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Stealth has become the magic word in contemporary weapon systems. Contemporary work on stealth has its roots in long-standing efforts to reduce the visibility of military aircraft through camouflage paint schemes. However, as electronic sensors have replaced the eyes of pilots as the primary means of tracking other aircraft, more intricate means of defense were needed.

 

Stealth Technology

Often thought of simply as the use of special materials to render aircraft invisible to radar, stealth is actually a complex design philosophy to reduce the ability of an opponent's sensors to detect, track and attack an aircraft (or other platforms such as warships). Since a variety of sensors would be used in this process, design of a stealth vehicle requires careful trade-offs among different techniques. The great secrecy surrounding stealth programs is designed not simply to protect a particular stealth technology, as it is to protect the choice and mix of techniques that have been used in a specific system.

A variety of technologies are may be combined in order to make itself "invisible" to radar. These technologies include a smooth surface, "flying wing" design, radar absorbent materials (RAM), engines hidden in the body of the airplane, and electronic countermeasures (ECM). Each of these features contribute to the attempt fool enemy air defense systems. The planes low radar cross section (RCS) reduces the range at which ground-based and air-based radars can detect the aircraft. The RAM absorbs most of a radar's signal, and the aircraft's wing-shaped and rounded design redirects much of the remaining power away from the radar source. Engines are buried in the fuselage with air intake and exhaust ducts placed on the top of the aircraft in order to reduce the heat trail, and hide the jet engine's compressor blades from radar detection. ECM is a last resort attempt to confuse the radar operator through jamming and ghost imaging.

The benefits of stealth technology is inherently obvious. Especially since, 70 percent of Soviet-style air defense systems use radar detection and tracking. However, as the next section on limitations will illustrate, the other elements of air defense detection and tracking; infrared (IR), electro-optical (EO) and visual, also need to be circumvented if an aircraft is to be truly "stealthy."

Limitations

There is no one optimum stealth design, but rather each mission requirement generates an appropriate mix of techniques. Implementation of stealth is not without penalties. Some of the materials used require special and costly maintenance. The maneuverability of an aircraft can be compromised by the introduction of stealth design features. As was the case with the F-117A, each B-2 bomber will have its own covered maintenance facility, since the B-2's low observable features require frequent performance of structural and maintenance activities.

Stealth requires not only design compromises, it also imposes operational compromises. Sensors to locate targets pose a particular problem for stealth aircraft. The large radars used by conventional aircraft would obviously compromise the position of a stealth aircraft. Air-to-air combat would rely on passive detection of transmissions by hostile aircraft, as well as infrared tracking. However, these techniques are of marginal effectiveness against other stealth aircraft, explaining the limited application of stealth to the Advanced Tactical Fighter.

Aircraft for attacking targets on the ground face a similar problem. FLIR can be used for precise aiming at targets whose general location is known, but they are poorly suited for searching for targets over a wide area. A radar on the aircraft to scan for potential targets would compromise its position. In order to locate targets, stealth aircraft may rely on an airborne laser radar, although such a sensor may prove of limited utility in poor weather. A more promising approach would be to use data from reconnaissance satellites, either transmitted directly from the satellite or relayed through communications satellites from processing centers in the United States.

There are limits to the utility of stealth techniques. Since the radar cross-section of an aircraft depends on the angle from which it is viewed, an aircraft will typically have a much smaller RCS when viewed from the front or rear than when viewed from the side or from above. In general stealth aircraft are designed to minimize their frontal RCS. But it is not possible to contour the surface of an aircraft to reduce the RCS equally in all directions, and reductions in the frontal RCS may lead to a larger RCS from above. Thus while a stealth aircraft may be difficult to track when it is flying toward a ground-based radar or another aircraft at the same altitude, a high-altitude airborne radar or a space-based radar may have an easier time tracking it.

Another limitation of stealth aircraft is their vulnerability to detection by bi-static radars. The contouring of a stealth aircraft is designed to avoid reflecting a radar signal directly back in the direction of the radar transmitter. But the transmitter and receiver of a bi-static radar are in separate locations — indeed, a single transmitter may be used by radar receivers scattered over a wide area. This greatly increases the odds that at least one of these receivers will pickup a reflected signal. The prospects for detection of stealth aircraft by bi-static radar are further improved if the radar transmitter is space-based, and thus viewing the aircraft from above, the direction of its largest radar cross section.

Several analysts claim stealth aircraft such as the ATF will be vulnerable to detection by infrared search and track systems (IRST). The natural heating of an aircraft's surface makes it visible to this type of system. The faster and aircraft flies, the warmer it gets, and thus, the easier to detect through infrared means. One expert asserts "if an aircraft deviates from its surroundings by only one degree centigrade, you will be able to detect it at militarily useful ranges." In fact, both the Russian MiG-29 and Su-27 carry IRST devices, which indicates that the Russians have long targeted this as a potential stealth weakness.

Stealth aircraft are even more vulnerable to multiple sensors used in tandem. By using an IRST to track the target and a Ladar (laser radar), or a narrow beam, high-power radar to paint the target superior data is provided.

The most basic potential limitation of stealth, is its vulnerability to visual detection. Since the ATF is 25-30 percent larger than the F-15 and 40 percent larger than the F-18, for example, it will be much easier to detect visually from ranges on the order of 10 miles. When one considers that stealth characteristics will drastically reduce the effectiveness of several types of guided air-to-air missiles, fighter engagements will probably move back to the visual range arena. In this context, the cumbersome F-22 would be at a distinct disadvantage.

Another potential "limitation" of stealth technology has little to do with its capabilities. Rather, some question the effect the pursuit of such hi tech aircraft will have on the US aerospace industry as a whole. These aircraft would not be available for foreign export until well into the next century. During that time, competitors such as the Gripen, Rafale and EFA will be peddled aggressively by European exporters. One analyst estimated that US foreign sales saved the Pentagon "about $2.8 billion through surcharges to recover part of their development costs and perhaps another $4 billion through the learning curve effect of higher production runs." Thus, America's stealth success could actually backfire, on its larger aerospace industry by causing it to forfeit sales to a new generation of top-of-the-line, although less formidable, European fighter aircraft.

Programs

F-117A — Development of stealth aircraft began in the early 1970s, with the Experimental Stealth Tactical (XST), code-named "Have Blue." This project resulted in the Lockheed F-117A, with 20 of these aircraft ordered from Lockheed by the Air Force in 1981, and a total of 59 aircraft were produced. The F-117A first flew in 1983 and entered service at Nellis Air Force Base in Nevada in 1983. The original F-117A program envisioned over 100 aircraft, but soaring costs (each aircraft costs over $100 million), performance problems (several of the aircraft have crashed in training flights), limited payload (the aircraft can carry only two 900 Kg laser guided bombs internally), and the lack of a clearly defined mission all contributed to the curtailment of the program.

 


F-117A Nighthawk
Although the F-117A exhibits breakthrough low-observable characteristics, it was not built from scratch. Designers modified F-16 flight controls and F-18 engines. Lockheed officials say that using and improving on existing technology, rather than re-inventing the wheel, allowed them to make the F-117 at half the cost and in half the time of equivalent aircraft.

The F-177A first saw combat in the American intervention in Panama in December 1989, when two of the aircraft were used to attack an airfield, but this mission was marred by pilot error which caused one of the aircraft's bombs to land far from the intended target. The F-117A performed well in Desert Storm, which may be the primary reason that the aircraft's production line, once slated for closure, has recently been revived.


ATB - B-2 — The Stealth Bomber project was first announced by the Carter Administration in the heat of the 1980 Presidential campaign, in response to Republican criticism of the decision to cancel the B-1A bomber. Since its unveiling in November 1988, the B-2 has been the focus of mounting criticism of the inexorably growing cost of the project, the regularity with which its schedule has been delayed, and doubts about mission requirements.

B-2 Bomber

The B-2 will be the most expensive aircraft ever procured, and by some estimates each bomber will literally cost its weight in gold. The General Accounting Office estimated that the cost of the 132 aircraft program in then-year dollars would total $68.8 billion, based on a $36.6 billion cost in constant FY81 dollars. By mid-1988 the cost estimate for 132 aircraft had grown to $43 billion (in constant 1981 dollars). In the Spring of 1990 Secretary Cheney's decided to reduce the buy from 132 aircraft to 75, with a budget in then-year dollars of $61 billion. Based on the costs required to bring the B-1B up to its intended performance (an additional $8 billion over the original $20 billion price) the eventual cost of the more technologically challenging B-2 could exceed $1 billion each.

Two missions for the B-2 emerged from the veil of secrecy. Some advocates argued that the B-2 is needed to offset improvements in Soviet air defenses, and that the exertions the Soviets would make to augment their air defenses to counter the B-2 will inhibit their efforts in strategic offensive and conventional forces. Others argue that the B-2 is needed in order to attack Soviet mobile missiles such as the SS-24 and SS-25. But given the high cost of the project and competing budget priorities, neither of these rationales has proved particularly compelling to the Congress. Secretary Cheney's decision to reduce scope of the program proved a watershed. House and Senate conferees agreed to spend only $1.8 billion in 1992 on the B-2. Nothing more can be spent on the aircraft without the approval of the full House, which has been consistently opposed to the program. While supporters of the Stealth Bomber say the aircraft's future is unclear, the $1.8 billion figure was a distinct setback. Critics claim that the agreement literally kills the program.

Non - US Programs

Great Britain has expressed interest in developing its own low-observable aircraft. The US Air Force has clearly indicated its interest in selling the F-117 to the United States' closest ally. It is more likely, however, that London will acquire certain stealth technologies that it can use in its down programs, than buy the finished product. Britain plans to begin work on a stealth aircraft in the next five years, and have a functioning technology demonstrator by the end of the 1990s. The RAF says it will develop an upgraded Tornado that will be akin to the US Navy's AX strike aircraft. The RAF has been conducting radar absorbent material (RAM) experiments on Tornados since at least November 1990.

One phenomenon that worries US defense officials is the technology lag between the time the United States fields a particular system, and the time its adversaries do. For example, while the United States' top line fighter was introduced in 1975, the Soviet's top fighter, the MiG-29's initial operating capability (IOC) was 11 years later in 1986. Thus, "their" best aircraft is based on technology 11 years more modern than "ours." Secretary of Defense Cheney (1989 - 1992) voiced concern that this may apply to the fielding of stealth technology, and that 11 years after the F-22s IOC, for example, we will be facing a brand new Russian stealth fighter.

Article credit: VI - STEALTH AIRCRAFT: EAGLES AMONG SPARROWS?, Federation of American Scientists