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In an age where the battlefield is as much about innovation as it is about strategy, the Defense Advanced Research Projects Agency (DARPA) continues to push the boundaries of what’s possible. One of its latest endeavors, the Rubble to Rockets (R2) program, is a testament to the agency’s forward-thinking approach. This program aims to redefine how critical structures, like rockets, are manufactured on the battlefield using scavenged, locally available materials.
The Need for R2
Traditional manufacturing methods rely on a well-established supply chain of high-quality materials. But in a contested logistics environment, such assumptions can become liabilities. Supply chains can be disrupted, making it difficult or even impossible to obtain the necessary materials. This is where R2 steps in, envisioning a future where soldiers can produce essential equipment using whatever materials are at hand—be it rubble from destroyed buildings, abandoned vehicles, or other salvaged debris.
Breaking Away from Conventional Paradigms
Current production systems are optimized for specific materials and conditions, making them inflexible. If the material input changes, it often necessitates a costly and time-consuming redesign. This rigidity is particularly problematic in a military context, where adaptability and speed are crucial.
The R2 program seeks to overturn this paradigm by creating a flexible manufacturing framework that can adapt to a wide range of materials and conditions. Instead of relying on pristine, factory-produced materials, R2 focuses on utilizing indigenous materials—those that can be scavenged from the environment at the point of need. The program’s goal is to develop a system capable of converting these materials into functional components, such as the structural elements of a sounding rocket.
Current initiatives for forward production of structures are advanced but operate on the premise that high-quality raw materials will always be available, leading to designs that lack the flexibility needed for environments where supply chains are compromised. Material conversion—such as atomization, wire extrusion, and sheet production—typically occurs in large foundries under tightly controlled conditions using pristine materials. This process is not feasible at the point of need, where materials may be scavenged and of varying quality. Structural applications of such materials are limited due to the extensive qualification and analysis required, and the presence of unknowns, such as alloy composition or surface conditions, further restricts their use.
These systems are inflexible; any deviation in material input or operations outside of a controlled factory setting necessitates costly redesigns due to the rigid production and design frameworks. Even minor material changes or alterations to single components require extensive analysis and testing, making the system inflexible and dependent on fixed inputs for fixed outputs.
The program’s scope includes the redesign and fabrication of a sounding rocket using various scavenged feedstocks, with potential applications of this technology extending to other critical needs in similar environments. The key innovation lies in developing a design framework that can account for the system-level effects of materials and components. This would allow both existing and future systems to quickly adapt to new materials and fabrication methods, such as additive manufacturing, thereby significantly reducing the risks associated with adopting new technologies.
The Vision: From Rubble to Rockets
Imagine a scenario where soldiers in a remote or contested area need to launch a rocket but have no access to their usual supply chain. With the R2 system, they could gather available materials—perhaps pieces of destroyed buildings, rusted metal, or even plastics—and convert them into the necessary components for a rocket.
To achieve this, the R2 program focuses on three key areas:
- Material Conversion: Developing technologies that can transform diverse, often contaminated, materials into usable forms. This might include processes like friction stir extrusion of wire from shredded aluminum or the conversion of pulverized glass and metal into new, structurally sound components. R2 aims to demonstrate material conversion at a rate of 0.1 m³/day from scavenged and processed feedstock. This will be verified through iterative design trials and pressure testing of representative rocket motor chambers to simulate peak load survivability.
- Material Characterization: Creating models that can predict the properties of these converted materials with high accuracy. This is essential because the performance of the final product, such as a rocket, depends on the reliability of its materials.
- Adaptive Design: Developing an adaptive design framework that can quickly update a component’s design based on the available materials. This system would need to be efficient enough to run on a standard laptop, enabling soldiers to make real-time decisions about the trade-offs between material quality, structural integrity, and mission requirements. Proposers must demonstrate the ability to rapidly update a government-provided sounding rocket design with new materials. They will be periodically challenged with government-provided material streams within their defined domains of applicability, for which they must predict material properties and update the design within the timeframes specified in the metrics table. Performers should also demonstrate the capability to vary payload size to achieve selected ranges while ensuring the overall design meets the minimum range of 35 km.
Advancements in material conversion techniques and a better understanding of how contaminants affect materials could unlock new possibilities for using widely available, lower-risk materials. This would also improve the supply chain’s resilience and reduce the energy footprint associated with material processing. The R2 program seeks to open these new avenues, making it possible to utilize scavenged materials for structural applications in challenging environments.
Material Families and Processing Parameters
The R2 program categorizes materials into broad families based on their composition and processing requirements. These material families include: Each material family is further defined by its primary constituents, known as base materials. Examples of base materials within each family include:
- Metals: Defined by their primary element, such as iron (Fe) for ferrous metals, aluminum (Al), nickel (Ni), or titanium (Ti).
- Ceramics: Defined by their primary compounds, such as aluminum oxide or yttrium-stabilized zirconia (YSZ).
- Plastics: Defined by their polymer family, such as polyvinyl chloride (PVC), polycarbonate (PC), polyether ether ketone (PEEK), or polyphenylene sulfide (PPS).
- Composites: Defined by their resin and reinforcement combinations, such as polyethylene (PE) with glass fiber or epoxy with carbon fiber.
- Natural Materials: Defined by their primary compound, such as cellulose in wood or paper.
Purity
Purity refers to the percentage of the material stream, by mass, that is composed of the base material(s). It is crucial in determining the quality and suitability of the material for various applications.
Form
The form describes the material’s condition when input into the processing system. Common forms include:
- Bulk Material: Large components or thick sections.
- Particulate: Ground or chipped materials.
- Wire
- Powder
Material Stream
A material stream is a combination of a single material family, base material(s), and form(s). The R2 program encourages the development of processes capable of handling highly diverse material streams, including blended streams that contain multiple material families in varying concentrations. This approach aims to minimize the need for extensive cleaning and sorting of materials at the point of need.
Domain of Applicability
The domain of applicability refers to the range of material streams that a proposed process can handle. Proposers are encouraged to define their domain of applicability broadly, incorporating a diverse array of material streams. Quantitative and qualitative descriptions of the differences between material streams within the domain of applicability are required. Examples of quantitative metrics might include density, melting point, and elastic modulus of the base materials, as well as the characteristic size (length scale) of the material forms.
Proposers should aim for a broad domain of applicability that aligns with the processing capabilities of their proposed technology, with clear pathways for handling various material families and conditions. While DARPA does not expect proposers to cover every possible material family, base material, purity level, or form, competitive proposals will address a wide range of environments and scenarios.
Characterization
A key aspect of the R2 program is the accurate characterization of material properties to enable reliable design predictions. Proposers are tasked with updating and developing material informatics models to predict the minimum material properties of diverse material streams with high confidence. This involves reducing errors in material property prediction to ensure the material can be effectively used in structural applications.
To achieve this, proposers may consider integrating online analysis techniques (e.g., monitoring torque or power usage during material conversion) and rapid testing methods (e.g., hardness testing). However, novel approaches tailored to the specific process and material characteristics are highly encouraged. Proposers should aim to leverage material informatics to enhance the accuracy and reliability of material property predictions, enabling the flexible and adaptive use of diverse materials in structural design.
Material Property Prediction and Adaptive Design Framework
The approach to material property prediction in the R2 program emphasizes working “in reverse”—using new materials to predict property data, rather than starting with material data to predict new materials. This involves predicting the properties of the feedstock and final manufactured product, including any necessary heat treatment or post-processing to enhance material performance. The primary goal is not to fully characterize the material but to efficiently establish a lower bound design value that captures system-level effects. To achieve this, multiple standard mechanical testing and statistical methods can be employed to build and validate predictive models, balancing the improvement of material properties with minimizing errors across a broad solution space.
The program also focuses on developing an adaptive design framework characterized by low computational size, weight, and power (C-SWaP). The objective is to efficiently update a base design to accommodate structural changes for components with newly predicted material properties, ensuring they meet or exceed specified performance metrics. Proposers are encouraged to explore various evolving technologies, such as change propagation analysis and machine learning/artificial intelligence (ML/AI)-assisted finite element analysis (FEA), while alternative or integrated approaches are also welcome to meet the program’s goals.
The adaptive design framework assumes a fixed outer mold line (OML) and maximum flight loads for the government’s sounding rocket design. Proposers are challenged to develop a trained model capable of rapidly (within one hour) updating the design, confirming its viability, and predicting impacts on performance metrics like range based on the available materials. The designs should be manufacturable within the complete system CONOPS, integrating the target manufacturing approach, and require the production of demonstration components to validate both material properties and design performance.
Competitive proposals will feature a low C-SWaP that allows processing on standard-issue laptops or similar basic computing devices, with more complex model training or analysis conducted using alternate computational resources. Additionally, these proposals should enable end-users to understand and make informed trade-offs between range and payload. DARPA is specifically seeking a framework capable of producing versatile, adaptive designs rather than singular point solutions for given materials.
The Path Forward
The R2 program seeks to harness material informatics and cutting-edge processing and manufacturing techniques. These will be implemented through a rapid, iterative design process, culminating in a subscale pressure test validation at the end of each primary phase. The overarching objective is to work with increasingly diverse and unpredictable materials while simultaneously enhancing the complexity and performance of the final structures. The vision for this technology includes the possibility of converting pulverized vehicular, structural, and other complex salvaged materials into manufacturable feedstock.
The R2 program is structured in multiple phases, each designed to progressively push the limits of what can be achieved with indigenous materials:
- Phase 1 (Base): An 18-month effort to establish proof-of-concept. This phase will focus on converting pristine local materials into usable forms and testing them in increasingly challenging environments.Starting with pristine materials, the program aims to predict material properties and adaptively update the structural design of a 200-350mm diameter sounding rocket based on these predictive changes in system-level performance. The goal is to develop a flexible and deployable manufacturing platform capable of adapting various raw materials for structural fabrication. The R2 program focuses on converting feedstock into usable form factors with the highest possible material property performance. The program aims to overcome current limitations in processing diverse, complex, or contaminated indigenous feedstock by developing innovative tooling and processing methods that can accommodate widely variable inputs. By utilizing insights from current material conversion efforts, such as friction stir-extrusion of wire from shredded aluminum, along with advancements in tooling design and process control, conversion systems will transform into material processing units capable of working with scavenged feedstock.
- Phase 2 (Option): Also an 18-month phase, this stage will expand the system’s capabilities, introducing more complex and less pristine materials into the mix. The goal here is to refine the technology to handle a wider variety of materials and conditions.
- Phase 2 Demonstration: This final phase, not yet solicited, would involve a live test—launching a rocket built entirely from converted materials. This would be the ultimate proof of concept, demonstrating that the R2 system can not only adapt to different materials but can also produce fully functional, mission-critical equipment.
Competitive proposals are expected to feature an integrated system that includes novel material conversion technologies, in-line characterization of material properties, and the capability to rapidly iterate component development. This approach will focus on understanding the system-level effects of material variability and deviations, allowing for adaptive final designs that meet the program’s performance metrics. DARPA plans to select a diverse range of performers working with multiple common primary material streams, such as aluminum, steel, plastic, glass, and paper. Proposals should also demonstrate a clear understanding of available, developing, or novel material stream-dependent deployable manufacturing concepts and how these integrate into the overall CONOPS (Concept of Operations) for the R2 system.
The Future of Warfare Logistics
DARPA’s R2 program represents a significant leap forward in military logistics and manufacturing. By enabling the use of scavenged materials, R2 could reduce the military’s reliance on traditional supply chains, making forces more self-sufficient and resilient in the field. This capability could prove to be a game-changer, not only in terms of operational flexibility but also in reducing the logistical footprint of military operations.
In a broader sense, the R2 program could have implications beyond the battlefield. The ability to create high-performance materials from waste could revolutionize industries like construction, recycling, and even space exploration, where resource availability is limited. As DARPA continues to push the boundaries of what’s possible, programs like R2 remind us that the future of technology often lies in the most unexpected places—like the rubble beneath our feet.
