Air Power: Weapons - Gauging the Lethality Edge of the F-35 | ADM Mar 2009
Abraham Gubler
The F-35 is a revolutionary weapon system differing from the aircraft it will replace and the tactics they will use in a far more significant way than previous recapitalisation of air combat capability.
It will achieve its lethality by introducing very low observability (VLO) to radar (ie stealth), unmatched networked sensors and weapons, automatic flight control system allowing the pilot to focus on fighting not flying, new weapons and new tactics.
This new lethality edge will make each F-35 strike fighter around five times more lethal than the legacy McDonnell Douglas F/A-18A/B ‘Hornet' tactical fighter and General Dynamics F-111C strike aircraft.
Quantifying improvements in lethality by capability recapitalisation is a difficult practice in the open source.
In the case of the F-35 this call can be made with some reliability thanks to the US Government Accountability Office's (GAO) force structure report "Department of the Navy's Tactical Aviation Integration Plan Is Reasonable, but Some Factors Could Affect Implementation" (GAO-04-900).
Using US Navy and industry experts with access to classified capabilities this report provided a lethality value to a range of current and future US Navy aircraft.
The lethality index did not factor in endurance and serviceability but just the combat power potential averaged in offensive and defensive missions for each aircraft.
Using this index and the legacy RAAF force structure of 21 F-111C (using the F-14D as a surrogate on the index) and 71 F/A-18A/Bs as the baseline we can calculate the progressive improvement in combat power.
The bridging RAAF force structure of 24 Boeing F/A-18F Block II ‘Super Hornets' and the 71 F/A-18A/Bs would have a lethality of 1.65 times that of the legacy force.
The force structure after the full Air 6000 Phase 2A/2B acquisition of F-35As with the retention of the Super Hornet fleet would have a lethality of 5.1 times that of the legacy force and 3.1 times that of the bridging force.
Overall capability will be further improved by increased sortie generation rates and longer aggregate endurance, not to mention the availability of force multipliers like the Boeing ‘Wedgetail' airborne early warning and control (AEW&C) aircraft.
Stealthy as a Golf Ball
One of the principal ways the F-35 will achieve such high lethality compared to legacy platforms is by reducing its reflection of radio frequency waves.
While such stealth is a highly classified element of defence technology published sources and comments from the F-35 Project Office indicate that the F-35 will have a frontal radar cross section (RCS) of at least -30 decibels per square metre (dBsm).
This is the equivalent to the same radar return from a sphere with a diameter of 3.6cm (0.001m2) - the same size as a golf ball - a significant reduction from an aircraft over 10m wide and 5m high.
The F-35 achieves this VLO through close attention to the shape of its outer mould line and the use of radar absorbent materials (RAM).
The mould line is determined by use of Petr Ufimtsev's Physical Theory of Diffraction that enables designers to predict the radar reflectivity of a particular shape.
The exact shape of a stealthy F-35 is yet to be revealed as the three prototypes rolled out to date (AA-1, BF-1, AF-1) are all vehicle systems test beds and will not be used for testing the aircraft's RCS.
Attempts to calculate the reflectivity of the operational F-35 based on the outer mould line of these prototypes cannot be accurate.
Only the RCS test stand model and specific, yet unseen, mission system prototypes will incorporate the outer mould line of the production F-35.
Further the F-35 will have its VLO optimised for its tactical usage rather than that of the three preceding stealth aircraft; the Lockheed F-117A, the Northrop Grumman B-2A and the Lockheed Martin/Boeing F-22A.
These aircraft are optimised for penetrating air defences to achieve their different missions. Penetration entails entering the detection and engagement zone, travelling through it and exiting the other end of the threat system.
The F-117A and F-22A need to penetrate this zone because they lack the air to ground sensors and weapons needed to suppress and/or destroy enemy air defences (SEAD and DEAD).
The B-2A, the Northrop Grumman X-47B and the 2018 bomber for USAF's Next Generation Strike System (NGSS) program all need to penetrate enemy air defences because they have the long range required to strike targets deep within national boundaries behind one or more layers of enemy air defences.
This mission only applies to those countries with the geography and military power to have such layered defences and is not very relevant to Australia's geostrategic situation.
The F-22A and F-35 lack the range and endurance - limited to over 600 NM (1,000km) for their maximum unrefuelled strike radius - to carry out these types of deep strike penetration missions.
Rather than attempt to penetrate deep inside enemy air defences the F-35 is customised for SEAD/DEAD and will be the most capable ‘Wild Weasel' (the original project name for developing SEAD/DEAD) system fielded to date.
By combining VLO, mission systems and new weapons the F-35 will be able to find, suppress and destroy the most advanced and mobile air defence systems with low risk.
Like all stealth aircraft the F-35 is not invisible but -30dBsm enables it to only be detected by the most sensitive radars and at very close range.
The integrated mission systems of the F-35 will also enable it to use its Northrop Grumman AN/APG-81 active electronically scanned array (AESA) radar in both an electronic support measure (ESM) and electronic attack (EA) modes.
Combined with other aircraft digital sensors, this will enable a ‘telescopic' capability for detecting electronic emissions from enemy air defences and a high power tactical jamming and deception system.
The US Navy's Next Generation Jammer (NGJ) to replace the EDO AN/ALQ-99 used by current EA platforms will use AESA technology for the emitter.
The F-35's Lockheed Martin/BAE Systems Electro-Optical Targeting System (EOTS) and the APG-81 operating in an inverse synthetic aperture radar (ISAR) mode will have advanced imagery capabilities for detecting camouflaged ground based air defence (GBAD) systems.
All of these sensors on the F-35 aircraft will be data fused to maximise target location and identification and they will also be connected to off board sensors through high level networking.
The F-35 will be equipped with the Harris Multifunction Advanced Data-Link (MADL) to enable secure and VLO high bandwidth transmission.
This data link will enable the Wild Weasel mission F-35 to be fully networked without compromising its emission control (EMCON) status and expose itself to detection by enemy ESM.
Replacing the Raytheon AGM-88 High speed Anti-Radiation Missile (HARM) in the DEAD roll for the F-35 will be the Boeing Joint Dual Role Air Dominance Missile (JDRADM).
Next Generation Air to Anything
JDRADM is currently in the capabilities, integration, and development analysis phase of development and is expected to enter system design and development (SDD) phase in 2012-13 with production from 2020.
JDRADM will combine high capability air to air (ATA) with anti-radiation and smart bomb capabilities for a single munition.
It will also be designed to fit within the size and weight margins of the Raytheon AIM-120 Advanced Medium Range Air to Air Missile (AMRAAM).
JDRADM will be a post Block III weapon for the F-35 that will leverage many of the aircraft's mission systems for enhanced overall capability compared to pre-F35 weapons.
JDRADM will have increased standoff range compared to HARM and AMRAAM and a two way data link significantly improving long range performance and enabling co-operative engagement (missile and F-35).
It will also be a true 360 degree weapon with rear hemisphere engagement capability and high off bore sight (HOBS) seeker engagement.
This seeker will be a dual mode sensor with the radar element operating in multiple frequencies during the engagement cycle.
This will enable use of X band for search followed by Ku band for engagement and Ka band for terminal manoeuvre to optimise active targeting.
Lethality is improved by aiming the warhead independent of the attitude of the missile.
Developed under the Multi-Role Responsive Ordnance Kill Mechanism (MR ROKM) warhead technology program this warhead will focus as much destruction force as possible towards the target based on the seeker's last look.
This will improve lethality against air and ground targets and decrease collateral damage potential against targets hiding in civilian areas.
JDRADM will also have an anti-missile mode enabling it to destroy threats to the F-35 after they have been launched.
One criticism of the F-35 is it lacks enough internally carried stores to be combat effective.
Each F-35 has two internal weapon bays able to carry two stores: one AMRAAM sized weapon and one MK 84 2,000 lb (908kg) general purpose bomb sized store.
The later can be replaced by another AMRAAM enabling up to four AMRAAM or JDRADM sized stores to be carried.
However, the weapons bays each have far higher weight and volume potential than just two AMRAAM stores.
The current configuration is optimised for the primary strike mission of the F-35 and already development is underway to increase storage.
To get the most out of the JDRADM capability and enable more mission flexibility the USAF Air Force Research Laboratory (AFRL) has conceived several addition configurations.
One configuration abandons all the rules of missile carriage - especially keeping onboard a missile that has failed to operate - and can carry as many as six AMRAAMs per bay.
But in line for fielding on Block V of the F-35A is a new configuration with up to four AMRAAMs per bay.
This will enable each F-35A to carry at least eight JDRADM missiles from the 2020s.
For example this will enable a single F-35 mission to engage and destroy four enemy fighter interceptors, destroy a GBAD targeting system, shot down a missile targeting the F-35 and then destroy two separate targets.
Air to Air Superiority
The F-35 will be the first modern aircraft designed to an entirely new concept of within visual range (WVR) air to air combat.
It has been highly criticised for lacking dogfight manoeuvrability because of high wing loading and low thrust to weight ratios.
However it is the new mission systems of the F-35 not physical performance that will provide it with an edge.
Specifically it will be the first fighter able to engage in WVR combat without the need to change its vector - speed, heading or altitude - to achieve kills against manoeuvring fighters.
It will achieve this capability digitally by using the Northrop Grumman AN/AAQ-37 Distributed Aperture System (DAS) combining six electro optical sensors positioned for full spherical coverage around the aircraft.
DAS will enable the F-35 to automatically detect, track and identify all air and ground targets within several tens of kilometres around the aircraft.
It will be used to warn the pilot of incoming aircraft and missile threats as well as providing day and night vision and precision tracking of friendly and neutral aircraft for tactical manoeuvring and collision avoidance.
DAS will significantly enable all aspect WVR engagement when partnered with the right HOBS missile capability like the JDRADM and the AIM-120D version of AMRAAM or those infra red guided missiles with lock on after launch (LOAL) capability like the MBDA AIM-132 Advanced Short Range Air to Air Missile (ASRAAM) and the next block of the Raytheon AIM-9X ‘Sidewinder'.
Legacy aircraft like the Sukhoi Su-27 (NATO: FLANKER) can only engage with their missiles in a frontal arc limited by the low off bore sight capability of their missiles; 60 degrees for its Vympel R-73 (NATO: AA-12 ARCHER) missile.
So in order to engage from the merge - when two fighters pass each other on reciprocal courses and usually used as an even starting point to a dogfight - it needs to rapidly turn at least 120 degrees (taking over five seconds) to bring its missiles into their engagement sphere.
By using the DAS and missile data link the F-35 is able to fire straight away to its rear and update the missile to ensure target lock on and destruction.
Such an engagement would be well within the time required by a turning FLANKER from the merge to engage a non evading F-35.
This unique capability enables the F-35 to avoid significantly changing its vector during WVR engagement with the subsequent loss of speed resulting in flight stall.
Highly manoeuvrable fighters like the FLANKER, F-22 and F/A-18 are designed with aerodynamic features and engine thrust vectoring to delay the onset of stall or provide post stall controlled flight.
These fighters also need high acceleration in order to rapidly restore lost speed thanks to their extreme manoeuvring in air to air combat.
With its HOBS engagement capability the F-35 can remain on steady vector and in a high energy state far longer than more impressive (on paper) dogfighters like the Su-27 and F-22.
While other fighters lose energy as they manoeuvre to allow engagement the F-35 will retain its high speed state and decide to reengage or disengage if needed to continue with a strike mission.
Not only will the DAS combined with HOBS or LOAL be an effective defensive tactic for a strike mission F-35 it will also enable much improved air superiority capability compared to legacy fighters.
This advantage will be similar to that enjoyed by the much faster fighters - in climb and dive - of the Allies during the later part of the WW2 when they destroyed huge numbers of the previously invincible high manoeuvrability Zero fighters of Japan.
This tactic will not just be limited to beyond the merge situations but true all aspect engagement within the appropriate missile's kinematic bubble around the F-35.
With the JDRADM weapon this bubble will be extensive and with networked sensors potentially enable all aspect beyond visual range (BVR) engagement.
Far from being a vulnerable "baby seal" the F-35 will be the most lethal WVR combatant in the air.
The Australian Contribution
Weapons like JDRADM combined with block improvements to current stealthy strike weapons like the Raytheon AGM-154 JSOW [Joint Stand Off Weapon] and Lockheed Martin AGM-158 JASSM [Joint Air to Surface Standoff Missile] will provide the bulk of the F-35's high end engagement capability.
They will also be supplanted in the 2020s by new weapons in early stages of technology development including hypersonic BVR air to air missiles designed to match the long detection ranges of AESA radars and the high speed Next Generation Cruise Missile (NGCM) for time critical targets.
But medium sized air forces like Australia will need lower cost weapons with long range and precision engagement against complex targets.
While the Boeing JDAM [Joint Direct Attack Munition] family remains a weapon of choice they lack the range to be used against medium range air defences (MRAD) and to provide wide area ‘provincial' coverage for Joint Terminal Attack Controllers (JTAC) operating as part of counter insurgency forces.
Adding digitally controlled glide bomb kits to JDAM and similar precision bomb kits provides this capability.
The Defence Science and Technology organisation (DSTO) Project Kerkanya started in the 1970s and has now produced the JDAM Extended Range (JDAM-ER) glide bomb kit for Mk 80 series bombs.
While there have been many glide bomb kits developed for the Mk 80, including those with folding wings and integrated with smart guidance kits, the use of a Kerkanya technology provides unmatched range.
Using a glide profile algorithm and the streamlined wing and tail the JDAM-ER should be capable of over 140km (75 NM) when launched from 30,000 feet at Mach 0.9.
From a 2,000 feet release at Mach 0.82 it still achieve an impressive 43km (24 NM). Range is sacrificed for steep terminal dives to enable hard target penetration.
By comparison a glide bomb with fixed cruciform wings is unlikely to reach a range further than 60km (33 NM) when launched from altitude at subsonic speeds.
Unpowered JSOW and the Boeing GBU-39 Small Diameter Bomb (SDB) can only reach 111km (60 NM) significantly less than the JDAM-ER.
What JDAM-ER lacks is a multimode engagement capability and suffers limitations thanks to its sole reliance on the GPS signal for precision engagement.
At long glide ranges even small degradation of GPS by defensive jamming can have considerable effect on the accuracy of the weapon.
GPS exclusive targeting is also vulnerable to mapping errors in conflict zones that are often fought using 19th century maps that can generate considerable target location error.
Also sole reliance on GPS limits the targets under proscriptive rules of engagement (ROE) that require target identification by imaging.
The solution is combining JDAM-ER with a multi-mode seeker nose to provide increased targeting capability.
There are a range of seekers that could be incorporated into JDAM-ER to provide this capability.
Since Boeing have partnered with DSTO to produce the JDAM-ER (their subsidiary Hawker de Havilland produces the wings) re-use of the under development GBU-40/42 SDB II's multi-mode seeker and two way data link could provide the terminal engagement improvements.
Another option would be to use the off the shelf Mk 80 nose kits of the RAFAEL SPICE [Smart, Precise-Impact and Cost-Effective] smart glide bomb.
SPICE uses GPS to approach the target but then activates its dual mode electro optical seeker head to find its location with a unique scene-matching algorithm.
In this mode SPICE does not identify its target with the seeker but instead compares the position of multiple terrain features to calculate its own precise position.
The system is robust enough to not be effected by weather, countermeasure, camouflage, new terrain features, snow coverings, etc and is completely passive.
Circular error probably (CEP) is 1-1.5m providing very high accuracy (SDB I is 5-8m).