In the future (around 2010 to 2020), it should become possible to do away with the radar rotodome and rely on conformal phased-array and synthetic aperture antennas to integrate the AWACS air surveillance mission and the Joint-Stars ground-surveillance mission onto a single platform. This could well be a very high-flying stealthy aircraft, with most of the crew replaced by advanced computers. AWACS, with a top speed of only Mach .78 and a radar cross section somewhat greater than the broad side of an average office building, has been fortunate in its long operational career, since it has never faced an enemy with long-range, high-speed anti-radiation missiles. Right now, though, with the E-3 in the prime of its service life, such a solution is several decades away from fruition, and the Sentry is still the undisputed king on the aerial chessboard.
Ordnance: How Bombs Got “Smart”
IF you read analyses of military aviation, especially in the mass media, you might get the impression that air forces are concerned with aircraft, not with weapons. The guy who flies a plane into the wild blue yonder is a steely-eyed, heroic officer and gentleman. The guy who tinkers with missile guidance systems at a workbench is an enlisted nerd. Aircraft are more glamorous than ordnance. But without ordnance to deliver on targets, the only thing airplanes can do is watch. And while we have seen that reconnaissance is a valued and important mission for aircraft, it is the delivery of ordnance on enemy targets that makes airpower a credible combat force.
The story of today’s ordnance is the story of how bombs and bullets got “smart.” Since the end of World War II, most of the developmental money for new conventional (i.e., not nuclear, chemical, or biological) weapons has gone into guided systems that have held the promise of “one round, one hit.” Some systems, like the Sidewinder air-to-air missile and the Paveway laser-guided bombs, have almost fulfilled that promise. Others have not done so well. Nevertheless, after the 1991 Persian Gulf War, when the 10% of the weapons dropped that were smart did something like 90% of the damage to critical strategic targets, you can count on all types of weapons getting smarter. While the use of the unguided rocket or “dumb” bomb may not yet be over, their days are clearly numbered.
Meanwhile, the variety of weapons that a modern combat aircraft can carry simply boggles the mind. Recently, another defense writer contacted me to ask about Air Force munitions programs. So confusing was the variety of the programs we discussed, that we decided this book would try to explain as many of the different things that U.S. Air Force aircraft can shoot at, launch at, or drop on our enemies as possible.
AIR-TO-AIR MISSILES
Though rapid-firing cannons are a vital part of the weapons mix that make fighters both dangerous and effective, bullets aren’t smart. Once they leave the muzzle of a gun, they can only follow a ballistic path determined by the laws of physics, no matter what the target does. A guided missile, on the other hand, can alter its flight path after it is launched, which greatly increases the probability of a hit. If you look at the world record books since the end of the Korean War, the vast majority of air-to-air kills have been achieved by guided air-to-air missiles (AAMs). Maybe not as righteous as a gun kill, but as any fighter jock will tell you, “A kill’s a kill!”
AIM-9 Sidewinder Missile
The first experiments with guided AAMs were done in Nazi Germany during World War II. In an attempt to keep their fighters out of range of the defensive machine guns of the massed air fleets of bombers and fighters attacking their homeland, the Germans developed a series of air-to-air missiles. Luckily for the Allied air forces, the Ruhrstahl X-4 came too late to make it into service. This compact, wire-guided missile was designed to be “flown” by the pilot of the firing aircraft using a small joystick. It was a halting step on the way to the AAMs of today, but it was a first step nevertheless.
Following the war, a number of nations began to develop SAM and AAM designs, hoping to knock down the fleets of nuclear bombers that were expected to dominate the next major conflict. Most were designed to use the new technology of radar that had matured during World War II. The problem with radar-guided missiles was that they were relatively heavy, vastly complex, and required the firing aircraft/battery to track the target with its own radar. In order to allow the missile to get within lethal range of the target aircraft, you had to either “illuminate” the target with a radar beam (called a fire-control radar), or track the outgoing missile in flight and radio flight commands (called command guidance or “beam riding”). Early fighters equipped with these bulky systems had to be large, placing aircraft designers of the day under great pressure to build aircraft with performance equal to their smaller, gun-armed competitors. It seemed for a time that designers of missile-armed fighters would just have to grit their teeth and wait for technical advances in power plants, electronics, airframes, and computers to make the promise of air-to-air missiles a reality.
Then suddenly, out of a brilliant, unorthodox scientist’s garage laboratory in the high desert of California, came an elegantly simple solution to the problem of missile guidance. The scientist was Dr. William B. McLean, at the Naval Ordnance Test Station (NOTS) at Inyokern, California (today the Michelson Laboratory of the U.S. Naval Weapons Center at China Lake, California). In the late 1940s, in his home garage workshop and on his own time, he built a simple device that could track an aircraft by the heat emissions from its power plant. This meant that a missile seeker could be developed to track a target without any sort of radar guidance from the firing battery or aircraft.
The key was a small electronic detector, called a photovoltaic cell, which was capable of detecting heat—or infrared radiation emissions in the short-wavelength region of the electromagnetic spectrum. The early infrared seekers used detectors based on lead sulfide, a material whose electronic characteristics are altered when it becomes saturated by infrared radiation. These seekers were not looking for the heat given off by the exhaust gases of a jet engine (as mistakenly reported for decades). On the contrary, what the tracking elements of the first-generation heat-seeking missiles were looking for was hot metal, or more specifically, the infrared radiation given off by the hot metal of jet or piston engine exhaust ports. The major technical advantage of infrared seekers is that they can be more compact, lighter, and cheaper than radar missile seekers. This allowed Dr. McLean and the engineers at NOTS to design a missile, initially known as Local Project (LP) 612, that only weighed about 155 lb./70.45 kg., in a tubular body only 5 in./12.7 cm. in diameter. To save money (which he did not have anyway), McLean used airframes from unguided 5 in./12.7 cm. High Velocity Artillery Rockets (HVARs), into which he packed the motors, warheads, and electronics. At the rear of each of the fixed tail fins is a small device that looks like a metal pinwheel. This is called a rolleron, and is used to stabilize the weapon while it is in flight. It’s one of the tricks thought up by Dr. McLean and his team to help keep the Sidewinder on a stable course, and uses the missile’s own slipstream through the air to generate gyroscopic motion to dampen any oscillations induced by the guidance system. The rolleron was on the first missile, and is still there today. LP612 also had the advantage of being a “fire-and-forget” weapon—the pilot does not guide the weapon after firing. Tactically, this means the firing aircraft is free to maneuver or evade once the weapon is launched.
When the first test launches of what would become the Aerial Intercept Missile Nine (AIM-9) were conducted in 1953, the missile’s snakelike flight path towards the test targets provided the name it would carry for the next half century of service, the Sidewinder. From its first tests against target drones, it was a favorite of the pilots at China Lake, because of its high reliability and deadly accuracy. In addition, it could be rapidly and cheaply retrofitted on older aircraft, so a whole generation of existing fighters could enjoy the benefits of AAMs, without the weight penalty of a massive air-intercept (AI) radar for guidance. Sidewinder was quickly adopted by the Navy and U.S. Marine Corps as the standard short-range AAM of the day.
The
effectiveness of the little AIM-9 missile was demonstrated in 1958, when the Eisenhower Administration supplied the Republic of China (ROC)/ Taiwan with Sidewinder AAMs and launchers to equip its F-86 Sabrejets. The ROC Air Force was fighting daily air battles with MiG-17s of the People’s Republic of China, over two small islands in the Formosa Straits, Quemoy and Matsu. While the AIM-9s were responsible for shooting down only a small percentage of the MiGs destroyed in the battles (most were still shot down by the .50-caliber machine guns of the ROC F-86s), their impact was immense, and the word quickly spread around the fighter world about the deadly little AAM named after a rattlesnake.
Loral Aeronutronic AIM-9L/M Sidewinder air-to-air missiles loaded onto their launch rails. The seeker is contained in the rounded nose of the missile, and the fins are designed to provide good maneuvering control and minimize drag. Loral Aeronutronic
Over the next ten years or so, the early models of the AIM-9 (usually the AIM-9B variant) fought in theaters all over the world. In the skies over the Indian subcontinent (the 1965 India-Pakistan War), North Vietnam (1965 to 1973), and the Middle East (the June 1967 Six Day War), the Sidewinder was the most effective AAM in service. It shot down more enemy aircraft than any other AAM of the period, and put the longer-range, heavier, and more costly radar homing AAMs like the AIM-7 Sparrow to shame. So effective was the early AIM-9, that when several fell into Communist hands in the late 1950s and early 1960s, the Soviet Union produced an exact copy, the R-13/AA-2 Atoll, for use on its own fighter aircraft.
For all its successes, the Sidewinder had some significant limitations and shortcomings. Many of these became evident in Vietnam. For instance, the early-model AIM-9B Sidewinder was a relatively short-range (about 2.6 nm./ 4.75 km.) missile, and its seeker could only “acquire” a target and “lock” onto it if the firing aircraft was behind the target (within a 90° arc centered on the target’s line of flight). It also was susceptible to being decoyed by flares, infrared jammers, and even the sun. (If you fired at a target within about 20° of the sun, the missile would ignore the target and lock onto the sun.) The biggest problem, though, was the pilots’ lack of in-depth understanding of the missile’s performance “envelope” (aviator jargon for things like, “How fast can it turn, climb, or dive at different altitudes and velocities?”). In addition, the early electronics technology of the day (vacuum tubes) simply lacked the reliability to survive the shock of aircraft carrier landings and the tropical heat and humidity of Southeast Asia. As a result, several efforts were initiated by the U.S. military to improve the Sidewinder and other air-to-air missiles.
In 1968, a U.S. Navy study, the “Ault Report,” examined the poor performance of U.S. fighter, radar, and missile systems in Southeast Asia. One of the first results of this study was better training of U.S. pilots, to teach them how to maneuver their aircraft into the “heart” of the missile’s lethal envelope, thus maximizing the chances of a kill. The development of Dissimilar Air Combat Training courses (DACT, practice dogfights against fighters with different flying characteristics from your own aircraft, using electronic scoring systems that simulate the performance of real missiles) in the USAF and USN, particularly the Navy’s famous Top Gun school, did much to improve the performance of U.S. pilots in combat. As for the Sidewinder, there already was a series of product improvement programs in the works to remake the little AAM.
The first of these programs produced versions of the missile for the USAF (the AIM-9E) and the USN/USMC (the AIM-9D). Both versions, fielded in the mid-1960s, featured improved seekers that were cooled (thermoelectrically in the case of the AIM-9E, gas cooled for the AIM-9D). The -E models were converted from earlier AIM-9 B-model Sidewinders, and provided better low-altitude performance than the -B model. In addition, the -D had a more powerful rocket motor for greater range (up to 11 nm./20.11 km.) and an improved warhead. Later, the USAF further modified the -E model Sidewinder to the AIM-9J configuration, with improved aerodynamic surfaces and control for greater maneuverability and range (about 9nm./ 16.46 km.). This second generation gradually expanded the launch envelope, range, and performance of the various Sidewinder versions, so that a pilot could launch from anywhere aft of an enemy aircraft’s wings (the rear 180° hemisphere), from a fairly high off-angle (from the target aircraft’s centerline), and from maximum and minimum ranges. These versions of the Sidewinder helped the USN and USAF fighter forces decimate the North Vietnamese MiGs in 1972, and they were the backbone of the Free World’s short-range AAM inventory for the rest of the 1970s. A third generation, the AIM-9L, saw service in the 1980s.
The final, and currently deployed, third-generation version of the Sidewinder is the AIM-9M. Like the earlier AIM-9L variant, the “Mike” as it is called, is used by the fighter forces of the USN, USMC, and USAF on virtually every combat aircraft with an air-to-air capability. The Air Force normally deploys the “Mike” on fighters such as the F-15 Eagle and F-16 Fighting Falcon. Its dominant feature is the tubular airframe, 5 in./ 12.7 cm. in diameter, to which the forward (guidance) and aft cruciform fins are attached. At the front of the missile is a tapered nose section with a hemispherical seeker window at the tip. The 5 in./12.7 cm. dimension has been one of the little missile’s great virtues, as well as its biggest vice. On the plus side, it has meant that the basic missile and interface has remained relatively unchanged for over forty years. This has allowed aircraft designers to find a variety of inventive ways of adding Sidewinder to the weapons suite of fighters. In the case of the F-16 and F-18, the primary AIM-9 launchers were placed on the wingtips. The down side is that packing improvements into a 5 in./12.7 cm. tube can be difficult. For example, Israeli and Soviet/Russian AAM designers long ago abandoned the small diameter airframe, so they could pack larger motors and warheads inside.
It’s what is inside that airframe tube that counts, and the Sidewinder does as much with the limited space available as any missile in the world. The current -M version is some 113 in./287 cm. long, with a forward canard (BSU-32/B) wingspan of 15 in./38.1 cm., and a rear stabilizer (Mk 1) wingspan of 24.8 in./63 cm. Weighing in at 194 lb./88.2 kg., it was first produced in fiscal year 1981. At the front of the missile is the WGU-4A/B Guidance Control Section (GCS). Inside the GCS is the seeker, which is the ultimate in single-element infrared sensitivity. Composed of an indium-antimonide (InSb) detector element, cooled by an open-cycle Joule-Thompson cryostat, it is mounted on a gimbaled “head” behind a magnesium-fluoride (MgF2, a fragile material, but selectively transparent to infrared radiation in the seeker’s particular wavelengths) seeker dome/window. The seeker element feeds into a signal processor, which generates the commands for the missile’s four guidance fins, which are mounted on the side of the seeker-guidance section. The real beauty of the current system is that it scans in two different wavelengths or “colors.” This means that it is looking at both short- and middle-wavelength (infrared) light as well as the long-wavelength (ultraviolet) spectrum. It is a deadly combination.
Just forward of the rocket motor is the WDU-17 Annular Blast Fragmentation (ABF) warhead section. Previously, there had been a great deal of criticism over the relatively puny size of the Sidewinder’s warhead. Thus, when development of the third-generation AIM-9 began, the designers decided to enhance the destructive power of the 25 lb./11.36 kg. warhead. The previous versions had provided a mixed bag of weapons effects. The solution was a new kind of proximity fuse that would detect when a target aircraft got into lethal range and detonate in such a way that the force (and fragments) of the warhead would impact directly into the target aircraft. Composed of a ring of four pairs of laser-emitting diodes (somewhat like the IR emitter/detectors on your TV/VCR remote controls) and laser detectors, the DSU-15/B Active Optical Target Detector uses the laser detector ring as a way of determining when a target aircraft is within range. If the missile should miss the target (a rare occasion due to the accuracy of the guidance system), the warhead is designed to detonate and spew its fragmentation pattern at the target
aircraft. This is a particularly effective kill mechanism, since the second- and third-generation Soviet fighters that the AIM-9L/M was designed to attack had no self-sealing fuel tanks or fuel bladders. In fact, Soviet designs like the MiG-23/27 Flogger and the MiG-25 Foxbat usually had only a thin skin of aircraft-grade aluminum or stainless steel between their fuel supply and the open sky. This meant that if so much as a single hot fragment penetrated a fuel tank, the Soviet aircraft was probably going to be headed down in a ball of flames.
At the rear part of the airframe is the rocket motor. Over the years, the USAF and USN have differed over what they want from the propulsion system of the Sidewinder. In fact, this has been the basic philosophical difference between USAF and USN since the first of the improved Sidewinders began to roll off the lines in the 1960s. The Mk 36 rocket motor in the AIM- 9M favors the USAF point of view. With the Mk 36, an M-model Sidewinder can theoretically fly out to a range of up to 11 nm./20.1 km. with a maximum flight time of one minute.
What does all of this mean when it comes to real-world combat? Well, consider the performance of AIM-9L/M-series AAMs in U.S. service over a ten-year period from 1981 to 1991. In that time, some twenty-two missiles were fired, with sixteen guiding to hits, resulting in some thirteen “kills.” During the same period, foreign clients have scored an even better record, with two kills going to Saudi pilots, twenty-five to Royal Navy Sea Harrier pilots in the Falklands, sixteen to Pakistani aircrew, and probably several dozen more to the Israelis. This run of success may never be duplicated by any future model of AAM.