The Joint Strike Fighter, the JSF, is being developed by Lockheed Martin Aeronautics Company for the US Air Force, Navy and Marine Corps and the UK Royal Navy. The stealthy, supersonic multi-role fighter is to be designated the F-35. The JSF is being built in three variants: a conventional take-off and landing aircraft (CTOL) for the US Air Force; a carrier based variant (CV) for the US Navy; and a short take-off and vertical landing (STOVL) aircraft for the US Marine Corps and the Royal Navy. A 70 – 90% commonality is required for all variants. 

Lockheed Martin released a "finalized" design for the production F-35 in the summer of 2002. The following discussion describes most of the details in the present tense for readability, though of course no production aircraft has flown yet, and there still may be some changes in the configuration before that happens. 

The F-35 has a nose 12 centimeters (5 inches) longer than the X-35 demonstrator, while the tailplane has been moved back 5 centimeters (2 inches), and the tailfins have been rearranged a bit. All flight controls are electric, in principle providing easier maintenance and greater combat survivability than hydraulic systems. 

Compared to the USAF F-35A CTOL variant, the USN F-35C CV variant has a larger wing and tail, giving it better range and good low-speed carrier landing characteristics. The wing features folding wingtips. Of course, the F-35C has stronger landing gear and an arrester hook. The F-35B STOVL version has shorter tailfins, implemented as part of the weight-reduction redesign.

The Air Force F-35A has a refueling-boom socket behind the cockpit, while the F-35B and F-35C have a retractable refueling probe on the right side of the nose. The tricycle landing gear, with a forward retracting nosewheel and inward-retracting main gear, has single wheels on all assemblies in the F-35A and F-35B. The F-35C differs in having twin wheels on the nose gear to handle hard carrier touchdowns. 

The F-35's airframe makes heavy use of composite materials, with much work placed on reducing the cost of composite assemblies, which have traditionally been extremely expensive. In fact, the F-35 has been designed to be as cheap to manufacture as possible, using the latest computer-aided design and manufacturing tools. 

The F-35 is powered by a modified version of the P&W F119 engine, designated the "F135". While it is as powerful as the original F119, it is much cheaper, as it uses lower-cost components at the expense of greater weight. It has the same thrust levels as the F119, with 151 kN (15,420 kgp / 34,000 lbf) dry thrust and up to 222 kN (22,675 kgp / 50,000 lbf) afterburning thrust. The engine intake ducting is arranged in a "serpentine" fashion to eliminate radar reflections from the compressor blades. 

Although the P&W F119 engine was selected as the basis for the different engine options of the JSF, in 1995 the US Congress indicated a need for an "Alternate Engine" as a backup plan. The GE F120, originally designed for the F-22 Raptor program in competition with the P&W F119, was selected as the Alternate Engine, and refinements to the F120 for F-35 are under development by a collaboration of GE, Allison, and Rolls-Royce. Thrust levels will of course be similar to those of the F119. 

The shaft-driven lift fan for the STOVL F-35B is built by Rolls-Royce / Allison, and provides up to 80 kN (8,150 kgp / 18,000 lbf) of lift thrust. 

The F-35 has two weapons bays, each of which can accommodate a single "Joint Direct Attack Munition (JDAM)" GPS-guided bomb and an AIM-120 Advanced Medium-Range Air to Air Missile (AMRAAM). The F-35A and F-35C can carry two 900 kilogram (2,000 pound) JDAMS internally, while the STOVL F-35B is limited to internal carriage of two 450 kilogram (1,000 pound) JDAMs. The F-35A and F-35C variants have bulged weapons bays to accommodate the larger munitions; the F-35B's weapons bays also have less internal volume. The two bays have two doors each, with the AMRAAM fitted on a launch rail on the inner door. 

Four stores pylons can be attached to all variants to provide a much larger warload, at the expense of stealth. The inner pylon on each wing is rated for up to 2,270 kilograms (5,000 pounds), while the outer pylon is rated for up to 1,135 kilograms (2,500 pounds). 

Only the USAF F-35A has a built-in gun, with an "Advanced 27 Millimeter Cannon", an improved version of the Mauser BK-27 revolver-type cannon, in the left wingroot. The other variants do not have a built-in gun, but can accommodate a cannon pack plugged into one of the weapons bays. 

* Northrop Grumman is developing the sensor suite for the F-35. The initial design assumption was that the JSF would be a consumer of sensor data, obtaining information from specialized intelligence-gathering aircraft, satellites, and other sources. This approach promised to keep costs down. However, as the pieces began to fit together, something different emerged. This was partly due to the "bottom-up" realization that the new technologies being developed for the JSF were far more powerful than had been considered; and to the "top-down" realization that the numbers of expensive specialized intelligence-gathering aircraft would be small, while there could be thousands of JSFs. 

Now the F-35 is seen more as a producer of sensor data, with each aircraft interacting through high-speed data links with other aircraft to provide greater "electronic domination of the battlespace". If the other aircraft are F-35s, they will be able to cooperate to provide a capability greater than the mere sum of the parts. 

The heart of the F-35's sensors is the Northrop Grumman AN/APG-81 radar, based on the AN/APG-77 "active electronically scanned array (AESA)" developed for the Lockheed Martin F-22 Raptor. An AESA consists of an array of "transmitter-receiver (T/R)" modules linked by high-speed processors. Different T/R modules in the array can be allocated to different tasks, with more modules allocated to tasks that require greater power or sensitivity. 

The F-35's AN/APG-81 provides a range of functions, acting as a multimode radar; active jamming system; passive electronic defense system; and communications system. The system generates signals over a wide range of frequencies and pulse patterns in an unpredictable fashion to ensure "low probability of intercept", allowing the F-35 to "see but not be seen." The AN/APG-81 uses improved technology compared to the F-22's AN/APG-77, but airframe constraints mean that it has fewer T/R modules, limiting it to about two-thirds the range (165 kilometers / 90 nautical miles) of the AN/APG-77. 

The F-35 is also fitted with additional sensor systems, including a an "infrared search and track (IRST)" system for defense and air-to-air combat, and a targeting system for precision attack on ground targets. 

The IRST system is known as the "distributed aperture infrared system (DAIRS or DAS)". DAS includes six IR sensors mounted on different points of the fuselage to provide full-sphere IR detection and tracking. DAS can identify and pinpoint both incoming missiles and airborne targets. 

Targeting is performed by the "electro-optical targeting system (EOTS)", featuring a forward-looking infrared (FLIR) imager; a CCD TV camera; a targeting laser; and a laser spot tracker. Unlike typical contemporary targeting systems, EOTS is not turret-mounted. It has a wide aperture that is blended into the aircraft's nose contours, covered by a window that is opaque to radar, and remains operational through the entire mission. It is derived from technology developed for the Lockheed Martin "Sniper" targeting pod. 

Other avionics include a Northrop Grumman "communication, navigation, and identification (CNI)" system and a countermeasures suite provided by BAe Systems. 

* The F-35's software collects the inputs from all the sensors, as well as inputs relayed over a high-speed datalink, to provide sensor fusion and seamless data display. The software is executed on an "integrated core processor (ICP)". The ICP serves as a central "brain" for the aircraft, integrating all the other electronics systems and coordinating them for display to the pilot, and also executing the pilot's commands. This system is vitally important, since the F-35 is a single-seat aircraft, and the pilot needs help to carry out his or her mission. 

Northrop Grumman selected a "commercial off-the-shelf (COTS)" processor system for the ICP. The F-35 ICP is cheaper than the F-22's "Integrated Core Processor", which was designed a decade ago, but is an order of magnitude more powerful. 

One of the functions of the central processing system is to provide "automatic target recognition and classification (ATRC)". It can often identify specific targets, and if it can't say exactly what a target is, it can at least show which targets are different. 

The processing power of the F-35 has presented the electronics system developers with a formidable software challenge. The F-22 Raptor uses about 2.5 million lines of software, but the F-35 will use 5.6 million lines of code. The F-35 not only has a more advanced electronics system, but it operates in both air-to-air and air-to-ground modes, and is being built in three different versions. The software design strategy is focusing on modularizing the code so that the portions that are unique to each F-35 variant can be isolated, and the remaining code used as-is on all three variants. The portions that are unique to each variant are a minority, about 1.1 million lines. 

In addition, the code is largely executed by an interpretive software layer known as "middleware" that isolates the code from the specific details of the processor used. In principle, this will allow software to be ported to new processors as they become available, requiring only new middleware and maybe a few software tweaks. Interestingly, the code is written in C/C++, strongly suggesting that the military's effort to create Ada as a standardized programming language for defense projects was a dead end. 

The current plan is to have a comprehensive but minimal software suite for F-35 operational introduction, and provide improved releases to bring the F-35 up to full combat capability. F-35 electronics system designers hope to leverage off work done for the F-22 Raptor. 

* The pilot receives inputs from the F-35's electronic systems using an advanced cockpit layout, featuring a full-panel-width display, with dimensions of 20 by 50 centimeters (8 by 20 inches), plus a secondary flight display array, along with "hands on throttle and stick (HOTAS)" controls. It does not have a "head-up display", however, with this function taken over by a "helmet-mounted display" being developed by Visions Systems International, a collaboration of Kaiser Electronics and Elbit of Israel. 

The "smarts" of the F-35 will be particularly appreciated by pilots flying the F-35B STOVL version. Short takeoffs in the Harrier are a troublesome affair that require the pilot to have "three hands": one for the throttle, one for the stick, and the third for the lever that controls the direction of the Harrier's swiveling exhaust nozzles. An F-35B pilot, in contrast, simply flies the plane with stick and throttle, with the software handling the fine details of short takeoff. 

While the Harrier has reaction control thrusters driven by engine bleed to provide low-speed maneuverability, the F-35B simply modulates the four points of its vertical-lift system -- the pivoting exhaust, the two wing exhaust ducts, and the lift fan -- to provide control. This trick would be difficult or impossible to do manually. 

The X-35 prototypes are fitted with a Martin-Baker Mk.16E ejection seat. Production F-35s are supposed to use a new seat from the "Joint Ejection Seat Program". 

* The NATO air campaign against Yugoslavia over Kosovo in the spring of 1999 revealed a shortfall in electronic warfare (EW) capabilities. EW missions during the Kosovo campaign relied heavily on the venerable EA-6B Prowler, and Prowler crews were stretched to the limit. The F-35 is now being seriously considered as a EW aircraft to supplement and eventually replace the Prowler. 

Manufacture of the "EF-35", to give it a plausible name, would certainly even further increase production quantities for Lockheed Martin. Since the EW mission is regarded as requiring at least two aircrew, the EF-35 would have to have tandem seats, with the back-seater sitting where the lift fan / additional fuel tanks are in the current variants. However, the EF-35 is strictly a future prospect at the present time, with no commitment even to a formal investigation phase. Other future options for the F-35 are also under consideration, but any commitment to them seems a bit premature until the JSF actually goes into service. 

General Information. (Source USAF)
The requirement is for: USAF F-35A –air-to-ground strike aircraft, replacing F-16 and A-10, complementing F-22 (1763); USMC F-35B – STOVL strike fighter to replace F/A-18B/C and AV-8B (480); UK RN F-35C – STOVL strike fighter to replace Sea Harriers (60); US Navy F-35C – first-day-of-war strike fighter to replace F/A-18B/C and A-6, complementing the F/A-18E/F (480 aircraft). In January 2001, the UK MOD signed a memorandum of understanding to co-operate in the SDD (System Development and Demonstration) phase of JSF and, in September 2002, selected the STOVL variant to fulfill the Future Joint Combat Aircraft (FJCA) requirement. Following the contract award, other nations signed up to the SDD phase are: Australia, Canada, Denmark, Italy, Netherlands, Norway, Singapore and Turkey. 

The Concept Demonstration Phase of the program began in November 1996 with the award of contracts to two consortia, led by Boeing Aerospace and Lockheed Martin. The contracts involved the building of demonstrator aircraft for three different configurations of JSF, with one of the two consortia to be selected for the development and manufacture of all three variants. 

In October 2001, an international team led by Lockheed Martin was awarded the contract to build JSF. An initial 22 aircraft (14 flying test aircraft and eight ground-test aircraft) will be built in the programs System Development and Demonstration (SDD) phase. Flight testing will be carried out at Edwards Air Force Base, California, and Naval Air Station, Patuxent River, Maryland. In April 2003, JSF completed a successful Preliminary Design Review (PDR). The Critical Design Review has been postponed from April 2004 to 2005. The first CTOL F-35A has begun airframe assembly and is scheduled for its first flight in August 2006. The STOVL F-35B first flight is set for 2007. The F-35A fighter is expected to enter service in 2008, the F-35B in 2012. 

The Lockheed Martin JSF team includes Northrop Grumman, BAE Systems, Pratt and Whitney and Rolls-Royce. Final assembly of the aircraft will take place at Lockheed Martin's Fort Worth plant in Texas. Major subassemblies will be produced by Northrop Grumman Integrated Systems at El Segundo, California and BAE Systems at Samlesbury, Lancashire, England. BAE Systems is responsible for the design and integration of the aft fuselage, horizontal and vertical tails and the wing-fold mechanism for the CV variant, using experience from the Harrier STOVL programme.

DESIGN
In order to minimise the structural weight and complexity of assembly, the wingbox section integrates the wing and fuselage section into one piece. To minimise radar signature, sweep angles are identical for the leading and trailing edges of the wing and tail (platform alignment). The fuselage and canopy have sloping sides. The seam of the canopy and the weapon bay doors are saw-toothed and the vertical tails are canted at an angle. 

The Marine variant of JSF is very similar to the Air Force variant, but with a slightly shorter range because some of the space used for fuel is used for the lift fan of the STOVL propulsion system. The main differences between the naval variant and the other versions of JSF are associated with the carrier operations. The internal structure of the naval version is very strong to withstand the high loading of catapult assisted launches and tail hook arrested landings. The aircraft has larger wing and tail control surfaces for low speed approaches for carrier landing. Larger leading edge flaps and foldable wingtip sections provide a larger wing area, which provides an increased range and payload capacity.

The canopy, radar and most of the avionics are common to the three variants.

WEAPONS
Weapons are carried in two parallel bays located in front of the landing gear. Each weapons bay is fitted with two hard points for carrying a range of bombs and missiles. Weapons to be cleared for internal carriage include: JDAM (Joint Direct Attack Munition), CBU-105 WCMD (Wind-Corrected Munitions Dispenser) for the Sensor-Fuzed Weapon, JSOW (Joint StandOff Weapon), Paveway II guided bombs, AIM-120C AMRAAM air-to-air missile; for external carriage: JASSM (Joint Air-to-Surface Standoff Missile), AIM-9X Sidewinder and Storm Shadow cruise missile.

In September 2002, General Dynamics Armament and Technical Products was selected as the gun system integrator. The air force variant has an internally mounted gun. The Carrier and Marine variants can have an external gun pod fitted. 

TARGETING
Lockheed Martin Missile & Fire Control and Northrop Grumman Electronic Sensors and Systems are jointly responsible for the JSF electro-optical system. A Lockheed Martin electro-optical targeting system (EOTS) will provide long-range detection and precision targeting, along with the Northrop Grumman DAS (Distributed Aperture System) thermal imaging system. EOTS will be based on the Sniper XL pod developed for the F-16, which incorporates a mid-wave third generation FLIR, dual mode laser, CCD TV, laser tracker and laser marker. BAE Systems Avionics in Edinburgh, Scotland will provide the laser systems. DAS consists of multiple infrared cameras (supplied by Indigo Systems of Goleta, California) providing 360º coverage using advanced signal conditioning algorithms. As well as situational awareness, DAS provides navigation, missile warning and infrared search and track (IRST). EOTS is embedded under the aircraft’s nose, and DAS sensors are fitted at multiple locations on the aircraft.

RADAR
Northrop Grumman Electronic Systems is developing the advanced electronically scanned array (AESA) AN/APG-81 multi-function radar. The AN/APG-81AESA will combine an integrated radio frequency subsystem with a multifunction array. The radar system will also incorporate the agile beam steering capabilities developed for the APG-77. 

COUNTERMEASURES
BAE Systems North America will be responsible for the JSF integrated electronic warfare suite, which will be installed internally and have some subsystems from Northrop Grumman. BAE is developing a new digital radar warning receiver for the F-35. 

AVIONICS SYSTEMS
The following will supply the F-35 avionics systems: BAE Systems Avionics - side stick and throttle controls; Vision Systems International (a partnership between Kaiser Electronics and Elbit of Israel) - advanced helmet-mounted display; Ball Aerospace - Communications, Navigation and Integration (CNI) integrated body antenna suite (one S-band, two UHF, two radar altimeter, three L-band antennas per aircraft); Harris Corporation - advanced avionics systems, infrastructure, image processing, digital map software, fiber optics, high speed communications links and part of the Communications, Navigation and Information (CNI) System; Honeywell - radar altimeter, inertial navigation/global positioning system (INS/GPS) and air data transducers; Raytheon - 24-channel GPS (Global Positioning System) with digital anti-jam receiver (DAR). 

SYSTEMS
Other suppliers will include: ATK Composites - upper wing skins; Vought Aircraft Industries - lower wing skins; Smiths Aerospace - electronic control systems and electrical power system (with Hamilton Sundstrand), integrated canopy frame; Honeywell - landing system's wheels and brakes, onboard oxygen-generating system (OBOGS), engine components, power and thermal management system driven by integrated auxiliary power unit (APU); Parker Aerospace - fuel system, hydraulics for lift fan, primary flight control electrohydrostatic actuators (with Moog Inc), engine controls and accessories; EDO Corporation - pneumatic weapon delivery system; Goodrich - lift-fan anti-icing system; Stork Aerospace - electrical wiring. 

PROPULSION
Early production lots of all three variants will be powered by the Pratt and Whitney afterburning turbofan F-135 engine, a derivative of the F119 fitted on the F-22. Following production aircraft will be powered by either the F135 or the F-136 turbofan being developed by General Electric and Rolls-Royce. Hamilton Sundstrand is providing the engine control system and gearbox.

On the F-35B, the engine is coupled with a shaft-driven lift fan system for STOVL propulsion. The lift fan has been developed by Rolls-Royce Defence. Doors installed above and below the vertical fan open as the fin spins up to provide vertical lift. The main engine has a three bearing swiveling exhaust nozzle. The nozzle, which is supplemented by two roll control ducts on the inboard section of the wing, together with the vertical lift fan provide the required STOVL capability.