|Last Updated: Mon Jan 27 11:18:09 UTC 2014|
The RAAF's New Standoff Weapon
After a very rigorous evaluation program, the RAAF earlier this year selected the Lockheed Martin/Rafael AGM-142 Raptor as the new Stand Off Weapon (SOW) for the F-111. The decision came as a surprise to most observers, as it was generally expected that the slightly cheaper Rockwell AGM-130 rocket boosted glidebomb kit would have been the preferred choice. The RAAF however had good reasons for choosing the way they did, as will shortly be illustrated.
The AGM-142 will typically be carried in pairs by the F/RF-111C AUP. The missile is functionally split into a guidance and navigation section in the nose, the warhead section (denoted by red stripes), the rocket motor section, and the hydraulics and control section in the tail of the airframe. The blast /fragmentation warhead forms a load bearing fuselage section, whereas the penetration warhead is a sub-calibre munition mounted in a structural fuselage section built solely for this purpose. The conduits along the warhead section carry electrical cables between the guidance and navigation section and the aft hydraulics section.
Warheads may be interchanged. Late models of the AGM-142 now have provisions for adding a GPS receiver to the IMU, which would provide for high midcourse navigational accuracy in any extended range versions (using turbojet or longer burn rocket motors). Recent reports indicate that the RAAF now intend to use the AGM-142 also for anti-shipping strike. Compared to the established radar guided AGM-84 Harpoon, the AGM-142 has twice the warhead weight and thus killing power, as well the operator may select the most vulnerable aimpoint on the target vessel to maximise inflicted damage. The AGM-142 has similar range to the Harpoon when launched at altitude, but is supersonic and provides no warning of its approach to listening ESM as it uses a passive optical seeker (Artwork Carlo Kopp).
The SOW program grew out of a lengthy internal debate within the RAAF, which began in the late eighties. At that time it was becoming increasingly apparent that the regional air defence environment was becoming significantly more capable than in previous decades. Of some concern was the regional proliferation of the capable Soviet designed SA-10A/B/C/D (Almaz S-300P/PM/PMU/PMU-1/5V55/48N6) area defence SAM, late models of which had the potential to threaten the F-111 when attacking targets at low level using datalink or laser guided bombs.
The SA-10's Flap Lid phased array engagement radar supported by the Clam Shell FMCW low level acquisition radar are both reputedly quite resistant to jamming (see AA Sept 95), and it was readily apparent that the RAAF's existing inventory of weapons could expose the aircraft to potentially dangerous tactical situations when penetrating defended airspace. Clearly a new weapon was required to deal with such air defence environments, the alternative was the potentially prohibitive cost of losing aircrew and aircraft in any major regional or extra-regional confrontation.
A capability submission for a stand off weapon was then prepared during the early nineties by HQ ADF and subsequently endorsed. Once endorsement occurred, the RAAF defined an Equipment Acquisition Strategy (EAS) document which set out the process for selecting and acquiring a suitable weapon. While early thought favoured the AGM-130 weapon, further examination of alternatives indicated that the Rafael Popeye and its USAF AGM-142 derivative would be viable candidates and these two very closely related weapons were included in the shortlist. As the requirement was tightly defined in a number of key areas and only these types qualified, the RAAF dispensed with the customary ITR and tendering process and directly evaluated the two types.
The stated objective of the program is to improve the survivability of the F-111 when conducting strategic strike operations. Earlier DSTO studies indicated that this was best achieved by using a standoff weapon, and this conclusion drove the ADF's selection process. The evaluation criteria were therefore focussed on the selection of the weapon which would best reduce susceptibility to attack, while meeting defined mission objectives.
The RAAF evaluated three alternatives, these were the US FMS supplied Rockwell AGM-130 and Lockheed Martin/Rafael AGM-142, and the commercially bid Rafael Popeye as used by the Israeli air force. The evaluation was split into four components.
The first of these was the evaluation of the vendor's formal proposals for the supply of the weapon, and essentially involved analysing the paper proposals against the RAAF's stated technical and operational requirements.
The second component of the evaluation was a funded study of integration issues in relation to the F-111C AUP digital weapon system. This study, carried out for both weapons, identified the effort required in software and hardware modifications and integration testing to support the new weapon in the new digital avionic system.
The third component of the evaluation was a stores carriage compatibility report prepared by ARDU, which evaluated the required effort to certify the carriage, employment and jettison of either of the weapons on the F-111.
The fourth phase of the evaluation was carried out by DSTO, who had earlier determined that a generic powered stand off weapon was a better proposition than an unpowered bomb or glidebomb. The second part of DSTO's evaluation was thus split into a number of areas.
Both missile seekers were evaluated for resolution performance and sensitivity, and it was intended that both seekers also be flight tested to confirm the theoretical analyses. Only the AGM-142/Popeye thermal imaging seeker was flight tested, as the RAAF were unable to acquire an AGM-130 seeker in the required timescale.
Concurrently, DSTO conducted a survivability and lethality assessment of both missiles. The survivability analysis was based on a wide range of scenarios, and focussed both on aircraft survivability and missile survivability. These scenarios were based on both existing threat air defence capabilities and threat SAM and AAA capabilities projected out to 2010.
The lethality analysis focussed both on weapon accuracy and warhead effectiveness, for a very broad range of representative targets, specified by the Air Force. The intent was to determine the relative cost effectiveness of either weapon type, as this would determine in turn required war stocks.
As seeker accuracy was similar for both weapons, this analysis devolved down to assessing the lethality of the standard blast fragmentation warheads used in the weapons. Fragmentation patterns for the warheads were analysed against the intended target sets. The analysis concluded that the 800 lb warhead of the AGM-142/Popeye provided acceptable damage levels for virtually all intended targets, and the additional punch of the 2,000 lb Mk.84 warhead used in the AGM-130 provided little additional advantage. The RAAF intend to use the new weapon with both blast frag warheads and penetration warheads, although the latter were not evaluated in detail. It is worth noting that warhead weight alone is not a deciding factor with penetration weapons, indeed the speed and angle of impact and mechanical resilience of the penetrator make a greater contribution to the weapon's ability to punch through reinforced concrete than sheer mass does.
The conclusion of this complex evaluation process was that the longer ranging AGM-142/Popeye weapon provided significantly better aircraft survivability than the AGM-130 weapon, while still capable of inflicting acceptable damage levels on the intended target types. The additional lethality of the AGM-130 was not found to offset the greater risks imposed on the launch aircraft due its shorter launch ranges at all altitudes. As the principal intent of the project was to improve F-111 survivability, the ADF concluded that the AGM-142/Popeye was the more cost effective weapon.
Software integration with the F-111C AUP will commence in September, 1996 and is intended to continue until the weapon achieves IOC. Ground testing is scheduled for April 1998, with flight testing planned for Q3/Q4 1998. One test launch is planned for at this time. The Phase 1A of the program, intended to provide an Initial Training Capability (ITC), is planned for completion February 1999. Subject to budget approvals, the Phase 2 Initial Operational Capability is planned for July, 1999.
As an interesting side note, the USAF B-52G launch of a AGM-142 missile at the Woomera range was not, as incorrectly reported at the time, related to the evaluation. At that time the USAF intended to carry out a AGM-142 launch demonstration from a B-52 on an intercontinental sortie, to promote the USAF's new "Global Reach, Global Power" doctrinal model. The purpose of the demonstration was to show that the USAF could engage a point target flying directly from the continental US in a single pass standoff attack. The only two US allies which had suitable test ranges capable of supporting the release of a highly classified precision weapon were Israel and Australia. Given the then volatile political situation in the Middle East, Australia was approached and agreed to host the demonstration, with all expenses paid for by the USAF. A muddled DPR press release, which caused much upset in the SOW project office, led to a flurry of enquiries from trade press and bidders alike. Alas it was purely unfortunate timing.
The Lockheed Martin/Rafael AGM-142 Raptor
The early history of the Popeye is shrouded in the characteristic secrecy of Israeli weapons development programs. Whilst rumours do abound that the weapon is a derivative of the cancelled US Navy Condor missile, reputedly sold off to the Israelis after the program was abandoned, AA have been unable to confirm this.
The USAF's AGM-142 Raptor is a derivative of the basic Israeli Popeye weapon, with a moderate number of minor modifications intended to improve compatibility with USAF platforms and the USAF's logistical system. The weapon currently arms a fraction of the B-52 fleet and will be licence manufactured in the US in a joint venture by Israel's Rafael and Lockheed Martin.
The Rafael/Lockheed Martin AGM-142 Raptor is the USAF version of the Israeli Popeye missile, and has a range of minor modifications to suit the USAF operational environment. The missile weighs 3,000 lb at launch, has a range in excess of 50 NM when launched at altitude, and is extremely accurate with a thermal imaging seeker which datalinks a picture to the F-111 navigator's cockpit display. With an 800 lb blast frag warhead or penetrator, the missile is particularly lethal against high value targets such as air defence and command -control -communications sites.
During the late eighties the USAF sought a standoff missile for their B-52, to enable it to attack from outside the area defences of a target. The Rafael Popeye was then being introduced into IDF service on the F-4E, and the USAF in 1988 contracted Rafael and Boeing, the latter the authors of the B-52 offensive avionic system, to integrate the weapon with the B-52G and provide an initial supply of missiles, respectively. To date all USAF AGM-142 stocks have been supplied by Rafael, but future stocks will be supplied by the joint venture company, with some components manufactured in the US.
The missile was initially designated the Have Nap by the USAF, later redesignated the AGM-142, and recently renamed the AGM-142 Raptor. Unconfirmed sources indicate the weapon was blooded during the Gulf Campaign, and used to hit hard targets from outside Iraqi air defence coverage. The political circumstances of the period meant that the US has to date consistently denied the use of the weapon in the campaign, which would no doubt aggravate many Middle Eastern former coalition members.
The AGM-142 is a rocket propelled air to surface standoff missile, with inertial midcourse guidance and an electro-optical (TV or IIR) terminal seeker which relays a picture to the launch aircraft via a datalink. The weapon operator will then update the weapon's aimpoint using a datalink command channel from the launch aircraft, much like the GBU-15 (AGM-130) and Walleye glidebombs. The datalink equipment is carried in a weapon specific pod, as is the case with the GBU-15, AGM-130 and Walleye. The missile weighs approximately 3,000 lb, is 190" in length, 21" in diameter and has a wing span of 68".
The missile can be refitted on the flightline with either a daylight TV seeker, or a 8-12 micron band HgCdTe thermal imaging seeker, the latter only will be used by the RAAF. The seeker has selectable wide and narrow field of view modes, using an optical/mechanical selection mechanism. Wide FOV would be used initially to acquire the target, and narrow FOV then selected during the terminal phase of flight to allow the operator to precisely choose the aimpoint (eg window or vent) he intends to put the weapon through. The seeker is cooled by a closed cycle helium refrigerator powered off the missile's internal 28V DC rail, earlier USAF and Israeli models employed a open loop Nitrogen cooling system fed from a storage bottle.
Midcourse navigation is performed with an inertial measurement unit, built around three fibre-optic gyro (FOG) angular rate sensors and three mechanical accelerometers. The guidance system is built around an Intel 486 based processor module with up to 32 Megabyte of main memory, to provide for long term growth capability in the missile's software. The choice of the 486 CPU is unusual for an embedded weapons application, and reflects more than likely Israeli concern over the availability of more specialised Silicon, such as the Motorola 68k series, the MIPS 2/3/4000 series or the Intel i960 series CPUs currently favoured in US designs. The standard memory size in Popeye and AGM-142 rounds has not been disclosed.
The missile variant being procured by the RAAF is interfaced to the aircraft via a standard Mil-Std-1760 interface (unlike earlier variants), which incorporates a Mil-Std-1553B serial databus, an EIA RS-170 video interface, 28VDC power and triple phase 115V/400 Hz AC power. Once released, the weapon runs off a pair of sizeable internal 28VDC thermal batteries, one for electronics and the other for hydraulics. Unlike the Harpoon, an internal avionics heater element is not used, reflecting the climatic conditions common to the Middle East and Asia-Pacific.
The 1553B bus provides the launch aircraft with the means of communicating with the missile before release, and enables diagnostic access and initialisation of the weapon with waypoints and target coordinates. The proper operation of the seeker may be verified before launch via the RS-170 video feed.
Missile control is provided by cruciform, hydraulically powered tail surfaces. While the typical arrangement for missile hydraulics uses a gas pressurised reservoir and discards fluid upon use, the Raptor uses a closed cycle system powered by an electrical hydraulic pump, in turn powered off the hydraulic system's 28VDC rail. The weapon currently has electrical power sufficient to keep all systems operating for significantly longer than the missile's flight time with the existing powerplant. This suggests that future longer burn powerplants could be used to further extend the weapon's range by a significant margin. The existing constant thrust solid rocket propellant engine has a burn duration in excess of two minutes.
With the existing powerplant, the weapon will fly at transonic or supersonic speeds, subject to mission profile. Ranges on various profiles are classified, but are known to be well in excess of fifty nautical miles for high altitude launches. The missile is qualified for and has flight control software support for both low level and high altitude launches. The missile has an 800 lb warhead. Blast fragmentation or penetration casing versions may be fitted at depo level.
The weapon's datalink will transmit seeker video to the launch aircraft, and receive aimpoint update commands. The RAAF will be acquiring USAF standard datalink equipment, which has some differences from the Israeli standard equipment. The datalink pod will be carried beneath the lower fuselage of the F-111C AUP, in the same location as the AXQ-14 datalink pod used for the GBU-15. The pod uses a Mil-Std-1553B interface for commands and provides an RS-170 video feed to the cockpit. This provides a significant level of hardware compatibility with the F-111C AUP avionic suite, which will require primarily software changes to accommodate the new missile. Hardware changes are minimal, and involve replacing some connectors, adding some pylon wiring, and extending the Mil-Std-1553B databus to the aft ECM station. Datalink frequencies, bandwidths, modulations and signal formats are properly classified, so as to prevent third parties from developing electronic countermeasures. The datalink has a single antenna under the rocket exhaust nozzle, the type has not been disclosed but it is probably a cavity backed spiral or conical spiral, judged from the geometry of the radome and required antenna coverage.
USAF AGM-142 missiles have been subjected to two Product Enhancement Program (PEP) upgrades since deployment, with a third (PEP3) under way. The RAAF will acquire rounds to the PEP3 standard. In line with ADF policy, the RAAF will not disclose the number of pods to be acquired, nor the number of rounds planned. As the missile's cost, cca USD 1M, has been published in the US, the RAAF will not disclose the total program costs so as not to compromise policy on weapon stocks disclosure.
A issue for the RAAF to consider in the longer term is the AGM-142E, a 2,500 lb derivative of the basic weapon which retains the existing weapon's warhead and propulsion, but due a redesigned and repackaged electronics section is both shorter and 500 lb lighter. At the time of writing the E-model was awaiting clearance testing and was not on order by the USAF. Should the USAF acquire this variant, it would most likely come under serious consideration by the RAAF.
In operational use the RAAF will typically carry a datalink pod and a pair of Raptor rounds on the F-111C AUP aircraft. Whilst carriage of four 3,000 lb rounds is an option, the range and manoeuvrability penalties incurred suggest that this will not be a common sight in operational service. Should the F-111G receive a full AUP avionic upgrade, then they could also be made capable of launching the Raptor.
We can expect the Raptor to be used primarily to hit high value well defended targets such as command posts and bunkers, key air defence sites, early warning radar sites, strategically positioned SAM sites and critical infrastructure items. The weapon would be of particular value during the opening phase of an air campaign, as it would allow the RAAF to take down key nodes in the opponent's Command-Control-Communications network and Integrated Air Defence System. Once these are down, the IADS will collapse, allowing the use of cheaper munitions in most instances.
The combination of a high speed precision missile and a fast F-111 will defeat the SA-10 and SA-12 weapon systems, and any similar future SAM systems. The F-111 can shoot the missile at the boundaries of the SAM's coverage, retreat from SAM range while the Raptor closes on the target, and then via datalink control pick off the SAM's phased array engagement radar and command van. The cost argument is much in favour of the F-111/Raptor, as the targeted SAM fire control system is worth tens of millions of dollars, for the cost of a 1 million dollar missile. Moreover, the ability to execute sniper-like precision hits from outside the boundaries of lesser SAM system coverage provides the RAAF with a decisive edge in any confrontation. The low frontal radar cross section of the Raptor, which could be further reduced with absorbent coatings, makes its detection and engagement by an opponent extremely difficult, moreso if supported by jamming from the launching F-111 aircraft.
An issue will be the supply of intelligence for targeting purposes.The RAAF is at this time investigating the fitting of imaging synthetic aperture radar to some F-111 airframes. Such a capability would support the new SOW, as well as provide a potent strategic reconnaissance capability.
The acquisition of the AGM-142 Raptor SOW opens a new era in RAAF capabilities, and will provide a significant qualitative edge against any potential opponent in the wider Asia Pacific region. The high performance F-111C, re-engined and fitted with digital avionics, and armed with the Raptor, will be the most potent strike capability in service regionally, excluding the USAF's F-117A and B-2A. As the missile has inherent systems and performance growth potential, it will not be easily defeated. The marriage of the SOW and the Pig promises to be a successful one indeed.
Under any other circumstance a Herculanean task, this USAF Pig is carrying four SOWs. The RAAF is planning an IOC of mid 1999 for deployment of the AGM-142 Raptor Stand Off Weapon (SOW). A typical operational configuration will be a rear fuselage datalink pod and a pair of Raptor rounds. The combination of the supersonic/transonic Raptor and the high performance, by then re-engined, F-111C will defeat any air defence environment currently in existence or expected to exist in the Asia Pacific region until 2010 (LMC).
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