F-35 Integrated Sensor Suite: Lethal Combination

As the tactical aircraft enters the combat zone, an indication of a potential target pops up on the pilot’s multifunction display (MFD). Flying toward the area of interest, the pilot presses his finger against the touch-screen display and views a much clearer, close-up image of the target, which is identified as an enemy ground vehicle. The pilot presses the screen again, and target designation and weapons status imagery appears on the visor of his helmet-mounted display (HMD). Closer in, he views the target, now being automatically tracked; the crosshairs in the visor lock on to the target; and the pilot fires a missile that follows a laser beam to its destination. The pilot again views the MFD and notes that the target has been destroyed.

Sounds easy. And, flying the F-35 Joint Strike Fighter (JSF), that’s how easy target detection and destruction is meant to be, whether against ground vehicles, ships or enemy aircraft. Where the complexity lies is in the sensors, displays and prodigious processing power that make up the automatic targeting capabilities of this 21st-century, multibranch, multinational, supersonic fighter. The F-35 also is a multimission aircraft, to be produced by program lead Lockheed Martin Aeronautics Co. in three configurations: conventional takeoff and landing, short takeoff and vertical landing, and a carrier variant. All variants are to have more than 90 percent avionics commonality.

Key to the F-35’s targeting capability is sensor integration and data fusion. Mission systems software fuses data from the following sources:

– The electronically scanned array radar,

– The electro-optical targeting system (EOTS) with forward-looking infrared (FLIR) and infrared search-and-track (IRST) system,

– The electronic warfare suite, developed by BAE Systems,

– The electro-optical distributed aperture system (DAS), and

– The communication, navigation and identification (CNI) suite, providing identification friend or foe (IFF) and offboard data delivered via a high-speed data link.

The F-35 pilot receives unprecedented situational awareness from a mission systems package that incorporates modular open systems architecture, object-oriented design and, as often as possible, common commercial off-the-shelf (COTS) processors. Combined with onboard precision weaponry–missiles, smart bombs and a 25-mm cannon–the F-35 is meant to "compress the kill chain," a U.S. military goal emphasized by Chief of Staff Gen. John Jumper, who has stated that he wants the U.S. military to attain the capability of destroying targets "within single-digit minutes" of their detection.

AESA Radar

A primary element to achieve that goal in the F-35 is the active electronically scanned array (AESA) fire control radar developed by Northrop Grumman Electronic Systems sector. This long-range sensor, designated the AN/APG-81 radar, offers all-weather, standoff target detection, minimizing threat exposure. It probably would be the first onboard sensor to identify a target. The APG-81 is a fourth-generation radar, comparable to systems that Northrop Grumman has developed for the F/A-22 (APG-77 radar) and F-16 Block 60 (APG-80) and that Raytheon developed for the F-15C, the APG-63(V)2. Indeed, Lockheed Martin and its F-35 suppliers strove to leverage as much F/A-22 technology as possible.

Like these radars, the APG-81 has no moving parts, such as gimbals and motors, and little wiring to wear out. It is expected, therefore, to offer a long lifespan; a Northrop Grumman official claims 8,000 hours "would be reasonable to expect." To save space and weight, the company also incorporated a "twinpack" for the radar, combining transmit and receive chips in a single module.

The APG-81 comes with a synthetic aperture radar (SAR) terrain mapping function for air-to-surface surveillance and targeting. It is comparable to the terrain mapping radar used in reconnaissance aircraft, unmanned air vehicles, and the E-8C Joint Surveillance Target Attack Radar System (Joint STARS) aircraft.

The radar technology "is on many aircraft," according to Scott Porter, Northrop Electronic Systems’ director of business development for Aerospace Systems. "But we’re working to provide the F-35 radar with higher resolution for easily recognizable features on the ground and to have the radar look at bigger patches of real estate. We would like to cover three or four times more terrain than [what today’s radars] see now."

By activating buttons around the aircraft’s 20-by-8-inch panoramic, multifunction display (developed by Rockwell Collins’ Kaiser Electronics), the F-35 pilot can select from the radar’s many software-driven modes: target identification and tracking, air-to-air, air-to-ground, air-to-sea surface target detection and electronic warfare, as well as SAR ground mapping. It can designate both ground targets and airborne targets simultaneously. Being a pulse Doppler radar, the APG-81 can eliminate background clutter regardless of the target environment.

Another mode is the "inverse SAR" mode used to detect and identify surface vessels at sea. As the name implies, it works opposite the SAR mode, in which the radar software forms a composite picture of a ground target based on the movement of the aircraft. Rather, the inverse SAR mode "forms a composite picture of a ship based on the vessel’s motion on the sea," Porter explains.

For air-to-air operations, the APG-81 will support such features as passive search and multitarget, and beyond-visual-range tracking and targeting. It also will support a cued search feature, in which the radar is cued toward another sensor’s line of sight. That other sensor can be onboard, offboard or pilot-directed. Because the radar beam can move from point to point in millionths of a second, the F-35 pilot can view a single target as many as 15 times a second.

The APG-81 program is now in the system development and demonstration (SDD) phase, which continues through 2008. In early March Northrop Grumman delivered the first radar to Lockheed Martin for radome integration testing at the prime contractor’s Palmdale, Calif., facility. On Aug. 23, the radar was first flown in Northrop Grumman Electronic Systems’ specially equipped BAC 1-11. Initial flight testing of the radar began Sept. 8. Engineers will test the radar’s software modes during the flight test program.

EOTS

While the AESA radar provides the F-35 pilot with an all-weather, active targeting sensor, the electro-optical targeting system incorporates day/night passive sensors, unable to be detected by enemy warning systems. Providing high-resolution infrared imagery that is software-enhanced through signal processing, EOTS can give the F-35 pilot a closer look at the target area initially detected by the radar. "If you see [with the radar] a ground object of interest, you can pass the coordinates to the EOTS, to zoom in for long-range confirmation," says Porter.

"The two sensors complement each other," adds Mike Skaff, F-35 pilot/vehicle interface lead with Lockheed Martin. "Radar works well in weather, while EOTS is good for targeting, especially air-to-surface targeting, because of its high definition."

EOTS is part of the F-35’s electro-optical sensor system (EOSS), developed by Orlando, Fla.-based Lockheed Martin Missiles and Fire Control. Lockheed also serves as lead in the EOTS’s development, with support from BAE Systems. EOTS incorporates a targeting laser, TV camera and a third-generation infrared sensor.

What makes the internally mounted EOTS unique is that it is not turret-mounted. And its capabilities are comparable to those of the low altitude navigation and targeting infrared for night (LANTIRN) system but without the aerodynamic drag of a pod. (EOTS technology derives from Lockheed’s Sniper targeting pod.) Rather, the EOTS’ automatically boresighted sensor is positioned behind a glass-like sapphire housing that blends into the F-35’s nose, just under the radar antenna, easily accessible by maintenance personnel.

The EOTS incorporates an air-to-surface FLIR tracker and air-to-air IRST system. It also includes a single aperture design and advanced, third-generation focal plane array, as well as a "spot tracker," capable of tracking a laser beam directed by a remote source.

EOTS has been sent to Lockheed Martin’s F-35 mission systems integration lab in Fort Worth for testing in simulated scenarios.

The DAS

Like EOTS, the F-35’s distributed aperture system is incorporated in the fuselage design and does not require a pod. Six IR cameras–Porter calls them situation awareness "eyeballs" that create a flying "Imax"–are embedded in the aircraft, positioned to provide full spherical imagery around the aircraft.

The IR sensors form an integrated detector assembly inside the IR camera. The sensors form a total, passive picture around the aircraft, with "all of the information all the time," according to Porter. They give the F-35 pilot missile approach warning, countermeasures deployment, passive air-to-air radar, off-axis targeting for air-to-air missiles, and wide field-of-view day/night pilot vision. With off-axis targeting the pilot can assign a display of interest to the HMD and point his head to the intended target, designate and shoot. Providing through-the-cockpit-floor viewing, the DAS even assists the pilot in landing the aircraft. It can be used for after-dark, bomb damage indication (BDI), too, offering the pilot an alternative to using night vision goggles for damage assessment.

Also in the SDD phase, the DAS is being flight tested on an Air Force F-16 at Edwards AFB, Calif.

Each of the F-35’s sensors provides powerful situation awareness and targeting information, but their integration to form a single, fused image makes them even more powerful, while not burdening the pilot with information overload. Each sensor has its own processor to automatically determine the appropriate modes, acquire targeting data, and deliver the imaging data over a Fibre Channel backbone bus within the integrated core processor (ICP), where it is fused to present a clear, comprehensive picture of the target and its setting.

To analyze and prioritize the incoming targeting data, the ICP uses algorithms dedicated to the various tasks: air-to-air, air-to-ground and the target identification received from the CNI suite. And these algorithms are distinct from those used to fuse other onboard data, for example, the GPS and inertial nav data for a comprehensive navigation picture.

The fused targeting data can be overlayed onto a battlefield situation display that the F-35 pilot has uplinked from a ground base or another aircraft. The intent of these features is to produce battle scene awareness to support an observe, orient, decide and act (OODA) sequence for F-35 pilots.

In a typical scenario the pilot would first detect a beyond-eyesight target in a predominantly radar image on the MFD. As the target gets closer, the EOTS imagery automatically creates a clearer picture of the target on the MFD. At this point the pilot assesses an operational picture of the battle space, evaluates the threat responses and rapidly plans a route to secure minimum exposure and maximum weapon effectiveness, and determines the best choice of weapon.

Once he has made his decision to attack the target, the pilot would switch from the head-down to the head-up display in his helmet-mounted visor. "You look at the two displays like wearing bifocals," says a Northrop offical. In addition to presenting a center cross that locks onto the target for a point-and-shoot capability, the HMD also presents the status of available weapons, a symbol for IFF and indication of the target’s range, closure and velocity. With most of the target detection and presentation achieved automatically, the OODA process, from acquisition to destruction, can be done within the few minutes that Gen. Jumper set as a goal for engagement.

All told, the targeting sensors and processors make the F-35 not just a combat aircraft firing weapons, but a first-day-of-the-war, multimission aircraft able to perform autonomously, cooperatively or remotely, using information from offboard sources. In a cooperative mission, for example, the F-35’s ICP would package and format targeting data to form a waveform for delivery by the CNI to a ground base or other aircraft via Link 16 or an internal data link.

The suppliers of the radar, EOTS, DAS and other systems are performing much of the F-35’s software development and integration work–as much as 40 percent, a Lockheed Martin official estimates. The mission software (ultimately, an estimated 4.5 million lines of code written in C/C++) is still under development and will be completed in increments. The integrated core processor is in development, and integration testing will begin in the first quarter of 2006.

F-35’s CNI Suite

Contributing to the F-35’s targeting capabilities is another Northrop Grumman package: the communication, navigation and identification suite. Northrop Grumman Radio Systems, a San Diego-based business unit of the company’s Space Systems Division, is developing a suite of software defined radios (SDRs) designed to provide such functions as beyond-visual-range identification friend or foe, secure voice communications, caution and warning, intercom, and intraflight information sharing among multiple aircraft via a high-speed broadband data link.

The F-35’s CNI suite is comparable to the one Northrop Grumman developed for the U.S. Air Force’s F/A-22. "However, it has additional functionality driven by changes for network centric warfare and by the fact that the Joint Strike Fighter is a multibranch, multinational program and therefore must satisfy the needs of multiple customers," says Ken Fecteau, director of the F-35 CNI program at Northrop Grumman. "Also, we’ve been able to reduce the system’s weight and power use."

Reduced weight, along with improved supportability, has been achieved by minimizing hardware through an integrated avionics approach. Fewer components result in less aircraft maintenance and smaller logistics tail. To further facilitate maintenance the F-35’s CNI suite includes automated fault detection and isolation.

For communications the software radios in the CNI suite include UHF/VHF receivers and Link 16, an L-band networking waveform. It also is designed to accept the Joint Tactical Radio System (JTRS) waveform. The CNI suite will include TACAN navigation and interface with a GPS receiver. An instrument landing system and the GPS-based Joint Precision Approach and Landing System (JPALS) will be part of the CNI package.

Three-dimensional audio algorithms, to direct appropriate audible cues 360 degrees around the pilot are expected to be part of the CNI suite’s future growth.

In-Flight Reconfiguration

The communications radios in the CNI are multichannel and multiband, so they can be configured to perform multiple functions simultaneously. The F-35 pilot can reconfigure the radios manually in flight or have them preprogrammed on a cartridge as a mission load. The CNI system’s SDRs have the capability for reconfiguration while airborne, which supports dynamic missions and allows recovery from battle damage.

Seven PowerPC processors are plugged into the CNI suite’s two 6U racks, which provide redundancy in case one rack is battle damaged. Five of the processors are dedicated to signal and data processing; two other processors serve as interface modules. The two interface modules, one per rack, link the CNI processors with the F-35 integrated core processor. Each processor includes cryptographic algorithms to ensure both voice and data communications security.

In 2004 Northrop Grumman delivered legacy avionics boxes to prime contractor Lockheed Martin for initial flight testing. They included UHF/VHF communication, radar altimeter, intercom, integrated caution and warning, and IFF. The software radios for the CNI, now under development, will be delivered in June 2006 for testing in Lockheed’s mission systems integration lab in Fort Worth, says Fecteau. In September 2006 Northrop Grumman plans to deliver a CNI suite for installation in the F-35 program’s airborne test bed, a much-modified Boeing 737.

Perhaps the most guarded capability on the F-35 is its automatic target recognition. Lockheed Martin would only say that the aircraft will be continuously processing sensor detections regardless of the orientation (air or ground track). "Some tracks can be easily and rapidly resolved and categorized, while others will require some extensive processing to resolve ambiguities," says a Lockheed official. For automatic target identification, he adds, the F-35 aircrew "will be able to choose target types during the preflight mission planning process."

Multinational JSF

That the F-35 is meant to be a versatile combat aircraft is evident in the number of aircraft it replaces and the missions it is to perform. Three variants of the JSF are to be built: the conventional takeoff and landing (CTOL) F-35A, short takeoff and vertical landing (STOVL) F-35B, and the carrier variant F-35C. Among the aircraft the multimission F-35 is to replace are the U.S. military’s AV-8B Harrier, A-10, F-16, F/A-18 and the UK’s Harrier GR.7 and Sea Harrier. Outside of the United States, eight countries are involved in the F-35’s development: United Kingdom, Italy, Netherlands, Turkey, Canada, Denmark, Norway and Australia. The United States and UK have indicated their JSF requirement; the other countries are expected to place orders for F-35s but are still determining their air combat needs. The requirements for the U.S. and UK militaries, totaling 2,593 aircraft, are as follows: