April 1, 2006
F-35 Electronic Warfare Suite: More Than Self-Protection
The F-35 will combine radar warning, signals collection and analysis, passive emitter location and countermeasures functions in an integrated electronic warfare suite deeply linked to radar and imaging sensors. The design aims to bootstrap pilot situational awareness while boosting lethality.
By Ron Sherman
Electronic warfare (EW) systems allow modern combat aircraft to use the electromagnetic spectrum against the enemy. EW includes the ability to collect, identify and locate signals, detect hostile radars and missile attacks, and activate countermeasures to disrupt or degrade enemy offenses and defenses. While some aircraft remain dedicated to the EW mission, the F-35 is designed to accomplish a wide range of electronic warfare tasks simultaneously with air-to-air and air-to-ground functions in support of its overall mission. Taken together, the Joint Strike Fighter's (JSF's) electronic warfare system is designed to extend the pilot's situational awareness and to identify, locate, track and defeat enemy defenses both in the air and on the ground.
JSF designers are attempting an unprecedented level of integration--between elements of the electronic warfare suite and within aircraft mission systems. Older fighters like the F-14 had federated EW systems, explains Mark Drake, F-35 business development manager with BAE Systems, the designer of the F-35's EW suite. There was a box for the radar warning receiver (RWR) and a box for dispensing chaff and flares. The pilot would see a missile launch on one display and detect other signals in the environment through another system. The pilot was the ultimate information integrator.
The F-35's EW system, by contrast, would lessen that workload. JSF is designed from the ground up to be an integrated system that would incorporate all the different aspects of survivability and mission accomplishment, Drake says.
While the JSF package is not the first integrated EW system--the F-22 does the same--it is the "first real improvement on fighter-based EW systems that is clearly linked from the beginning to do a combination of jobs," he says. "The novelty of the JSF is its ability to draw together an abundance of data and formulate it into actionable knowledge for the pilots," permitting them to focus on tactics and strategies for overall dominance, says Eric Branyan, vice president of JSF mission systems for Lockheed Martin, the F-35 prime contractor.
Integration of EW sensors with the F-35's AN/APG 81 active electronically scanned array (AESA), communications and electro-optical distributed aperture systems puts offensive, defensive, coms and data-gathering sensors at the service of the pilot to process onboard and offboard data. The EW system employs a range of dedicated antennas and shares the AESA antenna for tasks such as electronic support measures or signals collection and analysis. The F-35's high-gain, electronically steered radar array provides jamming support under the control of the EW system. Because the AESA array provides very directional radio frequency (RF) output, the JSF could target a very small area and selectively jam it, which enhances survivability by reducing electronic emissions.
Integration of the EW system's elements is intended to reduce system volume and power requirements and increase affordability. But it also can aid survivability, compared with federated systems. Integrating the radar warning and countermeasures functions, for example, shortens response time. "The [systems'] handshake is intimate," Branyan says.
At a deeper level of integration, EW and other mission sensors are connected via a common, large-scale computing resource--the F-35's integrated core processor, or ICP. Integration at this level, for example, enables the electro-optical distributed aperture system (EODAS) sensor to support the deployment of countermeasures. Although the RF-based EW system and infrared (IR) -based EODAS system are built to run separately in different frequency domains, they are tied together at the ICP level. Instead of having the pilot operate EW and IR displays separately to detect threats with the individual sensors, "the airplane can deploy the optimal countermeasures with or without pilot action," Branyan says. This level of automation and improved situational awareness shortens the timeline of detection and response.
The integrated core processor aggregates and correlates multisource data and formulates solutions for presentation to the pilot, mixing the best data from each sensor. This maximizes detection ranges and provides the pilot options to evade, engage, counter or jam threats.
"The end result will be maximum situational awareness within individual cockpits and throughout strike packages, linked to command and control nodes, to ensure the battlespace is fully detected, understood and exploited," asserts Jon Waldrop, Lockheed Martin's director of international programs. At the EW system level, the F-35 will about equal the F-22 in performance, Branyan predicts. But because the newer aircraft's EW suite was developed from the start for reliability and affordability, it promises twice the reliability at half the cost, compared with legacy aircraft.
The F-35's EW system is all-digital, which translates to reduced size, weight and power requirements, as well as greater speed and accuracy. The ICP will process data at up to 1 trillion operations per second, and that capacity could double before the F-35 becomes operational, says Waldrop. Lockheed Martin selected a commercial-based ICP, which costs considerably less than its mil-spec predecessors and promises orders of magnitude more power.
Always active, the EW system would provide all-aspect, broadband protection. "If you were to put a ... circle around an aircraft, there would be no one quadrant, degree or section that is not covered instantaneously, all the time," Drake asserts. Six low-observable EW apertures are distributed around the aircraft--two embedded inside the leading edge of each wing and one in the trailing edge of each horizontal tail. Located inside the aerodynamic mold line of the aircraft, the EW apertures are designed to allow the aircraft to perform missions without altering its radar cross-section. One aperture can be used to identify the mode of a hostile radar, and two or more apertures can be used to determine the direction of enemy emissions. There are three, four-channel wideband EW receivers.
Of the various mission sensors, the EW elements, aided by the AESA antenna, probably would detect the enemy first, after which the aircraft's electro-optical system could scan it. The radar and EW apertures cooperate closely in the RF domain. The F-35's AESA antenna and the EW receivers are connected to support quick, long-range searches throughout the AESA antenna's bandwidth.
The radar warning function includes analysis, identification and tracking of hostile radars, as well as mode detection and monopulse, angle-of-arrival direction finding. The EW system discriminates one emitter from another by determining signal characteristics such as frequency, pulse width and pulse repetition frequency. Mode determination includes defining the operating function of an emitter at a given time, e.g., search, acquisition, tracking, based on known characteristics.
The self-protection system includes a response manager and RF/IR countermeasures. Two countermeasure dispensers are located in the aft area of the aircraft, carrying IR flares and chaff. The IR flares are relatively small, allowing more to be carried than was possible in predecessor aircraft. The EW system claims a 440-hour mean time between failures. An onboard diagnostics and fault isolation system, which automatically downlinks data to maintainers, allows line replaceable modules to be ready when the aircraft returns to base. This should simplify logistics and increase combat sortie rates.
Six years ago Lockheed Martin selected BAE Systems as the F-35's EW supplier. Now about 50 months into the F-35's 10-year development cycle, the company has completed proof-of-design work and met the form, fit, functionality and maturity goals established for this initial phase of development, Branyan says.
The F-35's flight test program is slated to commence in the fourth quarter of 2006, using the first seven aircraft. But these are "flight sciences" aircraft, fitted with only the basic avionics infrastructure to support coms and navigation functions. They will be used to evaluate flying qualities, stability, envelope expansion and weapons release.
Last July BAE Systems flight tested the EW system built to the proof-of-design maturity level. The company used a leased T-39, the military version of the Sabreliner business jet. This internally funded risk reduction effort conducted at the Naval Air Weapons Station, China Lake, Calif., "proved the system worked and exceeded all predicted performance parameters," Drake asserts. According to the company's announcement at the time, the EW sensors collected simulated RF threat data from ground emitters, using the system's digital receivers.
Block 0.5 Suite
The China Lake test provided airborne evidence of early system maturation and fed into the proof-of-manufacturing phase. BAE Systems is testing the proof-of-manufacturing-level electronic warfare system at its Nashua, N.H., facility.
Lockheed Martin expects to receive the equipment later this month in Fort Worth, Texas. With the initial Block 0.5 configuration, BAE Systems will deliver the processing architecture, apertures and about 35 percent of the software. These elements will be enough to start evaluating the basic functionality. In 2007 BAE will start delivering more capable, Block 1.0 software and the final countermeasures suite. The Block 1.0 EW version will be evaluated on system development and demonstration (SDD) jets. Block 1.0 also provides the initial operational capability (IOC) that will be installed on the low-rate initial production jets to be used in operational test and development.
When the Block 0.5 equipment arrives, Lockheed will perform testing in a simulation and stimulation environment. The EW system can be exercised from a flight simulator, which is "flown" to an area with simulated threats that test whether the EW system correctly identifies, tracks and engages the hostile emitters. Stimulation refers to the input of RF signal simulation in order to evaluate EW functions against simulated threats. Lockheed also will use an open air, full-scale F-35 model, mounted on a pole outside the facility, to further verify EW capabilities. The apertures can be installed on this open air model, so other aircraft can be put up to test the EW system and essentially "fly against it," Branyan says. Airborne testing of the integrated sensor suite is set to begin in the first quarter of 2007 on Lockheed's F-35 Cooperative Avionics Testbed, a modified Boeing 737, shown at left.
Flight testing of the EW system on the F-35A is planned to begin in the fourth quarter of 2008 with the first flight of a fully integrated "avionics aircraft." This aircraft will include the first full-production EW suite, slated for delivery in the first three months of 2007. The suite will be identical in all U.S. and international F-35 variants.
According to Dan Gobel, BAE Systems' vice president of F-35 programs, the development program is unique in using performance-based specifications instead of the traditional military specifications. "Performance" in this context refers to aircraft performance and supportability.
Performance-based specs have been a major factor in meeting cost and reliability goals. "We set defined goals very early in development," says Gobel. "In the critical design review, we were 10 percent below our weight goal and below the target for recurring fly-away costs." Last year BAE Systems quoted EW system weight as 185 pounds (84 kg).
Leveraging legacy technology and past problem-solving techniques helped solve early issues. BAE Systems' team, for example, used lessons learned from the F-22's AN/ALR-94 RF warning and countermeasures subsystem, which the company developed. "We made a point to involve the average guy on the line, all the way up to a vice president, from day one, as we designed the system," Drake says.
"Every element of the [F-22] team was interviewed at length, and the [design] problem was examined from every possible angle and from every level of seniority, expertise and function. They were asked what they would do differently if they had to do it all over again."
As a result, JSF's EW system--both the architecture and the manufacturing and assembly methodology--avoided processes, materials or techniques that would have increased cost or weight, or adversely affected supportability, Drake says. The design of the aircraft's low-observable antenna arrays, for example, benefited, as these elements "were a follow-on to a previous design," he says. By introducing producibility considerations at the beginning of development engineering, BAE asserts it was able to reduce production risk and increase system reliability and affordability. "It was a very good strategic decision," Drake says.
Also important is the use of spiral development practices to leverage the commonalities between the F-35 and F-22A. Waldrop says: "Every time the F-22A flies we learn more. We can now spiral advanced technology developed for the F-35 back into the Raptor." The similarities between both sensor suites allow for an unprecedented degree of technical cross-fertilization. The F-35's iterative flight test program will contribute significantly to JSF maturation, as well. The flight test schedule is built around a series of periodic block releases, allowing content and function to be influenced by test results.
JSF's EW suite uses an open architecture to simplify integration and future evolution. It uses industry-standard components, including software written in the C++ programming language, field programmable gate arrays (FPGAs), 6U circuit cards in the VME format, and PowerPC microprocessors. F-35 mission systems designers aim to avoid the rigidities of firmware "burned into" hardware devices to provide the flexibility for spiral updates.
Within the JSF's overall mission systems package there is considerable overlap between the sensors. The best example is the aircraft's electro-optical distributed aperture system. While not part of the EW suite, EODAS has six strategically placed, embedded sensors, providing a fully spherical, continuously operating IR shield that can identify and track threats such as missiles, vastly increasing pilot situational awareness, says Branyan. Operating in the midwave-IR range, EODAS can provide warning at "tactically significant ranges," he says. EW and EODAS are two elements of an integrated sensor suite designed to detect and identify the full spectrum of air- and ground-based threats. EW, coupled with EODAS, provides integrated RF-IR domain coverage, Branyan says.
"Within the battlespace, pilots must be continually aware of both threats and friendly assets," Waldrop says. "While integrated systems like EW and DAS significantly ease pilot workload, it's ultimately up to the pilot to prioritize threats to ensure mission success." In the case of long-range detection, he says, the pilot has more time to detect and assess the threat. The ability to find and analyze a threat well before it detects the F-35 maximizes both offensive lethality and survivability. But it's a definite advantage to know that the integrated EW suite continues to operate in the background.
"It is important to note that as F-35 pilots fly a mission, the integrated sensor suite provides full situational awareness," says Waldrop. Sensor information includes not only onboard radar, EODAS and EW, but also offboard information. This could involve data from E-3 airborne warning and control system (AWACS) aircraft, Joint STARS (E-8C ground surveillance) aircraft, data-linked air and ground intelligence, other combat aircraft, and both space- and sea-based elements. All the tactical/defensive information, both on board and off board, is fed to the pilot through the F-35's integrated core processor.
The JSF team has overcome some big systems integration challenges, including "the ability to provide the pilot with incredible amounts of information in a very intuitive way," enabling the pilot to maintain the tactical advantage over any adversary, asserts Waldrop. The aircraft's open architecture design and use of commercial off-the-shelf components, furthermore, should improve sustainment and allow efficient upgrades.
The overarching challenge, Waldrop says, is to detect and assess relevant events in the battlespace, drawing from and publishing critical data into the "infosphere." In the final analysis, he concludes, the ultimate goal of the pilot-JSF integrated sensor interface is to achieve "a maximum level of actionable situational awareness."