designer and programmer is to make that impossible.
To help the pilot make practical use of all this greatly expanded tactical information, the F-22 will incorporate decision-aid and management software which will help him or her to drive and fight the aircraft to its limits. In essence, the functions of the human WSO of the F-15E have been delegated to electronic systems rather than flesh and blood. But whether the extra help is human or machine, there is no doubt future pilots will need plenty of it to handle all of the information collected by integrated sensor suites and multiple off-board assets while still flying the plane. Automation is an absolute necessity if future combat aircraft are going to be manned by just one person. It costs over a million dollars to train a pilot or WSO, and personnel costs are the biggest single factor in the defense budget, so it is easy to understand the desire to minimize the aircrew required. The trick is to figure out just what the machines are capable of doing on their own, and what requires the pilot's human judgment. The key to this relationship is a cockpit design that lets the pilot glance at no more than four or five display panels to know exactly what's going on inside and outside the cockpit ('situational awareness').
An overview of recent advances in computer technology is beyond the scope of this book, but two areas are critical to our understanding of how an aircraft finds its target, destroys it, and leaves before the enemy can do anything about it. These areas are sensors and 'man-machine interfaces' or displays. In sensors, we'll look at the advances in the performance of radar, IR, and electronic-support-measures (ESM) systems made possible by the massive number-crunching power of today's computers. In displays, we'll look at how information is conveyed to the pilot so that he or she can use it to make better tactical decisions under the stress of combat.
SENSORS
Radar has been the most important sensor for fighter and ground-attack aircraft since the Korean War. And the operating principles of airborne systems haven't changed fundamentally since World War II. Until the 1970s, airborne radar systems, were mostly single-purpose air-intercept or ground-mapping /navigation systems. In 1975 the F-15A Eagle, equipped with the powerful Hughes APG-63, introduced a new era of multi-mode radars.
The APG-63 radar was the first all-weather, programmable, multi-mode, Pulse-Doppler radar designed to be used by a single pilot. Pulse-Doppler radars rely on the principle that the frequency of waves reflected from a moving object will be slightly shifted upward or downward, depending on whether the object is moving toward or away from the observer. Precise measurement of this Doppler shift allows the radar's signal-processing computer to determine the target's relative speed and direction with great precision. With a detection range of greater than 100 nm./182.8 km. against a large RCS target (like a Tu-95 BEAR bomber), the APG-63 combined long range with features such as automatic detection and lock-on. By allowing a digital computer to control most radar operations, the pilot was left free to concentrate on getting into position to make an effective attack. This computer, by the way, was just slightly more powerful than your standard first generation IBM PC (equipped with an Intel 8-Bit 8086/8088 processor; today many home appliances like refrigerators use a more powerful computer chip!). The most impressive aspect of the APG-63 radar system was the first-generation programmable signal processor (PSP), which effectively filtered out ground clutter, giving the radar 'look-down, shoot-down' capability. This meant that in broken terrain the pilot could successfully track and engage targets flying at low altitude, which previously were able to 'hide' amid the clutter of returns from trees, hills, rocks, and buildings. With some modifications to the PSP's hardware and software, the APG-63 could also provide real-time, high-resolution ground maps, allowing navigation in poor weather or at night. The radar ground maps were good enough for an experienced pilot to pick out vehicles, bunkers, and other targets. This ability would be further enhanced in the F-15E Strike Eagle fighter-bomber variant. Finally, the APG-63 can track one target while searching for others (track-while-scan or TWS).
The hardware of the APG-63 was as revolutionary as its software. The antenna is a flat, circular planar array, gimbaled in two axes so that it can maintain target lock-on during high-G maneuvers. This means that the F-15 can launch an air-to-air missile, turn up to 60deg away from the target (called off-boresight), and still maintain the track, even while the target pulls evasive maneuvers. The APG-63's subsystems, such as the power supply, transmitter, and signal processor, are packaged as individual line-replaceable units (LRUs), which reduces maintenance and repair time. An LRU is a box of system electronics (usually small enough to be handled, removed, and rapidly replaced by a single mechanic) that contains a major electronic or mechanical subsystem of an aircraft. When something inside an LRU fails, the entire box is sent back to the factory or a base/depot-level maintenance facility for repair.
The radar's horizontal or azimuth scan has three selectable arcs, 30deg, 60deg, or 120deg, centered directly in front of the aircraft. The vertical or elevation scan has three selectable 'bars' (a bar is a slice of airspace with a vertical depth of 1 1/2deg per bar)—2 bar (3deg), 4 bar (6deg), or 6 bar (90deg) — for varying vertical coverage. To cover a specific search pattern, the gimbaled antenna scans from left to right over the selected arc. At the end of the arc, the radar beam drops down one bar and scans back right to left. This continues until the entire bar scan is completed. With an antenna sweep speed of around 70deg/sec./bar, the largest search pattern (a 120deg, 6-bar scan) can take up to fourteen seconds to complete. Early Eagle drivers were very happy with their new aircraft's radar because, after years of peering into fuzzy, cluttered radar screens as if they were crystal balls, struggling to glean target data, the APG- 63 was a revelation. But the ultimate proof of a system only comes in combat. The USAF F-15Cs in Desert Storm, as well as those in Saudi and Israeli service, have proved the value of the APG-63 radar system. The F-15 has at least 96.5 'kills' of enemy aircraft to its credit, with no losses.
As good as the APG-63 was, the follow-on radar system for the dual-role F-15E Strike Eagle had to be even better. Hughes engineers used the APG-63 as the basis for the new APG-70 radar. When it was tested in 1983 on a modified two-seat F-15B, it was obvious that the Eagle's eyes had gotten even sharper. To keep costs and airframe modifications to a minimum, the APG- 70 used the same antenna, power supply, and transmitter as its predecessor. But the brains of the system were all new. A new radar data processor, PSP, and other modules replaced older APG-63 LRUs. The software package was completely new, with greater flexibility, making future modifications even easier. The APG-70 can simultaneously track and engage
Another remarkable feature of the APG-70 is called Non-Cooperative Target Recognition (NCTR). 'Cooperative' target recognition depends on the transponders carried by friendly aircraft, which return the proper coded reply when they are 'interrogated' by an IFF system. The relatively low reliability of this method has led to very restrictive rules of engagement (ROE) that require several independent means of verifying that a target is really, truly an enemy before a pilot is allowed to shoot it. All air commanders live in fear of 'fratricide' or 'blue-on- blue' accidents, and the tragic shootdown of two Army helicopters in Northern Iraq in 1994 by F-15Cs suggests that this fear is well founded. NCTR, which is quickly becoming standard on many U.S.-designed radars, is the ability to classify a target by type while it is still beyond visual range. How this is done is highly classified; and even mentioning NCTR around an Air Force or contractor site is likely to raise eyebrows and tighten lips. Nevertheless,
