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2015-2016 Assessment of the Army Research Laboratory (2017)

Chapter: 3 Sciences for Lethality and Protection

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Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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3

Sciences for Lethality and Protection

The Panel on Ballistics Science and Engineering at the Army Research Laboratory (ARL) conducted its review of ARL’s programs on battlefield injury mechanisms, directed energy, and armor and adaptive protection on June 23-25, 2015; and its review of ARL’s programs on kinetic lethality, including disruptive energetics and propulsion technologies, effects on target—ballistics and blast, and flight, guidance, navigation, and control on June 22-24, 2016, at Aberdeen, Maryland.

ARL’s research into lethality and protection sciences during 2015 and 2016 ranges from basic research that improves our fundamental understanding of the scientific phenomena and technology generation that supports battlefield injury mechanisms in human response to threats and human protective equipment; disruptive energetics; directed energy programs; flight, control, and guidance of munitions; and ballistics, blast, and target interaction programs that address weapon-target interactions and armor and adaptive protection developments to benefit the warfighter. ARL’s breath of lethality and protection sciences mission scope work is performed within the Weapons and Materials Research Directorate (WMRD), the Survivability and Lethality Analysis Directorate (SLAD), the Human Research and Engineering Directorate (HRED), and the Sensors and Electron Devices Directorate (SEDD). These directorates work collaboratively to execute their mission of leading the Army’s research and technology program and analysis efforts to enhance the protection and lethality of the individual warfighter and advanced weapon systems.

BATTLEFIELD INJURY MECHANISMS

Understanding the mechanism of ballistic injury is essential to the mission of ARL, specifically for protecting the warfighter against traumatic brain injury and extremity fracture injuries. All of the presentations related to injury mechanisms supported ARL’s recognition of the importance of this issue. The biggest challenge is bridging the science/engineering gap between the materials science—intensity of

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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soldier protective devices and the biomedical aspects of injury mechanisms, or, more precisely, quantifying the level of mechanical insult leading to significant injury. The program, as presented, is a start to bridging this gap. However, increased commitment of resources will be required for it to become state of the art, where it will have to be if it is to enable the protective devices relevant to the threats of the next 25 years. The program presented is a good starting point, but it needs to aspire to create state-of-the-art models of medical injury. This will require improved coordination with the technical leadership of the field. Understanding the mechanisms of injury to the degree needed to give effective protection is key to improved protective designs. Meeting this challenge is essential to the mission of ARL, and the areas of traumatic brain injury (TBI) and musculoskeletal injury will continue to be the main areas of concern, along with an increasingly sophisticated understanding of how mechanical insult impacts neural function. All models need experimental validation, and all experimental programs would benefit from increased use of statistical data evaluation and statistical experimental design.

Computational mechanics work on battlefield injury mechanisms and human response to threats and on protective equipment, including the mechanics of fibers and fiber composites, are being combined with experimental efforts to characterize, validate, and verify the computational results. This combination of efforts is laudable.

The program in human responses to threats is performed mostly by junior staff, who are pursuing research objectives focused on short- to medium-term objectives. While the staff are capable, the research is generally not state of the art. Studies were described that focused on the assessment of neuronal response injury using a blast tube injury model with cells grown in monolayer on a flexible membrane. The flexible membrane is also subjected to defined strains in order to model the induction of cell injury. Primary end points include cell viability, calcium signaling, and cell morphology. Long-term goals are to develop a mechanistic understanding of neuronal responses in 2D and 3D culture systems in response to well-defined strain fields. Extension of these studies to assess damage to brain tissue, whole organs, and/or tissue-engineered models of the regional damage would be worthwhile. The results of clinical functional magnetic resonance imaging (fMRI) studies of TBI might help to target specific regions of the brain for in-depth analysis. Overall, given the current state of neurosciences and the advances in optogenetics and other techniques, the biological studies described were relatively rudimentary. It is unclear whether on-site senior investigators with expertise in neuroscience participated in this program of study. Collaboration seems to be taking place with one postdoctoral fellow’s former senior Ph.D. advisor, but further outreach is needed, including with neuroscience investigators in academia, to augment the military’s broader TBI research portfolio.

A second set of studies focused on the assessment of neuronal responses to injury using a micro-explosion model involving cells grown in monolayer submerged in an aquarium-based environment. Primary end points include cell viability, calcium signaling, and cell morphology. Future plans are to study neuronal responses in 2D and 3D culture systems placed within a gel-contained model of a human skull. The quality of the biological studies is rudimentary. The investigations do not appear to include the use of a model system in which the stress fields imposed on the cells have been fully characterized. A gel-containing human skull is an interesting model system, but it will require careful correlation of the estimated in vivo force microenvironment with the in vitro system created in their model system.

A third set of investigations focused on assessing the impact of anthropomorphic variability on the mechanisms of human injury, identifying sites of maximum vulnerability, and determining options for designing improved protective garments and equipment. Clinical computerized tomography (CT) data sets are acquired of soldiers killed in action (KIAs) in order to refine existing computational models of human injury and protection. Collaborative efforts have been pursued with the University of Maryland Shock Trauma Center and other programs. The quality of the scientific studies is high and utilizes an

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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appropriate mix of theory, computation, and experimentation applying state-of-the-art laboratory equipment and numerical models. Extension of these studies to CT and MRI data sets of personnel who are injured in the field but not KIA would be worthwhile. The work designed to predict lumbar burst strength is a start but does not represent the thinking of current investigators in the field. It is necessary that the researchers develop communication channels with research leaders to increase the sophistication and applicability of the approach. While the pig skull work was a reasonable approach, it is unclear if the pig skull is relevant to the critical human skull issues that need to be understood.

The computational efforts in the human biomechanics area are somewhat behind the state of the art in computational mechanics of soft tissue. Specific details include the use of linear tetrahedral elements instead of hexahedral elements for soft tissue response, and there was a lack of viscoelastic properties for material response at high strain rates and high pressures. Further, there was only limited inclusion of the effects of statistical variance into necessary parameters of the computational problem to assess these effects. Such information is essential when computationally modeling humans and humanlike responses. The computational team needs to increase the sophistication of the models appropriate for the problem and needs to interact more extensively with subject-matter experts in human and soft tissue material response in the Army research community and the wider research community.

Overall, the biological programs appear connected programmatically, but they seem isolated from a scientific perspective. There appears to be little synergy or communication between the individual researchers. This lack of synergy is particularly significant to the junior staff, who could benefit greatly from strong mentoring by the appropriate technical communities. They need to become familiar with the current state of the art in their research areas and move quickly to achieve that state. They could also benefit from increased management support to help them learn how to overcome the administrative barriers associated with purchasing supplies and equipment.

To bring the current program to state of the art will require increased coordination of ARL technical personnel with the relevant biomedical communities and the hiring of scientists experienced in the computational modeling and experimental exploration of the effects of mechanical trauma on people, especially in the cases of injuries to the brain and extremities. Current personnel would benefit from experienced mentorship and connections to the field as practiced in university and other government laboratories. The equipment was reported to be consistent with beginning stages of the work and commensurate with the early-career status of the researchers and the brief time (1-2 years) that the program has been in operation. There is little evidence in these projects of the longer-range vision of ARL. The work presented continues to concern itself with current or near-term Army needs.

The research to better characterize the properties of materials relevant to protective systems is sophisticated and mature and is providing the data needed to understand the mechanical performance of protective devices. The project on the ballistic response of knitted materials is a small, well-executed modeling effort that is very relevant and important to ARL needs. While the work is not particularly novel, the results are unique and will be useful for the future design of protective equipment. The study of fiber mechanical properties under very high strain rates is impressive and is likely to provide data needed to better model soft and hard armor design and performance. Nonetheless, the scope of both the experimental and computational programs need to be broadened.

ARL reported a new internal program to study the chemistry and processing of the next generation of protective fibers. This program is supported by newly installed facilities, and it will focus on the modification of existing polymers with additives designed to increase overall performance (nano-composites) and gel spinning of polyethylene. These represent a reasonable start, but there are other areas of both chemistry (next-generation Kevlar, self-healing materials) and processing (nanofiber production, melt spinning precursors) that need to be assessed as potentially attractive research areas

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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for ARL. The understanding and improvement of polymeric components in protective systems is core to the ARL mission. As with the new programs in biology, mentorship and interaction with area leaders is necessary to ensure that the program is state of the art and aimed at producing materials to satisfy current and future (2040) Army needs.

Overall, ARL is to be commended for initiating programs that link the biology of injury to the materials and constructs designed to protect the warfighter. It is difficult to move into new areas and quickly develop state-of-the-art programs—and to assume leadership. The programs reviewed generally demonstrated technical skill in the chosen areas but often were not state of the art, and they seemed out of touch with the relevant scientific communities. There is an obvious challenge in moving quickly from beginner to leader, but this also provides great opportunity to assess the relevant science and engineering and devise programs to leapfrog to the next level of understanding. The program in battlefield mechanisms, human response, and human protective equipment is conducted by a strong cadre of scientists, and a credible program is under way.

Summary of Accomplishments

Battlefield injuries are an important area of research for ARL, because a better understanding of the mechanisms of injury is vital to improving protective measures. This is especially true for protection of the head, where there is considerable uncertainty about allowable levels of shock, which greatly affects protective options. The research projects presented were appropriate to the problem, and the staff is competent. The projects are short to medium term, which is reasonable for the early stages of a new program. As would be expected in a new research area, there are challenges to be overcome.

Challenges and Opportunities

Current projects are not the state of the art. Work at the cutting edge is difficult to maintain in a small program that does not have the option afforded to larger programs of pursuing multiple approaches simultaneously. Nevertheless, a greater effort could be made to assess the current research in the field and move closer to that cutting edge.

The program seems isolated both within ARL and from the larger outside scientific community. The burdens of being a small, new program in a new discipline within a large organization are many. There are fewer opportunities for constructive discussions and feedback, less chance for synergistic collaboration, and poorer awareness of current developments relevant to their own work. There are administrative burdens associated with procuring materials and supplies that are unfamiliar to the procurement branches of the laboratory. The cumulative effect of fighting through these issues will take a toll on the researchers’ time and is a distraction from the pressing needs of maintaining a competitive research program. Management could consider assigning a single administrative contact person, who would become familiar with the unusual needs of the program and, perhaps, act as an advocate for the program within the administrative channels. A long-term vision needs to be developed. The beginnings of this thinking were presented, but they are not yet sufficiently developed to be useful. Such a long-term vision could express a philosophy that helps guide resource allocation and program direction.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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DIRECTED ENERGY

The ARL S&T campaign plans 2015-2035 and technical strategy documents1,2 categorize directed energy (DE) as a focused area under the much broader category of electronic warfare (EW), in accordance with the Army’s definitions. The ARL posture designations for both radio frequency (RF)-DE and laser-DE are collaborate rather than lead. The subsuming of DE under EW and a collaborate-only posture indicate that ARL has downgraded the priority of DE within its technology portfolio from its previous robust effort. The consequence of this status change was evident in the current programs presented: They appear to be a small collection of seemingly unrelated projects. In addition, the current program, with the exception of the project in solid-state laser sources for tactical applications, seems to be concluding soon. Noticeably absent from almost all presentations was any thought of how the operational needs that the current systems were designed to meet would be satisfied in the 2035 time frame highlighted by the ARL director.

In view of the currently fragmented DE program, ARL needs to take a strategic look at the DE area to determine its ongoing priority and refocus ARL’s effort with a view to the 2035 time frame. This strategic review needs to include consideration of future capabilities that the Army will need that DE might fill, and what DE capabilities might be fielded by our adversaries for which the Army will need countermeasures. A focused ARL DE program would benefit from a systems-level study addressing future Army missions in which DE could play a role and in which DE effectiveness and alternatives to DE are traded off. In this study, ARL could expand and diversify the laser program to seek avenues for integrating the technology with platforms of importance to the Army. Additional missions for DE could include illuminators; multispectral sensing, identification, tracking, targeting, and damage assessment; electronic protection/ countermeasures for enhanced Army platform survivability against optical and IR guided weapons; and nonlethal weapons. Such a broadly based study is the necessary first step in planning a robust and relevant DE program to address the Army’s future requirements. ARL has a significant capability in solid-state laser development—an obvious focus area for the future. In most cases the six projects reviewed met or exceeded the evaluation criteria, which included the following: Does the technology maturation employ appropriate laboratory equipment and/or numerical models? Is the research team properly qualified? Do the facilities and laboratory equipment seem to be state of the art?3 Are the projects crafted to employ the appropriate mix of theory, computation, and experimentation? Specific concerns about individual projects related to these criteria are included in the following evaluations.

A highlight of the overall program in DE is the project on adaptive and scalable high-power, phase-locked fiber laser arrays. This work is a notable achievement, is recognized as such by the technical community, and appears to be ready for the next step, transition to the field.

The Department of Defense (DOD) recently articulated an electromagnetic (EM) maneuver warfare initiative. While ARL researchers did not reference this initiative, if all the services were to develop joint and independent programs as part of this effort, that could give ARL an opportunity to reexamine its role and strategic opportunities in EM maneuver warfare.

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1 U.S. Army Research Laboratory, Army Research Laboratory S&T Campaign Plans 2015-2035, Adelphi, Md., September 2014.

2 U.S. Army Research Laboratory, Army Research Laboratory Technical Strategy 2015-2035, Adelphi, Md., April 2014.

3 Note that the panel did not visit any laboratories during this year’s review, so the assessment of the state of the art of the equipment is based solely on the presentations and briefings.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Research Projects

RF-Enabled Detection Location and IED Neutralization Evaluation

The scientific quality of RF-Enabled Detection Location and IED Neutralization Evaluation (REDLINE) research is comparable to that at leading federal, university, and industrial laboratories, both nationally and internationally. This is a first-class effort with full understanding of, and direct access to, operational needs and with a clear systems approach to reducing technical risks and delivering a successful experimental prototype.

The research program reflects a broad understanding of the underlying science and of research conducted elsewhere. The experimental confirmation of a complex propagation, detection, identification, and predetonation process is impressive.

This project is ready to begin the next step, deployment in the field. There is still an applied research effort needed to investigate detection, identification, and predetonation of increasingly advanced, emerging threats. The poster presenters mentioned the potential for mounting the capability on unmanned aerial vehicles. This seems to be a good idea, especially if ARL seeks to investigate the evolving improvised explosive device (IED) threat beyond the near term.

Hostile Fire Detection

In general, the scientific quality of the research is as good as that achieved at leading federal, university, and industrial laboratories, both nationally and internationally. The investigators used standard codes and modeling techniques. Although not strikingly novel, the work was credible and demonstrated useful integration of known techniques. The investigators also appeared to have access to intelligence about specific threats that may not be widely known.

The research program reflects a broad understanding of the underlying science and research conducted elsewhere. The researchers have addressed the major issues associated with detection and geolocation of threats such as rocket-propelled grenades and small arms. There was an appropriate level of modeling and predictive work to address near-term deployment but not longer-term strategic innovation. The prototype work that has been exercised in limited deployment responds to a near-term problem. Advanced (2035 horizon) modeling, diagnostic, sensor development, and test capabilities were not brought up.

Operational data from full field deployments would drive next-generation innovation and improvement in identification and geolocation signature analysis for targeting support. This would produce results that could ultimately be transitioned to the field in a continuous upgrade process.

Adaptive Techniques for Advanced Radar Tracking and Optimization

The scientific quality of the research is basically sound in the context of unclassified university research, but it is not up to the standard of leading federal, university, and industrial laboratories working in this area. There appeared to be little or no awareness of existing, similar work in advanced radar development other than some unclassified university research. Reaching out to a major radar program, perhaps one of the Army’s programs, might have revealed similar, prior work and identified what is and is not already in existence.

As for appropriate laboratory equipment and numerical models, there appear to be adequate computing resources but no association with radar R&D facilities or laboratories to ensure a practical base of

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

experiment and experience. It is also not clear whether the signal interference modeling is relevant to existing radar clutter, interference, or jamming environments. Such interference can depend on the design characteristics of the radar under consideration, so general approaches may not be directly relevant.

There could be projects that, with improved direction, access, and resources, produce results that can be transitioned ultimately to the field. Possible collaboration with the Navy’s extensive efforts in sonar tracking and optimization may be fruitful. The freshly conceived algorithms and use of greater computing power might provide useful insights to radar R&D facilities and developers. Some algorithms may be interesting for specific interference waveforms as spectral crowding increases.

Solid-State Lasers

The scientific quality of the research is comparable to that achieved by leading federal, university, and industrial laboratories. This research is aimed at identifying candidate materials, methodologies, and techniques for scaling solid-state lasers to mission-significant powers within the constraints of space, weight, and power. Although many laboratories are doing similar work, ARL is concentrating its effort in eye-safer spectral regions that are of critical importance for the Army. The research program reflects a broad understanding of the underlying science and of research conducted elsewhere. ARL’s work is known and respected by laser scientists at other institutions.

Programs crafted to employ more modeling would provide an enhanced mix of theory, computation, and experimentation. Given the objective of this project, the researchers need the capability for simulating, even crudely, an entire system from wall plug to target. This is the only way an analysis of alternative materials and architectures can be performed. Such an analysis would permit more informed choices for R&D paths to follow.

Adaptive and Scalable High-Power, Phase-Locked Fiber Laser Arrays

This research program is devoted to developing high-power (tens of kilowatts) fiber lasers by coherently combining lower power systems. The researchers have successfully combined seven lasers, each of which can continuously produce as much as 1.5 kW. A novel method has been developed for coherently combining the multiple beams. This is the critical element of any high-power fiber system. Feedback from a diffractive element located at the output aperture provides an optical signal that serves to phase lock the laser array. Another strength of this method is the modest bandwidth requirement for the feedback system (only 15 kHz), which is very attractive from the perspective of developing a reliable weapons system. Coherently combining the individual laser beams occurs at approximately 10 m from the output aperture, which is well into the far field. Beam quality is also actively monitored in the far field so as to optimize the efficacy of the phase-locking process.

The impact of this ARL laser system appears to be significant. In follow-on work, the Defense Advanced Research Projects Agency and the Lincoln Laboratory of the Massachusetts Institute of Technology have scaled this system so as to combine as many as 21 lasers. Although it is not clear at this point whether the ARL system will ultimately be incorporated into a real weapons system, it is evident that the system architecture has influenced other work. Low-power versions of the ARL design are, for example, being developed for civilian use. Another impressive aspect of this program is that it has resulted in six patents.

The high-power fiber laser system is the result of a decade of work at ARL. This program demonstrates the value to DOD of investing in novel research over a prolonged time. A further accomplishment is the understanding of the physics of intense optical fields propagating in a fiber. One practical outcome

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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of this understanding was the finding that fiber core diameters as large as 20 µm could be used while maintaining beam quality.

Nonlinear Propagation and Target Effects of Ultra-Short-Pulse Lasers

This basic research project examined nonlinear propagation in the atmosphere of an ultra-short-pulse (1 psec) laser beam in a self-generated, ionized channel. The researchers observed that the ionized channel through which the beam propagated was much more stable at a pulse repetition frequency (prf) near 1,000 Hz than at a frequency of 50 Hz. The causal physics was conjectured to be that the channel remained steady at the higher prf owing to the lack of thermal dissipation of energy of the nitrogen and oxygen plasma that formed the channel.

Also reported was that the beam, when incident on solid surfaces, created ripples in the surface of the material over the area covered by the beam. This phenomenon was previously reported by others for metals and semiconductors but was demonstrated for the first time on polymers by the ARL team.

The researcher showed a strong knowledge of the experimental laser techniques and knowledge of previous literature. It was not made clear, though, why the experimenter followed the path he did. The quality of the work appears to be high and the facilities used at ARL were adequate for investigating this phenomenon. It was not clear, however, if computational modeling was performed to substantiate the proposed model. The experimenter did not have a clear idea of where this work was headed and how the Army might benefit from it.

Summary of Accomplishments

The REDLINE team has developed a kill chain concept for the detection, geolocation, identification, and triggering of IEDs. Model predictions and prototype experiments verified the performance of the harmonics-based approach, and the program has advanced to early system prototype testing.

Investigators working in the hostile fire detection area have developed diagnostic, modeling, and prototype hardware capability of detecting and geolocating hostile fire for enhanced soldier survivability. The work addresses three major areas in disrupting the lethality chain: threat signature characterization and identification; analysis of intervening and interfering material; and sensor systems response.

Significant field testing has enabled the development of a large, well-understood archive of unique multispectral data that was used to construct databases for rapid threat identification. ARL’s work expands and improves the database of medium wavelength infrared (MWIR) and ultraviolet (UV) threat information. The analytical tools available to model EM propagation through both the atmosphere and various types of obscurants employed fundamental, well-understood concepts. The analytical tool for modeling intervening media and obscurants is a unique capability that was developed with academic collaborations and was empirically validated. The models have been integrated with various types of sensor payloads and packaged into the prototype hardware. The work has produced a patent on optical gunfire rocket and explosive flash detection that has been embedded in the electro-optical (EO)/IR sensor hardware. The investigators have taken the work from innovation to field prototype.

In the program developing adaptive techniques for advanced radar tracking and optimization, the concept involves a radar pre-look at the spectral signal environment prior to each dwell and uses algorithms to select quieter frequency gaps to form appropriate waveforms that minimize received interference while retaining required waveform resolution.

This experimental work on adaptive and scalable high-power phase-locked fiber laser arrays was outstanding; the experimenters clearly understood the issue and why it was being pursued, and they

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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described well the problems that had to be overcome to produce the results of this beam combining experiment. Given the available laser power, the results were impressive and are headed in the right direction for producing a high-quality (M2 ~ 1) combined beam from 6 to 8 fiber lasers that are all phase-controlled using an innovative optical feedback technique. Effective use of laboratory equipment was demonstrated. Whether or not this work can combine a sufficient number of fiber lasers to produce a 100 kW class laser is not clear.

Challenges and Opportunities

Limited test results of the REDLINE team confirm theoretical predictions of range, detection, and identification. However, an ROC curve (probability of detection versus probability of false alarm) based on test results and model predictions is not yet complete. Similar test data are needed for the likelihood of killing an identified target. Such a comprehensive characterization is needed, especially in a cluttered urban environment, as part of the program to verify that the system is operationally viable. This information will be required if the range of the system, say, by utilizing an unmanned aerial vehicle, is to be considered.

Also, the REDLINE team indicated an upcoming transition to 6.3- and 6.4-funded development. However, there is still 6.2-funded R&D to be performed, including characterizing emerging trigger threats and other countermeasures and design modifications to accommodate those evolving threats. Because the IED threat is expected to continue, a critical need exists for a continuing research program to address the projected and potential advances of the threat in the coming decades.

No strategic plan was presented for further development and maturation of the models for hostile fire detection, for advanced sensor capabilities, or for continuing experimental evaluation of future threats. To be effective, contributors and researchers need to become involved with established radar S&T and R&D groups—for example, such groups within the Army—to gain feedback on the viability and value of the approach compared to earlier work. The qualifications of the research team in the area of adaptive techniques may not be up to the research challenge, given the team’s lack of access to operational radars and ongoing radar developments. There does not seem to be a core radar group within which this work is performed, so it is unclear why the work is under way in this particular research campaign. This may be a strategic question for ARL relative to the Army technical infrastructure. (The Naval Research Laboratory has had a robust radar research program for years.) The facilities and laboratory equipment may not be state of the art compared to the signal processing laboratories of advanced radar programs. Indeed, there appears to be no radar test site, data collection capabilities, or other laboratories associated with this work. The program is not crafted to employ the appropriate mix of theory, computation, and experimentation nor was there a connection to any existing or new radar and radar R&D facilities.

ARMOR AND ADAPTIVE PROTECTION

ARL has a strong record of achievement in the basic and applied sciences and the engineering of penetration and protection. The ongoing work described in the review showed how ARL is building on this tradition of excellence to provide the knowledge basis for future Army needs. This is a core competency that underlies Army capabilities.

The presentation on penetration, armor, and adaptive protection provided an impressive overview of ongoing research aimed at meeting shorter- and longer-term issues. The shift of focus from the goal of addressing short-term Army needs to the goal of carrying out research that will maintain world leadership in this area for future Army needs was evident.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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The depth of knowledge of the staff and the evidence of interaction between staff members were impressive. They were also aware of and knowledgeable about projects other than their own. It is important that ARL ensure a steady supply of new staff into this critical area and that newcomers can benefit from the experience of senior researchers.

There was significant evidence of teamwork and integration among the projects in, for example, adaptive protection. There were examples of linkage of experiments and computational modeling to provide physical insight into problems, to aid in new designs, and to explore new concepts. The combination of modeling and experiments is essential in many cases, but there are circumstances in which it is appropriate to focus on a single mode of inquiry: experiments carried out as discovery science; modeling to develop an understanding of scenarios that are impossible or prohibitively expensive to investigate experimentally; development of new modeling approaches and techniques that promise to enhance predictive capabilities of ballistic phenomena; and development of new experimental methods that promise to provide a better understanding of the physical mechanisms underlying ballistic phenomena. ARL described a ceramic armor concept that was made possible by a previously developed experimental technique aimed at enhancing a basic measurement capability.

The staff apparently have freedom to pursue new ideas that can lead to breakthroughs that might otherwise be found more slowly, if at all. An example was the armor concept, a serendipitous discovery developed nearly to completion before being fully funded.

Developing a predictive capability for damage and fracture in metals, ceramics, and polymers underlies the efficient development of new material systems for protection and for penetration. At present, there is no framework that has penetration capability. However, experimental, theoretical, and computational advances being worked on in other countries are making such a capability seem possible in the not-too-distant future. A systematic approach based on understanding the key physical processes is needed because of the wide range of material systems that are becoming available. There are so many possibilities that a trial error-and-correction approach would be too expensive. It is important that ARL develop a leadership capability in this area. That requires the ability to identify damage and failure mechanisms in material systems of interest, the theoretical expertise to model these failure mechanisms, and the computational ability to simulate armor concepts and designs for the range of conditions encountered in the field. It is unlikely that a detailed quantitative capability will be developed. A more realistic expectation is a predictive capability that ranks the response of proposed armor systems to various threats and provides scaling relations that can be confidently used to transfer laboratory-scale tests to field condition response. Success in this area requires hiring and developing a critical mass of staff and having the needed experimental and computational capabilities.

Modeling

As pointed out above, ARL uses both experiments and modeling to develop new armor concepts and designs. ARL’s use of modeling is maturing and is becoming better integrated into armor development and design. The researchers presented evidence that ARL was using numerical simulations to explore armor concepts more expediently than could be done through experiments. There were also examples of modeling being used to provide physical insight into experimentally observed phenomena, and there were examples of concepts and designs being examined that could not be tested experimentally with current capabilities.

Numerical simulation represents a key capability for ARL in the armor and adaptive protection area. ARL staff are customers for and collaborators with developers of advanced computational tools. Much of this activity involves codes developed at Department of Energy (DOE) National Nuclear Security

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Administration laboratories (Lawrence Livermore National Laboratory [LLNL] and Sandia National Laboratories [SNL]). These tools include ALE3D (LLNL), ALEGRA (SNL), and CTH (SNL). Some usage of multiphysics Sierra codes (SNL) was also reported. These are probably the appropriate tools for ARL’s problem set (impact, high rate, energetic materials, and electromagnetics), because they scale well on parallel platforms and are the most advanced tools available. There was some use of commercial codes (e.g., LS-DYNA) as well, which allows ARL to exploit developments in, for example, crash-worthiness analysis as it relates to the automobile industry.

ARL’s relationship with the ALEGRA and CTH development teams at SNL has allowed it to drive the code development to address its own needs. ALEGRA is an arbitrary Lagrangian-Eulerian code with electromagnetics capabilities that is well-suited to a specific subset of ARL’s problems. ARL staff are trained in use of the code, and this seems to have improved the sophistication of the analyses conducted. ARL is a significant user of CTH (SNL Eulerian shock physics code) for armor and adaptive penetration applications; in fact it is perhaps the largest DOD user as measured by central processing unit hours. This is ARL’s workhorse code for impact problems. ALE3D is utilized for these problems as well. ARL staff members develop constitutive models to describe material behavior for all of these codes, which speaks to the level of sophistication of ARL modeling.

There was some evidence of the use of multiple codes to address different physics in a single problem. Use of the codes in this way will likely increase in the future, although coupling of codes is a challenging endeavor that will make the development of general frameworks for the coupling of codes increasingly useful.

ARL researchers indicated that their overall framework for multiscale modeling is also intended for armor and adaptive protection problems. The multiscale modeling work will likely become increasingly important for modeling complicated material behavior.

There was evidence that the researchers’ computational work was limited by the available classified computing capability. ARL indicated that a 100,000 (node or core) machine was available for unclassified work but only a 15,000 (node or core) machine existed for classified work. For 3D magnetohydrodynamic calculations with ALEGRA, thousands of cores are required for several days—a significant portion of the computing power available at ARL. ARL therefore does much work of this type in a 2D axisymmetric configuration. Although this is less computationally expensive and is useful for many problems, it limits ARL’s capability to explore oblique impact conditions and other scenarios that are not axisymmetric. Also, as ARL works to develop its parametric studies and its verification, validation, and quantification of margins and uncertainties (V&V/QMU), many more simulations will be required, further straining the available computing power. ARL needs or will soon need more powerful classified computational platforms in order to accomplish its mission. A challenge in justifying more powerful classified machines is that ARL’s relatively small classified user community places high demands on the machines at some times and lower demands at others, potentially leaving significant portions of a large computing cluster idle. A potential solution to this is to utilize designs that allow sections of a large computing cluster to swing between unclassified and classified mode. In this manner, the allocation of resources can more effectively address the needs for the two types of computing resources.

Developing predictive models for damage and fracture for armor and adaptive protection applications is an important research direction, and in these circumstances the material response is not likely to be entirely deterministic. Therefore, the scientific and evidentiary value of this research effort will be greatly enhanced by adopting a ubiquitous statistical perspective. Understanding the nature of the assumptions and approximations underlying predicted or anticipated behavior and how these can be updated as data/knowledge is gained will improve ARL’s ability to develop technologies to adapt and survive in extreme and hostile environments. Furthermore, statistical scatter in experimental data could

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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be an indication of subscale behavior with implications for modeling, so its impact on predictions needs to be explored through sensitivity studies and uncertainty quantification methods.

Experimental Aspects

ARL’s work in armor and adaptive protection is also supported by experimental work. ARL utilizes its in-house capabilities for ballistics testing, which appears to be fairly well developed. Nonetheless, ARL needs to develop a wish list for experimental capabilities as well as a timetable for obtaining them for future needs.

ARL is also utilizing unique national facilities such as the Dynamic Compression Sector at the Advanced Photon Source at Argonne National Laboratory (ANL) and the proton radiography (pRad) capability at the Los Alamos National Laboratory (LANL). Utilizing advanced facilities in this manner will advance ARL’s science base and leverage these important national capabilities.

There were also instances in which ARL identified important technical developments and brought them to ARL. For example, it is developing a flash tomography capability and a capability to utilize photon Doppler velocimetry (PDV) in its work. It is important that ARL continue to find important technological developments and bring them to ARL when appropriate. In the case of PDV, ARL would benefit from engagement with the wider PDV community (e.g., the PDV workshop) and, if possible, seek out a short course that would train staff in the use of the PDV. ARL will also need to figure out how to exploit PDV effectively in its work.

The panel encourages continued development of the relationship with the additive manufacturing group at ARL and with experts around the country. Additive manufacturing has the potential to enable new armor concepts but could at the same time lead to new threats from adversaries.

There was significant discussion of the use of energetics to solve armor and adaptive protection problems, but there was little discussion of the science of energetics. The armor and adaptive protection group needs to engage more with the energetics group at ARL as well as with outside experts. For example, there are several concepts that rely on modification of explosive sensitivity that may be beyond current ARL capabilities. Technologies being developed in this area have the potential to enable significant advances in armor capabilities. Furthermore, state-of-the-art tools for modeling energetic materials are being developed elsewhere at ARL that may be applicable to armor and adaptive protection problems. The science of energetics in the context of armor and adaptive protection may be significantly different from that science in the context of warheads, so the ARL group working on armor and adaptive protection may benefit from a workshop on energetic materials for reactive armor. They might also encourage the Army Research Office to establish a Multidisciplinary University Research Initiative in this area.

Summary of Accomplishments

ARL has a strong record of achievement in the basic and applied sciences and the engineering of penetration and protection. Its presentation of experimental and modeling results and progress in penetration, armor, and adaptive protection provided an impressive summary of ongoing research aimed at meeting short- and longer-term mission needs.

There was significant evidence of teamwork and integration among the projects, in, for example, adaptive protection. Examples of the connection between experimentation and computational modeling that gave physical insight into problems were especially noteworthy; such work is likely to aid in developing new designs and exploring new concepts.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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The benchmarking of simulations with experiments and the emphasis on bringing advanced technology (particularly in the X-ray region) to bear on diagnostics were impressive.

Challenges and Opportunities

One challenge for those working in applied classified areas of armor R&D is to figure out ways to interact with outside experts. Ways to do this include participating in appropriate forums (classified meetings, interlaboratory workshops, international exchanges); identifying canonical unclassified problems and cases that can serve as conduits for collaborations with universities and other outside experts; and conference participation, which is very important even for those who cannot present because their work is classified. Conference attendance by those working in classified areas helps them remain up-to-date in their fields.

Rigorous procedures for the validation of model-based predictions that are consistent with current state-of-the-art methods use experimental data and the propagation of uncertainty as well as the characterization of associated modeling errors. This requirement is exacerbated by the complex multiscale and multiphysics interactions relevant to many predictive efforts that are under way at ARL in the armor and adaptive protection areas.

As ARL works to develop its use of parametric studies and V&V/QMU, many more classified simulations will be required, further straining the available classified computing power. ARL needs to elucidate a strategic plan for more powerful classified computational platforms in order to accomplish its short-term and current mission needs and to support future mission needs and deliverables. It also needs to continue development of its relationships and projects examining the utilization of additive manufacturing (AM) to address current and future Army needs. There is an opportunity for the ARL additive manufacturing group to interact and collaborate with experts around the country at DOD facilities and federal agencies and in academia and industry. Additive manufacturing has the potential to enable new armor and protection as well as new weapon concepts; AM could also lead to new threats from adversaries, which means new challenges to our warfighters. There is a need as well for procedures to qualify and certify AM materials to meet Army needs. AM has become a realm where new ideas are being developed and where the future Army is being enabled, so that ARL could become involved in AM work, and ARL needs to develop a strategic plan in this area. ARL’s modeling programs could embrace the importance of variations, errors, and margins for establishing thresholds and statistics that support the development of predictive capability and design capability.

The presentations on damage and failure modeling demonstrated that modeling of damage evolution, fracture, and failure is a critical prerequisite for developing predictive and design capabilities in penetration mechanics. It is critical that ARL establish a focus in this area as soon as possible.

DISRUPTIVE ENERGETICS AND PROPULSION TECHNOLOGIES

The disruptive energetics and propulsion technologies reviewed in 2016 highlighted research and technology advances in four areas: synthesis activities, propellant simulation, extended solids, and multiscale computational modeling.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Summary of Accomplishments

Synthesis Effort

This is a commendable, relatively new effort to develop a chemical synthesis effort at ARL. Other laboratories have moved away from this important area for the Department of Defense (DOD) and the country as a whole. Synthesis efforts stimulate many other efforts at ARL—new materials challenge and sharpen skills in formulation, characterization, and testing activities. Some new molecules were synthesized, which is the first from ARL for many years. This is a milestone for ARL and the research area. The particular work presented to the panel represents a good research direction (specifically looking at nitroglycerin replacements) that could yield better migration behavior eventually. It is notable that materials are being sent to Aviation and Missile Research Development and Engineering Center (AMRDEC) and to academia, showing good collaboration and interactions. There is a good focus on all possible applications (propellants and explosives), rather than just explosives as a main focus. There is also consideration of what the ultimate formulations are (how molecules might interact with nitroglycerin, for example), the possible toxicity of their materials, and not just making a new molecule to publish. This team wants to make materials that make a difference to the Army.

Propellant Simulation

This area is a traditional strength of ARL that positively impacts and supports Army needs (and other research efforts) well beyond ARL. It needs to be vigorously supported and maintained. Effort is needed to execute succession planning to sustain ARL’s strengths in this area as staff retire.

The propellant simulations presented suggest that the observed propellant burning rate slope break is from the interaction between mechanics and reaction. This is an important result and has significant implications. Basic combustion theory supports this. Specifically, the burning rate depends on pressure raised to the overall reaction order divided by two (rb α pn/2). Therefore, for overall reaction orders of two (n = 2) that are typical, the pressure exponent is about 1. Therefore, above the slope break, where exponents are well over 1, it is highly unlikely that the slope break is chemical in origin, as some have suggested previously. This work also suggests future directions for research. For example, the oxidizers or binders could be chosen to mitigate fracture. Also, particle size or morphology (even porous oxidizer perhaps) might affect the slope break phenomena. There is good interaction with experiment and modeling in the embedded wire propellant project.

Extended Solids

This is an ambitious and high-stakes project. It is the most high-risk/high-payoff project of the extended solids program that was presented to the panel. It is commendable that some materials have been scaled to more reasonable quantities (grams), but scaling remains a significant challenge. The issue of stability (could be extremely stable or unstable) is another challenge and is an area where theory and modeling can play a major role. In some projects, theory and experiment were well connected, but some projects had evolved to an exploratory mode with little theory guidance.

The small-scale characterization experiments (laser shock, electrostatic discharge, specific impulse or Isp from strand burns) are in need of a more scientific underpinning to connect with more than 10 g sample properties. A detailed analysis of these experiments is needed. For example, can it be shown that shock speed in the laser shock experiment could be related to detonation speed? Also, can these

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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small-scale characterization experiments be repeated by other groups—a basic requirement of scientific advancement? How well do all these approaches work for standard materials where large-scale experimental data is available?

Multiscale Computational Modeling

A fundamental weakness of macro-scale continuum simulation methods in heterogeneous energetic materials is the loss of detailed material information at scales below the resolution of computational elements or cells. Homogenization is acceptable when average response is desired on the relevant length-time scales, or when validation is carried out with experiments that similarly measure average properties. However, problems like explosive initiation and impact thermal runaway, or specifically explosive failure, requires the prediction of rapid dynamic phenomena operating in highly unstable threshold regimes, where subgrid material structure, such as porosity and multipoint material correlations, dominate the transient response. It is precisely these regimes that need to be characterized in order to understand performance and safety margins, and the uncertainties stemming from process and manufacturing variability. ARL is making good strides in this area and is encouraged to continue to broaden its efforts. A transformative capability that predicts dynamic response on component scales of interest via comprehensive treatment of the scale relevant physics will truly lead to an improved understanding of the response of new and traditional energetic materials.

To this end, novel tools and analyses that reveal the complex dependencies and correlations between nonlinear transient processes in complex microstructures and the underlying stochastic variation of microstructure are needed. This understanding could be used to develop a statistical description of heterogeneous materials that can be incorporated into macro-scale continuum methods that embed mesoscale response as suggested by lower scale (mesoscale) simulations. The correlation of grain scale microstructures and material shock response is the key and essential feature of bridging scales to the continuum level.

Challenges and Opportunities

In the development of improved propellant energetic materials, more interaction with computational modeling efforts is needed, and it appears that that is already starting. Also, this group has plans for several new molecules and seems to have a good plan to achieve the results. This could be a growth area for ARL and is encouraged.

There are plans to do phase-contrast X-ray experiments at ANL in support of the extended-solids projects when a new facility is available. Some of these experiments may be attempted with current capabilities at ANL; ARL’s staff is encouraged to explore what experimental aspects of their research could be started now with the current facilities at ANL.

There is good interaction between experiment and modeling with the embedded wire propellant project, although there was not time in the presentation to the panel to show this, and it was not in the experimental poster. Future work in this area might consider reactive wires or printed wires.

In the effort to address the scales greater than atomistic quantum levels, dissipative particle dynamics has been demonstrated as a promising approach for coarse-grain numerical simulations. Nonetheless, it still represents an intermediate scale toward coupling to the continuum level. Although ARL researchers are well aware of this intermediate level, and perhaps the sequential hierarchical approach may be a good method to bridge scales, it just needs to be more complete. A clearer roadmap for a better picture

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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of bridging the scales to the continuum would have given a clearer way of defining where, ultimately, computational modeling for reactive materials is headed.

A plan for validating the multiscale modeling was put forth based on continuum-level testing and diagnostics. This has been the traditional approach in assessing modeling at the continuum level, but it is still removed from validating the bridging of scales. There is a vision forward to address material strength effects based on continuum-level constitutive modeling; however, the link to dissipative particle dynamics (DPD) models still remains questionable. In the effort to address the scales greater than atomistic quantum levels, DPD has been demonstrated to be a promising approach for coarse-grain numerical simulations that implicitly couple to molecular-length scales.

An area where continued attention needs to be focused, and which represents a great opportunity, is investing in the characterization of inter-material interfaces. The study of interfaces provides opportunities for bridging length and time, approaches to how these scale more effectively (possibly with statistical or probabilistic treatments), and seeking connections (validation, insight, etc.) to experiments that reveal subscale behavior are needed.

EFFECTS ON TARGET—BALLISTICS AND BLAST

The teams working on materials synthesis and propellants demonstrated high technical competency and in-depth understanding. The teams are commended for making progress in technically challenging areas related to the development of new energetic materials, propellants, and blast effects on targets. The teams clearly demonstrated their understanding of the necessity for experimental validation and are making significant progress. ARL is encouraged to continue move in this direction. ARL is complimented for putting forward some of its early career researchers in this topic area. They showed strong technical competency and poise.

Development of New Energetic Materials

The efforts at synthesis of energetics are cutting-edge work and are showing results in the newly developed promising chemicals. This is a high-risk/high-payoff effort, so ARL could expect that most candidate materials may not, ultimately, transition to Army applications and systems.

One significant challenge in the development of new materials is evaluating or screening candidate materials when only small quantities are available. There is some promising work to develop approaches for testing and screening candidate materials utilizing state-of-the-art diagnostics such as PDV. ARL needs to complement the experimental efforts with modeling efforts that might suggest alternate geometries (e.g., cylindrical) and perhaps allow additional information (e.g., model parameters) to be obtained from the data.

Propellants

The modeling of solid propellants appears to be state of the art. Currently, the reaction modeling approach uses laminate/mixture theory. Good progress has been made in understanding detrimental formation of cracks and the sudden nonlinear increase in burn rate as a function of pressure (referred to as the exponent break). It was shown that this break is not due to chemistry alone (an increase in gas-phase reactions as a function of pressure); rather, it appears that it is due to mechanical processes—for example, the growth of microcracks that increase surface area. There is a desire to push the exponent break to somewhat higher pressures to permit extended range. This enhanced understanding of what

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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causes the break could lead to possible reformulations for improved performance. Validation of the modeling effort is ongoing, including, for example, experiments with a wire or foil insert. Although it was acknowledged that real propellants are heterogeneous, the modeling effort continues to focus on the laminate/mixture theory approach. The current approach could be maintained since it continues to provide fundamental insight. However, ARL needs to pursue a complementary modeling approach that includes the material heterogeneity, because this will ultimately be required to make further progress on the problem.

Energy Release—Target Effects

ARL staff showed recognition that a better understanding of chemical kinetics is required for advancements in solid rocket propellant technology (e.g., propellant reformulation to increase performance). ARL has a computational effort to calculate decomposition and energy release during deflagration, including the impact of additives. The thermochemical parameters and reaction path parameters are being estimated via quantum chemistry modeling, and the researchers are building a library of chemical kinetics reactions and mechanisms. This is a worthwhile endeavor and needs to be pursued. However, effort to validate the modeling effort through experiments was not described. If there is not a parallel effort to support some sort of validation, one needs to be initiated.

A study to investigate the shock energy absorbed by a target appears to be primarily experimental, although the study did show a complementary numerical simulation. The focus is to develop the diagnostic capability to quantify the details of shock impingement. The experimental procedure has the capability to measure air shock speeds as well as see ground reflections and a secondary shock (presumably the result of a collapse of the initial shock and a spherical collapse and rebound of the initial shock’s interaction with the explosive/air interface). However, the computation effort focused on an ideal spherical shock expanding and impinging on the target. The researchers also showed the shock impinging on an inclined plate, and the experimental technique could easily quantify the complex shock interactions. With the wealth of experimental data, there could be more of an effort to simulate the actual experiment to validate the modeling capability. The investigators however are disconnected from the potential users of a validated computer code. In addition, the investigators show a shock impinging on a helmet with a polycarbonate shield but showed a 25 psi shock impinging on the helmet. No soldier could even come close to withstanding such an overpressure. So, a different question is this: Can the experimental technique resolve shock data at values that would represent aggressive but survivable loading of a helmet? To investigate interactions of face plate, helmet, TBI, and other factors, the loading conditions need to be accurate. Thus, the effort is worthwhile, but the focus needs to be adjusted to be relevant.

A relatively new study is focused on developing a diagnostic capability to interrogate and measure the very beginning of a reaction. The phenomena, such as electronic transitions, occur on a time scale of femtoseconds to nanoseconds. A significant amount of time was involved in ordering equipment and setting up the experiment, and the initial results look promising. It would probably be useful to initiate a parallel modeling effort that might help to interpret what is being observed.

It is well known that energy release rate is dependent on the surface area of the burning propellant. A desire is to fabricate an optimal shape propellant using 3D additive manufacturing techniques. Modeling is being used to develop appropriate geometric web designs to tailor the burn rate to achieve the ideal constant breach pressure response. Additionally, the modeling includes thermal effects (coefficient of thermal expansion) since the burn rate is a function of initial propellant temperature. As part of the technical effort, the coefficients of thermal expansion were determined for several propellants and celluloids. Part of the design process is addressing the question of whether temperature-sensitive glues

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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could occlude surface area at higher temperatures. It is not clear at this time if the goals of the technical effort—for example, developing 3D additive manufacturing techniques applied to solid propellants and temperature-sensitive glues to control surface area—will be achieved in the remaining year of the project.

Summary of Accomplishments

The teams working on materials synthesis and propellants demonstrated high technical competency and in-depth understanding. The teams are commended for making progress in technically challenging areas. The teams understand the necessity for experimental validation and are making significant progress, although more work needs to be done. The efforts at synthesis of energetics are clearly cutting-edge work and are showing results in the newly developed, promising chemicals.

In the experimental characterization of small quantities (few grams) of the new energetic materials being developed, the fidelity of the experimental data may permit development of energy release models. This is an exciting direction of research, and promising opportunity, supported by ARL’s thrust in this area.

Challenges and Opportunities

Some promising work is ongoing to develop approaches for testing and screening candidate energetic materials. However, it remains a significant challenge to develop useful ways to characterize energetic materials to assess if they are promising when only smaller quantities are available (under 2 grams). Synthesis chemists would benefit from working with materials scientists to generate useful characterization information. The analysis of new materials development for propellants and ballistics applications needs improved collaboration with the Materials Research Campaign which could help improve progress in the development of better propellant materials.

Another important challenge is the scale-up path for new materials. In at least one case (plasma-assisted deposition of carbon oxide materials), the ARL team appeared not to have given much consideration to the scale-up process. Because the scale-up process is likely to be difficult and can keep new materials from being useful to the Army, ARL teams need to include scale-up considerations in their work as early as practical.

ARL needs to take a more systematic approach to characterizing the physical (microstructural) and chemical properties of the new materials that have been synthesized through techniques such as Raman, nuclear magnetic resonance, and TEM. Enhanced characterization represents a potent opportunity to support predictive model development with microstructural data and validate the microstructures and chemistry produced in the synthesis efforts.

In some of the research projects, minimal computational components were visible. In the solid-propellant burn rate enhancement for missile propulsion research, where both experiments and modeling were done, no direct comparison between the two was shown. The ARL researchers need to include both experiments and simulations in their research projects.

FLIGHT, GUIDANCE, NAVIGATION, AND CONTROL

Guidance, navigation, and control (GN&C) are what elevate an unguided projectile to a smart munition or a guided missile and are more focused on the objective of reducing the expected miss distance, increasing the reliability and accuracy of engaging the target, and, finally, increasing lethality. Precision on the battlefield remains a potent game changer, and the development of better techniques

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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is fundamental to the Army’s future success. The function of navigation and guidance work together to determine the course to the target, and controlling these functions is the key to this entire discipline. Because of the close interrelationship of these topics, GN&C are combined together as opposed to three separate subjects. Before detailed discussion on the topics, there are a few overarching observations in regards to GN&C.

The broad area of ARL’s GN&C research and technology needs further review because what the panel saw was only a slice of all the work being performed in this area. It was not apparent how the GN&C research presented was selected and, further, how it ties to the overall strategy and objectives of the various campaigns. Several researchers expressed frustration about obtaining commercial off-the-shelf (COTS) software in a timely manner. Their comments indicated that Army information technology security does not recognize the mission of ARL and the importance to procure software in a timely manner; that is, ARL researchers want their software needs to have a higher priority. This restriction requires attention and needs to be addressed by ARL management. The procurement of storage for data was also noted to be a major shortfall requiring ARL management action.

The ARL GN&C management indicated that ARL interactions with the Armament Research, Development and Engineering Center (ARDEC) are very healthy, but their interactions with the AMRDEC are fair at best. While the planning process for research project selection in the GN&C area appeared to be very thorough, the presentations to the panel did not reflect that high-level planning process. As a consequence, the presentations did not seem cohesive or to be well coordinated. Finally, through questioning of the oral and poster presenters, repeated lack of in-depth knowledge of the state of the art in GN&C was noted, and there was a lack of references to external experts (elsewhere in DOD, industry, universities) as well as both internal and outside literature.

Kinetic Lethality

The kinetic lethality topic investigates the relationships that cover the flight maneuverability, target acquisition, and delivery to within a designated CEP (central error probable) for guided projectiles and missiles. The goal is to look at design factors proactively in simulation concurrently with technology development that many times takes place at one of the Research, Development and Engineering Centers (RDECs). The milestones for this ARL work are defined, seem appropriate, and appear feasible in the time frames allotted. This 6.2-funded work (early applied research) may lead to shorter-term applications than the 6.1-funded work (basic research), although both may have longer-term implications. Simulation with its verification and validation (V&V) appears to be a cost-effective avenue for ARL. Trying to visualize what will and can be achieved in the long term is a challenging nonlinear feedback problem worthy of increased ARL effort. The work seems to be a good positive progression in this direction. The equipment and tools that are being used are appropriate (but old) for these early investigations. The ARL team collaborates quite often with ARDEC and occasionally with AMRDEC.

The ARL researchers would benefit from greater access and participation within the DOD laboratory system and contractor communities who have, in several notable cases, made advances that may accelerate the research at ARL. Some of the work reviewed has been published in technical journals and conference proceedings, some of which are classified. Exposure of ARL’s work is necessary and is achieved through presentations at important conferences. Travel restrictions have been eased over the past 2 years, and funding for travel is being budgeted.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Shock Energy on Target

This R&D project uses a reflective screen and laser illumination to image the reflection of blast wave from a target. The goal is to be able to measure shock wave reflection processes by obtaining incident and reflected shock wave velocities from optical images obtained with a shadowgraph-like method. While an interesting notion, relating shock wave velocities to energy transfer requires the interpretation of complex three-dimensional flow fields in order to learn about the actual interaction of the blast wave with the target surface. Mechanical measurements of the surface deformation (strain gauges, digital image correlation, and force transducers) would directly yield information on the target energy absorption and provide important checks on the optical methods, which will be difficult to interpret except for the very simplest targets.

Impulsive Control for Highly Maneuverable, Small Diameter Munitions

Scoping study on the use of thrust vector control to maneuver Mach 2 gun-launched projectiles and detailed examination of specific aerodynamic issues was presented to the panel. This scoping study used engineering correlations for solid rocket motor performance and conventional vehicle performance, stability and control model based on steady aerodynamic coefficients (lift, drag, moments, and derivatives). Aerodynamic coefficients were based on computational fluid dynamics using steady-flow solutions based on Reynolds Averaged Navier-Stokes (RANS) modeling for turbulent flow. Open loop vehicle performance simulations with elementary rocket motor thrust models demonstrated the ability to change vehicle heading and 150 m offset in cross-range trajectory during 500 ms burn. But this simulation involves very high angles of attack that excite oscillations in the projectile attitude, which results in large-amplitude, slowly decaying oscillations in angle of attack. It is not clear if these concepts can or will be translated into weapons systems even in the long term and needs to be explored strategically to determine if this line of investigation is warranted.

High-G COTS Component Survivability

In an effort to allow for cheaper and faster production of military technology, ARL is looking into the use of COTS components in vision-based guidance systems. ARL has designed experiments to determine and quantify failure criteria of COTS servos with the use of the air guns to reproduce multiple millisecond high-gravity (g) environments. A predictive model analyzing probability of failure of COTS components based on changes in duration and g-level was determined and later found to be inaccurate due to a lack in experimental severity.

3D-printed materials being used to develop new technologies for the warfighter are being implemented in designs under the assumption that bulk mechanical properties and isotropy apply. Experimental strength properties of 3D-printed glass-filled nylon were found to be largely over estimated in the datasheet given by the material supplier. Internal and interfacial properties are being determined, and soon the strength losses will be explained. These material models are now being inserted into explicit finite element models to further support vision-based component and assembly design.

Scientists and engineers focusing mainly in the area of the sciences for lethality and protection are teaming up with other campaigns with specialties in the area of materials research to combine new materials technologies with scalable dynamic experimental processes in order to determine material susceptibility to high-g environments. The findings will determine if these novel processes and materials can be implemented in guidance systems and munitions in order to reach desired lethal effects at standoff ranges in visually constrained environments.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Vortex-Fin Interaction Predictions

Canards are effective aerodynamic maneuver control actuators for guided missiles and projectiles. However, vortices emanating from the canard tips (and sometimes root area) usually interact with aft control or stability surfaces to cause adverse roll moments that can lead to reduced, or total, loss of roll control. The vortex-fin interaction problem has been addressed for decades, but accurate, a priori prediction of the interaction dynamics has not been demonstrated. Engineering-level prediction codes with added vortex modeling reasonably predict the aerodynamic loading (forces and moments) for low-to-moderate angle of attack. Computational fluid dynamics (CFD) predictions provide more underlying physics to higher angles of attack. However, any validation of these simulations is usually restricted to comparing the total loads on the whole flight vehicle, usually without any flow visualization or component (fin/canard) loading measurements. This reduces the ability to determine how accurately the vortex-fin interaction is being predicted—for example, are differences due to the vortex-fin interaction or inaccuracies elsewhere in the flow field? A recent experimental wind tunnel study by SNL provides not only fin loading data, but particle image velocimetry data providing the flow velocity components and turbulence statistics. Validating CFD with this experimental data will allow determination of metrics such as mesh cell density required for adequate vortex resolution, quantifying numerical diffusion of the vortex, and the level of vortex resolution required for adequate determination of the vortex-fin interaction forces and moments. ARL has long been a leader in the use of CFD on high-performance computer systems to study the aerodynamics and flow phenomenology of Army munitions. Collaborations could help to leverage this work to obtain additional validation data and provide a conduit to transfer knowledge gained to the design and development community through improvements to the engineering-level codes.

Validation of numerical simulations (RANS) of vortex-fin interactions against SNL wind tunnel data (M = 0.8) is positive. Strong participation in the American Institute of Aeronautics and Astronautics meetings and DOD/DOE Technical Cooperation Program (TTCP) activities is encouraged. Exploring the transition from CFD++ to new software (Kestrel developed by the National Aeronautics and Space Administration) that will use next generation of modeling (large-eddy simulation or LES), which will enable higher-fidelity modeling of complex flowfields, is also encouraged. Kestrel will need to be extended to include models of control systems and 6 degree-of-freedom rigid-body-dynamics (RBD) that are already included.

Vortex-Fin Interactions on Bodies of Revolution

Accurate determination of flight behavior is critical to the development of new, affordable precision munitions. The current focus for maneuverability is the use of moveable lifting surfaces on the fore-body (canards) of a fin-stabilized projectile. The vortices shed by the trailing edge of the canards are known to have an impact on aerodynamic performance and have been studied for years on high-fineness-ratio missiles. The current research focuses on improving understanding of the canard-trailing vortex on the aerodynamic performance of a short length-to-diameter, fin-stabilized munition when the canards are deflected for a roll, pitch, or yaw maneuver. The in-house research utilizes high-fidelity CFD (traditional and coupled with rigid body dynamics simulations) to increase the understanding of the flow phenomena. Some experimental data for validation of forces and moments has also been collected in-house, and collaboration partners are investigating and collecting additional experimental methods. The increased understanding of the flow phenomena will allow lower-fidelity tools to be enhanced and may eventually allow for the impact of the interference effects to be minimized, thereby allowing greater maneuver authority.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

Coupled CFD-RBD simulations of bodies of revolution with fin-canard configurations using commercial software (CFD++) and RANS modeling (the same approach as DeSpirito) is a credible approach. Key issues are related to loss of control authority by fins due to impingements of vortices from canard tips and canard-body joint, particularly when the projectile is at a high angle of attack. Control surface influence can be canceled out or even reversed due to changes in surface pressure distribution and separated flow that result from vortex impingement. Control authority (in terms of blade section aerodynamic coefficients) is a sensitive function of the projectile angle of attack as well as the local fin or canard section angle of attack. The simulations demonstrate the importance of validation against experimental data for specific configurations. Experiments are in progress through informal collaborations with the Air Force Research Laboratory (AFRL) water channel experiments (12-scale model) and visualization experiments at Stanford University and West Point.

Polar Coded Apertures for Compression Spectral Imaging

In recent years, a number of low-cost precision munitions have been developed. These munitions rely on GPS for navigation, which is vulnerable to jamming and suffers from target location error. Vision-based navigation overcomes these deficiencies and has been successfully used in many unmanned aerial vehicle applications. Unfortunately, the infrared (IR) cameras typically employed in military applications are too expensive for low-cost munitions programs. Compressive sensing (CS) allows high-resolution images to be obtained from a low-resolution imager, or even a single sensor, thereby reducing cost. The advantages of a CS IR imager can be directly extended to spectral imaging, which has been shown to increase targeting and detection performance. Initial research focuses on the design of a stand-alone compressive spectral imager in a controlled laboratory environment. The aperture code is optimized both in its geometry and binary pattern to enhance image quality. A continuous motion model is integrated into the CS algorithm to remove image blur. Simulations show accurate spatial and spectral reconstructions using only a fraction of the full amount of measurements. Hyperspectral simulations of up to 128 bands are included. A laboratory experiment is currently in progress to validate these simulation results.

Line-of-Sight Rate Estimation Algorithms

One of the key campaign initiatives (KCIs) is desired lethal effects at standoff ranges in constrained environments. Inside this initiative lies the goal of being able to engage a moving target with a gun-launched projectile. The line-of-sight rate is a component of angular velocity and would be measured by a gyro attached to a gimballed seeker that was perfectly pointed at the target. The gun-launched projectile environment prohibits perfect gimballed seekers, and so the line-of-sight rates need to be estimated from strap-down seekers and subtactical-grade microelectromechanical systems inertial sensors. While others in the missile community have worked with strap-down seekers, prior literature treated the line-of-sight rate estimation problem separately while assuming error-free altitude estimates. Basic research was performed to create algorithms that accounted for nonnegligible altitude errors. It was also found that the altitude and line-of-sight algorithms could be used to aid the seeker-target-tracking algorithms. These algorithms are being implemented onboard microprocessors for a series of flight experiments using real maneuverable projectiles. Estimator performance is being measured against post-processed sensor data that serves as a truth source.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

Emerging COTS Measurements and Flight Experiments

Image-based navigation uses computer vision to estimate navigation states of projectiles and provides ARL with a strategy to achieve guided lethality in GPS-denied environments. Extracting navigation states from computer vision results (scene features or target identification) requires modeling the projective transformation performed by the imager system in converting the external scene into a two-dimensional digital image. Errors in the imager model used by the projectile guidance system were seen to result in corresponding errors in navigation state estimates. These errors need to be modeled in order to effectively design the projectile guidance system and predict its performance.

Not only do guidance systems for gun-launched projectiles need to survive the setback loads of launch, but changes to the performance of electromechanical components due to shock need to be understood such that the system design can account for shock effects. COTS imager systems provide ready access to rapidly progressing imager technology, but these imagers are not adequately characterized by the manufacturer and have not been designed for performance in a high-g environment. Assessment of the effects of shock on COTS imagers is an area of research not addressed by the academic community studying vision-based navigation for robot applications.

This research effort at ARL presents a strategy for evaluating the performance of navigation imagers in the areas of resolution, sharpness, color perception, projective transformation, and imager boresight. Imagers are characterized both before and after exposure to a shock-event-simulating gun launch. Changes to the imager as a result of the shock event are modeled as a source of error in the projectile navigation states, and this model is incorporated into the simulation environment for design and evaluation of the projectile guidance system.

Summary of Accomplishments

The ARL aspires to be the nation’s premier laboratory for land forces. The lethality and protection program at ARL has made significant headway in contributing toward achievement of this goal. They have succeeded in establishing relationships with top RDECs and some university laboratories that are also leaders in these areas—although there are not many. However, ARL needs to broaden its technical network to include other services (some of which may be international) and with major industries in the GN&C research and engineering area. For example, the largest missile company in the world has no one involved (collaborating) with ARL in the areas reviewed. Given ARL’s published S&T campaign plans to decide to lead, collaborate, or watch in all technical areas, ARL in the GN&C area needs to decide how important the state of the art in the aspects of GN&C is to the Army and where ARL will engage and at what level and with whom.

Although not immediately apparent, the ARL research team has made significant progress toward developing the technical underpinnings of advanced guided munitions in the areas of aerodynamics, guidance and control, and terminal homing. This includes insights into vector thrust aerodynamics, image correlation, and navigation fixes without GPS, in addition to the potential advances in energetic materials. The work, taken together, appears to define a new generation of precision guided munitions.

ARL has attracted some outstanding personnel, especially new Ph.D.’s, and is undertaking interesting and relevant work on par with academic departments. ARL needs to continue to invest in its staffing in this manner.

Impressive research is ongoing in the areas of vortex-fin interactions research and high-maneuverable, small-diameter munitions research. While potential achievements in these areas are still in progress, several were considered noteworthy. Progress in the turbulence control of vector thrust control seems

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

exceptional for furthering the capabilities of next-generation munitions. Areas such as navigation, image recognition, and terminal homing will likely become a breakthrough when taken together in the context of technology demonstration. Specific examples are discussed below.

Flight Control

This work was well represented by a poster on the topic of vortex-fin interaction predictions of elementary configurations with experimental validation. The principal investigator is well known in this small technical community and very well respected. The caliber of the work is high. Flight control is of course key to smart projectile development, and several topics of similar nature are being pursued. The ARL work is unique and did not overlap with other work, although these topics are standard fare for missile developers.

Navigation

Navigating in a so-called denied environment leads to some reinventing and improvement on some old techniques. The presentation to the panel on polarized skylight navigation was very interesting and well prepared. It introduced work well performed by researchers below the Ph.D. level. This kind of work is important and essential for highly effective R&D organizations.

Shared Vision

The ARL GN&C research team seemed to have a shared vision. However, it was difficult to surmise this vision, as it was not explicitly stated in any presentations. Rather, the vision that emerged from numerous discussions was to develop a gun-launched, rocket-propelled, guided projectile of moderate range. Everyone appeared to either be researching critical elements and features of this vision or performing what might more accurately be called risk reduction for potential technology demonstration (e.g., shock tests). The team has made progress in guidance and control (that the team calls navigation), aerodynamics, and terminal homing parts of the kill chain. However, because the vision is not quantitative, it is not possible to perceive how far the research technology needs to be “stretched” or whether the selected area of investigation is capable of meeting the technical needs. For example, an analysis of the munition concept might show image compression if the image data is not a productive avenue. Alternatively, it is likely that with a short time to go after target detection by the munition, a direct image and comparison with targeting image will be required, with potentially different research issues.

Transition

In discussing how to transition research results to the 6.3-funded research community, the concept of technical demonstrations was mentioned and is a good idea, particularly if performed in a collaborative manner with industry. However, there needs to be a systems engineering context to facilitate the potential transition. This is not in opposition to the spirit of research but can inform the degree of understanding of potential risks as well as critical technologies and phenomena.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

Challenges and Opportunities

ARL has a strong legacy of outstanding work in exterior ballistics and maintains a modest core competency today, with significant limitations due to the emphasis on simulation versus testing and experimentation. The limitations of simulation and challenges to progress were clearly recognized in several areas, such as high-angle of attack flow simulation, shock boundary layer interactions, vortex-fin interactions, and rocket motor exhaust with external flow field. The staff are engaged with other laboratories to obtain experimental data sets to validate simulations and working with DOD TTCP programs to exchange information. One of the limitations is the lack of coupling to in-house testing programs (which were historically a strength of ARL) that can be used to both provide validation data for the simulations and to test concepts that are beyond the capabilities of current simulation technology. The effort is an important research area for ARL, but the CFD effort has to be coupled to an equally strong laboratory and a robust and well-funded field-testing effort. This is the main weakness of this program—an excessive reliance on CFD. Lack of in-house testing and a laboratory experimentation program is a definite weakness in this area for ARL. The staff has been proactive about seeking out and piggy-backing on test programs at other DOD laboratories, but without a strong testing program closely coupled to the CFD efforts, ARL will not be a leader in this area. This is a negative for attracting and retaining staff in this area because of the inability to interact with experimenters on a daily basis. To have a robust research group in this area, there needs to be a critical number of experimenters, analysts, and numerical simulation subject-matter experts.

The ARL research community appears to be aligned in their vision of developing and improving the precision of guided munitions. However, it was not clear which performance attributes present the greatest technical challenge to ARL scientists. A number of researchers cited prior open literature and appeared to openly publish in the research areas; however, there appeared to be little awareness of prior DOD sensitive and classified research, development, and even deployed capabilities. For example, approaches for tracking targets moving behind obstacles or through jamming strobes is well described and have been implemented in the air defense and strike communities of all services. As another example, a thoughtful research effort in polarized skylight for munition attitude and guidance (navigation) was presented that might benefit from collaborative engagement with the broader DOD navigation community, even though this community is working in different performance regimes. A Defense Technical Information Center search would likely provide indications of these prior accomplishments and ongoing work and would provide a basis to visit and establish collaborations with the key experts from across DOD.

ARL staff in the flight GN&C area needs to survey prior research (classified and unclassified) and undertake field visits to industry and academia as relevant to select topical areas to increase knowledge of the state of the art in the flight GN&C area. This review needs to particularly focus on the state of the art in the following: (1) target estimation and tracking that has been addressed by the air defense radar community across DOD and airborne surveillance ground tracking technology; (2) gun shock tolerant electronics and actuators that are well characterized in industry; and (3) tracking under measurement constraints, which has been addressed by the radar community. In this regard, the polarized skylight navigation research presented will benefit from broader engagement with the celestial navigation community.

Working to improve accuracy of hypersonic projectiles in adverse environments is a clear challenge worthy of continued effort. An opportunity exists for ARL to improve in GN&C by working more closely with both the other services and with major industry. The ARL work made little reference to work performed by research groups in the other services (e.g., AFRL) and showed almost zero knowledge of work done in industry. In fact, there appeared to be little or no joint collaboration with the largest companies in the United States who have worked GN&C for many years.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

Few researchers at ARL have ever used statistically designed experiments or shown use of Bayesian techniques in the analysis of data, even though the laboratory is well known for its work in Dempster-Shafer techniques in other areas of research. This lack is evident in the flight, guidance, navigation, and control project planning, setting objectives, and execution. Improvements that will result in major cost savings and accuracy of interpretation of experiment results can be found by using the design of experiments that has been shown and well demonstrated by the National Nuclear Security Administration laboratories. Also, finding interaction amongst causal variables in determining response equations for experimental results can only be found using design of experiments techniques (e.g., Design and Analysis of Experiments by Douglas Montgomery 8th edition, 2013). Design of experiments remain a critical way to linking cross-cutting technologies and analysis techniques while maximizing optimization of resources and saving costs.

OVERALL QUALITY OF THE WORK

ARL’s research on lethality and protection ranges from basic research that improves basic understanding of scientific phenomena to the generation of technology that supports the following: (1) battlefield injury mechanisms, human response to threats, and human protective equipment; (2) directed energy programs; (3) ballistics and blast programs that address weapon–target interactions and armor and adaptive protection developments; (4) disruptive energetics; (5) kinetic lethality—propulsion and launch/effects on target; and (6) flight, guidance, navigation, and control.

Its research on battlefield injury mechanisms is important for ARL because a better understanding of these mechanisms is vital to improving protective equipment. This is especially true for protection of the head, where there is considerable uncertainty about allowable levels of shock, which greatly affects protective options. The most impressive accomplishment of the battlefield mechanisms–human response–human protective equipment program is that a highly competent cadre of scientists is at work and a credible program is under way. A long-term vision for the battlefield injury mechanisms projects could serve as a philosophy that helps allocate resources and set program direction. Almost all of the topics presented in this subsection—battlefield mechanisms, human response, and human protective equipment—had a combination of computational and experimental approaches. The real-time interplay of experiment and computation is needed.

ARL’s campaign plans categorize directed energy (DE) as a focused area under the much broader category of electronic warfare (EW), in accordance with the Army’s definitions. The ARL posture designations for both radio frequency-DE and laser-DE are to collaborate rather than lead. The subsuming of DE under EW and a collaborate-only posture indicate that ARL has downgraded the priority of DE within its technology portfolio from its previous robust effort. The consequence of this status change was evident in the current programs presented: they appear to be a small collection of seemingly unrelated projects. ARL needs to take a strategic look at the area of DE to determine its ongoing priority and focus the effort accordingly, with a view to the 2035 time frame; the strategic review needs to include consideration of future capabilities that the Army will need that DE might fill, and what DE capabilities might be fielded by our adversaries for which the Army will need countermeasures. A focused ARL DE program would benefit from a systems-level study addressing future Army missions in which DE could play a role and in which DE effectiveness and alternatives to DE are traded off. A highlight of the overall program in DE is the project on adaptive and scalable high-power phase-locked fiber laser arrays. This work is a notable achievement, is recognized as such by the technical community, and appears to be ready for the next step in transition toward field deployment.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

ARL has a strong record of achievement in the basic and applied sciences and engineering of penetration and protection. The R&D described in the armor and adaptive protection area showed how ARL is building on its tradition of excellence to provide the knowledge basis for current and future Army needs in protecting our warfighters. This remains a core competency that underlies Army capabilities across the entire DOD, and it needs to be preserved and nurtured. There was significant evidence of teamwork and integration among the projects in, for example, adaptive protection. Examples of the link of experiments and computational modeling to provide physical insight into problems were especially noteworthy, with potential to aid in developing new designs and exploring new concepts. Benchmarking simulations with experiments and the emphasis on bringing advanced technology (particularly in the X-ray region) to bear on diagnostics were impressive. Developing a predictive capability for damage and fracture in metals, ceramics, and polymers underlies the efficient development of new material systems for protection and for developing approaches to needed penetration capabilities. At present, there is no framework that has this capability. However, experimental, theoretical, and computational advances being developed in other countries are making such a capability seem possible in the not-too-distant future. A systematic approach based on understanding the key physical processes is needed because of the wide range of material systems that are becoming available. Material modeling for these systems would beneficially include reliable modeling of the effects of temperature and pressure—two effects that are mostly underrepresented in much of the computational and experimental effort.

ARL’s synthesis effort is a commendable and relatively new effort at ARL to develop a chemical synthesis effort and is encouraged to continue and grow in the future. A blended focus on various applications (propellants and explosives) is needed, rather than just explosives. This is a high–risk/high-payoff effort, so ARL could expect that most candidate materials may not, ultimately, transition to Army applications and systems. The propellant simulation R&D clearly remains a traditional strength of ARL that is positively impacting and supporting warfighter and Army needs, and it needs to be supported and nurtured. Evidence of good interactions between experimental and modeling efforts were seen in the embedded wire propellant project. In the extended solids focus area, it is commendable that ARL has scaled some materials to more significant quantities (grams), and ARL needs to pursue scaling to larger quantities for testing as possible. ARL’s multiscale modeling efforts are tackling hard problems like explosive initiation and impact thermal runaway or, specifically, explosive failure. Each of these requires the prediction of rapid dynamic phenomena operating in highly unstable threshold regimes, where subgrid material structure, such as porosity and multipoint material correlations, dominate the transient response. ARL is making good strides in this area and needs to continue to broaden its efforts. A transformative capability that predicts dynamic response on component scales of interest via comprehensive treatment of the scale relevant physics will truly lead to an improved understanding of the response of new and traditional energetic materials.

ARL needs to complement the experimental efforts to date in its energetics and propellant projects with modeling efforts that might suggest alternate geometries (e.g., cylindrical) and perhaps allow additional information (e.g., model parameters) to be obtained from the data. ARL’s modeling of solid propellants appears to be state of the art, with the reaction modeling approach using laminate/mixture theory. Further, positive progress was evident in understanding the detrimental formation of cracks and the sudden nonlinear increase in burn rate as a function of pressure. Validation of ARL’s modeling effort is clearly ongoing, such as experiments with a wire or foil insert, and is needed as an important component in all energetic and propellant projects. As it is well known that energy release rate is dependent on surface area of the burning propellant, the goal to fabricate an optimal shape propellant using 3D additive manufacturing techniques needs to be pursued. ARL’s modeling in this regard to develop appropriate geometric web designs to tailor the burn rate to achieve the ideal constant breach pressure

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×

response is encouraged. Additionally, the modeling includes thermal effects (coefficient of thermal expansion), since the burn rate is a function of initial propellant temperature and appears promising. As part of this technical effort, the coefficients of thermal expansion were determined for several propellants and celluloids. Part of the modeling and design processes needs to address the question of whether temperature-sensitive glues could occlude surface area at higher temperatures. Developing 3D additive manufacturing techniques applied to solid propellants and temperature-sensitive glues to control surface area for Army applications is exciting and necessary.

ARL’s research team has made significant progress toward developing the technical underpinnings of advanced guided munitions in the areas of aerodynamics, guidance and control, and terminal homing. This includes insights into vector thrust aerodynamics, image correlation, navigation fixes without GPS, in addition to the potential advances in the energetic materials. The work, taken together, appears to define a new generation of precision-guided munitions.

ARL has attracted some outstanding personnel, especially new Ph.D.’s, and they are undertaking interesting and relevant work on par with academic departments. ARL needs to continue to invest in its staffing in this manner. The research in the areas of vortex-fin interactions research and highly maneuverable, small-diameter munitions research is impressive. Because flight control is, of course, key to smart projectile development, ARL’s research programs in this area are a positive development and growth areas for ARL and the Army. In the GN&C R&D area, ARL needs to decide in which areas it will lead, versus collaborate, versus watch or follow. Strategic thinking by ARL in the GN&C area—to define how important the state of the art in the aspects of GN&C is to the Army and where will ARL engage and at what level and with whom—is deemed to be critical.

Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
×
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Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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Suggested Citation:"3 Sciences for Lethality and Protection." National Academies of Sciences, Engineering, and Medicine. 2017. 2015-2016 Assessment of the Army Research Laboratory. Washington, DC: The National Academies Press. doi: 10.17226/24653.
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The National Academies of Sciences, Engineering, and Medicine's Army Research Laboratory Technical Assessment Board (ARLTAB) provides biennial assessments of the scientific and technical quality of the research, development, and analysis programs at the Army Research Laboratory (ARL), focusing on ballistics sciences, human sciences, information sciences, materials sciences, and mechanical sciences. This biennial report summarizes the findings of the ARLTAB from the reviews conducted by the panels in 2015 and 2016 and subsumes the 2015-2016 interim report.

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