F-22 Raptor Avionics
Avionics share as large a part in the success of a fighter as the ability to maneuver and fly fast, or to "turn and burn." The design issues that had to be addressed involved solving the technical and organizational challenges of running the program. Also crucial to the design, was the reduction of pilots' "housekeeping" responsibilities.
The F-22 has the first integrated avionics suite ever flown on a combat aircraft. The Northrop/Grumman-Texas Instruments APG-77 radar, Lockheed Martin electronic warfare suite and the TRW communications/navigation/IFF subsystems are all included.
The requirements for the F-22's avionics system are derived from the F-22 Weapon System Concept, the guiding design principles for the overall weapons system. The integrated avionics system is one of the key elements (the others being stealth, maneuverability, and supercruise) that gives the F-22 the tactical advantage against the threats of the future.
The avionics system requirements are based on zones of operational interest. These zones, based on enemy and own ship capabilities, determine the information requirements for each object encountered in the mission. Today's fighters have some of the same sensing capabilities and subsystems to be controlled, but their federated architecture (that is, each avionics function has its own processor and essentially works independently) makes the pilot the integrator of data and the manager of all the supporting subsystems.
The F-22 operational concept, and the sophistication of the various systems requires integration at many levels, including sensor control, sensor data fusion, the architectural components that support these functions, and the displays that are the primary means of communication with the pilot. The key attributes of the avionics system are driven by the other weapon system characteristics such as stealth, supercruise, reliability, availability, and need for growth capacity.
Integrated avionics means different things to different people.
- To the pilot, it means all the information is coordinated and available from a single source.
- To the software engineer, it means access to shared data about the situation, the mission, and the aircraft systems.
- To the hardware designer, it means common modules in a single backplane with the connectivity and bandwidth to support the required processing.
Coherent presentation and control (the pilot's view of integration) is not simply a way of organizing functions or routing lots of data to a single display. It actually includes additional functionality, such as situation assessment and weapons fire control. The software view of integration means that the various functional pieces of the software must have efficient access to globally coherent information, such as track files, navigation data, mission data, and aircraft system status information. A hardware architecture built on common components, common modules, standard buses, and common operating system provides the infrastructure for the processing and communication between the processes described above. In addition, modular approach allows for easy expansion of capacity and capability, fault tolerance, and reconfiguration.
Translating the system requirements into a producible, affordable, and maintainable design was the work of the Engineering and Manufacturing Development (EMD) program. The basic concept, derived from the Pave Pillar program in the 1980s (which included development of Integrated Communications, Navigation, Identification Avionics (ICNIA) and Integrated Electronic Warfare System (INEWS) systems) was to provide all the signal and data processing resources in a central collection of modular processors, linked to the sensors, subsystems, and pilot by high-speed data busses. The F-22 architecture provides just such a system, interfaced to the air-cooled, flight safety critical systems such as the flight control system.
The TRW Communications/Navigation/Identification (CNI) system includes an intra-flight datalink, JTIDS Joint Tactical Information Distribution System link, and an Identification Friend or Foe (IFF) system. Boeing is responsible for mission software and avionics integration. The aircraft has a Litton LTN-100G laser gyroscope inertial reference, a global positioning system and a microwave landing system.
The F-22's avionics suite features extensive use of very high-speed integrated circuit (VHSIC) technology, common modules, and high-speed data buses. The avionics suite is a highly integrated system maximizing performance allowing the pilot to concentrate on the mission, rather than on managing the sensors as in current fighters. Technologies incorporated in the F-22 include a Common Integrated Processor (CIP), a central "brain" with the equivalent computing throughput of two Cray supercomputers; shared low-observable antennas; ADA software; expert systems; advanced data fusion-cockpit displays; integrated electronic warfare system (INEWS) technology; integrated communications, navigation, and identification (CNI) avionics technology; and fiber optics data transmission. Nearly all of these elements were demonstrated during dem/val in a prototype architecture.
The Hughes-built Common Integrated Processor (CIP) serve as the "brains" for the F-22's totally integrated avionics system. CIPs are the central, networked computers that enable the integration of radar, electronic warfare, and identification sensor data, as well as communication, navigation, weapon, and systems status data into coherent, fused information for communication to the pilot via multi-function displays. Rather than radar, the electronic warfare system, and the electronic warfare system having individual processors, the CIP supports all signal and data processing for all sensors and mission avionics.
The CIP modules have the ability to emulate any of the electronic functions through automatic reprogramming. For example, if the CIP module that is acting as radio dies, one of the other modules would automatically reload the radio program and take over the radio function. This approach to avionics makes the equipment extremely tolerant to combat damage as well as flexible from a design upgrade point of view.
There are two CIPs in each F-22, with 66 module slots per CIP. The CIPs (which is quite literally the size of a oversized bread box) are liquid cooled avionics racks containing both signal processing and data processing modules inserted into common backplane. They have identical backplanes, and all of the F-22's processing requirements can be handled by only seven different types of processors. There are 33 signal processors and 43 data processors interconnected via a fault-tolerant network. Each processing element is manufactured and packaged as an approximately 6x7x3/8ths inch line replaceable module (LRM) for ease of flightline maintenance.
Each module is limited by design to only 75 percent of its capability, so the F-22 has 30 percent growth capability with no change to the existing equipment. Currently, 19 of 66 slots in CIP 1 and 22 of 66 slots in CIP 2 are not populated and are available for growth. There is space, power and cooling provisions in the aircraft for a third CIP, so the requirement for a 200 percent avionics growth capability in the F-22 can be easily met. There is coordinated plan for technology growth that would help keep the CIP at state-of-the-art levels. As electronics continue to get smaller and more powerful, it is conceivable that there could be 300 percent increase in avionics capability.
The exponential explosion of computer technology in recent years has allowed the F-22 team to radically alter every aspect of the program from detailed design through manufacturing, communication, and into the cockpit itself. An example of the effect of the advances in computer technology is a comparison between the computers used in the Lunar Module and those used in the F-22. The Lunar Module's computers operated at 100,000 operations per second and had 37 kilobytes of memory. Today, the F-22's Common Integrated Processor main mission computers operate at 10.5 billion instructions per second and have 300 megabytes of memory. These numbers represent 100,000 times the computing speed and 8,000 times the memory of the Apollo moon lander.
The AN/APG-77 radar is the F-22's primary sensor and is a long-range, rapid-scan, and multi-functional system. A Northrop Grumman-led joint venture with Raytheon is developing the active-element electronically scanned array radar. Northrop Grumman is also responsible for the radar sensor design, software, and systems integration.
The AN/APG-77 radar is an active-element, electronically scanned (that is, it does not move) array that features a separate transmitter and receiver for each of the antenna's several thousand, finger-sized radiating elements. Most of the mechanical parts common to other radars have been eliminated, thus making the radar more reliable. This type of antenna, which is integrated both physically and electromagnetically with the airframe, provides the frequency agility, low radar cross-section, and wide bandwidth necessary to support the F-22's air dominance mission. The radar is key to the F-22's integrated avionics and sensor capabilities. It would provide pilots with detailed information about multiple threats before the adversary's radar ever detects the F-22.
The AN/APG-77 radar a novel type of electronically scanned phased array. In what is likely to be the most advanced airborne radar in the world, individual transmit and receive modules are located behind each element of the radar array. The transmit function of the solid-state microwave modules supplants the traveling wave tubes used in prior radars like the APQ-164. The active, electronically scanned array (ESA) configuration has a wider transmit bandwidth while requiring significantly less volume and prime power. The system represents about half the weight of an equivalent passive ESA design. Each of the hundreds of individual solid-state devices generates only small amounts of power, but the aggregate for the entire array is substantial.
The F-22 s APG-77 electronically scanned array antenna is composed of several thousand transmit/receive modules, circulators, radiators and manifolds assembled into subarrays and then integrated into a complete array. The baseline design used thousands of hand-soldered flex circuit interconnects to make the numerous radio frequency, digital, and direct current connections between the components and manifolds that make up the subarray. Northrop Grumman Corporation, of Baltimore, MD, has developed an improved manufacturing process for F-22 aircraft radar components. The new process could result in a cost avoidance of nearly $87 million on the planned production run for the aircraft. By replacing the hand-soldered flex circuit interconnects with automated ribbon bond interconnects, the first pass yield of the subarray assembly has been vastly improved.
The AN/APG-77 radar antenna is a elliptical, active electronically scanned antenna array of 2000 transmitter/receive modules which provides agility, low radar cross section and wide bandwidth. The radar is able to sweep 120 degrees of airspace instantaneously. In comparison to the F-15 Strike Eagle's APG-70 radar takes 14 seconds to scan that amount of airspace. The APG-77 is capable of performing this feat by electronically forming multiple radar beams to rapidly search the airspace.
The system exhibits a very low radar cross section, supporting the F-22's stealthy design. Reliability of the all-solid-state system is expected to be substantially better than the already highly reliable F-16 radar, with MTBF predicted at more than 450 hours.
The APG-77 radar offers significant advantages over previous combat radars. Among its most attractive benefits is the integration of agile beam steering. This feature allows a single APG-77 radar to carry out multiple functions, such as searching, tracking, and engaging targets simultaneously. Agile beam steering also enables the radar to concurrently search multiple portions of airspace, while allowing continued tracking of priority targets.
The Low Probability of Intercept (LPI) capability of the radar defeats conventional RWR/ESM systems. The AN/APG-77 radar is capable of performing an active radar search on RWR/ESM equipped fighter aircraft without the target knowing he is being illuminated. Unlike conventional radars which emit high energy pulses in a narrow frequency band, the AN/APG-77 emits low energy pulses over a wide frequency band using a technique called spread spectrum transmission. When multiple echoes are returned, the radar's signal processor combines the signals. The amount of energy reflected back to the target is about the same as a conventional radar, but because each LPI pulse has considerably less amount of energy and may not fit normal modulation patterns, the target would have a difficult time detecting the F-22.
The F-22 and its APG-77 radar would also be able to employ better Non-Cooperative Target Recognition (NCTR). This is accomplished by forming fine beams and by generating a high resolution image of the target by using Inverse Synthetic Aperture radar (ISAR) processing. ISAR uses Doppler shifts caused by rotational changes in the targets position to create a 3D map of the target. The target provides the Doppler shift and not the aircraft illuminating the target. SAR is when the aircraft provides the Doppler shift. The pilot can compare the target with an actual picture radar image stored in the F-22's data base.
The F-22's Communications/Navigation/Identification (CNI) 'system' is a collection of communication, navigation, and identification functions, once again employing the CIP for signal and data processing resources. Each CNI function has its associated aperture installed throughout the aircraft.
Included in the Communications/Navigation/Identification (CNI) system is an Inter/Intra-Flight Data Link (IFDL) that allows all F-22s in a flight to share target and system data automatically and without radio calls. The Inter/Intra Flight Data Link is one of the powerful tools that make all F-22s more capable. One of the original objectives for the F-22 was to increase the percentage of fighter pilots who make 'kills'. With the IFDL, each pilot is free to operate more autonomously because, for example, the leader can tell at a glance what his wing man's fuel state is, his weapons remaining, and even the enemy aircraft has targeted. Targets can be automatically prioritized and set up in a shoot list with one button push. A 'shoot' cue in the head up display alerts the pilot to the selected weapon kill parameters and he fires the weapons. Both a pilot's and wing man's missile flight can be monitored on the cockpit displays. Classical tactics based on visual 'tally' (visual identification) and violent formation maneuvers that reduce the wing man to 'hanging on' may have to be rethought in light of such capabilities. This link also allows additional F-22 flights to be added to the net for multi-flight coordinated attack.
The Electronic Warfare 'system' is also a collection of apertures, electronics, and processors (again using the CIP) that detect and locate signals from other aircraft and controls the F-22's expendable countermeasures (chaff and flares). The EW aperture locations provide all-aspect coverage, and the system includes a missile launch detection capability.
The F-22's electronic warfare system includes a radar warning receiver and a Lockheed Martin Sanders missile launch detector.
The Stores Management System (SMS) controls weapons launch sequences, including door control (for the internal weapons carriage) and emergency weapons jettison.
Boeing manufactures the power supplies for most of the F-22's electronic systems. The power supply modules designed for the F-22's avionics are cooled with polyalphaolefin (PAO) liquid coolant to carry away heat generated by the supplies' power-conversion process. The reduced temperature allows the component's power output to increase from 250 watts to 400 watts. Each module measure 6.41 inches by 5.99 inches by 0.58 inches and weighs 1.8 pounds.
The PAO cooling concept also applies to all types of Line-Replaceable Modules (LRMs) in the CIP. Liquid flow-through cooling improves reliability, lending to an mean time between failures (MTBF) of 25,000 hours. The coolant, which is routed through the module, comes from the F-22's environmental control system (ECS). The LRM concept is the baseline for all of the power supply modules built for the F-22 to minimize maintenance time. Built-in diagnostic routines pinpoint a failed power supply on an F-22 and allow maintenance personnel to remove it, replace it and verify proper operation within 15 minutes.
The avionics racks, located in the forward fuselage, contain the processing, not only for the mission avionics, but also for the Vehicle Management System (VMS) and Integrated Vehicle System Controller (IVSC). The flight worthy racks, including the liquid-flowthrough racks required for the CIP, are now in production.
Two Litton LN-100F ring laser gyroscopes in the forward fuselage provide the aircraft a self-contained method of knowing where it is. These inertial measurement units, placed nose to nose behind the radar on the aircraft's centerline, are operated off separate data buses to provide independent measurement data. In normal flight, IRS data is fused with Global Positioning System (GPS) data to provide an extremely reliable navigational capability. The IMUs are the only completely reliable source of data for the aircraft at attitudes above 30 degrees angle of attack (AOA). One of the IRS units feeds data directly into the CIP for gun control steering.
The software that provides the avionics system's full functionality is composed of approximately 1.7 million lines of code. Ninety percent of the software is written in Ada, the Department of Defense's common computer language. Exceptions to the Ada requirement are granted only for special processing or maintenance requirements. The software development plan, though stretched as a result of past funding constraints, has remained essentially unchanged since the start of Engineering and Manufacturing Development.
The avionics software was integrated in three blocks, each building on the capability of the previous block. Each block cycle is a sequence of subsystem deliveries, integration testing at the Avionics Integration Lab (AIL) at Boeing (see AIL in the Test Facilities section), and then delivery to Lockheed Martin in Marietta, Ga., for final integration into the aircraft and check out, as well as support to the aircraft.
Block 1 is primarily radar capability, but Block 1 does contain more than 50 percent of the avionics suite's full functionality source lines of code (SLOC) and provides end-to-end capability for the sensor-to-pilot data flow. The fourth EMD F-22 was the first to have a full avionics suite, and it flew in mid 1999.
Block 2 is the start of sensor fusion. It adds radio frequency coordination, reconfiguration, and some electronic warfare functions. Block 2 was integrated into the aircraft in late 1999.
Block 3 encompasses full sensor fusion built on enhanced electronic warfare and CNI functions. It has an embedded training capability and provides for electronic counter-counter measures (ECCM). It was integrated into the aircraft in the spring of 2000. Block 3.1, which adds full GBU-32 Joint Direct Attack Munition (JDAM) launch capability and Joint Tactical Information Distribution System (JTIDS) receive-only capability, was integrated in April 2000.
The Block 4 software was post-Engineering and Manufacturing Development. It was integrated on the Initial Operational Capability F-22s and included helmet-mounted cueing, AIM-9X integration, and Joint Tactical Information Distribution System send capability.
CIP hardware was available well before the subsystem application software code and unit test phases began for the Block 1 software. For some of the higher risk software, such as sensor data fusion, specific algorithm testbeds have been constructed, and prototype software, which is instrumented to measure performance (correlation times, accuracy, etc.). has been operational since the start of EMD.
The Flying Test Bed (FTB) represents an interim test environment between the controlled, but static environment of the ground labs, and the dynamic flight testing of the F-22. Sensor systems installed in the aircraft, CIPs, as well as operator consoles and instrumentation were used to test avionics capabilities prior to release to the F-22.
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