Mobile Missile Defeats F-16
The loss of a U.S. Air Force F-16 fighter over Bosnia brings up an interesting issue in missile countermeasures. Apparently the airplane was brought down by a radar-guided surface-to-air (SA)-6, a mobile missile that is difficult to defeat. The F-16 was one of two aircraft on patrol at medium altitude. A two- missile salvo was fired, one of which exploded between the two aircraft, and one of which hit the Captain Scott O'Grady’s aircraft; O’Grady ejected as the cockpit section broke up.
The United States has invested heavily in missile countermeasures, and, SA-6s have been in service for many years. When the F-16 was lost, much public attention focused on whether the airplane had been carrying an appropriate jammer—which begs another question.
A jammer must be triggered by some type of warning. Typically a distinction is drawn between short-range (man- portable) infrared guided missiles, and longer-range radar-guided Weapons. A passive radar warning receiver on board the airplane can, in theory, pick up the guidance signals used by radar missiles, triggering the appropriate jammer.
The man-portable weapons are a more difficult proposition because they operate passively and are not dependent upon radar trackers of any type. Missile-approach warning systems have been developed specifically to detect these missiles so as to trigger countermeasures. They need operate only in clear air, since the missile must see the target at the moment of firing, so that it can lock on; hence it cannot be fired at an airplane flying above clouds. At present the most common choices are infrared and ultraviolet detectors that pick up the missile’s exhaust plume.
First-generation warning systems did not indicate the direction from which the missile was approaching since they were intended only to trigger flare launching. Recent infrared-guided missiles such as the U.S. Army’s Stinger can measure target motion, and thus can distinguish a moving target from decoys fired backwards. The appropriate counters are powered decoys, which, fired forward, look to the missile like a moving airplane, and infrared jammers. Effective countermeasures require some estimate of the direction from which the missile is approaching, which dictates a new generation of warning systems that are currently under development.
The SA-6 is a semiactive missile whose operating principles are similar to those of U.S. Navy’s Standard Missile (SM-1) and the U.S. Army’s Hawk. At launch, such missiles normally lock on to radar energy reflected from the target. A radar warning receiver picks up the illumination, and the target’s pilot is aware that he is in danger from the moment the illuminator has been switched on, normally even before the missile is launched. The more agile the target, the better the chance that it can use that warning time to escape altogether. Some semiactive missiles have been modified with autopilots, so that they can be launched toward a target well before the operators switch on the illuminator. In the Aegis system, for example, this capability (an autopilot controlled by an uplink from the launch ship) makes it possible for several missiles to share a single illuminator.
At a somewhat simpler level, however, the autopilot makes missile ambushes possible. Because the illuminator is switched on so late in the missile’s flight, the pilot may have insufficient time to evade or to jam. This idea apparently was used first by the Israelis, who shot down a very fast MiG-25 with a U.S.-supplied (and -modified) Hawk missile. Without the ambush feature, the Hawk could not have shot down the highflying aircraft. It appears that the Soviets developed a modification package for the SA-6 that allowed the missile to be fired well before the illuminator was switched on and that the Bosnian Serbs’ SA-6 had been modified.
What now? The SA-6 may provide almost as little warning as a man-portable missile, with the important difference that it is an all-weather missile uninhibited by cloud cover—as indeed it was in the case of the F-16 and the emerging generation of missile warning systems will be of no avail, because they are not all-weather.
There is an interesting alternative: pulse-Doppler radar. If the peak power is low enough, this type of radar is difficult for an enemy to detect, so (at least in theory) using it does not make a helicopter significantly more vulnerable. Many U.S. helicopters are equipped with such a device, the ALQ-156. A modified version was planned for the A-6E. Neither was particularly directional. So the ALQ-156 was never a candidate for the current-generation missile approach warning system.
The F-16 loss suggests that the ALQ-156 or some type of radar, rather than a passive infrared or ultraviolet, may be the appropriate basis for future development. The main objection must be that any radar with sufficient range will itself give away the airplane carrying it, so that pilots may well prefer not to turn it on. In recent years, however, considerable work has been done on stealthy (usually spread-spectrum) radars. For that matter, additives can drastically reduce the detectable infrared and ultraviolet radiation from the exhaust plume of an incoming missile; the revival of radar warnings systems may be inevitable.
There is another possibility. Current fighter radars are designed to cover only the hemisphere—or less—forward of the airplane, since that is the volume in which the airplane s missiles can engage targets. The current generation of air-to-air weapons, however, both radar- and infrared-guided, lock on after they are launched, and thus, in theory, can cover the entire sphere around an airplane. It may well follow that the next generation of airborne radars, perhaps using conformal-array antennas on the aircrafts’ skin, should cover the entire sphere. In that case they are likely to detect incoming missiles as well as nearby aircraft.
The larger lesson of the F-16 loss is that even forces such as those fielded by the Bosnian Serbs may be able to acquire fairly sophisticated weapons. Apparently, the presence of a modified SA-6 came as a surprise. Prior to the shoot down, there had been no particular interest in the sort of missile-launch warning systems required. If the account above is correct, one lesson is that intelligence concerning modifications to existing weapons often will be less than satisfactory. It is not that our intelligence is inadequate, but rather that some information is unlikely to be available when needed.
The existing combination of radar warning systems for longer-range missiles and infrared or ultraviolet systems for short-range, man-portable weapons, appears to be logical, but in fact it depends on detailed knowledge of the threat. One major advantage of a radar-based warning system is that it is likely to detect virtually any antiaircraft missile, no matter how it is guided. It is insurance against intelligence surprise. Perhaps robustness against our own likely ignorance ought to be recognized as a major virtue.
There are already, incidentally, other forms of antiaircraft missile guidance; one uses a laser. For some time the South Africans have been developing a family of autopilot-equipped missiles, some of them infrared-guided. Such a weapon could be fired through clouds on the basis of search-radar data and lock on after clearing the weather. This would preclude any evasive action by a pilot since warning systems rely on tracking- radar, as opposed to search-radar, emissions.
Some will undoubtedly see in the loss of the F-16 yet another argument for quickly adopting stealthy aircraft, on the ground that a really stealthy fighter would not have been in any danger from radar-guided missiles. It is by no means clear, however that stealth covers the full radar spectrum; it seems likely that it is limited at both the low- and the high-frequency ends. It seems likely, for example, that a large enough fixed-array high-frequency (HF) radar could detect and track a stealthy airplane well enough to cue, for example, a millimeter-wave radar or laser tracking/designation beam. (See the author’s “HF Radar Shows Promise,” Proceedings, July 1995, pages 83-84.) Missiles and missile warning systems are likely to remain features of the aerospace future, whether or not we invest in a new generation of stealthy airplanes.
It seems ominous that none of the radar manufacturers represented at the June 1995 Paris Air Show seemed particularly interested in displaying anti-stealth systems—as though low radar cross-section technology was not nearly the panacea it has seemed. It also may be significant that the B-2 was displayed at Paris, the first time it has been flown (at least openly) outside the United States. The flight clearly gave the French, and probably others, an opportunity to measure the airplane's radar cross section at various frequencies. The B-2 could easily be tracked visually, and its track compared to what radars of various types saw. One might conclude that whatever radar cross-section secrets the B-2 represents are no longer considered particularly important.
The Two-Way Street (continued)
A major theme at this year’s Paris Air Show was the intensifying competition between European and U.S. military aircraft industries. Few new projects are in prospect. They include the C-130 tactical transport replacement (Lockheed’s C.-130J versus the European Future Large Aircraft [FLA]) and the next-generation army attack helicopter (Bell Helicopters’ AH-1 Cobra versus the Eurocopter Tiger).
Europeans make the case that only buying European will keep a European aircraft industry live. Their U.S. rivals argued that Europeans will enjoy a major share of production, and also that their aircraft will be substantially less expensive than all-European solutions.
The United States scored early when Bell Helicopters signed a cooperative agreement with Romania to produce 96 AH-IF attack helicopters. They will be produced in Romania with first deliveries beginning in 1999. The AH-IF is an upgraded version of Bell’s AH-1S.
Similar arguments would apply to the choice of a U.S. lighter versus the Eurofighter 2000 and presumably to the Royal Air Force’s choice of its next maritime patrol aircraft (a P-3C variant versus say, an Atlantique variant). In the case of the Eurofighter advocates claim that it will deliver 15% better performance than an F-22 for 85% of the price; many Americans believe that these figures should be reversed.
The most important current multinational naval projects are the British-French-Italian Project Horizon frigate/destroyer, which will be armed with the French Aster missile, and the German-Dutch-Spanish trilateral air-defense frigate (the German version is the Type 124), which will be armed with Standard Missile (SM)-2 and Evolved Sea Sparrow. Project Horizon in particular seems likely to be subject to major delays associated with its missile system.
These projects are subject to continuous negotiation, in hopes of developing something close to a single configuration which fits several radically different national requirements.
Ironically, Europe also has produced a much simpler approach in the German MEKO frigate, in which the builder imposes a common hull and the buyer chooses a combat system from an international menu. Negotiation and compromise are minimized It now seems possible that this approach will be applied to small carriers for Italy and Spain.
The Royal Navy already is buying an amphibious carrier, to be named Ocean. The hull is being built to commercial standards at one yard to be fitted out elsewhere. The Spanish Navy wants a second carrier, and the Italian Navy is interested both in a large amphibious ship and in a second carrier. It now seems possible that both will buy the existing British hull, fitting it out locally as desired. If the carrier projects proceed, they will make an interesting alternative pattern for multinational defense work. In a frigate or a carrier, about half the cost of the project is its weapon system. If the weapon system is made (or at least chosen) locally, then the purchasing country can feel that it is getting a very large share of the overall project. Yet there is little or no need for a complex international organization to run the program; the buyer is merely purchasing a bare hull, and fitting it out at home. The MEKO concept has been a brilliant success; big pan-European aircraft programs have not.
Maybe the key is that the aircraft programs have been centrally directed, and represent, in current political terminology, big government. The MEKOs and the carriers are decentralized programs. They do not need big bureaucracies to succeed; in fact, they work best with the least bureaucracy.