Discovery and Invention Technology Thrusts
Ordnance as defined by ONR refers only to the warhead component of a munition such as a missileor gun-launched projectile. The other aspects of a munition are reported elsewhere. These include the guidance and control and propulsion and fuzing. However, it must be recognized that there is a complex relationship between ordnance and all the other attributes of a munition. For example, hypersonic propulsion enables the munition to reach the target in much shorter times and provides the velocity for deeper penetration into hard and deeply buried targets. Similarly, improved guidance and control allow lethality to be achieved by precisely delivering the warhead on or very close to the target rather than increasing the size and explosive content of the warhead.
Effort in the adaptive ordnance area is devoted to advancing warhead technologies to achieve better effectiveness. This is to be done by achieving higher energy levels for the warhead and by devising novel ways of applying the energy to targets, both of which are expected to lead to more rapid mission execution with less ammunition expended. The “adaptive” characteristic apparently refers to the idea that the explosive yield can be controlled to suit target type and engagement scenario. Work on achieving directional control of warhead effects based on information received from fuzing sensors was not mentioned, so is assumed to be taking place in other parts of the ONR program. The scope of the effort extends beyond adaptive features.
The concept is to develop energetic penetrating materials that exploit the synergy between the properties of the ordnance and those of the target to maximize damage to the target. The lethality of warheads is enhanced by a combination of kinetic and chemical energy released by reactive fragments when the target is hit. The cumulative effect of various damage mechanisms can increase the probability of target kill. Integrating the energetic penetrating materials in the structure of the warhead and optimizing the packaging and delivery options can also improve effectiveness.
However, current mathematical models and materials characterization do not yet allow quantitative predictions that would be useful for the design of the ordnance. Also an open question is how easily a target could be modified and protected from such optimized adaptive ordnance.
Work in reactive materials has two parts. The first includes development of more energetic explosives and the use of reactive materials as fragments to be applied explosively to the target in addition to the energy released within the target by the warhead bursting charge. The briefing indicates that projected advances are being regularly validated through experimental work, which appears to be well organized and productive. The reactive materials are of several compositions. The current baseline composition is aluminum (Al) powder suspended in a perfluoro polymer (PTFE or a similar derivative). When a conventional explosive propels a reactive fragment of Al/PTFE into a target, the fluorine in the PTFE reacts violently with the Al. As the Al/PTFE passes through the wall of a target, it reacts with oxygen in the air to produce an explosion within the target, causing much more damage.
Other energetic material compositions include thermitic material such as Al+MoO3 with a PTFE binder. This material is also known as a metastable intermolecular composite. The fluorine serves to initiate the reactivity of the Al. There are other fuel plus oxidizer thermitic materials that can advance this technology.
The second part of the work is the development of honeycomb warhead structures into which the explosive material can be infused. While somewhat less advanced, the work appears to be sound. There are several approaches to enhancing the energy of the warhead. These include new energetic molecules, the use of finely divided (nanosize) metal powder (e.g., aluminum or hydrides such as aluminum hydride), new metastable states, and sol-gel techniques for encapsulating these materials. Nano laminate materials also offer the possibility of hard energetic cases that will withstand penetration at high velocity and contribute energy when detonated via intermetallic reactions. The work is well coupled with the national effort in energetic material —the National Energetic Material Program and the Joint DOD/DOE Office of Munitions memorandum of understanding.
As presented to the committee, this D&I thrust encapsulates Code 351's weapons-related efforts in the Missile Defense Future Naval Capability (MD FNC). The objectives of the MD FNC are as follows: (1) respond to the Joint Requirements Oversight Council (JROC)-approved Joint Theater Air and Missile Defense mission need statement and capstone requirements document and (2) demonstrate emerging and maturing technologies that span the full spectrum of theater air and missile defense. See <www.onr.navy.mil> for additional details.
One aspect of reactive-materials work needs some attention. Reactive fragments enhance lethality by causing a large explosion within the target. A countermeasure that might be employed would prevent the reactive fragment from penetrating the target. Thus, it is necessary to incorporate the reactive materials in robust penetrating fragments to ensure that the explosive reaction takes place within the target. Additional efforts should be undertaken to develop multifunctional missile bodies (energetic structural composites) and high-density fuels with focus on nano thermites. Modeling and simulation work should emphasize coupling reaction kinetics with mechanical energy due to impact and to improving estimates of timing and fragment design for penetration.
Thermobaric explosives are a variant of a Russian composition based on cyclonite/Al/isopropylnitrate. Its virtues are that it produces a long-duration hydrostatic pressure and thermal wave inside a target such as a building or tunnel. This technology is not generally useful in achieving lethality in open areas. However in urban warfare and in the neutralization of tunnels, caves, and buried enclosed structures, the long-duration pressure and thermal pulse can significantly enhance target defeat.
Thermobaric explosives work is aimed at eventual Navy participation in an advanced concept technology demonstration (ACTD) of an improved thermobaric weapon. Time did not permit discussion of the characteristics of the candidate explosives or experimental results to date, but the developmental approach seems reasonable. A briefing chart indicates that the transition strategy is to produce 10 to 20 thermobaric weapons as warfighter deliverables to be residual assets. The committee hopes that this was an error made during chart preparation, and that the weapons will be used only as part of the ACTD. The production of 10 to 20 thermobaric weapons would serve to conduct experiments as part of the ACTD and to count also as residual assets, which are a requirement of ACTDs. If they are to be issued to warfighters, safety qualification will be necessary.
The initial effort of the Navy to develop thermobaric weapons was driven by the rapid response to the war in Afghanistan. The Navy now needs to conduct a reasonable R&D effort to improve the composition of a fieldable thermobaric explosive composition. Such a composition would ideally have an initial low-level explosion to disperse the fuel reactants of the composition and trigger a deflagration similar in concept to fuel air explosives. The deflagration would grow as the reactant fuels are further combusted by the oxygen in air. In addition, any combustible materials in the structure would be added to the combustion-driven shock wave inside the target.
ONR should ensure that any thermobaric weapons delivered to operational units, even for ACTD purposes, are subjected to safety review and analysis, the results of which are shared with the persons who will use the demonstration weapons. They should be issued for warfighting purposes only after the conduct of operational test and evaluation.
Survivability work also has two parts. The first is the response of a weapon or launch platform to accidental hazards and its vulnerability to attack. The response of a munition to thermal events (e.g., fire) has been troublesome to the Navy onboard its vessels. This is commonly called the cook-off hazard. It is for this reason that the Navy is focusing on the fire problem while also conducting conventional trials against other threats such as occur when a weapon is dropped or when it is hit by enemy fragments.
To predict the violence of explosions caused by cook-off, the Navy is utilizing cook-off models. Because DOE faced this hazard with nuclear weapons, the Navy is adapting the DOE models to its needs. Cook-off model validation is needed to more confidently predict the violence of explosions caused by cook-off. The applicability of the models to newer explosives has not yet been demonstrated. This work is expected to lead eventually to confidently predicting the cook-off behavior of an actual ordnance item, but no timetable was given.
The second goal of ordnance survivability is to improve the ability of ordnance to penetrate deeply into a target without exploding prematurely owing to the shock of target entry. Work in penetration-survivable explosives aims to develop explosives that perform well in adverse thermal and shock environments so they can be used as payloads in hypersonic weapons against deeply buried targets. Early successful experiments were conducted using a very insensitive DOE explosive based on triaminotrinitrobenzene to demonstrate this capability. Further work will be necessary to develop a Navy composition suitable for large-scale manufacturing.
The Navy should continue to develop its capabilities to model the cook-off response of weapons. It should develop a highly interactive experimental and calculational program. This should be done in continued close collaboration with the DOE laboratories.
The Navy must develop a more tractable explosive composition for use in its penetrating munitions. This should be done in concert with the other Service laboratories under the aegis of the National Energetics Program.
The Navy has a distinguished history of research, development, and testing in the field of directed-energy weapons (DEWs) including high-energy lasers (HELs). Beginning in the 1970s with the development of the Navy pointer-tracker and the Navy chemical laser, many milestone experiments have been conducted in propagation and lethality, including full-scale tests against aircraft and missiles. The Navy HEL program essentially ceased in the mid-1990s and after a hiatus of 6 years was reestablished in FY02. The Navy also sponsored and was active in a charged-particle beam DEW program that was being considered for naval ship self-defense in the 1970s and 1980s.
An assessment of the new ONR HEL program must be tempered by the fact that it has been in existence officially for less than a year and there are no major technical results. Moreover, no real
information was presented on total funding estimates or technical objectives for FY03 and beyond. Observations will be limited, therefore, to programmatic objectives for FY02 as outlined in the briefing.
To establish a perspective on the FY02 ONR-managed HEL effort, it is useful to note that the funding total of $31.8 million consists of $6 million from ONR, $9.4 million from the DOD Joint Technology Office (JTO), $2 million from NAVSEA, and $14.4 million from congressional add-ons. There are also inherent research benefits derived from the use of the DOE-funded Jefferson Laboratory, where the free electron laser (FEL) testbed is housed. While the intent of this assessment is to evaluate the use of ONR funds in HEL research, it is necessary to comment on aspects of the overall program.
The $6 million of ONR HEL funding is divided among three more or less equal efforts: FEL testbed enhancements to increase power output; propagation and lethality experiments; and mission analysis including the shipboard integration of HEL systems and CONOPS. Congressional add-on funds are also being used for lethality testing and mission analysis and for lethality tests against specific materials, such as ceramic radomes at the White Sands Missile Range (WSMR) HEL test facility. The DOD Joint Technology Office (JTO) supports laser propagation research, high-power solid-state laser development, and FEL upgrades and lethality testing. NAVSEA is supporting technology development through SBIR projects.
High-Energy Laser Efforts
As a general observation, the ONR program is well balanced among the basic elements of HEL system requirements and its funds, as well as those from outside sources, are being managed in an effective manner. The FEL testbed has been operating 24/7 for several years at a nominal 1 kW. It is currently (second and third quarters of 2002) being reconfigured for 10-kW service. No risk appears to be associated with this upgrade. When operated with additional power and higher beam currents, the configuration for 10 kW can be extended to 100-kW operation with modest risk. For 100-kW operation, the largest risk is associated with mirror cooling. Extension to 1 MW involves some risk. In order to keep the footprint of the proposed shipboard FEL to an acceptable length (the laboratory configuration extends about 30 meters in its greatest dimension) and in order to minimize the field and weight requirements of the bending magnets, the accelerator voltage has been held to about 200 MeV. If the objective is to reach 1 MW of optical power, beam current must be increased to about 600 milliamps, and space charge effects may limit operation. Current computational models show that beam currents of this magnitude may be at the upper end of feasibility. If operating levels above 1 MW are required, the necessary energy probably cannot be achieved with greater currents. Rather, the voltage must be increased. This, in turn, will increase the length dimension of the footprint of the FEL and the weight of associated wiggler and bending magnets.
Current program concepts are to build a ship-portable 100-kW machine if the 100-kW machine is successful in testbed operation. The portable unit will address the engineering problems associated with shipboard integration and will be used for propagation and lethality studies.
Preliminary designs for the portable machine will incorporate the following:
Recovery of beam energy with a decelerator;
Modest shielding for the weak x-rays that will result from the dumping of residual low-energy electrons after deceleration;
An overall footprint of about 30×8×8 meters; and
Wall-plug-to-photon efficiency of 4 percent for the 100-kW machine and 8 percent for the 1-MW machine. (The efficiency of the current 1-kW machine is 0.5 percent.)
For reasons of propagation, 1 micron has been selected as the preferred laser operating wavelength. However, the presence of such an HEL in the fleet at sea and in littoral environments presents a danger to the eye that would require compensating changes in Navy operating procedures. Moreover, use of this unsafe wavelength might violate existing treaties to which the United States is a signatory. The optical absorption curve in the vicinity of 1.0 micron is very steep. Optical transmission through the maritime atmosphere might fall by a factor of between 10 and 100 as one moves the laser's operating wavelength from 1.0 micron to, say, 1.2 microns. While there may be a reasonable level of confidence that a 1-MW FEL compatible with shipboard operation can be built, there is at present no reason to think that an extrapolation to a shipboard 10-or 100-MW FEL is feasible.
A detailed systems study of these implications should be conducted, including the trade-offs of alternative laser operating wavelengths, as needed.
The Navy pioneered pointing and tracking experiments in the 1970s for fleet defense against air and missile targets. As noted in the ONR briefings, the new target set is diverse and includes asymmetric threats such as terrorists on jet skis. The ONR program should include the pointing and tracking problem associated with targets that must be acquired in sea clutter such as small boats or jet skis. The program should demonstrate that the Navy has the ability to detect, identify, and point the laser at these proposed new targets at very low elevations.
The attempted development of high-power solid-state lasers has a long and checkered history. Other than a brief discussion in the read-ahead materials provided to the committee, the state of the art in this area and the competing approaches were never mentioned. ONR should prepare a summary to compare competing techniques with their choices.
A significant ongoing effort in solid-state laser is being conducted at the Lawrence Livermore National Laboratory under Army sponsorship. It is called the heat-capacity solid-state laser (HCSSL) since the lasing material is allowed to rise in temperature while still functioning and then allowed to cool. It has achieved approximately 12 kW. The program in place will develop a 100-kW demonstration solid-state laser that will be mountable on a small vehicle such as a high-mobility multipurpose vehicle (HMMV).
Propagation of laser radiation also has a long history of theoretical and experimental study. ONR should provide a historical record that explains why the current approach of laboratory simulation is being pursued and what it will add to the existing body of propagation knowledge.
The Navy should also consider the inclusion of high-power microwave weapons in its ship self-defense portfolio, particularly for close-in asymmetric threats. This would include the vehicle mounted active denial system developed by the Air Force Research Laboratory for the Marine Corps. This might provide a powerful nonlethal disincentive to any terrorist approaching a ship. A more powerful variant of this could enhance ship self-defense by neutralizing any attacking weapons.
In 1999, a cost operational effectiveness analysis (COEA) supported the use of naval guns for naval surface fire support. Specifically, the analysis concluded that a 155-mm advanced gun concept was the most cost effective of the options considered. The Navy adopted the COEA recommendation with the caveat that its interim capability be maintained by incremental upgrades of the 5-in. gun firing a rocket-assisted extended-range guided munition (ERGM). The 5-in. upgrades met the total range requirement of 41 nmi (minimum threshold) to 63 nmi (stated objective) established by Operational Maneuver From the Sea (OMFTS) battle philosophy. The COEA used Navy-approved scenarios and target sets at distances greater than 63 nmi. The 155-mm gun with a scaled-up version of ERGM proposes to extend the range to 100 nmi, thereby encompassing a higher percentage of the target set.
The generic problems facing the use of guns in the mission of fire support are the following:
Targeting of fixed, relocatable, and moving targets,
Total response time for delivery of weapons to the target,
Weapon guidance, and
Rate of fire.
The ONR programs in this and other thrust areas address most of these problems. In gun technology, the main thrust areas are these:
Projectiles (including warheads, fuzes, aeroshells),
Guidance for projectiles,
Propulsion for rocket-assisted projectiles, and
Launchers, internal ballistics, and gun propulsion.
Much of the technology in these areas can be synergistically applied also to missiles. In general, the committee found the programs in this area to be useful, in particular for application to the 155-mm gun/ projectile system. Indeed, as has been mentioned, much of the work is directly applicable to present and future missiles. However the committee believes, as discussed in the recommendations of Chapter 2, that the Navy is approaching the range limit with gun systems and that any further requirements for increased range would be better served by missile systems. Pushing rocket-assisted gun-launched projectiles for more range than that demonstrated introduces new problems: hotter propellants, gun barrel erosion, and more severe in-tube environments. While there is no current Navy requirement for ranges longer than 100 nmi, there is discussion of ranges of 200 to 400 nmi, to match the Osprey range. (It has been noted that the Marine Corps needs rockets or missiles, not guns, for long-range fire support.) The presentation further alluded to the use of light gas guns and rail guns. The committee notes that the Army is doing engineering designs on an electrothermal chemical gun for its Future Combat Vehicle that has a higher muzzle velocity than a powder gun and reduces the vulnerability of magazines since it requires no conventional gun powder. Rather, it uses onboard electrical energy to convert an inert material such as polyethylene into a plasma to propel a projectile.
An electromechanical gun may also have promise, but it requires a tremendous amount of electrical energy and volume for compulsators and similar electrical pulse generators. There is also concern over the lifetime of the launch rails.
The committee cautions ONR that system studies should be performed before any funding is given for experimental studies and that these long ranges should be handled with missiles. Specific findings and recommendations for each of the thrust areas are provided below.
ONR has technology programs addressing the following:
Increased warhead lethality by using mission-responsive ordnance, kinetic-energy projectiles, advanced energetics with reactive warhead materials, and higher-yield explosives.
Higher-performance projectiles by improving the aerodynamic drag characteristics of the projectile. This program culminated in the barrage round, which was a ballistic conical round that achieved a range of 43 nmi in 3 minutes time of flight after launch from a 5-in. gun. This work has apparently been terminated for reasons not made clear.
ONR programs in this area have provided useful analysis tools for aerodynamic predictions of range for various low-drag shapes and for warhead lethality predictions.
The committee endorses the work being performed or already completed in the projectile area.
Guidance for Projectiles
A number of ONR-funded programs in this area have provided big payoffs, which have transitioned into Navy acquisition programs. These include MEMS, Global Positioning System (GPS) receivers, and tightly coupled guidance systems. Future thrusts after FY04 are programs in three areas:
High-acceleration load guidance and control systems,
GPS antijam and/or non-GPS guidance systems, and
Infrared and millimeter-wave seekers.
The payoff of guidance improvements is manifold since they are applicable to missiles, decrease the number of rounds required to kill a target, and ease other problems, such as logistics support.
The committee is impressed with the success of previous ONR investigations into low-cost, high-accuracy guidance systems.
Launchers, Internal Ballistics, and Gun Propulsion
ONR has funded programs in this area aimed at improving the propellants for rocket-assisted projectiles. These have resulted in propellants with high Isp operating at higher pressures than conventional rocket motors. The main efforts in this area are concerned with achieving higher-performance propellants and minimizing the barrel erosion that is associated with these hotter propellants. Most of the work that was presented to the panel dealt with the gun erosion problem. The committee believes that there should be a better way of identifying new barrel coatings to minimize erosion than the cut-and-try method that is presently being followed. On the other hand, the committee found the composite material barrel concept interesting and suggests that it should be continued. The schedule by which the work is to be advanced appears not to allow sufficient time for model validation and application.
The committee believes that range performance beyond the 60 or so miles already demonstrated should not be sought for this technology. The longer range fire missions are probably better handled by solid-rocket-propelled ballistic missiles. The attendant barrel erosion problems lead to the need for barrel liners, and high setback acceleration requirements and the logistic issues associated with a gun round that is large (and requires a double tamp loading) are problematic. While interesting to work on, in the committee's view these problems are barriers to the effective use of guns in the longer range fire support role.
PRECISION TARGETING AND GUIDANCE
The principal science-and-technology objective of this thrust is to develop the targeting and engagement technology base required to support naval combat through improved responsiveness, precision, and dependability against targets that are time-sensitive, that are stationary or moving, that are in urban or close-support settings, and that can be soft or hard. This technology should also improve the performance of tactical airborne and shipboard fire-control systems. Products of this thrust are applicable to current and future weaponry that may be operated manually, automatically, or autonomously. These products should support hit-to-kill weapons, provide positive target identification with greater than 90 percent acquisition probability, minimize the likelihood of collateral damage or vulnerability of the weapon launch platform, and be capable of operating at any time of day and in a wide range of operational environments. Phases of operation include search, detection, acquisition, track, classification, identification, target and aim-point selection, raid count, commit-to-fire, prelaunch, postlaunch, midcourse, terminal intercept, and damage assessment. The committee notes that its observations regarding scene correlation and fusion discussed in reviewing the TCS image video analysis thrust apply here as well.
While there is growth in the total Code 351 budget for FY00-FY03 (see Table 1.1), the breakdowns reflect a movement away from discretionary spending and D&I toward externally mandated programs and FNCs. Furthermore, there is a complete lack of 6.1 funding in this area. It is noted that related ONR and non-ONR programs may contribute to the goals of this Code 351 thrust and are not the subject of
this review. The committee applauds increased efforts to transition the fruits of scientific and technological research to the operational Navy, where the direct payoff lies. Nevertheless, it is concerned that increased emphasis on short-term goals will materially detract from Code 351's ability to explore innovative concepts that ultimately could provide even greater benefits for naval operations.
There are many examples of fundamental research areas that could have considerable impact on responsive targeting and precision guidance, but they were not briefed to the committee. These include multispectral sensing methods, incorporation of contextual information in target detection and identification, advanced state estimation, supervised and unsupervised neural networks, optimal stochastic approximation, rule-based techniques for decision making, and human-machine interactions and interfaces. The committee notes, for example, that the holy grail of automatic target recognition under harsh, deceptive, and dynamic environments remains as far in the future as ever under the current Code 351 program. Even if these cutting-edge technologies are being addressed elsewhere, their omission from the Code 351 agenda slows the pace with which they could be introduced to related FNC processes.
The read-ahead package for this thrust provides a good technical summary of 12 subthrusts. In the remainder of this section of the report, the committee addresses the three subtasks that were presented to the committee. The committee notes that there is commonality among the technologies if not the direct goals of the three subtasks. ONR can play a critical role in assuring that there is beneficial communication and collaboration among these projects. The committee was not briefed about related on-going programs within the sister Services. Because these topics are of such broad significance and research efforts are costly, it is important that the ONR coordinate its programs with those funded by the Air Force Office of Scientific Research (AFOSR), the Army Research Office (ARO), DARPA, and individual DOD laboratories.
Imagery-Enabled Strike Targeting and Weapon Guidance
This subtask is further subdivided into three parts: (1) precision target handoff (PTHO; 6.2), (2) direct attack munition advanced seeker kit (DAMASK; 6.3), and (3) digital precision strike suite (DPSS; 6.3). The PTHO program, completed in FY01, developed techniques for real-time location of targets (within 5 m) from tactical sensor images, and incorporation of national imagery and data from tactical sensors, decreasing the reliance on GPS. The DAMASK program, also completed by FY01, demonstrated laser-guided-bomb delivery accuracy (less than 3 m) using commercial off-the-shelf (COTS) technology and image-based guidance with and without GPS. The DPSS program was begun in 1998 and is scheduled to enable the fielding of an operational system in FY06. It will allow a pilot to designate a target of opportunity from real-time imagery (e.g., forward-looking infrared (FLIR) or synthetic aperture radar (SAR) data), will convert the location of a static target to World Geodetic System (WGS)-84 coordinates, will cue weapon release, and will register seeker video with a template for improved accuracy.
The DPSS program appears to be well motivated and to have a good likelihood of success; therefore, the committee recommends that funding be provided to continue the program. The committee
notes, however, that funds for continued research and exploratory development of methods for operation in more challenging environments (e.g., desertlike areas that have few features for image registration) are not programmed. Furthermore, additional research should be conducted on ways to reduce false alarm rates, to improve target identification, and to handle moving targets. It recommends additional D&I funding in this area.
Standoff Weapon Automatic Target Recognition
The critical issues for automatic target recognition (ATR) are adaptation to dynamic mission conditions, predictability of ATR performance, and automatic recognition of mobile targets (both moving and static but relocatable on short notice). Target sensing may benefit from the use of laser radar (LADAR), which can provide three-dimensional information and can extend the range at which targets can be identified. LADAR offers the possibility of achieving better target resolution in angle and in range. At low grazing angles, a LADAR can locate the target more precisely by measuring the true range rather than projecting back to ground level using an assumed target height. One possible application of such systems is in a submunition-dispensing variant of the Tomahawk cruise missile.
Reliable adaptation to dynamic mission conditions enables real-time retargeting of a cruise missile, including strike on multiple targets. Seeker and system development has started, with flight demonstrations to begin in FY03. There remains the issue of deciding whether or not to accept and act upon the information provided by ATR. Here, it is critical that a good upper bound be placed on target location error, for if the error is too large, the risks of collateral damage and unnecessary expenditure of a weapon are too high to allow deployment. Image processing for ATR is computationally intensive by any measure, and existing equipment does not allow current methods to be executed in real time. The problem is exacerbated by moving targets, natural features and cover, deceptive actions of the enemy, and discriminating of military targets from civilian resources. Results to date are impressive from a narrow technical viewpoint, but there is much work to be done before implementation could be considered. At a minimum, the complicating factors noted above must be taken into account.
Code 351 should provide to those working in this area added guidance on broader goals and the likely pathways to achieving operational ATR, challenging important 6.1 and 6.2 enabling technologies. In particular, the committee recommends that much greater effort be directed at the 6.1 and 6.2 levels, toward solving the complicating problems of ATR, most particularly integration of data from possibly disparate sources and automated intelligent decision-making with this information.
Precise Tactical Targeting
The goal of this subtask is to develop a systematic approach for using a standoff platform to provide affordable, near-real-time target information for GPS-guided weapons, with initial operational capability of 10-m accuracy in 2007 and demonstration of 1-m accuracy in 2010. The approach uses distant GPS control station data for improved platform location accuracy, low-cost inertial measurement of
platform position and attitude, COTS digital electro-optical cameras for imaging the target and its surroundings, triangulation and/or laser ranging for target positioning, and advanced estimation algorithms. It also uses imagery and terrain models from other sources to register the standoff observations. The targeting problem is made difficult by the obliquity of the target viewing angle, intervening terrain, seasonal variations, new construction and ground clearing, battle damage, cloud cover, and lighting. The project is well described, and it reflects a logical progression toward a worthwhile goal.
The committee recommends that the precise tactical targeting program be continued and that it be augmented by appropriate 6.1 funding, which also may benefit the previously reviewed programs.
PROPULSION AND AEROMECHANICS
The ONR work in Code 351 dealing with Propulsion and Aeromechanics that was briefed to the committee appears primarily under two headings: (1) hypersonic weapons and (2) integrated high-payoff rocket propulsion technology (IHPRPT). However some aspects of propulsion and aeromechanics also appeared in several other briefings, including those on adaptive ordnance, mission response ordnance, precision strike navigator, high-speed antiradiation demonstration, and gun barrel erosion (and fatigue). Here the committee deals primarily with the first two topics, hypersonic weapons and IHPRPT, but it also touches briefly on the others elsewhere in this report in the appropriate sections.
A general observation is that the success and risks associated with these topics are significantly dependent on our ability to create and understand at a fundamental level the behavior and response of structures and materials in very hostile high-temperature, high-speed flow environments. It is not clear that the several efforts have taken full advantage of the possible interactions with the basic and applied research community in structural mechanics and materials. Thus to the extent that this is true, the committee encourages closer interaction with the basic research community and suggests the consideration of an expanded discovery and invention activity in the aeromechanics of complex systems and the development of new and improved materials.
Hypersonic Weapons Technology
This thrust is to develop a high-speed strike capability through a hypersonic weapon vehicle. There is good partnering with DARPA and others and a thoughtful, well-planned research and development effort culminating in a flight demonstration. However, a rich array of technology challenges and opportunities remain. These range from the development of an inlet isolator and nozzle to subsonic and supersonic combustors. From the briefing it is not clear how these are integrated into the D&I process, including not only the ONR program, but also AFOSR, ARO, and so on. In particular, the structural integrity of major system components might benefit from an enhanced activity in the D&I portfolio of ONR.
HyFly Program. The hypersonic strike weapons system concept involves the development of a hypersonic air-breathing cruise missile capable of sustained mach 6.0 cruising at 90,000 ft with 4,400 ft/sec average velocity, a 600-nmi range and submunition deployment capabilities. The critical issues addressed are guidance and control, airframe, ordnance, and propulsion. Propulsion challenges are high specific impulse for long range, high thrust for high acceleration, continuous thrust for maneuverability, and throttleability. The propulsion approach involves the development of a dual-combustion ramjet engine concept. The coating of a hafnium-carbide-coated combustor section tested at Mach 6 had started to flake away, even though the woven carbon filament was intact. The mid-body is being made of cast titanium. The technical challenges facing structures and materials are mainly due to mission requirements that cause high thermal, mechanical, and acoustic loads and the fabrication of complex shapes undergoing gradients of stress and temperature. The current choices for materials are Inconel nose cone, C-SiC inlet, coated C-C or C-SiC combustor, aerogel insulation materials, and a titanium airframe.
Key Technologies in the Hypersonic Weapons Technology Program. The airframe technology area— i.e., airframe components and heat transfer technology—is progressing in a timely fashion, with careful consideration of metrics such as survivability, weight, and affordability. Designing with passive cooling requires a superior thermal protection system (TPS). Several candidates have been considered for TPS, with the RX-2390 having been chosen. Newly emerging high-temperature resin systems have been studied for the airframe skin (IM7/PT30). Multifunctional ordnance items have been looked at, that can survive high impact and thermal shocks, that are lethal, and that have a dual-mode capability (surface reaction and penetration). The guidance and control technology area is addressing mechanical survivability, electronic properties at temperature, and thermal protection. The goals are to have GPS track through reentry and hypersonic RF seekers. The propulsion technology area focuses on the dual-combustion ramjet with enhanced mixing.
The emergent ideas are passive reradiation cooling, enhanced mixing, and unconventional control by replacing control fins with low-mass reaction jets.
Consideration should be given to a closer synergy with and enhanced effort in basic research into structural integrity that could be relevant to this activity in hypersonic weapons.
Because one of the key issues in converting this technology into viable weapons will be the cost per round, producibility and material costs should be considered early, when making decisions on concept design.
Integrated High-Payoff Rocket Propulsion Technology
This effort is directed at achieving a substantial increase in the specific impulse of rocket engines through operation at higher pressures. It is a key part of a national program that is jointly sponsored by DOD, NASA, and industry. The goals include a significant increase in rocket propulsion capability by 2010 by increasing weapon kinematics, decreasing weapon size, and decreasing the number of weapon systems. The roadmap includes an air-launch demonstration, an advanced air-to-air rocket technology demonstration, a surface launch propulsion demonstration, and a gun-launched rocket demonstration.
The critical technologies and technical challenges include these: high-burn-rate, reduced-smoke propellants; highly loaded grain designs with adequate thrust, high-pressure, stable motor operation; high pressure, strength, and stiffness of composite cases; and low-erosion nozzle materials. The high burn rate and reduced smoke challenge is being addressed with modified end burner grain designs. The high-pressure requirement due to smaller nozzle throat in turn necessitates propellants that operate at high pressure, and there is also need for erosion-resistant nozzle materials. Even with nozzle materials like rhenium, erosion is substantial at 4,000 psi. For the propellant management devices, composite cases with high-temperature resins and high-strength fibers to allow for the high-pressure operation are being considered. In a nutshell, operation at higher pressures is leading to excessive erosion and even failure of the nozzle structure. Fortunately, and very recently, one might even say “magically,” a technology has been developed that eliminates erosion and ensures structural integrity—the integrated omnivector cone (INOVEC) phase II demonstrator. The details of this technology were not shared with the committee.
Overall this program represents an impressive achievement. However to more fully evaluate the significance of the achievement in realizing improved propulsion performance and its implications for ONR R& D investment, the technology for solving the erosion and structural integrity issues would have to be known.
Because of the very demanding properties of the materials being considered for high-temperature and high-pressure applications, the committee recommends that the materials' producibility and overall cost per round be carefully considered in the trade-offs for design solutions. Also, the committee encourages the ONR to attempt to trace back the investments that were made that led to the development of the technology that has resolved the high-pressure erosion and structural failure issues, to determine if this is an example where the ONR D&I process has made a significant contribution to an FNC.