after the end of the Cold War brought an end to destructive EMP testing of aircraft, being replaced by far cheaper computer simulations as technology improved. Despite going without maintenance for over 20 years, 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.