Precision Standoff Attack

Attack aviation continued to enjoy more than a decade of dominance over the ground, but it came to an abrupt end in Vietnam where Soviet air defence technology – built around the radar-directed SAM – startled the world with its sophistication and lethality.

Today, the see-saw battle between air and surface is still in doubt as Soviet-built air defence systems, containing thousands of missiles, project their radar detection and tracking coverage well beyond 30 miles in range and from a few hundred to more than 90,000 feet in altitude. Similarly, Soviet warships bristle with radars and radar-controlled SAMs and guns, and they are growing steadily more lethal. An example is the newly deployed Kirov, a nuclear-powered battle cruiser that uses high-technology radar and electro-optical systems to detect and fire on approaching aircraft and missiles

Flying straight in is out

In the surface attack problem today, flying straight in toward a target is out of the question. And attempting to penetrate by streaking in at very low or very high altitudes can lead to distinct disadvantages in either case. Strike aircraft tactics have relied primarily on low-altitude penetration to minimise exposure to air defence radars and thus enhance survivability. However, newer Soviet low-altitude SAM radar systems are believed to have pierced the traditional safe haven of treetop-level flight. And the newest Soviet interceptors apparently are equipped with lookdown, shoot-down radar that can pick up the low-flier.

There are also other very serious disadvantages of flying very fast at 100 to 200 feet above the surface, not the least of which is the problem of avoiding collision with the surface. Target acquisition and weapon delivery are made very difficult by the need to dodge obstacles and evade air defences, which uses up precious time needed to concentrate on weapon delivery. Then, too, the unusual skills demanded by low-altitude operations inevitably increase the problem of pilot training.

From treetop level to medium altitudes, strike aircraft enter the ‘no man’s land’ of the air-versus-ground battle. Here they are exposed to an awesome array of anti-aircraft defences. Flying even higher may actually increase their chances of survival. For example, at 50,000 or 60,000 feet, survivability is significantly improved (although still in doubt) over that at, say, 10,000 feet because the penetrator is outside the lethal envelope of a large percentage of Soviet anti-aircraft weapons

A strike pilot over enemy territory knows he must hit the target on the first pass. If he misses, he’ll probably have to come back again and perhaps even a third time – if he’s still alive. His first pass can stir up a hornet’s nest of anti-aircraft fire, making immediate re-attack extremely hazardous. The situation has been eased considerably by technological advances in precision attack systems.

Lasers Improve first-pass accuracy

First introduced in combat in the early 1970s, laser-guided bombs and powered air-to-surface missiles produced a remarkable improvement in first-pass accuracy. For example, toward the end of the Vietnam war, one squadron carrying laser-guided weapons demolished an important bridge near Hanoi in a single pass with no losses. Until then, the bridge had survived nearly 600 sorties by aircraft dropping hundreds of tons of conventional bombs.

One of the first ‘smart’ air-to-ground weapons is the Maverick, which the US Air Force started developing about 10 years ago. It uses a tiny television camera in the nose that images the potential target, enabling the missile’s guidance system to lock on. Unfortunately, Maverick and weapons like it can be adversely affected by clouds and darkness, problems that have led to the procurement of infrared and laser variants.

One drawback of laser-guided bombs and missiles is that either the attacking aircraft or a forward observer on the ground has to focus the laser beam on the target long enough to guide in the ordnance. This, of course, can leave the targeter exposed and vulnerable to the enemy defence system. Also, clouds and weather can cause the weapon to lose the guiding beam. Weapons with infrared seekers are not the complete answer either because they can be lured away from intended targets by flares, chaff and other types of decoy measures.

Standoff weapons are coming

The US decision to develop a family of jet-powered, air-breathing tactical cruise missiles gives Allied military services the prospect of launching all-weather tactical weapons from well outside the current and projected lethal range of hostile air defence systems. Examples of these new standoff weapons go by such names as MRASM (Medium Range Air-to-Surface Missile), Harpoon and Tomahawk. All have far more built-in ‘intelligence’ and sensory capacity than their predecessors and are also considerably more lethal.

The weapons themselves represent a major advance in air-to surface attack technology. But while they provide the long-range punch needed to reach and hit well-defended targets from a safe standoff distance, their effectiveness depends on the accuracy of the targeting information fed into their guidance systems before launch.

The challenge confronting attack system designers is therefore to provide a capability in the launching aircraft for finding both fixed and moving targets at these unprecedented ranges and with sufficient resolution to classify them as actual threats. Classification of targets is a critical need, particularly when friendly and enemy forces are operating in the same area. In addition, once the targets have been classified as threats, it would be extremely desirable to be able to select the highest priority ones to be attacked – that is, to pick out the enemy missile cruiser from among its escorting destroyers.

A targeting solution is at hand.

A solution to the problem appears to be at hand. For several years, Grumman and the Norden Systems subsidiary of United Technologies (a leading designer of airborne radar) have been working as a team on a unique standoff targeting radar system concept termed AWSACS, or All-Weather Standoff Attack Control System. Developed under continuing US Navy sponsorship, AWSACS technology has been proven in our laboratory and in-flight demonstrations.

Briefly, AWSACS involves use of high-resolution image forming radar and high-speed digital radar signal processing for fixed- and moving-target detection, acquisition, classification and tracking. And, because it can be done with the same technology, it would also be possible to control the standoff weapon after launch by transmitting periodic targeting updates to its guidance unit during mid-course and terminal attack phases.

AWSACS makes best attack plane better

AWSACS technology can be applied to various conventional Army, Navy and Air Force standoff air-to-surface weapon delivery systems, extending their survivability and effectiveness in missions aimed at neutralising hostile land and sea forces. For example, incorporated in the Navy’s A-6EIntruder, AWSACS would give the medium attack plane’s radar the ability to classify ships and other targets from longer standoff ranges in adverse weather and then to attack them with precision-guided weapons.

With a payload capacity of 18,000 lb, the Intruder would have the unique ability to classify and prioritise targets for these weapons from a safe standoff distance in virtually any weather and even if the enemy were operating in total electronic silence.

Targets classified in near real-time

In addition, the combination of AWSACS’ high-speed digital radar signal processor and the A-6E’s powerful central computer lends a completely new dimension to air-to-surface operations; the ability to classify distant targets in virtually real-time. This would allow continuous updating of the targeting information being fed into the missiles poised under the Intruder’s wings.

Thus, not only could accurate target designation be furnished a standoff weapon right up to the very moment of launch, but also afterwards, if that weapon were fitted with a transponder/ command decoder to accept target update commands from AWSACS in flight. By means of this modification, standoff weapons could be given aim-point corrections during midcourse or, if desired, all the way to target impact.

Such accurate post-launch target updating would make it possible to guide weapons such as Harpoon in standoff attacks against land targets, for which it presently has only a limited capability. It would also ease the problem – but not the danger – of delivering older existing weapons, such as the Maverick missile. The range limitations of these weapons presently force the attack plane to fly relatively close in toward a heavily defended target in order to get within striking range.

Technology demonstrated earlier

Although the claims being made for this system’s revolutionary capabilities may appear somewhat extreme, it should be remembered that the technology involved has been successfully demonstrated both in the laboratory and in Navy-sponsored flight tests as part of an earlier phase of the Grumman/Norden development. The AWSACS program continues that development for potential application in the A-6E – a very logical approach, considering the relatively modest cost of adding unique targeting capabilities to this most sophisticated of today’s all-weather attack aircraft.

An interferometric relative angle measurement unit and a synthetic aperture radar, or ‘SAR’, target imaging system comprise the most advanced electronic elements in AWSACS. Synthetic aperture radar is, of course, not a new technology having been developed more than a decade ago for use primarily in reconnaissance systems. Grumman’s is the first application of real-time, in-flight-processed SAR for targeting and weapon delivery in a tactical attack aeroplane.

Dramatic Increase in accuracy and range

In developing and integrating this new standoff system, Grumman achieved data that indicate an astounding 1500-fold improvement in radar image detail over conventional airborne radars. Pre-launch targeting with such unprecedented resolution should result in a dramatic improvement in weapon-delivery accuracy and standoff range of ‘off-the-shelf’ air-launched weapons – not to mention the added effectiveness achievable through post-launch targeting updates.

A-6 radar gets a ‘300-ft’ dish

Synthetic aperture radar works in remarkable ways. It produces incredibly sharp images by receiving and processing radar return signals over a significant distance when the aircraft’s radar beam illuminates the target area. As the attack aircraft flies an angle 10-50 degrees off the target, these signals are processed onboard to reconstitute an image with a degree of resolution normally obtained only by a much larger antenna than those carried by attack aircraft. The SAR antenna, though actually only three feet in diameter, operates as if it were hundreds of feet wide – a ‘synthetic’ effect.

We can perhaps best understand how the SAR develops high-resolution target imagery by comparing it, somewhat simplistically, with conventional airborne radar to which objects on the ground ahead appear to be moving toward the aircraft at the same flight speed. Objects detected at right angles to the flight path are no longer moving toward the radar but are just about to begin receding. For every angle between straight ahead and 90 degrees off to the side, objects actually move toward the aeroplane with a velocity unique to the particular bearing angle they form. But this fact is lost upon the conventional radar which ‘paints’ the instantaneous view determined by the pointing angle of the antenna upon receiving a given radar echo, or return.

SAR creates a synthetic world

Synthetic aperture radar, on the other hand, collects the mass of energy reflected back from the target area and then performs a very fine-grain division of it into individual velocity elements, using this information to construct a picture. The resulting radar picture is so detailed as to have an almost photographic quality but, unfortunately, it tells basically nothing about the ground targets except their velocity and range relative to the aircraft. SAR alone thus cannot provide a targeting solution because it develops neither the altitude nor the accurate azimuth information needed to direct a weapon at a target.

The situation becomes more complex for moving targets on land and ships at sea. Because moving vehicles have different velocities than the terrain around them, they appear as echoes in erroneous positions on the SAR display. Ships at sea present even more complicated velocity problems because of their rolling and pitching, which can lead to image distortion.

The need was for a simple yet accurate way of converting the strange synthetic world of SAR imagery into real-world measurements of feet, inches and angles that could be used to pinpoint targets and guide weapons to them.

Angle processor is unique

The answer is a unique ‘relative angle processor’ which works on the SAR information. Using a Grumman-derived technique, the processor performs an analysis of the radar return signals reaching the right and left halves of the antenna to determine respective angles of arrival and, from these, the exact angle between the targets or between targets and guided weapons. We succeeded in converting from the velocity dimension of the SAR picture to a simple measurement of relative position.

Acquisition/classification of the target is only a part of the AWSACS capability. It also can guide the weapon precisely to the target. This is done by installing a transponder in the weapon, similar to a ground beacon used for aerial ground support missions. The transponder is interrogated by the aircraft’s radar while the weapon is in flight and responds by giving its location. After having located the weapon’s position relative to that of the target, the AWSACS radar transmits pulses directing the weapon to fly along a path that will intercept the target.

System also assesses target damage from afar

The weapon is automatically guided with no need for the flight crew to intervene. Visual displays in the cockpit continue to show both the weapon (or weapons) and the target all the way to point of impact – and afterwards, even through the smoke and debris of explosions – avoiding the need to overfly the target for damage assessment as may be required on present strike missions.

In the final approach and dive onto the target, weapons under AWSACS command give the A-6 bombardier-navigator a very high degree of control over explosive patterns, thus further ensuring maximum strike effectiveness. If, during the weapon’s final approach to the target, it is not on target, it can be disarmed by a signal from the A-6. This option helps preclude damaging established sanctuaries or enclaves of friendly forces.

AWSACS can be a ‘force multiplier’

While we have been discussing one AWSACS ‘mothership’ controlling one or more of its own standoff weapons, it’s important to note that there is also the option of having one or two AWSACS-equipped A-6Es control a much larger number of standoff weapons – including their own and those carried by other types of aircraft in a strike formation. Even weapons launched by ships, submarines and ground installations can be brought under AWSACS control.

And what need might so much firepower serve? As an example, a massive strike by dozens of precision standoff weapons might be needed to counter an overwhelming force of invading enemy armour on land or a major enemy task force at sea.

The AWSACS is thus shown to be a ‘force multiplier’, allowing aircraft of lesser systems capability to be used in all-weather strike operations without adding to their cost, weight or system complexity. It effectively integrates so-called high- and low-mix aircraft to provide a strike force capable of simultaneously executing attack, air superiority and defence suppression missions.

In addition to multiplying the strike force, AWSACS also would multiply the return-on-investment in both aircraft and ordnance. That is, for a relatively small expenditure, there would be huge savings in terms of fewer sorties required to knock out heavily defended targets, fewer weapons expended (reducing the cost of weapon delivery) and reduced aircraft attrition.

Stopped traffic can’t elude SAR

Vehicles moving along roads or across fields have always posed a special problem for attack planes. A standard radar MTI, or moving target indicator, can be frustrated when a vehicle stops, since it is the vehicle’s motion, not its presence, that is detected. An enemy might thus halt all tank and truck traffic when under air attack to avoid having them show up on radar.

This tactic simply won’t work with AWSACS. From a distance, the system will track such targets down to zero velocity. It can designate such a target as one that had been moving, and then continue to press the attack with great precision.

AWSACS also inherently resists a wide variety of electronic countermeasures (ECM). Limited radar transmission times and a secure guidance ‘message’ structure minimise the possibility that enemy ECM will penetrate the AWSACS plane-to-weapon command loop. To pose a threat to AWSACS, which uses synthetic aperture radar techniques, an enemy would have to produce vastly higher jamming power levels than those presently required to jam real-beam radars. And, even were these power levels to be achieved, such powerful jammers would themselves become ideal targets for home-on-jam missiles.

Reduced cost is a key advantage

Reduced cost is a key advantage of the AWSACS concept. As we noted earlier, it would add greater standoff capability to selfpowered or unpowered air-to-surface missiles which have been in inventory for years or just beginning to appear. AWSACS modification of these for mid-course targeting updates or update to impact would make them significantly more effective.

In attacking enemy ships at sea or land-based targets such as tanks, the system can achieve the same degree of success for a fraction of the cost of using conventional standoff or unguided Rockeye-type weapons. As a further cost advantage, the system retains its high-value electronics safely aboard the A-6E aircraft rather than in the weapon where they would be lost on impact. But, in the final analysis, AWSACS will more than pay for itself by cutting down on losses of aircraft and their irreplaceable aircrews.

In upgrading the present inventory of attack ordnance and using the new tactical cruise missiles more effectively, reducing the cost of weapon delivery, and enhancing the survivability of strike forces under all weather conditions, AWSACS should deliver exceptional value for the funds required to implement it. Attack aircrews will welcome it as a means of keeping the upper hand in the deadly battle between air and ground.