designs. The CIA started Project Kempster, which tried to develop ion guns that would be mounted on the A-12. These would ionize the thin air in front of the plane, which would reduce its RCS. (The phrase "Cloaking Device" comes to mind.) Kempster proved unsuccessful, and more conventional systems were developed for the A-12.[851]
In contrast, the Model 147 drone initially used radar-absorbing blankets, a contrail suppression device, and the now-standard black paint. The Lightning Bug's maximum altitude of between 50,000 and 65,000 feet, and a subsonic speed, placed it within reach of both MiGs and SAMs, but their small size made the drones difficult to "squash." The later model Lightning Bugs carried additional equipment to jam missile radar, and a device that caused the drone to take evasive maneuvers when illuminated by a MiG's radar. Despite the accomplishments of these aircraft, the inability of the available technology to meet the political need for an undetectable aircraft eliminated any possibility they would be used over the Soviet Union.
SAMS AND STEALTH
While for the Dark Eagles a reduced RCS was a critical design feature, this did not figure in the design of operational fighters and bombers. They, like the B-17s and Lancaster bombers of World War II, relied on conventional countermeasures packages to overcome air defenses, as well as such techniques as flying through gaps in radar coverage and attacks on air defense sites. With the start of the Vietnam War, the threat again changed. In addition to interceptor aircraft and anti-aircraft guns, U.S. aircraft now faced SAM missiles.
SAMs were initially a difficult challenge for tactical aircraft. What was needed was the means to defeat a weapon that was faster than a conventional jet fighter, and which was guided to the target aircraft by radar. The technology necessary existed, although it took time to develop. This involved improved countermeasures, Wild Weasel aircraft to suppress the SAMs, and, finally, maneuvering to avoid any incoming SAMs.
These proved effective in Vietnam, but following the war there was a split in the assessment of the future threat. Even with the proliferation of new Soviet SAMs, and improvements in radar technology, the opinion in the tactical units was that countermeasures, Wild Weasels, and maneuvering could still overcome the threat posed by any new enemy air defense. They were "Manly Men," who could out fly SAM's, given the proper warning. The need, as they saw it, was more of the same— improvements in the existing technology.
Others had a different opinion. Their threat assessment was not based on U.S.
success against SAMs in Vietnam, but, rather, on the Israeli failure in the 1973 Yom Kippur War. The threat they saw was that countermeasures were susceptible to technological surprise when faced with the multi-layered, interlocking network of SAMs, radars, and guns that the Soviets and Third-World countries were deploying. What was needed against this threat was not the kind of incremental approach that the tactical units wanted, but, rather, a whole new approach. What was needed was what had long been part of the earlier Dark Eagles, a reduced RCS. To be effective, however, a level of reduction was needed which was of a magnitude greater than that achieved with the U-2 and A-12.
This also required a change in outlook. Because of the A-12 and SR-71, the assumption had been that the key to survival was ever-greater speeds and altitudes.
The CIA had considered such possible high-speed replacements for the A-12. In mid-1964 General Dynamics completed a feasibility study called Project Isinglass, which proposed an aircraft able to reach Mach 4 to 5 at 100,000 feet. This was followed in 1965 by a McDonnell Aircraft design called Project Rheinberry. This was to be a rocket-powered aircraft launched from a B-52 that could reach Mach 20 at 200,000 feet. The cost of development would have been equally spectacular, and could not be justified given the on-going reconnaissance satellite programs.[852]
In the face of the threat of improved SAM systems, this faster and higher assumption had to be turned on its head. Such speeds were incompatible with stealth, due to the sonic boom and infrared energy the vehicle would produce. Rather than hypersonic, or even supersonic speeds, stealth required a subsonic vehicle. Its operating mode would be like that of a submarine. Just as a submarine relies on silence while cruising slowly in the depths of the sea, a stealth aircraft would have to use a similar philosophy to conceal itself in the sky.
The question was one of whether the technology existed to create a truly invisible aircraft. In the two decades since Kelly Johnson had begun Project Rainbow, the goal had proven to be as elusive as a rainbow's end. How it was finally accomplished illustrated the changes made in those intervening years, including who made the innovative discoveries, how they did it, and the tools they used.
While Eisenhower's scientific advisers on the U-2 and A-12 included Nobel Prize winners, the stealth breakthrough did not came from academic scientists, but, rather, was made by a pair of "computer nerds": Bill Schroeder, a Lockheed mathematician, and Denys Overholser, a Skunk Works programmer. To create a stealth aircraft, Schroeder turned the aircraft design process inside out. Kelly Johnson, in building the U-2, A-12, and D-21, started by designing an aerodynamic shape that could fly, then tried to reduce its RCS. What Schroeder did was to make the conceptual breakthrough that a complex shape such as an airplane could be simplified to a finite set of flat surfaces. In effect, he designed a shape with the smallest possible RCS, then tried to make it fly. Overholser made this possible with a computer program to calculate an airplane's RCS. This was far more efficient in the initial design stage than pole testing a model, and allowed the shape to be modified in the computer.
The result, the "Hopeless Diamond,"with its wings made of flat plates, would never have occurred to an aerodynamicist. To an aerodynamicist, this was heresy.
Airplanes were streamlined; they had curved surfaces. Wings are not made up of flat plates, they had curved surfaces. But this was not about aerodynamics; it was about electrical engineering.
Yet all Schroeder's and Overholser's work would have meant nothing without another technological advance. Despite its strange shape, the Hopeless Diamond was structurally similar to a conventional aircraft. Had the shape been discovered in the 1960s, the basic airframe could have been built, but it would never have flown. The Hopeless Diamond shape was aerodynamically unstable. The aircraft stability control systems which existed in the 1960s, even the one developed for the A-12, could not have coped with the Hopeless Diamond. It was not until the early and mid-1970s that the multi-axis computer control systems necessary for such an unstable vehicle were developed. It was the computer revolution that made stealth a reality; without computers it would not have been possible to calculate the radar cross section of a given shape, or to make it controllable.
By early 1977 two prototype stealth aircraft were being built under the code name "Have Blue." The program had now become the most closely guarded secret since the Manhattan Project of World War II. Despite the loss of both of the Have Blue aircraft during the test program, the RCS test results were phenomenal. Stealth had arrived, and with it a revolution in Air Power.
TOWARD AN INVISIBLE HORIZON
What then of the future of stealth? Contrary to popular opinion, predicting the future is easy. In the mid-1950s, for example, it was confidently predicted that ballistic missiles would make manned aircraft obsolete. It was also predicted that we would now have flying cars.
The problem is that the political, technical, and social factors which influence the future are so unpredictable as to border on the irrational. Another problem is that we tend to imagine the future as a direct projection of the current moment, rather than looking to the past to see how far we have come and the ongoing trends which have brought us here. To illustrate this point requires a thought experiment.
Imagine for a moment it is the mid-1950s. Forget all that will happen in the next four decades. In the world you know, Eisenhower is President, Elvis is king, both televisions and countermeasures use vacuum tubes, the transistor is still experimental, a computer is a huge mainframe unit which takes up a room,
the B-52 is just entering service, airliners use propellers, the launch of the first satellite is still in the future, a manned flight to the Moon is the definition of the impossible, books are written on a typewriter and calculations are done with a slide rule. A technological prophet announces that:
I predict that in forty years, computers will be sold in stores and will be as commonplace as televisions are in the 1950s. These computers will fit on a desktop, while others are small enough to sit in your lap. All these computers are vastly more powerful than any existing 1950s mainframe computer. Many are bought by parents for their children to do homework. Publishers require books to be prepared on these computers; the typewriter is obsolete. These computers are linked together by a communications system called the 'Internet' which allows you to send messages and do research at universities, libraries, and other institutions anywhere in the world.
If this had really been said to a mid-1950s audience of people working in the electronics field, they would have thought the speaker was out of his mind. Yet the technical, political, and social trends that would create the PC were already developing.
Having given this cautionary tale, it has to be said that the future of stealth is a reflection of its past. Have Blue was built with the sole purpose of finding out if stealth would work on a real airplane. Stealth was the only design consideration.
In the design of the F-117 A, the basic Have Blue shape was retained. A few changes were made to correct defects found in the Have Blue, and to accommodate operational equipment. Despite this, in the F-l 17A, stealth superseded other design considerations such as range or payload. It was a short-range, light attack aircraft. With the B-2, the situation is more complex. As with the other early aircraft, stealth came first. However, its stealth capabilities had to accommodate the long range and large payload of a strategic bomber.
Each was a highly specialized, single-mission aircraft. They had also been built under the tight secrecy which enveloped stealth from the late 1970s to the end of the 1980s. The effect of this secrecy was to make stealth a highly specialized concept, one that seemed to apply only to a narrow set of missions, rather than to aerospace technology as a whole. In the decade which followed, and the first combat use of stealth, this changed.
At the end of the 1990s, as this is written, stealth is no longer the first and only design consideration. Rather, it must be balanced with the more traditional requirements of speed, range, payload, weight, maneuverability, and cost. More important, stealth was no longer hidden behind a wall of secrecy. The concept was now integrated into the mainstream of aircraft design, rather than being a separate "Black" aspect. The F-l 17A, B-2 and the F-22 are all openly on display at the annual Edwards AFB air show, as are the stealth UAVs, the GNAT 750, Darkstar, and Global Hawk.
An example of the changing view of stealth is the F-22 fighter. In today's air combat, the preferred method is a first-shot kill with long-range air-to-air missiles.
Historically, most pilots lost in air combat were shot down by planes they never saw. The F-22's stealth features are an extension of this, giving it the ability to destroy an enemy plane, without warning, with a missile fired from miles away. If the ability to make a long-range kill was the only consideration, then a pure stealth design would serve.
In a close-in dogfight, however, a pure stealth-centered design would be at a disadvantage, as it could be slower, underpowered, and much less maneuverable than its conventional opponents. In the case of the F-22, the designers were unwilling to totally compromise its performance in the name of stealth. Several features of the F-22 increase its radar cross section, but that was the price for better maneuverability.
Although the basic shape of the aircraft may be the primary driver of stealth, the design considerations now include existing airframes. An aircraft's RCS can come from relatively small features, such as a gap in an access door. It therefore makes sense that a "clean-up" program, involving discovery and fixing of such reflection sources, as well as addition of Radar Absorbing Material to areas such as intakes, could result in a militarily significant reduction in a plane's RCS. The prime example is the B-IB. This was a redesign of the original B-1A to incorporate a reduced RCS. Subsequently the "Have Glass" program was undertaken in the late 1990s to add stealth features to F-16 fighters. Although this cannot give an F-16 the tiny RCS of a true stealth aircraft such as an F-l 17A or a B-2, Have Glass has made F-16s much more difficult to spot in air-to-air engagements.
The effect of both the more balanced design philosophy and the addition of stealth to existing airframes is to blur the boundaries. In the 1970s and 1980s, there were stealth airplanes, and there were conventional airplanes. The boundaries between them were fixed and rigid ones of secrecy and technology. Today the lines are not hard and fast. Is the F-22 a stealth aircraft? Yes, without question, but not in the same ways as the F-l 17A or B-2. Are the B-lBs and Have Glass F-16s stealth aircraft? No, but they are stealthier now than when the prototypes made their first flights.
A different factor influencing the future of both stealth and military aviation is the increasing importance of cruise missiles and UAVs. Like stealth, the cruise missile concept dates to World War I. The first was the "Kettering Bug," a small pilotless biplane built by the U.S. Air Service for attacks on Germany. It entered production in the final months of the war, but did not see action before the Armistice.
World War II saw wide-scale use of V-l missiles by Nazi Germany. During the 1950s and 1960s, the air force operated Mace and Matador cruise missiles, while the navy Regulus cruise missiles were based aboard ships and submarines. The problem with all these weapons was a lack of accuracy. They could only strike area targets, such as cities or airfields with nuclear weapons.
In the late 1970s, at the same time as the stealth breakthrough was made, the development of scene-matching guidance systems changed this. The missile could now find its way to a target by matching specific landmarks, in order to correct its flight-path. A navy Tomahawk or air force Air Launched Cruise Missile (ALCM) could navigate hundreds of miles, taking an evasive course to avoid air defenses, and then hit a specific building in the heart of a city.
They were seen as strategic systems, designed to attack targets inside the USSR with nuclear weapons. The threat facing them was the massive Soviet air defense system. The Tomahawk and ALCM could both be spotted on radar. Even their small size and low-altitude flight could not guarantee their survival in the face of hundreds of S AMs. The need was to make the cruise missiles harder to detect, enabling them to strike even the most heavily defended Soviet targets. The technology to do this had already been developed for the Have Blue.
The initial stealth cruise missile tested was Lockheed's Senior Prom. Although this program is still Black, it is reported that the Senior Prom missile was a smaller version of the Have Blue. It was designed for carriage by B-52s. It is further understood that the "Hangar 18" building on the Groom Lake flight line was actually built to support this program. With the B-52 inside the hangar, the test missiles could be loaded aboard without being seen. The Senior Prom program was subsequently canceled, however.[853] Its replacement was the Advanced Cruise Missile (ACM). The ACM resembles a larger Tomahawk, but with a faceted nose, a flush air intake, and forward swept wings and small tail surfaces to reduce its RCS.[854]
Subsequently, another stealth cruise missile entered development, Northrop's Tri-Service Stand-Off Attack Missile (TSSAM). Just as Senior Prom used the Have Blue shape, TSSAM had the same shape as the Tacit Blue, only turned upside down.
While the Tacit Blue was called "The Whale," the TSSAM became know as the
"Killer Whale." According to one story, persons joining the program were given an initial briefing using a "model" of the TSSAM to illustrate its odd shape. This model was a Twinkie with cardboard wings and tailfins. (This same Twinkie was used throughout the several years the TSSAM program continued, saying something presumably about preservatives.) The TSSAM carried a conventional w
arhead, had a highly advanced terminal guidance system, and was designed for use by a number of aircraft, including the B-52, B-2, F-16, and FA-18. However, like the Senor Prom, TSSAM was canceled.[855]
While the various attempts to build stealth cruise missiles have met with mixed results, with Senior Prom and TSSAM never entering production, and the number of ACMs built were limited, the role of the cruise missile has grown. The scene matching guidance system was originally designed to allow a much more accurate strike with a nuclear weapon, increasing the probability of destruction. This guidance system also allowed tactical strikes using conventionally-armed cruise missiles. This increase in accuracy was essential for the missile to have any utility, due to the small warhead size.
Tomahawks and ALCMs were used in Desert Storm, and they have been the weapon of choice for reprisal raids, including Desert Fox. They have the advantage of accuracy, to minimize civilian casualties, while being unmanned, their use does not pose the risk of U.S. pilots being captured or killed. At the same time, stealthy UAVs were under development for reconnaissance missions. Unlike the one-way missions of the cruise missiles, the UAVs would conduct their overflights, then return to a base for a landing.
In the past several years there has been considerable debate about combining the two roles to create an Unmanned Combat Aerial Vehicle (UCAV). As the name implies, this is a UAV with a role beyond that of passive reconnaissance, but, rather, active air-to-ground or air-to-air missions. The concept of a UCAV has specific advantages and possible shortcomings. A UCAV would not face the limitations of a human pilot. It could, for example, be able to make 20-G maneuvers, allowing it to fly rings around a manned aircraft. It would also not have to accommodate the volume of a cockpit, giving it the freedom of design to use unique stealth shapes, as well as reducing size, weight, and cost. At the same time, there is the question of whether the cost savings of eliminating the pilot would not be exceeded by the expense of the systems needed to replace the pilot. The missions envisioned for a UCAV are much more complex than flying from A to B and back again.[856]
Dark Eagles: A History of the Top Secret U.S. Aircraft Page 41