On January 17, 1991, at 2:30AM, the opening attack of Operation Desert Storm was set in motion. Tasked with crippling Iraq’s command and control, shipborne Tomahawk and B-52 launched AGM-86 cruise missiles were employed to infiltrate targets within Bagdad.
Alongside this initial inrush of deep striking assets, was a new class of weapon. This attack was the first public debut of a stealth aircraft facing off against one of the largest air defense networks in the region.
The iconic Lockheed F-117 Nighthawk, the first stealth strike platform, were among the first sorties to enter the heavily defended airspace of Baghdad.
In order to understand how stealth technology emerged, we need to quantify what stealth is. Stealth isn’t one specific technology, but rather a mantra of design that incorporates low observability.
Of all the potential threats faced by combat aircraft, detection and tracking by radar pose the most risk. Radar, infrared, and optical detection all rely on the bouncing of electromagnetic radiation of an object in order to gather information from it.
However, radar differs in that the source of the reflected radiation is actively emitted from the observer. With passive methods of detection, the target’s own emissions or ambient light are used.
While detecting an aircraft provides a warning, in order to defend against it, it must be tracked. Tracking is the determining of a target position, velocity, and heading from a reflected signal.
While some defense weapons can track optically, infrared tracking is the predominant method for close range air defense due to its ability to see the heat of an aircraft through the atmosphere. Infrared tracking works by using an infrared sensor similar to a camera to "look" for the highly contrasting signature of hot jet exhaust gases and the warm aircraft body, against the ambient air temperature.
The first military use of radar began around the start of world war 2. One of the more notable uses was in the air defense of England. By 1939 a chain of radar stations protected the East and South coast provided early warning to incoming aircraft.
Fast forward to today and most military airborne radars, including those found in radar-based anti-air missiles, operate in the 5 cm - 1 cm wavelength microwave range as it provides a good compromise between range, resolution and antenna sizing.
The goal of radar stealth is to both mask an aircraft from being detected, tracked and fired upon from a distance. This is known as beyond visual range engagement. As distances close, radar-based engagements may transition into IR based targeting either low to the ground, or among adversarial aircraft within a dogfight.
Early attempts at stealth were based on observations of radar on existing designs. It was discovered early on that the shape of an aircraft determined its visibility to radar, its radar cross-section or RCS.
Soviet mathematician and physicist Pyotr Ufimtsev published a paper titled Method of Edge Waves in the Physical Theory of Diffraction in the journal of the Moscow Institute for Radio Engineering. Ufimtsev’s conclusion was that the strength of the radar return from an object is related to its edge configuration, not its size.
Astoundingly, the Soviet administration considered his work to have no significant military or economic value, allowing to be published internationally.
During that time period, Lockheed’s elite Skunk Works design team was working on a stealth proof-of-concept demonstrator called Have Blue. The engineering team struggled with predicting stealthiness as the program they created to analyze radar cross-section called ECHO-1 failed to produce accurate results. Denys Overholser, a stealth engineer on the project had read Ufimtsev’s paper, realizing that he had created the mathematical theory and tools to do a finite analysis of radar reflection.
Ufimtsev's work was incorporated into ECHO-1. The iconic early stealth looks was a direct byproduct of the computational limit of computers of the time, which limited ECHO-1’s ability to perform calculations on curved surfaces.
Northrop began working on a technical demonstrator of its own, know as Tacit Blue. Tacit Blue attempted to demonstrate a series of then advanced technologies including forms of stealth that employed curved surfaces. During the late 1970s, momentum was building for the development of a deep penetrating stealth bomber. By 1979, the highly secretive Advanced Tactical Bomber program was started, under the code name "Aurora".
With the success and dominance of the US stealth programs, the technology has worked its way into other applications such as the canceled Comanche RAH-66 reconnaissance helicopter, the Sea Shadow, the USS Zumwalt.
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