Identification of Promising Naval Aviation Science and Technology Opportunities (2006)

Just as the list of disruptive capabilities discussed in Chapter 2 is by no means exhaustive of the possibilities that ONR could pursue, so too the S&T opportunities identified in this chapter are not exhaustive. Committee members used their experience and expertise to provide a high-level assessment and to suggest where emphasis should be placed with respect to investments in Discovery and Invention (D&I) programs (6.1 and early 6.2) and Exploitation and Development (E&D) programs (late 6.2 and 6.3). The D&I programs tend to be longer-term, higher-risk efforts that, for the purposes of this study, tend to fall into the 2011 to 2025 time frame. The E&D programs tend to be shorter term with reduced technical risk, and are aimed for early insertion and transition to the fleet in the 2007 to 2010 time frame.

The recommended S&T opportunities, wherever possible, are categorized as (1) naval unique (required only by naval missions), (2) naval essential (important for naval and non-naval missions), and (3) naval relevant (useful for naval and non-naval missions).

The committee identified seven S&T functional areas as highly relevant to naval aviation: avionics technology, sensors, propulsion and power, structures and materials, human systems integration, survivability, and the core technologies of aerodynamics and modeling and simulation. For each disruptive capability the committee identified the S&T areas it believes require a focused development effort in order to make the capability a reality in the future. Table 3.1 shows

the mapping of each capability and its subsets to the functional S&T areas. Discussion regarding the mapping rationale and suggestions for particular S&T areas of focus within each functional technology area are presented below.

The superiority of U.S. naval aviation and the realization of the “know quickly and act decisively” concept are critically dependent on situational awareness, excellent communication and coordination, rapid precision strike, and greater employment of unmanned aircraft. Advancement of avionics technology is integral to each of these concepts. The committee believes that significant technology challenges exist and that ONR should play a leadership role in the development, experimentation, and evaluation activities conducted to mature these new capabilities.

At this time, however, ONR appears to be disengaged as a leader and sponsor of avionics technology development. In a 2001 study the Naval Studies Board’s Committee for the 2001 Assessment of the Office of Naval Research’s Aircraft Technology Program observed that “ONR is exiting the field of avionics technology development” and asserted that, with minor exception, the avionics work at ONR was focused on engineering “fixes” to current systems rather than investing in technology for the next generation.² The current committee has not seen evidence that this trend has been reversed.

Although the 2001 report was more favorable in its assessment of ONR’s work in autonomy for UAVs, this committee notes that the Navy’s previous centerpiece program, UCAV-N, has been moved to the Defense Advanced Research Projects Agency (DARPA) as part of the Joint Unmanned Combat Air System program. In addition, the committee was informed that the investment in autonomous technology at the 6.1 D&I level is to be reduced from $4 million to $2.5 million for fiscal year 2005.³

The committee recognizes that great advances in computing speed, memory density, wireless networks, and distributed computing are being driven by commercial market forces; thus, although these are critical enablers of future naval avionics, they are likely not appropriate investment areas for ONR. Further, significant work on aircraft avionics relevant to several of the identified disrup-

tive capabilities is being executed in the other military Services.⁴ Thus, a systematic review of avionics technology to identify naval-aviation-unique gaps is needed. ONR should be a leader and principal focal point for this systematic evaluation within the Navy. ONR should then be the principal sponsor of a cohesive program for the development of new technologies to meet the identified gaps.

Although ONR is in partnership with the larger aviation community, the committee believes that the advanced avionics technologies involved in three of the identified disruptive capabilities—namely, multispectral defense, unmanned air vehicles, and intelligent combat information management—will be central to the future of naval aviation and therefore of high interest to ONR. Specific comments on these areas follow.

Current low-observable (LO) technologies rely primarily on shaping and materials. These technologies are well understood, and their use has proliferated in many countries. Naval aviation can expect to encounter today and in the future adversarial air platforms with varying degrees of LO signature. The challenge for naval aviation will be to exploit all platform signatures—first for its own survivability and second to counter any adversary. Shaping and materials can achieve significant reductions in signatures, but they will not be sufficient for naval aviation in the future. Current technology permits tactically significant reductions in both radio frequency (RF) and infrared (IR) signatures.

Visual and acoustic signatures are very important to low flyers, and “all-aspect” stealth is very important to high flyers. Both need dedicated S&T efforts.

The next LO frontier is visual signature reduction. It could possibly involve active systems that change color or hue, reflectivity, or emittance. Conceptually, a visual LO system blends vehicle visual signature information with that of the background. If the vehicle is moving, this visual LO system must be very agile, with extremely fast response rates. An air platform with an active visual LO signature reduction system could be a really disruptive capability.

Active systems would have to be employed by naval aviation in order to reach the signature levels necessary to win against future adversaries. Active systems would require advanced high-speed electronics with robust sensors and detectors, high-speed networks, and advanced processing algorithms.

Significant advancements in the level of autonomy will be required to improve the effectiveness of UAVs, which will be required to function collaboratively in a complex and threat-filled environment and in conjunction with manned aircraft. Operating such vehicles from a rolling ship deck as part of a mixed wing of manned and unmanned systems is unique to naval aviation.

To deal with these challenges, these UAVs must process sensor data, identify unexpected threats and opportunities, perform dynamic planning, communicate, and execute their missions with limited human intervention. Because of these difficult requirements, the committee recommends a reinvigorated ONR focus on high-level intelligent autonomous technology⁶ that enables the following:

• Constellations of self-organizing and self-directing UAVs with human “control by exception” for automatic surveillance, reconnaissance, targeting, and attack;

• Development of an integrated digital system for providing automated communications (both RF and optical) and control between swarms of UAVs and ground stations to include networking of imagery, signals intelligence, Global Positioning System geolocation through sequencing antennas, and software-controlled radios;

• Self-contained automatic carrier landing capability with very-low-probability-of-intercept emissions from the aircraft platform (either manned or unmanned) and an aircraft carrier that does not have to emit a signal; and

• Reduced need for human involvement in UAV operations.

In addition to the need for a greater emphasis on technologies that enable autonomous operations, a principal challenge and a key element of the successful operation of multiple UAVs in a complex battle space will be the achievement of dramatically enhanced situational awareness for the remote “pilot-commander.” Such situational awareness will be crucial during strike operations (especially decisions about weapons release) and the naval-unique close-quarters operations of manned and unmanned systems on the carrier deck. Consequently, ONR should pursue a technology development program that enables:

• Simultaneous operations on carrier decks with manned and unmanned aircraft characterized by robust situational awareness, fault tolerance in both systems, and a significantly improved command and control architecture; and

• “In-cockpit-like” situational awareness for the remote UAV “pilot-commander” through the robust low-latency downlink of critical sensor and video data and the development of advanced synthesis and presentation technologies such as virtual reality techniques for visual, aural, and tactile feedback.

Operating UAVs in conjunction with manned aircraft on an aircraft carrier deck is perhaps the most naval-unique challenge facing naval aviation. Such operations will significantly disrupt carrier deck procedures as they are known today. Mixed-wing operations on the carrier deck will require a significant infusion of technology to provide robust situational awareness to all participants, fault tolerance in both the individual systems, and the command and control architecture needed to achieve efficient and safe operations.

Positive control of the unmanned aircraft will be required by the carrier deck personnel who currently communicate with pilots via hand signals. Methods are needed for the carrier deck personnel to instruct UAV aircraft, confirm receipt and understanding of these instructions, and interrupt operations. The technology could include a vision system for the UAV, a data terminal for personnel, or remote “pilot” operator stations with advanced situational awareness capabilities.

Naval aircraft need a new digital high-speed intelligent combat information management and display system (IMDS) that prioritizes and synthesizes the volumes of information generated on board the aircraft and provided by other participants on the Navy FORCEnet.⁷ This system would be the principal pilot interface to all aircraft navigation, communications, sensor, display, self-defense, and weapons systems. It would automate many of the functions and lower-level decisions made today by the pilot to enhance situational awareness and avoid information overload.

An IMDS would be enabled by a fully integrated avionics architecture (a federated system of sensors, displays, processors, and countermeasure sub-systems) and would require significant supervisory intelligence as it automates/ manages aircraft functions. The on-board IMDS would exploit an underlying Internet Protocol (IP) connection to FORCEnet and automate the pushing and pulling of mission-critical data from the network to meet higher-level mission objectives. It would interface to other nodes: aircraft, UAVs, command and control, databases, sensors, weapons, and so on.

Research and development into IP-based, high-bandwidth, optical aircraft intranet structures for on-board data management systems could greatly reduce the cost and weight of the avionics infrastructure. Additionally, cost-effective ways are needed to retrofit current analog/1553 digital bus aircraft with state-of-the-art digital high-speed architectures.

The IMDS would also be an advanced operator-vehicle interface to provide enhanced situational awareness and higher-level interaction with the pilot. To create this system and its component technologies requires human factors research into information assimilation and cognitive decision tools. This subject is covered in some detail in the section below titled “Human Systems Integration.”

Achieving Sea Power 21 and Marine Corps Strategy 21 is critically dependent on the pervasive use of sensors and their capabilities for intelligence, surveillance, and reconnaissance; for threat warning; for targeting; for weapons’ guidance; and even for such mundane things as controlling the physical configuration of aircraft in flight and detection of failing or failed components for condition-based maintenance or for modes of fault tolerance and self-healing. The range of available sensors is extremely large and diverse—encompassing sophisticated electromagnetic modalities from ultralow microwave frequencies through the conventional microwave bands to millimeter wave (MMW) regions and on into the optical ranges of the infrared, the visible spectrum, and beyond, as well as inertial sensing, the detection of chemical and biological agents, acoustic and seismic sensing, and environmental sensing of temperature, humidity, wind conditions, and so on.

Table 3.2 represents a partial listing of Navy-relevant sensor technologies and suggests the extremely wide range of topics that the term “sensors” encompasses.

The key to the success of network-centric war-fighting concepts in naval aviation is the cooperation of multiple sensors and sensor platforms and the successful implementation of multisensor fusion, exploiting the information from multiple sensors distributed throughout the battle space to create, in real time, continuous and complete battle space awareness. The Navy’s Cooperative Engagement Concept has shown the effectiveness of a such a distributed sensor (i.e., radar) configuration, although the specific implementation, which places enormous loads on the communications (e.g., directional point-to-point, high power, very wide bandwidth), is probably not a model for future, more general, FORCEnet implementations.

From the point of view of the disruptive capabilities listed in Table 3.1, it is clear that sensors, in one form or another, must play a crucial role in any new concept that arises. However, although this is undoubtedly true, Table 3.1 does not call out sensors for enhanced attention either because the committee thought

that the technology is being adequately developed as a whole by government, contractors, and universities or because the ONR programs on sensors currently appear to be on a reasonable path to needed future capabilities. New sensor technology developments do not seem to be required for the particular disruptive capabilities identified in the previous chapter.

Indeed, in general, ONR’s radar and optical sensor work seems mainstream—that is, comparable to the state-of-the-art work available in the government, university, and contractor communities as a whole. In particular, ONR’s (Code 31) work on multifunctional RF antennas (i.e., common hardware for radar and communications at multiple frequencies) is novel and of great importance for future platforms that implement FORCEnet interconnections—for the resolution of cross-platform radar/communication interference issues and for just plain real estate reasons.

Of course, there are always sensor challenges to be met and new ideas and opportunities to exploit in every application. Below are some comments on the technical challenges inherent in the disruptive capabilities listed in Table 3.1 as requiring focused efforts in sensors.

For multispectral defense, the challenge is to characterize the background along the line of sight of the threat so that a UAV can respond by actively altering its signature to minimize its contrast with the background. Although this capability is not difficult in static situations, the dynamics of flight (speed, maneuvering, angles, etc.) will stress sensor response capabilities dramatically.

The very small sizes and severely limited on-board power capacity of micro-UAVs create special sensor challenges that, although they have already been addressed for modest-sized UAVs, require a dedicated S&T effort.

Sensor aperture compatibility with aerodynamic requirements is a very difficult problem as both may be compromised. Forward-pointing sensor apertures are not easily made compatible with the slender pointed shapes and shock-wave-withstanding structures dictated by hypersonic aerodynamics. Even conventional radar-guided missiles (e.g., Hawk, Patriot) suffer difficult bore sight errors because they must receive microwave signals through aerodynamically shaped radomes. Full imaging with optical sensors, which is desirable for high-resolution, precise, end-game tracking of a hypersonic missile, could be seriously compromised by the need to look through a complex pointed optical element (i.e., the tip of the hypersonic vehicle) or through a structure whose shock-wave resistance might vary considerably with angle of attack. Side-looking apertures could more easily be made compatible with the aerodynamics, but without a direct forward field of view a vehicle or a missile must resort to complex flight paths to compensate for the unfortunate blind spot that results.

The ability to reliably “see through” weather, obscurations, and foliage and to penetrate water is desired for many future naval applications. While optical systems are limited to clear-air environments, conventional radars and MMW systems are relatively insensitive to weather, smoke, fog, and so forth, and MMW

imaging is of particular interest for both active and passive short-range, high-resolution imaging in obscured environments.

Laser detection and ranging (LADAR), with its high-resolution three-dimensional geometric imaging capabilities for looking through holes in the foliage canopy, and ultralow-frequency microwave synthetic aperture radar, which is barely affected by dry leaves, show promise for foliage penetration. Both are currently under active investigation by the Army Research Laboratory and DARPA.

“Blue” LADAR technology can penetrate to various depths in the ocean typically measured in a few “extinction depths.” Although this capability is advantageous in some parts of the ocean, it is inadequate in many littoral environments, harbors in particular.

While the disruptive capabilities discussed above do not seem to require the development of completely new sensors beyond current state-of-the-art capabilities, there are a number of sensor technology issues that Navy S&T should be monitoring or actively involved in. Three of the most interesting are discussed briefly below.

Digital Creep. Most sensor systems generate their information via an analog measurement of the environment and then conversion of signal information into a digital format for processing and subsequent extraction of information. As the performance of digital chip technology continues to increase exponentially, the trend in sensor systems is to convert the signal to digital closer and closer to the front end of the system and to exploit the compact storage and computational power inherent in modern digital circuits to provide on-board signal processing and information extraction—thus producing very capable “smart” sensors.

Military optical systems have already become largely digital, with sophisticated, high-density focal plane arrays, on-board and sometimes on-chip signal processing, and the like. Radar, too, has been heading in the same direction (with DARPA encouragement), albeit more slowly because the analog-to-digital (A/D) challenges of directly digitizing microwave signals are enormous, given the requirements for very high speed, power-hungry sampling. Yet the benefits of practical (and affordable) A/D capability—including freedom from environmentally induced drift, the possibility of microwave-insensitive wide-band digital phase shifting, and the physical benefits of replacing microwave wave guides by fiber-optic communication links—could be significant. Navy S&T should closely follow the trend toward digitalization and consciously apply it to other than optical and radar sensor modalities.

Nanotechnology. Nanotechnology has much to offer for enhanced sensor capabilities. Operating at nano-level (10⁻⁹) dimensions, it is becoming possible to construct many artificial materials that do not appear in nature and that could have novel and unusual mechanical, electrical, or optical properties. Recently, oriented carbon nanotubes, for example, which can be made in insulating or semiconducting forms, have been shown to have the capability to act as optical detectors. Single-electron transistors, constructed via rapidly developing nanotechnology techniques, also offer promise for future novel applications to sensors.

Perfect Imaging. Thirty or more years ago it was noted that if a material with a refraction index equal to –1 could be found, then perfect imaging, free of diffraction-induced wavelength limitations, could be implemented.⁸ Materials with a dielectric constant ε and a magnetic permeability μ both equal to –1 have not been found in nature, and so the concept of making “superlenses” has not yet been demonstrated. A few years ago, however, artificial materials consisting of oriented wires (for ε control) and embedded rings (for μ control) were constructed⁹ with a resulting refractive index of –1 at microwave frequencies, and the possibility of “perfect imaging” or superlenses has been demonstrated. An active research community has sprung up to exploit this idea.¹⁰

With the potential to bypass the diffraction limitations of radar antennas, so-called perfect imaging could offer major advances in radar sensors, particularly for MMW imaging from small platforms where physical limitations restrict usable aperture size. This new approach is a high-risk effort but is worth watching closely.

Currently, the ONR propulsion program is rather limited and evolutionary in character. To support the Navy in Sea Power 21 and Marine Corps Strategy 21, ONR needs to stretch its vision farther into the future and start work on some revolutionary propulsion technologies. The committee suggests that a good place to start would be the technologies needed to enable the identified disruptive capabilities areas of UAVs, hypersonic weapons delivery, and heavy-lift vehicles.

ONR participates with the Air Force, General Electric, and Pratt & Whitney

FIGURE 3.1 Pulse detonation engine. SOURCE: Office of Naval Research.

in the Integrated High-Performance Turbine Engine Technology (IHPTET) and the Versatile, Affordable, Advanced Turbine Engine (VAATE) programs. These programs integrate various materials and component technologies and demonstrate technologies in a realistic engine environment that is well instrumented. The IHPTET program is intended to achieve a 20 percent improvement in fuel consumption and 30 to 35 percent improvements in thrust, range, payload, and maintenance cost. These improvements would be substantial evolutionary gains accomplished over a mid-term period. The IHPTET program does not involve high-risk, potentially disruptive technologies but rather is a more conservative attempt at advancement of capabilities.

Jet engine noise reduction is another area of interest to ONR. The specific plans for this area have not been made clear. A program that addresses exhaust noise as well as compressor noise should be pursued.

One ONR research program addresses the important problem of jet engine flame-out; another examines the use of active control of combustion processes for enhanced mixing and performance. Active combustion control is a promising research area from which several valuable enabling technologies may develop. Research in this area of active control should continue and should be broadened and deepened as a core activity in combustion.

ONR does have a research effort in the area of pulse detonation engines.¹¹ See Figure 3.1. This relatively simple and inexpensive engine design could sub-

stantially reduce costs for weapons delivery systems (e.g., cruise missiles that currently use expensive gas turbine jet engines). This is a high-risk controversial concept for several reasons. It would have an inefficient thermal cycle since entropy-producing discontinuous compression waves are used to compress the combustible mixture. Also, the required mechanisms to cause detonation of fuel-spray/air mixtures in tubes no longer than a few meters can lead to complexities, volumes, weights, and costs that were not originally envisioned. For example, long nozzles, electric arcs, and rocket propellants have been considered.

The search for less costly weapons delivery should be broadened beyond the pulse detonation engine. One approach would involve studies of potential schemes that use rockets or ramjets (including hypersonic ramjets) for sequential ballistic/ glide or powered flight trajectories that enable a missile to survive defenses as it flies to its target. Studies should address both the cost and the feasibility of this approach. A jet-assisted takeoff-boosted ramjet should be considered as a low-cost propulsion system. Two-stage vehicles could be studied in which the first stage has a turbojet engine and the final stage has a rocket or ramjet engine. Of course, the intention is to recover the first stage. Recovery mechanisms could be studied for cost and feasibility. The first stage might be a UAV that flies back to the carrier; it could be a UAV seaplane, or it could fall with a parachute into the sea. ONR should engage in fundamental research related to novel concepts that offer the possibilities of such cost reductions.

Hypersonic flight with continuous combustion of liquid fuels is an area that requires further study for optimization of the supersonic combustion process. Although the Air Force has a program on hydrocarbon-fueled scramjets,¹² relatively little is known about the scientific foundations for injection, atomization, and vaporization of liquids into a supersonic air stream. Emerging concepts that bypass the problems of supersonic combustion could also be examined (e.g., crossed-field electromagnetic deceleration of incoming air and acceleration of product gases).¹³

There is a need for a heavy-fuel engine for smaller rotary-wing UAVs. Currently, only light-fuel engines are available in certain size ranges. Efforts should not be restricted to scale-down of existing propulsion technology. New concepts should be considered.

ONR is currently not engaged in the aeronautics of long-range, long-endurance, small (10 cm to 1 m) fixed- or rotary-wing UAVs. These would require highly efficient engines (or other power sources) that overcome the adversities of

increased surface-volume ratios at small scales (e.g., increased heat loss per unit of energy converted, increased friction dissipation per unit of energy converted). Mere scale-down of existing designs will not work; new concepts and the associated research and enabling technology development are needed. A major new effort in miniature propulsion systems should be established.

There is also the need to study aerodynamics issues for miniature UAVs. In some new concepts, propulsion and aerodynamics might become more strongly integrated. See the “Core Technologies” section of this chapter for further discussion.

The naval interest in airborne laser weapons may have synergy with propulsion and airborne power needs. Lasers are very energy inefficient in that only a small fraction of the energy from the laser power source appears in the photon beam. Basic research to explore uses of the remaining energy for the purpose of propulsion or other airborne power needs should be undertaken.

ONR has considered propulsion and power as critical technology areas. Nevertheless, there is a strong need to strengthen and broaden S&T efforts in this domain.

Navy aircraft do everything that land-based aircraft do—but in a more hostile environment and under more adverse conditions, demanding readiness to respond in all sea states, in all weather conditions, and from both large and small ships. Catapult takeoff and arrested landings impose high-impact structural loads that threaten either fracture or low-cycle fatigue failure of landing gear and other structural components. The marine environment exposes all structural components to extremes threatening both corrosion and stress-assisted failures. Limited storage space leads to design options that differ markedly from those of comparable land-based aircraft, and these design differences impose materials selection options that may differ radically from those for their land-based counterparts.

These differences in environment and basing have led to selections of materials and design that make naval aircraft unique, and this pattern does not seem likely to change for UAVs. Persistence, rapid turnaround, fuel efficiency, and similar systems requirements will continue to demand advances in the development of lightweight stealthy materials and structural design principles for these unusual materials. The specific applications in naval aviation systems may be unique, but the underlying principles and D&I programs will strongly overlap and should complement those engaged in by the other Service S&T programs.

These issues concerning materials and structures have been appreciated by ONR in the development of its S&T program in support of propulsion and power for next-generation naval aviation. The committee was briefed on that program and its strong participation in the interagency IHPTET and VAATE programs. By contrast, based on the briefings received by the committee, there does not appear to be comparable attention given to the materials and structural issues associated with the other elements of naval air vehicle platforms.

The committee recommends that ONR examine the technology areas listed in Table 3.3 as a way to enable and realize the identified disruptive capabilities. Table 3.3 also suggests improvement goals for both the 2007 to 2010 and 2011 to 2025 time frames. Each of the recommended technology areas is identified as unique, essential, or relevant to naval needs.

While structural research and development in other areas is still required (e.g., high-altitude, long-endurance UAVs), the committee thought that, given a limited budget, the greatest benefit would be achieved by focusing on the areas of hypersonic weapons delivery and heavy-lift air vehicles.

Advanced structures are seen as a key enabler in both hypersonic and heavy-lift air vehicles. Each disruptive capability area drives the required structural developments to two different extremes: lightweight/high-temperature capability (hypersonic applications) and lightweight/high-stiffness capability (all applications, especially for heavy-lift air vehicles). As with all naval aviation, affordability, producibility, and supportability in a maritime environment cannot be sacrificed in the name of higher performance. For these disruptive capabilities to be realized and introduced into fleet applications, a systems engineering process is required to ensure that all of the needed capabilities are balanced.

The following paragraphs address some options that should be included in such a process to lower the development risk. No exhaustive listing is attempted, and the specific topics selected should be identified after careful interagency discussions to clarify the desired breadth of an expanded program and the Navy-specific and Navy-relevant aspects of new investments. A more comprehensive NRC examination of materials for all future DOD needs¹⁵ should be consulted as these programs are developed by ONR.

In the area of hypersonics, key revolutionary developments (order-of-magnitude improvements) to achieve lighter weight, high-temperature capability, high strength, and producibility are needed to enable next-generation applications.

Within this disruptive capability area, two distinct hypersonic applications have been identified: air-breathing-based and rocket-based air vehicles. Greater structural research and development (in conjunction with high-temperature materials) are required to enable the design and integration of the aircraft/missile inlets/ exhausts, control surfaces, primary edges, and so on. These advanced structures must also be robust enough to enable optimum design flexibility for aerodynamics and aerothermal considerations for hypersonic flight.

In addition, attributes that the ultimate system may require, such as LO or subsurface launch, will further complicate the systems design and also underscore the need for early research and development in high-temperature, structurally embedded LO sensor windows and apertures and watertight high-temperature seals. Furthermore, low-cost hypersonic structures will be required for missile applications.

If the Navy leadership, through a detailed systems engineering process, determines that manned or unmanned hypersonic aircraft should be based on and return to ships, the hypersonic-capable airframe would have to incorporate low-speed handling for ship recovery. This could entail propulsion systems capable of not only hypersonic flight but also short takeoff and vertical landings.

Of all the issues needing attention before serious application of hypersonic speed in missiles or vehicles, high-temperature materials and manufacturing technology for their fabrication into parts remain at the top of the list demanding further D&I. This is not so much a naval-unique issue as it is a naval-essential one. While programs exist in other agencies, they are inadequate to address all issues at current levels of effort. Naval participation in such programs will not only accelerate the development of critical technologies, but will also bring the Navy to the table as part of the DOD “smart buyer” team when acquisition begins.

Ceramic Materials. Unlikely to have any immediate effect on vehicle structural members, advanced ceramics are already beginning to impact rocket and turbine engine exhaust systems and turbine blades, the former as solid elements, the latter as coatings. The high strength required at the high temperatures inherent in hypersonic missiles will undoubtedly be achieved using ceramic materials. Many of these materials either do not yet exist or will require further S&T before applications can be considered by designers.

Metals. High-temperature materials, including molybdenum-based alloys, attract continuing attention for engine applications, promising increased thermal efficiency if oxidation problems can be overcome with suitable coatings. Significant investment is being made in the development of these materials under the IHPTET and VAATE programs. However, recent advances in the application of computational tools to the development of improved structural steels have led materials

engineers to believe that such developments are far from ready for application in hypersonic vehicles.

Years of investments by many agencies, including ONR’s Materials by Design program, have led to the development of many computational tools that individually contribute to materials development by enabling the calculation of specific properties and their links to alloy formulation and processing. Two recent DOD programs have led to advances in integrating these isolated computational tools into systematic design tools targeted at coupling materials development and system design to reduce materials development time and cost while optimizing the property suite. DARPA led the Accelerated Insertion of Materials program, an industry-focused effort to assemble existing software into system-based design tools. The Air Force Office of Scientific Research initiated and continues to fund a program on further development of the computational tools, known as Materials Engineering for Affordable New Systems. These two programs have yet to highlight material systems of special interest to the Navy, and it would appear timely for ONR to extend its interest in computational tools in this direction, with naval aviation materials only one of the anticipated areas of emphasis. The committee notes the existence of a Multidisciplinary University Research Initiative topic in this general area intended for initiation in fiscal year 2005, but suggests that this effort should be supplemented by and integrated into a strong core effort.

The committee notes that, among the many other issues that will be important in the design and construction of next-generation rotorcraft/vertical short takeoff and landing (VSTOL) and dirigibles as future heavy-lift vehicles, the scale-up in size from present prototypical vessels will demand lightweight structural members, with stiffness far exceeding that of any currently available materials. Furthermore, these members are likely to be subjected to low-cycle fatigue stresses that would be expected to severely limit the lifetimes of parts fabricated from today’s materials. Among the list of research options that should be considered is further attention to organic matrix composites. These materials have been the subject of broad investigation for decades, and their successful introduction into aircraft manufacture is strong testimony to the value of such long-term, sustained research and development investment programs. However, present-day materials are costly to produce and fabricate into parts, are not yet as “unobservable” as future capabilities demand, and are subject to corrosion (oxidation) damage at unacceptable rates, severely limiting lifetimes. Furthermore, when they are used as structural members, their sensitivity to fatigue fracture may be a life-limiting feature. Two important new advances in materials development promise to address these deficiencies and herald a new generation of organic matrix composites, but extensive research is required to achieve further basic

understanding and apply these principles to specific systems. These two advances are the increased availability of low-cost multiwall nanotubes for use as strengthening fibers and the invention of strategies for the fabrication of self-healing fatigue-resistant materials.

Nanotubes. Carbon nanotubes offer the opportunity for control of strength and electrical conductivity in the materials used as strengthening fiber for organic matrix composites. Single-walled tubes remain expensive and difficult to process, although that may change in the near future as a result of many research endeavors worldwide. Multiwall tubes are already available in large quantities at reasonable prices and may be quite suitable for composites fabrication. Research topics should include development of nanotube processing technologies; functionalization of nanotubes for and “compatibilization” with various organic matrices; characterization of mechanical properties, including lifetime in hostile environments; characterization of physical properties, especially mechanical properties and radiation visibility; and all of the above under various conditions involving process variables.

Self-Healing Composites. Current strategies for self-healing composites are based on inclusion of microscopic encapsulated epoxies that are activated by crack propagation and polymerize to strengthen the material ahead of the moving crack tip and arrest its further motion. This proven concept needs further development, primarily in the area of further miniaturization of the encapsulants to eliminate their current composite mechanical property degradation.

Human systems integration (HSI) optimizes the human part of the total system equation by integrating human factors engineering; manpower, personnel, and training; health hazards; safety factors; medical factors; personnel (or human) survivability factors; and habitability considerations into the systems acquisition process.¹⁶ All of these factors are critical to naval aviation. A committee review of the briefings and supplementary materials provided to it as well as answers to posed qu estions identified both strengths and weaknesses in the existing program for HSI and established the basis for recommendations for extensive program augmentation.

The following promising naval aviation S&T opportunities in HSI have been organized by time frame, naval relevance, naval capability, and level of research and are summarized in Table 3.4. Subsequent paragraphs amplify some of the proposed areas of research.

Naval aviation is unique in its requirement for maintaining situational awareness from seabed to space. To provide this capability, basic research in machine vision is essential for detecting and identifying entities from seabed to space. No human could maintain vigilance over this large domain. No human could detect entities at a reliably rapid rate. Given the mandate to reduce the number of personnel on aircraft carriers, dependence on machines for detecting and identifying entities is mandatory. A consortium of 220 organizations has developed an online machine vision information exchange.¹⁷ This would be an excellent place for ONR to leverage technologies and to identify category 6.1 research that is naval unique.

Next in consideration should be the tagging, tracking, and locating of space, air, surface, and subsurface entities to maintain total battle space awareness. The Air Force Research Laboratory (AFRL) has a long history of developing technologies for tracking air and ground targets.¹⁸ ONR’s collaboration with the AFRL to extend these techniques to surface and subsurface targets would dramatically move the Navy to total battle space awareness.

One part of battle space awareness that is consistently lacking is knowledge of own-force performance, including command and control performance. ONR is currently funding research in this area.¹⁹ This work could be developed into an automatic performance measurement system for shipboard and airborne command and control.

While the above S&T opportunities address naval-unique needs, the following address naval-essential needs. Basic research in information fusion is required by all three aviation Services to provide rapid and accurate decision support. ONR can use and leverage research reported by the International Society of Information Fusion.²⁰ This contact will also decrease the risk of technological surprise in this critical technology area.

In a more applied area, the AFRL released a grant notice in May 2004 for Revolutionary Automatic Target Recognition and Sensor Research.²¹ ONR collaboration with this grant process could leverage technologies for rapid and accurate decision support in naval aviation.

S&T opportunities for the 2007 to 2010 time frame that are naval relevant should be focused on interoperability. The least-understood interoperability issue is fitting a human into multiple roles. What are the dimensions of human interoperability? Is there an underlying skill that makes some sailors and aviators better able to perform various roles—pilot, mission planner, instructor, inspector, and so on? Are there human skills that are more interoperable than others? Are there aspects of tasks that enhance human interoperability? Are there organizational structures that enhance human interoperability? “Human interoperability” is not a new term; it was used in 2001 by then-Secretary General of NATO Lord Robertson in a now-famous speech.²² Again, this research is important not only for enhancing capability for naval aviation but also for avoiding technology surprise.

By identifying ways to select and train personnel for multirole tasks, applied research also addresses the requirement for reduced manning of ships. In addition to the ability to handle multiple roles with efficiency and accuracy, there is the ability to adapt. Given the reduced manning of naval aircraft carriers, designers will not be able to provide solutions for every contingency, or for every combination of personnel and role. Therefore, selecting and training personnel for adaptability will be a key element of mission success. Soldier adaptability is a critical component of Army transformation.²³ Again, ONR can leverage another Service’s research and apply it to naval aviation.

To provide minimally manned naval air operations, ONR must perform basic research in the synergistic teaming of manned and unmanned assets. The trade-offs of various levels of synergy have already been identified by the Army.²⁴ The Aviation Applied Technology Directorate has listed its desired capabilities for rotary-wing aircraft and UAVs. The research to best understand the potentials for

synergies and the risks of incompatibilities must be performed if naval aviation is to be conducted with mixed fleets of manned and unmanned assets.

To minimize the number of personnel on aircraft carriers, routine (deck scrubbing) and hazardous (patrol) jobs could be performed by fleets of semi-autonomous unmanned ground vehicles (for deck scrubbing), unmanned underwater vehicles (for underwater patrol), unattended ground sensors (for beach and harbor patrol), and UAVs (for ship, beach, and harbor patrol). The Space and Naval Warfare Systems Command has performed extensive research in this area already.²⁵ Again, ONR could leverage this research for naval aviation.

Identifying automation technologies for reducing or eliminating support personnel and providing autonomous carrier protection that could transition to the fleet in the 2011 to 2025 time frame would greatly reduce manning requirements. Such a capability is already listed in the Navy Functional Concept of Operations.²⁶ Autonomous aircraft carrier protection has been identified as a requirement by the Chief of Naval Operations.²⁷

A naval-essential capability in the 2011 to 2025 time frame is 24/7/365 combat readiness. With limited assets, the naval aviation community must have computer aiding. Computer aiding includes the support of human operators in all aspects of operations. Some basic research has been performed in adaptive automation in which a computer performs more tasks as operators/aviators become overloaded. The Office of the Secretary of Defense has funded work on adaptive automation for supervisory control of UAVs.²⁸ Supporting operators/aviators physically has not been addressed, nor has cognitive aiding. Does the operator/ aviator need enhanced perception, information processing, or response support? These questions have not been adequately addressed.

Given the need to provide 24/7/365 combat readiness, human operators must be used to their maximum efficient endurance. Methods must be developed for tactical fatigue reduction. Use of go/no-go drugs, sleep/rest schedules, and so on has been explored by the National Aeronautics and Space Administration (NASA)²⁹ and the AFRL.³⁰ These topics both present excellent collaboration opportunities for ONR, given the Navy’s unique seaboard accommodations. Also

critical to providing 24/7/365 combat readiness is reducing the risk of loss of naval aviators. This includes immersion protection for downed pilots and fullspectrum laser eye protection. Finally, maintaining combat readiness requires just-in-time training, which of necessity must be provided shipboard through embedded training, ruggedized sea-based trainers, and reach-back trainers. These trainers could also provide mission rehearsal.

Similarly, S&T 6.3 opportunities are focused on reducing risk to naval aviation personnel. These opportunities include spinal cord injury mitigation for both pilots and operators of high-speed boats, fuel-handling protection, multilevel security for training and mission rehearsal tools, and semi-automated forces behavioral models for training simulators. There is a 40-year history of research on spinal cord injury mitigation.³¹ Fuel-handling technologies have been developed by the Air Force³² and the Army Corps of Engineers.³³ The Navy has a long history of interest in mission rehearsal,³⁴ and ties between the Naval Aviation Training System Program Manager, PMA205, and ONR would enhance naval capabilities in this critical area. Finally, the Army has performed extensive research in semi-automated forces for training. The Army Program Executive Office for Simulation, Training, and Instrumentation has models that could be applied directly to naval aviation trainers.³⁵

Naval-relevant research in the 2011 to 2025 time frame also includes basic research in command and control and piloting that makes assimilation of information intuitive. The Space and Naval Warfare Systems Command presented its research at the 2004 Command and Control Research and Technology Symposium.³⁶ Such a symposium would provide ONR with collaborators as well as technologies to leverage and would reduce technology surprise.

Finally, 6.3 S&T opportunities for the 2011 to 2025 time frame include the use of handheld and wearable displays. Such displays have already been developed for F-15 maintainers.³⁷ One of the most time-intensive tasks aboard ship is maintaining the technical orders for aircraft and aircraft ground support equip-

ment. What if all technical orders were electronic, and what if only the relevant portions were presented during a maintenance task?

Survivability is achieved according to a multidiscipline approach involving avionics, sensors, propulsion/power, structures and materials, and so on. These areas must be worked on collectively as an integrated product to arrive at an affordable and survivable design. The ONR presentations reviewed by the committee did not address survivability either as a functional requirement of a particular ONR program or as a functional discipline within the ONR S&T program community.

Survivability is a committee concern in five areas, as indicated in Table 3.1:

• High-altitude, long-endurance UAVs will have a significant IR contrast signature due to the cold background.

• Tactical, high-performance UAVs will encounter similar LO challenges as manned tactical aircraft.

• Air-breathing hypersonic vehicles will have a significant IR signature due to their speed.

• Next-generation rotorcraft/VSTOL air vehicles will have unique rotor signatures.

• Heavy-lift vehicles will be large, low flyers with visual signature challenges.

The committee recalls that ONR used to have an overarching survivability systems engineering department that was chartered with defining the state of the art in terms of survivability (susceptibility, vulnerability, and recoverability) and developing a D&I road map to guide ONR’s activities. Coordination with other Services was part of the effort, since there exists a large database of technologies and programs that specifically address survivability concerns.

In addition to the aviation technologies discussed above, ONR must devote S&T efforts to the fundamental core technologies of aerodynamics and dynamic modeling and simulation. Two important application areas for these core technologies are discussed here: heavy-lift vehicles and UAVs.

A new DOD heavy-lift rotorcraft (currently designated as Air Maneuver Transport, and Air Theater Transport) in the 13- to 20-ton weight range with a capability to carry 50 to 60 passengers is under consideration for development by the Joint Services (Army, Navy) and NASA. There are ongoing efforts, with

participation from contractors, to conduct studies of trade-offs to help evolve and define the system’s requirements. The heavy-lift requirements (e.g., cruise speed, maximum dash speed, maximum payload, endurance, survivability), design considerations (dynamic system, rotor blades, flight control system, avionics, power plant, including engine), and operational envelope are still evolving and are not known to this committee.

The committee envisions that the new heavy-lift rotorcraft program will leverage many of the existing analytical tools in both government and industry in the development process. The committee also believes that it is critical that the naval-unique requirements be identified and defined up front as part of the overall joint services requirements to mitigate trade-off and design risks. Such a vehicle is critically important to the Sea Basing pillar of Sea Power 21 and to the Marine Corps in its vision of attacking from the sea. There will be many new S&T challenges in the development of this heavy-lift vehicle, and ONR should become engaged from the beginning in creating S&T solutions to the challenges.

There is a need to study aerodynamic issues for micro-UAVs. In some new concepts, propulsion and aerodynamics may become more strongly integrated. At the smaller sizes and lower speeds for these vehicles, the aerodynamics could differ significantly because the lower Reynolds number might easily be in a transition range. This could mean lower lift-to-drag ratios that adversely affect range. Microelectromechanical system technology might be used on lifting surfaces to provide triggers for inducing turbulence so as to reduce drag due to flow separation. Mechanisms for lift production might be completely re-examined; for example, unsteady aircraft motion could be used to produce lift plus possibly some propulsive thrust. The wing flapping of birds is just one example of how unsteady motion of air-vehicle components produces both lift and thrust. Again, scale-down of existing technologies probably would not be optimal, which implies a great need for research and technology development.

ONR should consider the dynamics of small UAVs that maneuver sharply (high forward and turning accelerations) to serve on missions that go beyond loitering at a distance from objects of interest that require proximity with survivability. The time scales for the dynamics of these aircraft decrease as the size decreases. Therefore, remote control introduces problems at the operator-machine interface. New types of automatic controls may be required to handle the fine aspects of flight while the remote pilot maintains general control. New propulsive schemes and new aerodynamic designs would be needed to enable the bursts of acceleration and sharp turns that protect these aircraft from destruction as they fly near hostile forces.

Beyond these specific problem areas, aerodynamics should be considered a core technology area to be sustained by ONR. For example, it does have substantial importance in hypersonic flight technology and as a key enabling technology for understanding and exploitation of dynamic fluid-structure interaction. The

state of the art for time-dependent or unsteady aerodynamics is ripe for rapid advancement and that, in turn, will enable new advances in the understanding of and better design for improved life of structural components for high-cycle fatigue, rapid maneuvers both desirable and hazardous (abrupt wing stall), and quieter aircraft and rotorcraft (reduced acoustic signatures).

Modeling of flow in engine combustors can also be in a similar range. Current capabilities for modeling fluid dynamics in the Reynolds number range below fully developed turbulence but above the laminar range are not reliable. Therefore, computational fluid dynamics (CFD) capabilities must be extended to handle unsteady transitioning flows.

Noise and vibration of rotorcraft can lead to detection by an enemy force and also to fatigue of the rotorcraft crew and structure. Development of the capability to create designs with dramatically reduced noise and vibration requires fundamental improvements in dynamic modeling and simulation. There is a pressing need for accurate and computationally tractable models of the unsteady flow field and its interaction with nonlinear structural elements, including rotor blades.

Similar fundamental issues arise in the design of turbo-machinery blades for long life in a harsh flow environment that too often leads to high-cycle fatigue of these blades.

The complex aerodynamic flow field in which aircraft and rotorcraft take off and land from an aircraft carrier or other ship can give rise to dynamic stability and control phenomena that also require fundamental advances in the understanding of unsteady aerodynamic flows to predict the motion and stability of flight vehicles in the shipboard environment.

Abrupt wing stall (AWS) is a dynamic phenomenon that is characterized by the feedback coupling between a complex (separated) flow field with the motion of the vehicle. Typically AWS occurs at high angles of attack and high subsonic/ transonic Mach numbers. Several currently operational vehicles, including the F/A-18, have experienced AWS during their development program. Current CFD models and simulation methods are inadequate to simulate AWS, and successful correlation between computational simulations and experiment (wind tunnel or flight tests) has not yet been fully achieved. Fundamental improvements in both understanding of the underlying physical phenomena and computational algorithms for efficient simulation are required.

In practice, each of the topics discussed above is often treated separately by largely distinct communities of engineers and scientists. Such compartmentalization tends to emphasize the differences and idiosyncrasies among these several topics. But fundamentally the underlying phenomena have much in common, and a vigorous D&I program in unsteady aerodynamics and fluid-structure interaction could pay rich dividends in the capability to model and simulate, and thereby reduce and ameliorate, rotorcraft noise, turbo-machinery high-cycle fatigue, and AWS.

• For the disruptive capabilities identified as highly desirable for Naval Power 21, the committee has identified the technologies requiring a strong, well-planned, focused effort to achieve an order-of-magnitude improvement. These can be categorized under the functional areas of avionics, sensors, propulsion and power, structures and materials, human factors, survivability, and the core elements of aerodynamics and dynamic modeling and simulation.

• ONR is no longer pursuing leading-edge survivability S&T, nor is it connected to the other Services and their efforts in this area.

• ONR should create an overarching survivability systems engineering effort that is chartered with defining the state of the art in terms of survivability (susceptibility, vulnerability, and recoverability) and developing a D&I road map to guide naval S&T activities. ONR should consider developing strong technology programs supporting the desired disruptive capabilities if these are to become a reality.