Aerospace

The SR-71 Blackbird's Predecessor Created "Plasma Stealth" By Burning Cesium-Laced Fuel

Lockheed's A-12 Oxcart spy plane, which the company developed for the Central Intelligence Agency, was a direct response to the growing vulnerability of its earlier U-2 Dragon Lady to hostile air defense networks. As such, the plane – the predecessor to the U.S. Air Force's iconic SR-71 Blackbird – was extremely high- and fast-flying, but also incorporated then-state-of-the-art features to reduce its radar cross-section. These included a combination of a stealthy overall shape and radar-evading structures, as well as the use of composites in its construction, and the incorporation of radar absorbing materials on its skin. A far less known, but still a key component of the Skunk Works plan to make the A-12 harder to spot on radar involved a cesium-laced fuel additive to dramatically reduce the radar signature of the plane's massive engine exhausts and afterburner plumes by creating an ionizing cloud behind the aircraft to help conceal its entire rear aspect from radar waves.

Even before the U-2 had become operational in 1956, the Central Intelligence Agency (CIA) had begun exploring potential successor designs. The next year, Scientific Engineering Institute (SEI), a CIA front, began laying out requirements for the new spy plane, including a need for a reduced radar signature. By 1958, proposals from Lockheed and Convair had emerged as the most feasible and the former firm's concept showed more promise when it came to what we would consider today to be stealthy features.