Lockheed’s A-12 Oxcart was the spy plane which the company developed for the Central Intelligence Agency
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 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, write Joseph Trevithick and Tyler Rogoway or TheDrive.com. Continue reading the original article
After the CIA chose Lockheed to develop what would become the A-12 in 1959, the company continued to refine its radar-defeating features.
However, there was one aspect of the plane’s radar signature that still proved difficult to manage, the exhaust outlets for the J58s and the giant plume from the engines at full afterburner, which was necessary to propel the A-12 to its blistering top speed of well over Mach 3.
“To overcome the afterburner problem of a large radar cross-section return from the aft quadrant, we proposed the use of [a] cesium additive to the fuel,” Kelly Johnson wrote in his A-12 history. “This was first brought up by Mr. Ed Lovick of ADP and its final development was passed over to P&W. It was eventually a basic part of our cross-section reduction methods.”
“The exhaust pipes were sixty inches in diameter, so they returned large amounts of energy at all frequencies of interest and over large angles to the rear,” Lovick, who also worked on the SR-71 and the F-117 Nighthawk stealth combat aircraft, wrote in his own book, Radar Man: A Personal History of Stealth. “We knew that the only way to prevent such echoes was, in effect, to close the apertures.”
Lockheed initially experimented with various metallic mesh screens, but quickly abandoned those efforts, according to Lovick. He says that Dr. Richard Bissell, the CIA’s Special Assistant for Planning and Coordination, who was managing the program, was so worried about this particular issue, he had considered calling for the scrapping of the entire development of a U-2 successor. That’s where the cesium additive, which eventually became known as A-50, came in an idea that Lovick claims saved the A-12 program.
The basic principle behind this is a concept known as “plasma stealth.” In the simplest terms, this involves creating a cloud of plasma, or ionized gas, around some or all of an object. The plasma then absorbs electromagnetic radiation, such as radar waves, preventing them from reflecting back. There are multiple ways to generate the required plasma Lovick’s idea was to inject an alkali metal, via a fuel additive, into the extremely hot exhaust streams, where the heat would turn it into an ionized gas.