HAVE BLUE - Experimental Survivable Testbed (XST)
Low observable characteristics and radar-absorbing materials had been employed in classified reconnaissance aircraft (both manned and unmanned) during the 1960s. However, previous efforts addressed stealth as an afterthought and incorporated stealth features to the extent that aerodynamic performance was not significantly affected.6 Furthermore, there were no serious efforts to employ such capabilities for a weapons platform, though a 1971 Air Force study had recommended undertaking prototyping experiments in order to prove out various laboratory concepts.
Superiority in conventional aviation had been one of the United States' primary conventional force advantages since 1944. During the Vietnam War, it became apparent that Soviet integrated air defense systems (IADS) challenged this superiority. While it was possible to counter Soviet IADS using jamming, defense suppression, and other active means, this required a very high level of effort. A case in point is the 1972 raid in which F-4 Phantoms firing laser guided bombs destroyed the Paul Doumer Bridge. Payloads during the primary raid were carried by 16 F-4s. They were accompanied by 8 F-4s that dropped chaff, 4 EB-66 electronic countermeasures aircraft, and 15 F-105G Wild Weasel aircraft to attack the radars that guided surface-to-air missiles. More aircraft were deployed to protect the primary mission than accomplished the attack.
The 1973 Middle East War provided an additional demonstration of the potential lethality of modern IADS. Israel lost more than 100 combat aircraft-a significant fraction of its front line posture-in only 18 days. Egyptian air defenses were not neutralized until late in the war, and then only by Israeli ground forces. Israel's American-made aircraft were among the most advanced and capable in the US fleet, with capable pilots. If the NATO air forces were to suffer the same loss ratios against the Warsaw Pact, they would be destroyed in weeks.3 Various concept development studies of Central European battlefield scenarios also predicted that NATO forces would be defeated, in part because of the effectiveness of the Soviet/Warsaw Pact IADS.
In 1974, Chuck Myers, director of Air Warfare Programs in the Office of the Director of Defense Research and Engineering (DDR&E), mentioned to Robert Moore, Deputy Director of DARPA's Tactical Technology Office (TTO), an idea he called the "Harvey concept," named after the invisible rabbit in a popular play and movie. The concept was to create a manned tactical combat aircraft with greatly reduced radar, infrared, acoustic, and visual signatures. A primary objective was to use only passive measures (coatings and shaping) rather than depending on support aircraft carrying jammers. By making it difficult for an enemy to find and attack such a plane, new types of deep air attacks would be possible, replacing the "air armada" tactics that had become the norm in Air Force and Navy aviation.
In 1974, the Department of Defense (DoD) hosted a Defense Science Board (DSB) study that identified the proliferation of advanced networked air defenses as a significant threat to U.S. aircraft. Wargaming a Soviet invasion across the Fulda Gap in Europe led to the conclusion that without some game-changing capabilities, U.S. and NATO forces would find victory extremely difficult. Shortly after the DSB study, Director of Defense Research and Engineering Dr. Malcolm Currie issued a memo stating that the level of innovation coming out of DoD research was inadequate, and he invited organizations to propose radical new ideas.
Robert Moore, deputy director of DARPA's Tactical Technology Office (TTO), nominated the "Harvey" idea, renaming it "High Stealth Aircraft" [the eventual plane built under this program was much larger than had been envisioned by Myers in Project Harvey]. Based on the DSB study and with support from the Office of the Secretary of Defense, DARPA began its journey to develop the technologies for aircraft with a substantially lower RCS than had ever been developed before. Ken Perko, who had worked in the Air Force's System Program Office for reconnaissance drones, became a TTO program manager.
A study began of whether a manned stealth aircraft could be produced. Perko asked five U.S. aircraft companies to examine two questions. First, what were the signature thresholds that an air vehicle would have to achieve to be essentially undetectable at an operationally useful range? And second, what were the capabilities of each company to design and build an aircraft with the necessary signatures? Only Grumman, Northrop, and McDonnell Douglas addressed the issue of signature reduction. Grumman's design wasn't competitive, and so in January 1975, DARPA issued contracts to McDonnell Douglas and Northrop to design a stealthy manned aircraft.
While these studies were underway, Lockheed's Russ Daniels learned of the project during a visit with Myers. Lockheed had not been invited to participate initially because it was not considered active in tactical aircraft [they had not produced a fighter in nearly 20 years]. Furthermore, Lockheed's work for the CIA on low observables during the 1960s for the A-12 / SR-71 Blackbird was a closely held secret. Lockheed aggressively sought to be included, lobbying several highlevel OSD and Air Force officials to be brought into the project. Once Lockheed obtained permission from the CIA to share its radar cross section (RCS) results from that program, Ed Martin, director of Lockheed science and engineering, contacted DARPA and requested permission to participate in the first phase concept development. Lockheed's proposal could not be funded because it arrived after the contract competition. Lockheed requested permission to proceed without compensation (and hence without having to share the rights to its technology). After much deliberation, DARPA Director Heilmeier granted this request, and allowed Lockheed into the study under a $1 contract - perhaps the best dollar that the U.S. government has ever spent.
The objectives of the Experimental Survivable Testbed (XST) - as it became to be known - were to identify precisely the signature levels that would permit an aircraft to avoid radar detection andto define an approach for achieving levels of reduction in RCS andother signatures. The initial study objectives were to identify precisely the signature levels that would permit a tactical aircraft to avoid detection (with emphasis on radar detection) and to define a technical approach for achieving such levels of reduction in RCS and other signatures. Perko's old Air Force organization, the Remotely Piloted Vehicle System Program Office, managed the contracting and provided technical assistance.
McDonnell Douglas was the first to identify what appeared to be appropriate RCS thresholds (although it couldn't design an aircraft to meet those values). Hughes Aircraft confirmed these. DARPA defined these thresholds as program goals. It was clear that Lockheed and Northrop were far ahead of the others in terms of stealth aircraft design. Northrop had a more comprehensive RCS prediction capability than Lockheed, but, at the time, both capabilities were based on heuristics and empirical testing.
However, in 1975, a Lockheed engineer named Denys Overholser came across a 1966 technical paper, "Method of Edge Waves in the Physical Theory of Diffraction," by Pyotr Ufimtsev, the Chief Scientist at the Moscow Institute for Radio Engineering, which had just recently been translated by the Air Force Foreign Technology Division. The paper showed how to predict radar cross sections for certain geometries. Using these formulae, Overholser realized that it would be possible to develop computer software that could predict the RCS of entire aircraft, as long as the aircraft were composed of these distinct geometric shapes.
Working on a tight schedule, ECHO I, Lockheed's first computational model for RCS prediction, was completed in less than 6 weeks. Overholser, responsible for leading the the RCS prediction program Echo 1 development team at Lockheed Skunk Works durng Have Blue, lists the four most critical factorsin RCS reduction as being "shape, shape, shape and materials." Echo 1 was limited to calculations in only two dimensions; this led designers to a faceted design rather than a smooth, seamless one. These facets are arranged so as to present the illuminating source with high angles of incidence, thus causing the primary reflected power to be in a direction of forward scatter, i.e., away from the source. Thus, with the possible exception of minor regions, few rounded external surfaces exist on the vehicle. Over the course of the stealth program, this code was refined, to include incorporation of other findings from Soviet open literature. RCS models validated the code's predictions. Hence, Lockheed possessed not only models that predicted RCS, but also a quantitative tool for designing aircraft with low RCS.
In the summer of 1975, Perko; Robert Moore, who had become Director of TTO; and DARPA Director Heilmeier met to develop a strategy for bringing these technical advances to fruition in a real weapons system. Given the magnitude of the anticipated advances, they decided that a full-scale flight demonstration would be needed to make the results convincing. An 1971 Air Force prototyping study had come to the same conclusion, but not with the same ambitious goal.
Heilmeier insisted that the program could not go forward without Air Force backing. Air Force support was highly uncertain, as the Air Force saw limited value in a stealthy strike aircraft, given the severe operational limitations that would be required to achieve a very low radar cross section. The proposed stealth aircraft would be relatively slow and unmaneuverable, giving it limited air-to-air combat ability, and it would have to fly at night - a far cry from the traditional Air Force strike fighter. There were also competing R&D priorities, most notably the Advanced Combat Fighter program (which eventually became the F-16). Moore believes that DARPA should have been prepared to proceed without Air Force agreement: "I knew the Air Force would have to come on board if we were able to fly by a radar undetected."
As part of his effort to obtain OSD support for Stealth, Moore went to General John Toomey in Director Defense on Research and Engineering (DDR&E) Organization, who had strong credentials in radar technology. DDR&E Currie was briefed on the concept and supported it. Working around the bureaucracy, Moore went back to Myers at DDR&E and suggested that he ask DDR&E Currie to request a briefing on the stealth work. Currie requested the briefing and was very excited about the idea, urging Heilmeier to proceed.
Thanks to Currie's earlier efforts to build relationships with the Service leadership, he was able to discuss the problem directly with General David Jones, the Air Force Chief of Staff, and General Alton Slay, the Air Force R&D Director. Although the Air Force remained skeptical as to a stealth strike fighter's value, Currie and Jones brokered a deal to obtain active Air Force support for the DARPA stealth program-provided that funding for the stealth development would not come out of existing Air Force programs, especially the F-16.
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