Jane s International Defense Review
October 2001
Pg. 34

Into The Valley Of Death

Surface-to-air weapons often pose the biggest challenge to air superiority, write Mark Hewish and Charles Gilson

Since 1990, Allied forces have been at risk in fewer than a dozen air-to-air engagements, which have traditionally posed the major challenge to air superiority. However, during the same period they have fired more than 4,000 anti-radiation missiles (ARMs) to suppress or destroy enemy surface-to-air missile (SAM) sites and anti-aircraft artillery.

The Serbian weapons that NATO aircraft faced during Operation 'Allied Force' over Kosovo in 1999 consisted mainly of Russian-developed SA-2, SA-3 and mobile SA-6 air-defense systems. Although designed and built in the 1960s and 1970s, these still posed a formidable threat. More modern systems, such as the SA-10, are more difficult to detect as well as being highly mobile and lethal.

The Kosovo conflict confirmed several basic lessons about electronic warfare (EW). First, the proliferation of advanced air-defense systems has severely compromised the survivability of non-stealthy aircraft unless they receive continuous EW protection in combat. Secondly, stealth and EW are complementary, especially when jamming is provided by stand-off platforms to support stealthy penetrators. Thirdly, because EW support is important for both stealthy and non-stealthy aircraft, a larger force of airborne jammers is necessary than had been anticipated only a few years ago.

Suppression of enemy air defenses (SEAD) typically refers to any mission designed to neutralize, destroy or temporarily degrade enemy surface-based air defenses by destructive or disruptive means. The two most recognized forms are stand-off jamming and attack with ARMs. In the last three years, a new term has emerged: destruction of enemy air defenses (DEAD), also known as lethal SEAD. The primary goal of SEAD is to ensure the survival of friendly forces, which is driven by the engagement timeline, while that of DEAD is to locate and destroy air-defense systems, in which target mobility is the determining factor. Both require precise geolocation to maximize their effectiveness.

Since an opponent will exploit aspects such as mobility and emission control to avoid detection, SEAD remains an important mission area. Aircraft survivability depends on the ability to stop the SAM from completing a successful engagement. Self-protection measures such as on-board jammers, and chaff or flare dispensers, provide a last-ditch defense. Ideally, though, the threat should be neutralized earlier by means of stand-off jammers and/or ARMs.

Stand-off jammers are largely pre-emptive, with their goal being to prevent an enemy's initial acquisition of supported aircraft. Once the SAM begins an engagement, the time available to suppress it is very short. Even with instantaneous, precision emitter targeting, the fly-out speed of the SEAD weapon would have to exceed the M3-6 reached by modern SAMs to ensure a favorable result.

The odds can be tilted in favor of the attacker by launching ARMs into a suspected threat area in advance of a strike package. The missiles can then immediately attack a SAM system when it initiates an engagement. The effect of this tactic has been that SAM operators will often choose not to turn on the radars. This achieves the mission of suppression and survivability, but leaves the SAM system available to fight another day.

DEAD can complement SEAD, particularly against radars that require fixed sites or are slow to relocate. Ideally, these missions should occur before strike missions are flown. If the SAM is to be targeted with munitions using the Global Positioning System (GPS) for guidance, it has to be located with sufficient accuracy. A weapon must then be launched, fly out to the GPS location and arrive before the SAM target has relocated. Man-in-the-loop weapons require much less precision, but good cueing is still required to allow the aircrew to find the target.

The DEAD mission will become an important part of air power in this new era, but the SEAD mission will always be required to ensure that warfighters have the best chances of surviving an encounter with a pop-up threat. Even aircraft flying DEAD missions will require SEAD support to counter such threats.

Several projects are currently under way to address SEAD/DEAD deficiencies, although it remains an area that has historically been underfunded. Reductions in US force structure have almost eliminated the use of dedicated aircraft for SEAD, which is now performed mainly by multimission platforms.

Since the retirement of the US Air Force's (USAF's) EF-111A Ravens in 1998, the EA-6B Prowler operated by the US Navy (USN) and Marine Corps (USMC) is the only dedicated tactical-jamming aircraft in the joint-service inventory (and is the sole operational airborne stand-off jammer available to NATO). The 124 aircraft equip 19 USN squadrons - 11 (including one reserve) based on aircraft carriers, and four allocated to expeditionary operations - together with four flown by the USMC. At any one time, however, only 82 are typically available.

During 'Allied Force', one-third of all available Prowlers were deployed to south-eastern Europe. This caused a ripple effect in other areas. The squadron based at Incirlik in Turkey was allocated to supporting the Balkans air war, resulting in a suspension of Operation 'Northern Watch' over Iraq. Another squadron was transferred from Iwakuni in Japan, forcing US-based aircraft to cover any emergencies in north-east Asia.

Prowlers will gain new capabilities in 2005 with the introduction of the Increased Capability-III (ICAP-III) package, which Northrop Grumman is integrating under a development contract worth approximately US$200 million. The aircraft are already being upgraded to Block 89A standard. ICAP-III adds the Northrop Grumman (formerly Litton) LR-700 receiver - forming part of a long-baseline interferometric system using antennas on the wings, nose and tail - and greater processing capability. This combination provides the emitter-location accuracy and speed necessary for reactive ('surgical') rather than pre-emptive continuous jamming, allowing energy to be concentrated on specific threats. It also provides sufficient data about the waveforms in use by an enemy to detect when they change, rather than flagging them up as new radars.

ICAP-III will additionally integrate several formerly separate jammers, such as the BAE Systems AN/USQ-113 that operates at communications frequencies, so that they can function simultaneously. Other aspects of the upgrade include the addition of Link 16 facilities, together with integration of the Multimission Advanced Tactical Terminal (MATT) and Improved Data Modem (IDM) into the overall system, and large-format displays for easier information interpretation. The EA-6B already communicates with F-16CJ fighters via the IDM for targeting.

The level of performance provided by ICAP-III is expected to form the baseline for an eventual successor to the EA-6B. The 22-month Joint Airborne Electronic Attack analysis of alternatives, initiated following the Kosovo campaign, is due for completion by the end of 2001. Boeing has proposed a Hornet variant referred to variously as the E/A-18 or F-18G Growler, carrying a version of the Prowler's AN/ALQ-99 jamming suite, which may attract support from the USN. The USMC would prefer to wait for an EW variant of the Joint Strike Fighter, if that project survives, and the USAF does not require a dedicated SEAD platform. Any new program would have to be initiated in Fiscal Year 2004 (FY04) or soon after, in order to accommodate the USN's desire to begin replacing its EA-6Bs in 2010.

In the meantime, both the AGM-88 High-Speed Anti-Radiation Missile (HARM) and its associated systems are undergoing upgrades that will significantly enhance their capabilities. The US armed forces are upgrading their AGM-88Bs and -88Cs by the incorporation of Block IIIA and Block V software respectively, resulting in greater accuracy and improved reliability. Raytheon is also relaunching production of the -88C for the USN, with deliveries continuing until early 2003.

The availability of new production rounds has led to increased international interest in the weapon, according to the company, which expects to receive two additional orders (including one from a new customer) this year. Six overseas countries already have the weapon in service: Germany (where it arms Tornados operated by the air force and the navy), Greece, Italy, the Republic of Korea, Spain and Turkey. According to a briefing presented by US Naval Air Systems Command (NAVAIR), the HARM-equipped Tornado ECR [Electronic Combat and Reconnaissance] version is "more capable than US platforms", being "by far the best platform/system in service in terms of its ability to find, identify and hit targets".

Germany and Italy have joined the USN in the HARM Precision Navigation Upgrade (PNU), developed by Raytheon in collaboration with Bodenseewerk Gerätetechnik (BGT) and Alenia Marconi Systems. The introduction of a kit that combines a tightly coupled inertial navigation system (INS) and Collins NavStrike II GPS receiver, replacing the present guidance systems based on mechanical gyros, is intended to increase weapon effectiveness while accommodating restrictive rules of engagement to reduce collateral damage and fratricide.

Flight trials of development hardware are due to begin in March 2002. Initial operational capability is planned for mid- to late 2003 in the US and Europe, although the schedule in the various countries could be driven by aircraft integration issues.

Raytheon is also conducting Phase II of the Advanced Tactical Targeting Technology (AT3) program (see below), sponsored by the US Air Force Research Laboratory (AFRL) and the Defense Advanced Research Projects Agency (DARPA), and continues to build the AN/ASQ-213 HARM Targeting System (HTS) that equips USAF F-16CJs. This is allowing the company to incorporate low-risk enhancements developed under the AT3 program into the R-7 version of HTS that entered engineering and manufacturing development earlier this year. The R-7 will provide real-time precision emitter targeting for SEAD and DEAD missions.

Raytheon is now bringing together these various development threads to provide an integrated system that would be more capable and less expensive than the present 'ready, shoot, aim' approach. If the target-location error is very large, the missile requires an expensive seeker costing typically US$400,000. For 3,000 rounds, this totals US$1.2 billion. An alternative approach would be to equip 300 aircraft with HTS at US$500,000 each, and fit 300 missiles with the US$50,000 PNU kit, at a total cost of US$165 million.

High-speed strike

The company is conducting internally funded studies of converting some of the HARMs which it is receiving back from the USN under an exchange agreement into a high-speed strike variant that could also engage 'time-critical' targets. This would involve incorporating the PNU, a facility for accurate emitter targeting, and a larger warhead. The studies include trade-off analyses to determine whether a terminal seeker would be necessary; if so, it would be simple and inexpensive.

The weapon would employ the existing propulsion system, but modifications to the flight profile would result in a higher average speed and what Raytheon describes as a "very substantial" range increase. At present, the flightpath is constrained by the need to point the seeker at the ground so that it can acquire emitters. Raytheon is also talking to potential customers for such a weapon, both in the US and overseas, together with foreign firms that may be interested in becoming involved.

The USN is already pursuing a further HARM upgrade to provide a DEAD capability. The Advanced Anti-Radiation Guided Missile (AARGM) is an otherwise standard HARM carrying a new front end, which combines a passive anti-radiation homing (ARH) facility with a GPS-aided INS and a millimeter-wave (MMW) radar terminal seeker. The last of these allows the weapon to continue to home on a threat emitter, even after it has shut down, and to engage other non-radiating targets.

Science and Applied Technology (SAT) has been developing technology for the new front end for more than a decade, initially under a series of Small Business Innovation Research (SBIR) contracts from NAVAIR. In 1998, SAT teamed with the Naval Air Warfare Center Weapons Division at China Lake to continue work under a co-operative research and development agreement to pursue AARGM technology development.

The first firing of an AARGM guided test vehicle (GTV-1) took place successfully on 28 August 2001. Following launch from an F/A-18 fighter at China Lake, the round successfully identified, tracked and guided to the simulated air-defense radar target, using inputs from the ARH section of its seeker, and impacted within the lethal radius of the HARM warhead. The next vehicle, GTV-2, will additionally incorporate the MMW radar.

AARGM forms the baseline for the Quick Bolt advanced concept technology demonstration (ACTD), being conducted jointly by NAVAIR and the US National Reconnaissance Office (NRO), which began in FY00 and is scheduled for completion in FY04. Quick Bolt adds the NRO-sponsored Embedded National Tactical Receiver (ENTR - see IDR 8/2001, p24), which allows the missile to receive updated targeting information via the Tactical Data Dissemination System while in flight. The missile also incorporates a burst transmitter that relays data from the final stages of an attack to assist in assessment of the weapon's effectiveness.

The US Congress added 'plus-ups' of US$15 million for AARGM and US$5 million for Quick Bolt in FY01, but overall funding reductions have led to a restructuring of the ACTD. The two test firings, planned for the first half of FY03, will now involve baseline AARGMs operating in conjunction with ENTR installed in an inert HARM carried on another missile station. US European Command (EUCOM), which is the user sponsor and the operations manager for Quick Bolt, will use the results in its military utility assessment to be conducted in mid-FY03. EUCOM had requested that it be allocated 10 residual rounds from the ACTD, but is now likely to receive only two. The USN may retrofit a total of approximately 1,350 HARMs to PNU or AARGM standard.

The science and technology program being pursued by the Office of Naval Research (ONR) in support of the Time Critical Strike future naval capability involves several 'enabling capabilities', including the defeat of short-dwell/intermittently radiating targets at long ranges. This will be addressed by the High Speed ARM Demonstration, with funding of US$30 million over four years from FY02. The High Speed ARM will combine technologies from AARGM, including its multimode seeker, with a new propulsion system and a modified HARM airframe.

Coverage enhancement

The baseline powerplant studied by ONR is that originally designed for the Advanced Air-to-Air Missile (AAAM), which was canceled in the early 1990s, although liquid-fueled ramjets and variable-flow ducted rockets are also under consideration. The weapon is planned to demonstrate twice the range and speed that can be achieved by a standard HARM, resulting in a fourfold increase in area coverage. The use of a modified airframe would permit internal carriage by the F-22 and Joint Strike Fighter.

Boeing is proposing several alternative approaches, including the use of a modified MBDA Meteor ramjet-powered air-to-air missile (AAM) fitted with an anti-radiation seeker (see below). Candidates for the latter include the multimode guidance section developed under the AARGM program, in which all items forward of the gimbal have a maximum diameter of 17.8cm. Northrop Grumman is offering a family of vehicles based on the Miniature Air Launched Decoy (MALD - see below). System development and demonstration of a weapon incorporating technologies from the ONR program could begin in FY05, with production starting in FY07 and the weapon entering service in 2010. The USAF may also join the program.

DARPA and AFRL are jointly funding the US$40-million Advanced SEAD Targeting advanced technology demonstration, also known as AT3, to develop methods for long-range passive emitter geolocation from multiple co-operating platforms. The latter would use existing datalinks and common precision timing to determine a target's GPS co-ordinates.

AT3 is intended to locate targets to within 50m circular error probable (CEP), in less than 10sec from a distance of more than 50nm. Requirements include the ability to form groups of participants on an ad hoc basis, and to locate multiple emitters operating simultaneously in a dense pulse environment. The program exploits advances in precision time standards, inexpensive wideband receivers based on multichip modules, and threat-association algorithms. Goals at the beginning of the program included a cost of less than US$250,000 for an AT3 module.

Following a down-select last year, Raytheon is conducting Phase II of AT3. The company flew hardware during Phase I, and will conduct further flight trials aboard two T-39s in the spring of 2002. AT3 is due for completion at the end of 2002, allowing the resultant technologies to transition to manned or unmanned platforms in FY03.

The Parallel Advanced Tactical Targeting Technology (PAT3) program, being conducted under separate contracts by Advent Systems, BAE Systems, CAE Soft and Raytheon C3I Systems, will continue for about six months after the end of AT3 itself. The objective of PAT3 is to demonstrate - by means of simulation, and analysis of data collected during the AT3 program - a range of innovative approaches to the most demanding problems of multiship target acquisition and geolocation. Areas of interest include techniques for signal de-interleaving, multipath mitigation, polarization exploitation, time- and frequency-difference-of-arrival (TDOA/FDOA) algorithms, and counter-countermeasures.

TDOA requires three or more collectors to provide the desired accuracy. Each measures the arrival time of a pulse from the target emitter. For each pair of co-operating collectors, the target can lie at any point along a hyperboloid. With three collectors, these hyperboloids intersect at the emitter. However, this assumes that all three collectors are conducting TDOA measurements on the same pulse. If this is not the case, ghost locations may result. FDOA can eliminate ghost solutions, as well as enhancing overall accuracy, by generating loci based on the difference in Doppler frequency resulting from each collector's velocity relative to the threat. These loci intersect with the TDOA curves at the correct emitter location.

In support of efforts such as AT3, DARPA and AFRL plan to conduct a demonstration of Tactical Targeting Network Technologies (TTNT) that could operate alongside existing systems such as Link 16. The aims for TTNT include the ability to support networks of 200 platforms, separated by up to 100nm, that can handle sensor and other data at a total rate of 10Mb/s. Each platform would transmit at rates from 10kb/s to 2Mb/s, with a delay of less than 2ms.

Candidate technologies include an advanced modulation underlay - such as very-wideband spread-spectrum or orthogonal frequency-division multiplexing (OFDM) - that could be added to Link 16.

The US armed forces are also pursuing other efforts to gain the benefits of collaboration between platforms. Project Suter, forming part of the Joint Expeditionary Forces Experiment conducted in October 2000, demonstrated how information-gathering platforms can team with shooters to defeat time-critical targets. A modified EC-130H Compass Call aircraft successfully combined with an RC-135 Rivet Joint and an F-16CJ. Each scenario concluded with an F-16CJ hard-killing the target. The USAF's UAV Battlelab has also conducted a series of demonstrations using unmanned aerial vehicles (UAVs) operating in conjunction with other platforms, such as the F-16CJ and RC-135, in support of SEAD operations.

Emitter geolocation

Avisys, working under a series of SBIR contracts from ONR, has developed techniques that would allow the AN/ALR-67(V)2 radar warning receiver (RWR) to provide emitter geolocation, with the accuracy required for targeting, in near-real time. The only modifications required are in software. An EP-3E Aries II signals-intelligence (SIGINT) aircaft would cue the RWR, installed on an F/A-18 or F-14D fighter, to search for the signal of interest. The receiver acquires that signal, measures its parameters, and tags the data with precise own-aircraft position and time inputs derived from the on-board GPS receiver and INS. The track file, signal time of arrival and position data are then sent to the mission computer, which transmits them back to an EP-3E via Link 16.

The Story Finder/Landmark system aboard the Aries II uses TDOA data, derived from the offboard RWR measurements and its own SIGINT receivers, to compute the emitter's precise geolocation. It then transmits this to tactical aircraft, where it is displayed and can cue high-resolution sensors such as a synthetic-aperture radar or forward-looking infrared (FLIR) set. The crew can then take the appropriate action: engage the target directly with precision-guided weapons, or avoid the threat. Meanwhile, the EP-3E uses the RWR-supplied information to expand and update its situational awareness of the battlespace.

Initial results confirm that the RWR can provide the necessary data, and that the bandwidth available from the Multifunction Information Distribution system can support the required data exchange. The system would be employed mainly against target-acquisition radars using rotating antennas, providing a geolocation accuracy of 20-25m.

The USAF's Lethal SEAD Program Office has assumed responsibility for the Northrop Grumman ADM-160A MALD that was originally sponsored by DARPA as an ACTD. Air Combat Command plans to order 116 rounds in March 2002 under a three-year 'Silver Bullet' procurement to meet its immediate high-priority needs. The UK Royal Air Force (RAF) has also expressed interest in acquiring the decoy. The ACTD, which had been scheduled for completion in early FY00, will now continue until the end of this year. This will include a further three flights to test modifications to the engine, followed by five to finalize the production configuration.

MALD is intended to be launched from tactical aircraft such as the F-16 in order to stimulate and saturate an enemy's integrated air-defense system. A study of the decoy's military worth conducted by the Air Force Studies and Analyses Agency on behalf of DARPA showed that the firing of 300 rounds - against an unspecified target set - on the first day of a major conflict could save 10 aircraft, plus their pilots. These savings would be compounded by the resulting increase in sortie generation from the second day onwards, and by a reduction in the enemy's stockpile of SAMs.

The baseline vehicle is 2.3m long by 15cm in diameter and weighs 45kg fueled. It has a range of more than 250nm, and an endurance of greater than 20min. The Signature Augmentation Subsystem (SAS), which increases the decoy's radar cross-section, covers VHF to microwave (J-band) frequencies. It employs antennas, transmitters and receivers mounted in the nose, wing and ventral fin.

Operational testing

MALD flew nine full-length missions during developmental testing, completed in August 1999, covering an average distance of 162nm in 21min. Operational testing followed in September 1999. The operational requirements document calls for a speed of at least M0.8, a 35,000ft ceiling, with an endurance of at least 35min at this height, and a minimum maneuverability of 2g. Navigation accuracy must be at least ±2nm, and the minimum number of waypoints is 20. Predicted values for the operational version are a maximum speed of M0.92, an endurance of 37min at 35,000ft, an accuracy of ±500ft and a total of 256 waypoints.

The USAF's operational assessment was generally favorable, with three major concerns: interference between the SAS payload and the GPS receiver; degraded performance against three key threats; and engine failures. Northrop Grumman has since corrected leaking of electromagnetic signals from the payload module, and narrowed the bandpass filter. Modifications to the Hamilton Sundstrand Power Systems TJ-50 turbojet include adopting direct lubrication of the aft bearing, which had a high failure rate, and redesigning the bullnose.

Northrop Grumman has worked from the outset to minimize the cost of MALD. Measures include the use of lightweight commercial sheet-molding compound - a chopped-fiber composite material that is employed in car bumpers and for the cross-vehicle beam of the Ford Ranger pick-up truck - for major parts of the airframe. This greatly reduces the parts count, and is simple and quick to fabricate. The compound has proved able to withstand the shock imparted by the two bomb-rack ejector pistons when MALD is launched.

The decoy was originally intended to have a unit cost of US$30,000 (in FY95 dollars), based on production of 3,000 units over three years. The present predicted figure is US$75,000 (in FY00 dollars), assuming production of 1,500 rounds over four years.

Northrop Grumman has also proposed a family of MALD derivatives. These include the Miniature Air Launched Jammer (MALJ), several rounds of which would be launched into the vicinity of an air-defense radar. They would then orbit that site, conducting stand-in jamming, to render it ineffective while a strike package transits the area. The use of MALJ in this role would free EA-6Bs to concentrate on jamming radars directly associated with SAM operations.

Another proposed implementation, the MALD Rapid Targeting System, would involve a flight of typically three such decoys interconnected by simple links similar to those used by cellphones. They would perform triangulation, using TDOA techniques to locate emitters to an accuracy of better than 10m within 10sec. This information would then be relayed directly to tactical aircraft via a satellite communications system such as Iridium.

Germany's BWB defense procurement agency is funding development of the BGT Armiger ramjet-powered ARM, which could enter service in 2008. The weapon, 4m long and 20cm in diameter, weighs 220kg. The Bayern Chemie solid-propellant ramjet provides a maximum speed of more than M3 and a range in excess of 150km. The accuracy conferred by the ARAS dual-mode (imaging infra-red/broadband ARH) seeker, which is claimed to be 1m or better, permits the use of a comparatively small (20kg) warhead.

Digital autopilot

Phase 2 of the program, being conducted under a BWB contract awarded in July 1999, includes development of the digital autopilot. The first ground-based firing is due to take place this Autumn, with two more to follow in 2002. These will investigate interaction between the missile's asymmetrical forebody and its four mid-body ramjet intakes. Trials of the seeker aboard a helicopter resumed in July.

The follow-on Phase 3 will integrate the seeker and INS/GPS mid-course navigation system with the missile for full flight trials. Guided firings are due to take place in 2003-04. BGT is having discussions with companies in other countries that could participate in Phase 3. These include AMS, which could provide a datalink allowing Armiger to receive target updates, together with industry in Sweden and Spain. These two countries are also seen as potential customers for Armiger, together with Greece and other HARM operators.

The UK RAF could also be interested in a variant of such a weapon, with the ARAS seeker fitted to the airframe and propulsion system of the Meteor AAM, as a successor to the MBDA Alarm. This would allow the missile to be carried on the semi-recessed launch stations aboard Eurofighter. Other customers for this platform, together with those for the Joint Strike Fighter, could additionally be interested in such a development.