Air University Review, November-December 1977
Charles A. Zraket
Stanley E. Rose
THE TECHNOLOGIES of aerodynamics, propulsion, and structures have produced a marvel in terms of the aircraft that have resulted; however, the technology that has produced the ability to command and control and to communicate with these aircraft has given us air power. This C3 technology has recently enjoyed an explosive growth in capability and reduction in cost that promise an even greater impact on air warfare than we have witnessed to date. The short history of the development of C3 technology for air defense is illustrative of the roots of command/ control capabilities for air power.
Following World War I, while air power advocates struggled to gain acceptance of their weapon, all nations disarmed rapidly. Airmen could do little toward improving air defenses. Yet, for the future of air defense, by 1935 the British had made a most important technological development, radar. Radar revolutionized the art of air defense. 1
After the outbreak of war in Europe in 1939, all nations had begun the construction of air defense systems. But only Great Britain had built a radar early-warning network capable of alerting and controlling the air defense system. When World War II began, Great Britain had a network of 20 radar stations. This radar network allowed the few Royal Air Force fighter squadrons to remain on the ground until the last possible moment before taking off to intercept the bombers. Largely because of the British early-warning network and other radar developments such as ground-controlled interception (GCI), airborne interception (AI), and identification, friend or foe (IFF), the Battle of Britain of 1940-41 was won by a numerically inferior fighter force.
The operation of the early radar systems was difficult since people had to interpret manually some hundreds of plots every minute, all subject to variable delays and to the personal errors of the observers. Quite trivial difficulties proved surprisingly hard to overcome. It was difficult to find room for all the plotters around the table, and they could not plot fast enough. They might disturb one set of plots when they leaned over to plot another aircraft. Such rather simple difficulties could be, and often were, the limiting factors on the use that could be made of the radar plots, and an intensive study of all the stages in plotting and filtering was made throughout the early years of the war.
In the U.S., a first step toward coordination of air defense was taken early in 1940 when the War Department created the Air Defense Command and sited about 95 radar sets--65 on the Pacific Coast. By early 1943, the danger of enemy air attack had passed, and in the following year the continental air defense system was dismantled.
During the early years of peace that followed the defeat of Germany and Japan, air defense seemed unnecessary. The victorious Western allies quickly demobilized and scrapped or stored most of their air defense weapons. However, by 1948, the cold war had begun, and as the split between the free world and the Communist nations widened most governments began to rearm. With the world's two strongest powers armed with nuclear weapons, defense against air attack assumed new importance. Nations on both sides of the Iron Curtain felt compelled to erect the most effective air defense system possible.
By the mid-1950s, the free world, under the leadership of the United States, had made substantial progress in constructing an early-warning radar network around the periphery of the Soviet Union and its satellites. Inside the Iron Curtain another radar network was poised to alert the Communist air defense system. Into these air defense systems went a substantial part of the defense budget of each nation.
In late 1950, the United States Air Force recognized the shortcomings of the continental air defense system in being at that time. As a result, the Air Defense Systems Engineering Committee (ADSEC)* combined air defense data-handling work at the Massachusetts Institute of Technology (M.I.T.) Digital Computer Laboratory with radar data-transmission equipment from Air Force Cambridge Research Laboratories. The results were favorable, and the Air Force then suggested the establishment of a laboratory to continue this program. In the spring of 1951, negotiations were carried out which first led to a five-month study (Project CHARLES) and, second, to the establishment of the Lincoln Laboratory in August 1951.
*ADSEC, a group formed in 1950 by the Scientific Advisory Board at the request of the Air Staff to study the overall problems of air defense.
It was during this study period that the use of a high-speed digital computer gained full momentum for application to air defense. Project CHARLES recommended the testing of such a computer in the ground environment by use of the Whirlwind I computer then in being at the Digital Computer Laboratory, M.I.T. This test was to provide information to the Air Force on the capability of such equipment to solve the ever growing air defense problem. The Cape Cod system, which was established as the experimental system, led to the development and deployment of an operational system for air defense.
The air defense art developed during the Battle of Britain is remarkably well preserved but automated in the Air Force's semiautomatic ground environment (SAGE) system, as it was called. This automation overcame many of the problems the British system experienced when it was saturated with a high traffic density.
At an FPS-3 radar station, for instance, the signals from the radar were processed so that they could be transmitted within the bandwidth capability of a telephone line. This was done by equipment at the radar station that integrated the video signal over one radar beam width and transmitted on the telephone line one range sweep during that interval. A number of radars were netted and sent their data to a SAGE direction center. The mapping station at the direction center consisted of a plan-position indicator (PPI) scope display of incoming radar data from a particular radar set. From this data, information displays were generated so that operators could make decisions and guide weapons to the target.
Charles Babbage's computer designs were limited by mechanical devices, and the engineers of the early 1950s were limited by vacuum tubes, which by today's standards would be impossibly bulky and unreliable. The first engineering model of SAGE's AN/FSQ-7 computer contained almost 60,000 vacuum tubes. Its memory, however, was small by today's standards--8192 words of 32-bit length, though that was later expanded to 69,632 words. The memory cycle time was six microseconds. Processing speed was a mere 75,000 instructions per second. And, though the drive to snatch new developments from the forefront of technology and press them into service has been a continuing thesis throughout computer history, the fact is that prudence governed the choice of tubes, rather than transistors, for the FSQ- 7 digital computer. Transistors were close, but they were not quite there; and the fate of the system could not be staked on them. So SAGE rode into the future on a technology that was swiftly being overtaken by a new generation.
But the SAGE computer was able to generate about 200 different kinds of displays, requiring up to 20,000 characters, 18,000 points, and 5000 lines every two and a half seconds. By time-sharing the central computer, each air defense routine could be operated at least once every 15 seconds. The 22 SAGE centers that eventually dotted across the U.S. and Canada were netted together with digital data communications and went into operation in the late 1950s and early '60S.2
From this point, advances in computer technology followed one of two distinct directions. There were the "number-crunchers"--large, powerful devices that manipulated enormous amounts of data and performed complex calculations at ever higher speeds. These were in essence the logical descendents of the systems gone before. And there were the representatives of a newer breed: the smaller, lighter, more reliable processors that were faster and more capable than their predecessors and which were being called on to do more diverse sorts of operations.
The technology of miniaturization put digital computers into the air. Before the days of transistors, digital computers were much too heavy and bulky to be airborne.
AT MITRE, we recently defined one measure of progress in computer circuitry. As the basis for developing a figure of merit, we used an element about a centimeter on a side--that is, an element that would have been a fraction of a vacuum tube 20 years ago, a single transistor 10 years ago, an integrated circuit today. This turns out to be a useful volume because the cost and reliability of these elements have been roughly the same over the past 25 years, but the computing power has grown. If you take as a measure of computer power--that is, the figure of merit--the product of speed (operations per second) and complexity (equivalent number of gates per package) that can be accomplished in our centimeter cube, and if you plot this over the past 25 years, you get an amazingly smooth curve with an improvement three orders of magnitude each decade--a factor of ten every three years or so. In 1950, the figure of merit was 105; now it is about 1012, and in 1980 it will be about 1013 or 1014-that is, about eight orders of magnitude greater than in 1950. Costs for the same performance have been decreasing at about half that rate, not including peripherals.
We know that this trend will continue for at least five more years because of the experimental and prototype equipments that exist today in laboratories and pilot production facilities. We are almost sure it will continue for ten to fifteen more years since many ideas are being explored and tested with radically new materials, new ways of interconnecting these materials, and new methods of fabrication. Also, we know we are a long way from violating the laws of physics. In these advanced projected systems, in order to store a bit or a logic-gate, it takes tens of thousands of atoms. In comparison, living material stores each bit of the genetic code pretty reliably with less than a hundred atoms.
Three orders of magnitude in performance per decade is a significant increase. When a technology is improving by several orders of magnitude and can be reasonably expected to continue at the same rate, so that perhaps another eight or nine orders of magnitude will be available for exploitation by the end of this century, then that can, in fact, have revolutionary as opposed to evolutionary implications. Similar improvements are taking place in high-speed and secondary storage and in analog techniques, such as Surface-wave devices and charged-coupled devices. 3
Although it is difficult to predict the effects of improvements of many orders of magnitude, there are some things that seem likely to us at MITRE. For example, the statement that computer scarcity will be replaced by computer plenty may seem odd because apparently computers are everywhere you turn. The very phrase "computational scarcity" sounds strange applied to computers. However, even though there are lots of computers, we still treat them as a scarce resource, try to ensure that they are used efficiently and that we not buy a larger one than is necessary. The situation is going to change, though, and we are going to be in the position where we can really get all the computation that is needed. Efficient use of hardware will, therefore, become less important, and other things will become the driving forces in C3 technology--e.g., software, sensors, and communications.
The application of command and control to other military uses multiplied after the development of SAGE. As would be expected, the availability of data processing to accomplish them has grown to accommodate the need. This phenomenon is illustrated in Figure 1, where command and control requirements have been plotted over the years. The capabilities of computers that have been responsive to these requirements are plotted on the figure. Machines of these capabilities have become possible because of the miniaturization of high-performance computer circuitry already mentioned. 4
Figure 2 further illustrates the effect of this technology on the practicability of acquiring this capability in terms of the dramatic decrease in cost per instruction over the last two decades. Note the order of magnitude cheaper capability available with a million instructions per second microprocessor. 5
The resulting technology of miniaturization not only allowed us to put Computation capability into the air but also made it possible for an aircraft to sense its environment and communicate securely with friendly forces. By sheer dint of computational force in an airborne radar, we are able to process returns of thousands of unwanted echoes per second from the terrain below, eliminate them all, and leave only the desired returned signal of a low-flying enemy aircraft. We can pick out targets that are reflecting radar power that is 60 dB below the signal reflected from the ground clutter. By means of this processing capability, small in size but powerful in concept, we can overcome the shortcomings of earlier radars that dealt with the clutter problem by ignoring (as the British filter officer did) signals from this region. Now we can purposefully look down from a moving radar platform into an ever changing overland clutter background, ignore the clutter, and extract the signal all automatically. This capability had a farreaching effect on the way that air warfare will be conducted. Its implications are only now being appreciated and embodied in such systems as the F-15 and E-3A Airborne Warning and Control System (AWACS).
Similarly, this same processing capability allows us to eliminate the familiar mechanically scanning antenna that often is the bane of the aerodynamicist looking for a clean profile. It is possible to process signals from a thin array of transceiving elements by inserting computed delays among them to form simultaneous beams in space that are equivalent to many equivalent rotating antennas. We can even adjust the antenna pattern to place nulls in the directions of unwanted signals.
Other sensors that the technology will support are the following:
Although much of the described technology helps make the aircraft more self-sufficient, maximum air power results only if we can communicate between aircraft and with the aircraft from ground-based command and control centers. Realizing this, the enemy will attempt to jam, spoof, or eavesdrop on the communication links.
The availability of digital signal processing spawned from these technologies has proved to be an answer to this threat to the communication links. By encoding the signal, thus spreading its spectrum in a way known only to friendly receivers, it is possible to force an enemy jammer to dilute his energy over a much broader spectrum than that of the actual information bandwidth. This encoding process also is the basis for protection against spoofing and eavesdropping.
The spreading of the spectrum of the signal is accomplished by dividing each information bit into many pseudorandomly coded bits. We can then recover these data bits at the other end by passing the pseudorandom code into a digital filter that matches the code at that instant of time. This filter is made up of digital shift registers with feedback paths that locally generate the same code that is being sent. Further processing allows the detection and correction of any errors in the data. The codes are very long and therefore do not repeat to allow the enemy to eavesdrop or spoof. The present state of the art in this technique allows the signal to be recovered even if the jamming signal is 20 dB higher at the friendly receiver.
New surface acoustic wave (SAW) devices where the matched filter is a tapped delay line (of variable delays) will allow signals to be extracted with jamming power levels 40 dB above the signal. Digital communication systems like this also lend themselves to a time division multiple access (TDMA) mode of use where many subscribers can use the communication link almost simultaneously. For instance, in the Joint Tactical Information Distribution System JTIDS) now being developed by the Air Force, a net of users contains 128 transmission time slots per second. Each time slot consists of a synchronization preamble so that the receiver's filter can synchronize its pseudorandom sequence to the correct position. Following this preamble, the information is transmitted in up to 233 error-coded bits, each in a spread spectrum and frequency hopping format.
This is a receiver-oriented system in which all participants have connectivity with all others and where, therefore, no central, vulnerable mode exists. The messages are encoded so that each receiver may select only that information of interest to it. This feature provides circulating bus architecture for the net's information base.
By means of such a net, many aircraft can be connected to each other and to control centers, thus achieving a force multiplying effect through the use of C3. Similar techniques could be used to provide more jam-proof tactical voice systems.
THE POWER of digital computers and their associated sensor and communication equipments has led us to a new concept of piloted aircraft control. You might call it the "digital airplane," a nickname that indicates one of the more important aspects of such an integrated system: it uses the comparatively fast, highly condensed kind of information processing made possible by the use of digital instead of analog data. Such an avionics system controls the aircraft's on-board systems and makes flight a vastly different affair--with new freedoms and new responsibilities.
An example of the digital airplane is the B-1 bomber, whose future at this time is at best uncertain. About two-thirds the size of the B-52, it can carry almost twice the payload--75,000 pounds. This aircraft is essentially run, managed, flown, maintained, and controlled by its computers, integrated and under the command and control of a small crew of four men.
The design of the instrumentation and controls is influenced by the availability of digital computers. This is manifested by the profusion of dedicated processors which deal with such functions as rotation, go around, angle of attack, and air vehicle limits--one processor--and engine instrument system, signal conditioning and distribution-another processor. There is a processor to manage the fuel center of gravity and one for a vertical situation display. Separate processors control the flight instrument signal converter, the gyro-stabilization system, central air data storage and manipulation, and the electrical multiplex subsystem.
The B-l's weapon systems involve five large general purpose computers: a general navigation avionics control unit, a weapon delivery avionics control unit, and a defensive avionics control unit; all use computers with 32-bit words. Two more computers control radio frequency surveillance, electronic countermeasures, and an integrated test subsystem that check out everything onboard. In addition, there are multiplex systems that interconnect all the on-board processing systems.
The important part about this aircraft is that it is an integrated system--an aggregation of subsystems under the control of higher-level systems that are themselves under the general direction of the pilot. He can make the aircraft do what he needs it to do, by executive control. What we have, then, is hot an airborne assemblage of a dozen or two dozen discrete systems but rather something like an organism--all of whose parts are functioning toward a common purpose under centrally coordinated control. And, that control is a mixture of machine organization and human judgment. 6
Over recent years, the development of air defense systems had reduced the effectiveness of bombers.. The improvements in radar, computational capabilities, and the augmentation of interceptors with supersonic surface-to-air missiles might have produced a strategic air power stalemate that would have continued except for the impact of the development and acquisition of the intercontinental ballistic missile (ICBM).
However, the maturing of the developments that made air defense command and control possible are now providing an opposing force that is making possible the penetration of air defense systems by means of adaptive countermeasures. The B-1 capability with its small crew is an embodiment of this trend.
In addition, recent maturation of a number of relatively independent technologies, such as composite materials, small turbine engines, smaller and more powerful warheads, compact and accurate navigation systems, and, most important, solid-state microelectronics, have made possible the development of an air-launched cruise missile that promises to enhance significantly the strategic bomber force. The highly accurate cruise missile provides the potential for additional attack modes, for suppressing and saturating defenses as a standoff weapon, and for increasing the number of strategic targets at threat by both widening and extending the effective flight path of the penetrating bomber. This conclusion is based on three factors: the cruise missile's small size and relatively long-range flight at low altitude; its potential for low cost; and the consequences of exploiting in C3 systems the major technological asymmetry enjoyed by the U.S. in microelectronies and large-scale integrated (LSI) circuitry.
Now the technology has enabled us to come full circle. Where the invention and development of the radar and digital computer have yielded a ground environment whereby the effect of defensive high-speed interceptors could be multiplied through command and control, the ability to place this command and control in airborne vehicles has also given the offensive aircraft more viability.
We are entering the age where bombers will not only have self-contained adaptive penetration systems but could also act as "airborne command posts" to fleets of accompanying pilotless vehicles. We will probably see a restoration, through this feature, of the balance between offensive and defensive air power that has for many years been tilted toward the defense.
The principal virtue of the manned bomber leg of the strategic Triad is the many ways in which the intellect and the versatility of the crew can be applied to a rapidly changing situation. At present, one of the ways that this flexibility is manifested is in dynamic selection of penetration aids where enemy defenses appear or by the choice of less hazardous routes or alternate targets. Therefore, built-in "smarts" or adaptability of the cruise missile--the role of command and control--can preserve this characteristic of the Triad by allowing aircraft crews executive control over a large, sophisticated penetrating force.
The open-loop operation, where each bomber launches its magazine of cruise missiles toward predestined targets, along paths determined by prehostility knowledge of defense positions, need not be tolerated with smart cruise missiles under the executive control of the bomber crew.
A smart cruise missile, which flies from about one to three hours and which operates semiautonomously and adaptively after launch under the overall control of the carrier, should have the self-contained capability of two-way communication with the carrier, the ability to sense electronically the environment through which it is flying, the ability to store and process this information for evasive maneuvers, and the ability to report this information and its status to the carrier. Based on this information, subsequent missiles that may have already been launched can be reprogrammed via a data link to attack alternate targets still within the missile's footprint. Also, missiles may be redirected so that their simultaneous time of arrival at a defended target can help to saturate the defense.
These capabilities will amplify the effectiveness of the carriers many fold, permitting new tactics to be employed and thereby exploit the U.S. advantage in electronics by providing a combined weapon system with high performance at relatively low cost.
To exploit fully this potential, the integrated command and control system should have the following capabilities:
SO FAR, we have mostly discussed the impact that C3 technology could have on strategic air power. Air power has had and will continue to have a profound impact on land/air battles where air cover, close air support, and air interdiction can provide precision firepower in tactical situations. Recently, we have seen the acquisition and buildup of mobile surface-to-air missile (SAM) capability to attempt to offset this tactical advantage of air power. As a matter of fact, the proliferation of shoulder-fired SAMs (e.g., Redeye) among our own troops has increased the fratricide problem to further inhibit the application of air power near the battle area. In addition to the SAM threat to air power, a direct measure against today's relatively unsophisticated tactical C3 is appearing in the form of electronic warfare (EW).
It is the application of new C3 technology for the secure, jam-proof control of tactical strike aircraft that will allow us once again to utilize air power to help friendly air /land forces move the forward edge of the battle area (FEBA) toward the enemy-held territory.
It is feasible with C3 technology now in research and development to gather a myriad of information from battlefield surveillance and target acquisition sensors and use these data in real time to arrange for and direct air strikes against ground targets. A ground target strike control center could assemble a strike force consisting of manned and smart unmanned aircraft, electronic warfare and defense suppression assets and in real time orchestrate such a force against time-critical ground targets.
It is conceivable that the manned aircraft operating beyond the FEBA could be directly augmented with accompanying smart cruise missiles under the executive control of the manned aircraft crews themselves. Cruise missile costs in quantity can probably be brought down to a small fraction of the cost of a manned aircraft. If they can be used in a way that increases the per sortie survivability of the manned aircraft, we can probably afford to make them expendable (nonrecoverable), even using large cruise missile/manned aircraft ratios per mission. These augmenting cruise missiles could be used in the following potential applications:
A tactical strike force, then, could consist of manned strike aircraft, CAP aircraft, and specialized cruise missiles, each capable of performing one or more of these tasks. In addition, the cruise missiles could perform decoy duties, and since they need not be recovered, they could carry a warhead to be delivered after the cruise missile performed its support function.
The key to achieving these capabilities is an overall tactical command, control, and communications structure that allows support rig cruise missiles to be controlled with a minimum of attention from busy aircrews and a ground-based distributed air-control facility to command and control this mixed force. To exploit the C3 capability which technologically exists, we must mount a development program concomitant with the cruise missile development to evolve systems like the tactical air control system (485L) into this capability.
In the twenty-five years since the beginning of SAGE, we have seen an explosion in C3 technology that multiplied the computing power of the SAGE FSQ-7 machine and shrank it in size to microscopic chips. Where the technology of C3 made defensive air power awesome, the miniaturization of the circuitry has now reaped the same benefit to offensive air power. Aircraft can now carry sophisticated sensors and computers that can exchange data with other computers by means of a secure anti-jam, digital data link.
We are now on the brink of another revolutionary change in air warfare. Manned aircraft can now command and control an accompanying armada of pilotless but smart cruise missiles. This combination has the potential of regaining from the defense some of the same command and control advantages.
In both strategic and tactical applications, a command, control, and communication capability is achievable which will:
To achieve this C3 capability, the following developmental activities must be pursued aggressively:
Finally, it is of interest to conjecture what impact the C3 technology may have on the future personnel requirements of the Air Force and the cost of new systems. We have been visualizing highly automated air warfare. The classical duties of the air officer--flying, navigating, flight engineering--are being taken over by the computer.
Automation will put more and more vehicles and firepower under the command of each Air Force officer, flight or ground crew. The era is coming where Air Force combat personnel will require more training as military tacticians rather than as only technicians or pilots. One impact of C3 technology on air warfare, then, may have the potential of allowing more emphasis on the development of air warfare tactics and tacticians.
The impact of C3 technology on the cost of air weapon systems shows up in two ways. First, we can put into the inventory effective air weapons that need not be man rated and thus trade off the cost and weight of a life support payload with a C3 payload. We can then attempt to produce unmanned air weapons at less than 10 percent to 20 percent of the cost of manned air weapons, but retaining the same firepower. Second, the recent trend toward higher life-cycle costs due to skilled labor-intensive maintenance and operations expenditures can be reversed with automatic checkout, redundancy, and throwaway modularity features available in the same technology that yielded C3 itself.
WITH A rigorous development and deployment program, the conjectures in this article could be operationally attainable within the next ten to fifteen years. If these advances in technology continue to accelerate and we capitalize on them, the future impact of C3 on air warfare before the turn of the century will indeed be revolutionary. It is beyond our scope here to attempt to predict the details of this revolution. But suffice it to say that the U.S. has, at this point, the initiative in this area as a fallout of its superior electronics technology and production know-how. Let us hope that we recognize the availability of this initiative and proceed to exploit it.
The MITRE Corporation
1. Denis Taylor, Introduction to Radar and Radar Techniques (New York: Philosophical Library: London: Newnes, 1966),
2. R. R. Everett, C. A. Zraket, and H. D. Benington, "SAGE--A Data Processing System for Air Defense," Proceedings of the Eastern Joint Computer Conference, Washington, D.C., December 9-13, 1957.
3. C. A. Zraket, "The New Challenge for Computer Simulation," 1976 Summer Computer Simulation Conference, Washington, D.C., July 12-14, 1976,
4. Allan Roger, "Semiconductor Memories," IEEE Spectrum, August 1975.
5. Information Processing/Data Automation Implications of Air Force Command and Control Requirements in the 1980's (CCIP-85) Executive Summary, AF/SAMSO, February 1972, p. 3.
6. Courtland D, Perkins, "Computers in Flight: A Historical Perspective of Computation in Aviation and Aerospace," November 22, 1976, AIAA Annual Meeting and Technical Display Incorporating the Forum on the Future of Air Transportation, 13th, Washington, D.C., January 10-13, 1977, Paper #77-271,7 pages,
Charles A. Zraket (S.M.E.E., Massachusetts Institute of Technology) is Senior Vice President, Technical Operations, for the MITRE Corporation and has spent his professional career at MITRE and M.I.T.'s Lincoln Laboratory in research and development activities. At MITRE he has managed large-scale projects in defense control and communication systems for DOD and air and ground transportation systems for the Department of Transportation. He has also directed MITRE's R&D projects in energy-related fields.
Stanley E. Rose (B.S.M.E., Worcester Polytechnic Institute) during the last 17 years at the MITRE Corporation was responsible for advanced planning in such areas as tactical command and control, communications, military air traffic control, range instrumentation, and space systems. He worked in industry at AVCO Corporation and was responsible for re-entry vehicle arming and fuzing systems development and penetration systems preliminary design. Mr. Rose was Chief Development Engineer at Avien, Inc., responsible for developing aircraft fuel gauging and fuel management systems.
The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.
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