During testing of a shaped charge that was intended as a third-stage self destruct mechanism, we gathered data on the fragmentation of an Al 6061-T6 case surrounding a shaped charge. Witness packs were placed around the charge in an arena-like configuration. These packs, comprised of Al 2024-T351 sheets and plywood, were placed 101 cm from the charge. Direct line-of-sight data was collected on two witness packs. A total of 161 fragments were recovered. The size and weight of each of these fragments was measured. The shapes of the fragments were analyzed as well as the fragment mass-cumulative mass distribution. These results are compared with fragmentation results with Al 2024-T351 where the fragmentation was caused by impact rather than explosive loading. The shaped charge-case fragments are more typically borderline in shape between flat and brick like, whereas the fragments from the hypervelocity impact (crater ejecta) are predominantly flat.

Orbital debris impacts on spacecraft are an emerging threat to space missions due to the exponential increase in the number of satellites orbiting the Earth. Debris characteristics (size, material, velocity, etc.) are not well known for the size range of 10 mm or less that is undetectable using Earth telescopes or radar observation. The objective of this research was to determine wether a concept designed to detect impact of particles in the similar to 1 to 5 mm range, find the location of the impact, and characterize the impacting projectile (velocity, size, angle, density), is feasible. The paper describes the design, fabrication, and tests performed on "witness plates" (the concept) made of two parallel layers of additively manufactured aluminum and instrumented with sixteen gages, eight on each layer. Laboratory experiments have shown that the waves can be recorded and properly interpreted to find location of impact, sound speed in the plate, and to estimate impact velocity. It was shown analytically that the amplitude of the first strain wave that propagates from the impact point is expected to decay as 1/r. This was observed as well in the signals recorded in the experiments. CTH computations were performed during the pre-test design phase and the post-test analysis phase. In fact, the numerical simulations have been key and pervasive in this research effort as they provided invaluable insight for the initial design and the correct interpretation of signal anomalies seen during the tests. Additionally, the computations confirmed the 1/r law derived analytically, i.e. that the assumptions for the derivation were justified. The main conclusions of the research are that, for a normal impact, the 1/r law for front gages can be easily used to determine the diameter of the impactor. It is possible that the back gages could be used to determine the density of the impactor as well. Finally, it was shown that oblique impacts generate an expected assymetry in the signals recorded. Though this aspect should be investigated further, the assymetry is probably uniquely related to the impact angle, which could provide the angle information.

V-shaped hulls for vehicles, to mitigate buried blast loads, are typically formed by bending plate. Such an approach was carried out in fabricating small test articles and testing them with buried-explosive blast load in Southwest Research Institute’s (SwRI) Landmine Test Fixture. During the experiments, detailed time dependent deflections were recorded over a wide area of the test article surface using the Dynamic Deformation Instrumentation System (DDIS). This information allowed detailed comparison with numerical simulations that were performed with LS-DYNA. Though in general there is good agreement on the deflection, in the specific location of the bends in the steel the agreement decreases in the lateral cross section. Computations performed with empirical blast loads developed by SwRI and by more computationally intensive ALE methods in LS-DYNA produced the same results. Computations performed in EPIC showed the same result. The metal plate was then bent numerically so that the initial plate had both hardening and residual stresses from the fabrication. When blast loaded, though the deflection reduced due to the hardening in the bends in the plate, the qualitative disagreement with the lateral cross section remains. The study then focused on the material strength model for the steel. It was observed that the difference in behavior between the experiments and the computations occurs in a region where the hull metal is unloading from its formative bend. It is argued that using a kinematic yield surface with hysteresis, rather than an isotropic one with no hysteresis as is commonly done with the Johnson-Cook model, better models the unloading and hence can better match the deformation seen in the experiments.

NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1 σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β , resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.

Tools have been developed to compare the dynamic deformation of vehicle hulls as they undergo blast-testing with numerical simulations. These tools allow quantitative comparisons and measurements over a wide area of the hull surface, rather than point comparisons as have been performed in the past. The experimental measurements are performed with the Dynamic Deformation Instrumentation System (DDIS) that was developed for TARDEC. Numerical simulations of the test article attached to Southwest Research Institute’s Landmine Test Fixture were performed with LS-DYNA using an empirical blast-loads model. The specific example highlighted in this paper is the deformation by blast testing of a hull component.

As part of DARPA’s Adaptive Vehicle Make (AVM) portfolio of programs, blast and ballistic survivability analysis tools were developed. The intent of these tools was to facilitate design and design optimization by making it possible for designers to perform survivability analysis from CAD and to automate the survivability analysis pipeline to allow optimization codes to invoke the survivability tools and obtain results. This paper describes some of the tools and their capabilities through highlighting five innovations utilized in the program: multi-fidelity modeling; automated meshing and welding; uncertainty quantification and 95% bounds; a large material property database and more accurate blast loads; and automating the entire computational pipeline.

Utilizing a large two-stage light gas gun and a large pendulum assembly, experiments were performed to measure the momentum enhancement (or increase in momentum transfer due to the ejecta) of an ARMCO iron target, two large hematite rock targets, a target of stones held by concrete, and a concrete block target. The choice of iron and iron rich materials was motivated by interest in the asteroid Psyche and the planned upcoming mission. The target comprised of a collection of stones, to mimic a rubble pile asteroid, was to provide insight into the Double Asteroid Redirection Test (DART) impact. The role of impactor size is important, and these tests were performed at a large scale, with 3-cm-diameter aluminum spheres as the impactor. Save for the concrete block, these impacts were in the vicinity of 5 km/s. There is a distinct difference in the amount of momentum enhancement (measured by & beta;) that occurs with ductile metals vs. brittle materials and this fact shows in these impacts. The momentum enhancement with a relatively brittle aluminum falls in between the two extremes of rock and iron. Computations were performed to compare with the ARMCO iron impacts. Data at a large scale is desirable to quantify momentum enhancement in the context of hypervelocity impactors deflecting celestial bodies such as asteroids or comet nuclei.

We present AircraftVerse, a publicly available aerial vehicle design dataset. Aircraft design encompasses different physics domains and, hence, multiple modalities of representation. The evaluation of these cyber-physical system (CPS) designs requires the use of scientific analytical and simulation models ranging from computer-aided design tools for structural and manufacturing analysis, computational fluid dynamics tools for drag and lift computation, battery models for energy estimation, and simulation models for flight control and dynamics. AircraftVerse contains 27,714 diverse air vehicle designs - the largest corpus of engineering designs with this level of complexity. Each design comprises the following artifacts: a symbolic design tree describing topology, propulsion subsystem, battery subsystem, and other design details; a STandard for the Exchange of Product (STEP) model data; a 3D CAD design using a stereolithography (STL) file format; a 3D point cloud for the shape of the design; and evaluation results from high fidelity state-of-the-art physics models that characterize performance metrics such as maximum flight distance and hover-time. We also present baseline surrogate models that use different modalities of design representation to predict design performance metrics, which we provide as part of our dataset release. Finally, we discuss the potential impact of this dataset on the use of learning in aircraft design and, more generally, in CPS. AircraftVerse is accompanied by a data card, and it is released under Creative Commons Attribution-ShareAlike (CC BY-SA) license. The dataset is hosted at https://zenodo.org/record/6525446, baseline models and code at https://github.com/SRI-CSL/AircraftVerse, and the dataset description at https://aircraftverse.onrender.com/.

To answer the needs presented by DARPA’s symbiotic design for cyber physical systems challenge, a fast-running, analytical aerodynamic model is developed to guide artificial intelligence systems in the design of unmanned aerial vehicles. As part of the program, aircraft are assembled using a corpus of parts, including commercial off-the-shelf and a few parametric components. Aerodynamic information of the design is required for simulation in a six degree-of-freedom flight dynamics code. In the analytical model, each corpus part is assigned a primitive shape which resembles the part geometry, including cylinders, streamline bodies, and plates/boxes. Appropriate transforms for each primitive are applied such that a surrogate aircraft is constructed, which is then aerodynamically analyzed. The model computes coefficients of lift and drag over a range of pitch angles and freestream velocities individually for each part. Aerodynamic interference between pairs of parts is considered for every pitch angle using analytical relationships and the surrogate aircraft geometry. The model’s estimation of drag enables the simulation of the artificial intelligence created designs and provides a source of feedback to encourage logical aerodynamic design choices.

The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on September 26, 2022 as a planetary defense test. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defense, intended to validate kinetic impact as a means of asteroid deflection. Here we report the first determination of the momentum transferred to an asteroid by kinetic impact. Based on the change in the binary orbit period, we find an instantaneous reduction in Dimorphos's along-track orbital velocity component of 2.70 +/- 0.10 mm/s, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact. For a Dimorphos bulk density range of 1,500 to 3,300 kg/m$^3$, we find that the expected value of the momentum enhancement factor, $\beta$, ranges between 2.2 and 4.9, depending on the mass of Dimorphos. If Dimorphos and Didymos are assumed to have equal densities of 2,400 kg/m$^3$, $\beta$= 3.61 +0.19/-0.25 (1 $\sigma$). These $\beta$ values indicate that significantly more momentum was transferred to Dimorphos from the escaping impact ejecta than was incident with DART. Therefore, the DART kinetic impact was highly effective in deflecting the asteroid Dimorphos.

When a high speed or hypervelocity impact occurs, a crater is formed. Size scaling of this event is of interest, meaning, for example, how the crater properties change as the projectile size increases. While penetration depth normalized by projectile radius is fairly insensitive to projectile size, there are other aspects of the cratering process that are quite sensitive to the size of the projectile, including mass of material liberated as ejecta and the amount of momentum that ejecta material has. It is show that there is reasonably good understanding of ejecta mass, but momentum enhancement is still a challenging topic, which we show through experimental results with two aluminums. We also discuss the same effects in concrete targets and the possibility of obtaining more understanding of the size scaling process with the upcoming DART impact into an asteroid.

The Double Asteroid Redirection Test (DART) spacecraft will impact into the asteroid Dimorphos on 2022 September 26 as a test of the kinetic impactor technique for planetary defense. The efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β , which is dependent on factors such as impact geometry and the specific target material properties. Currently, very little is known about Dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β . The DART Impact Modeling Working Group (IWG) is responsible for using impact simulations to better understand the results of the DART impact. Pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. This insight provides a basis for predicting the effects of the DART impact and the first understanding of how to interpret results following the encounter. Following the DART impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of Dimorphos and β resulting from DART’s impact. This paper summarizes, at a high level, what has been learned from the IWG simulations and experiments in preparation for the DART impact. While unknown, estimates for reasonable potential material properties of Dimorphos provide predictions for β of 1–5, depending on end-member cases in the strength regime.

To prepare for two NASA missions, Southwest Research Institute has been performing both laboratory tests and hydrocode computations of impacts at velocities between 2 and 5.5 km/s on rocks like pumice, sandstone, hematite, concrete, and on metals like aluminum and pure iron (ARMCO iron). All the targets were mounted on pendulums so that the momentum imparted by the projectile to the target could be measured. Note that, in general, the momentum acquired by the target after the impact is larger than the momentum of the projectile. This is due to the additional momentum from the ejecta that flies off the target in the opposite direction to the direction of the impact. Hydrocode computations with CTH and EPIC followed the experiments. This paper will present the laboratory results specifically on ARMCO iron, a material considered a “benchmark”, and the strength and weaknesses of the computations performed.

Abstract SwRI is developing a technology that will enable detection and characterization of micrometeoroid orbital debris (MMOD) while on-orbit. The technology includes an instrumented aluminum panel that can be installed on a satellite and, with the appropriate sensor and software suite, is able to detect and characterize impacts during the mission. The stress waves produced by the impact on the panel will be selected on-board by the software, treated, and sent to the ground for further analysis. The selection process will be directed by an algorithm that will be developed based on the experimental campaign and stress wave theory. CTH computer simulations in 2D and 3D were performed to study the viability and design the technology. Fully instrumented witness panels are being tested (August 2022) under hypervelocity impact using SwRI’s 0.17 in caliber two-stage light-gas gun. The small-scale panels were placed in the target tank to be impacted multiple times at velocities up to 6 km/s by a 3-mm al6061-T6 sphere. As expected, the strain magnitude depends on the distance to the impact point and, in general, decreases with distance.

Abstract Utilizing a large two-stage light gas gun, 3-cm-diameter spheres were impacted into Al 2024-T351 targets. The fragments were collected from the floor of the impact chamber and were analyzed. In particular, there is interest as to the fragment size distribution and the fragment shape distribution. The fragments were sorted in size, and those from roughly 0.1 g to 35 g were individually tabulated. This allowed the development of a fragment size distribution for these fragments. Then, all the fragments were optically analyzed to provide a quantitative characterization of their shape. The fragments are predominately flat, a shape that appears to correlate with an intersecting shear plane mechanism for the fragment formation in the crater formation. The fragment distribution shows that there are two different fragment formation mechanisms, which it is concluded are due to fragments formed in the interior of the crater entirely of interacting shear planes vs. those whose formation is influenced by the target free surface. The results are compared to other work on fragmentation.

An impact experiment was performed with a target of relevance to the upcoming DART impact. In this experiment, a collection of stones that is similar to a rubble pile was the target, though it was necessary to hold the stones in place (in this case with cement) since the target was hung vertically to perform the experiment. The stones–cement target has a higher density and a lower porosity than expected for Dimorphos, with the density being 2.92 g cm −3 . A 3 cm diameter aluminum sphere was launched at a speed of 5.44 km s −1 , which is similar to the anticipated 6.1 km s −1 impact speed of DART. The stones–concrete target was completely disassembled by the impact. The target was mounted on a pendulum. The swing of the pendulum was measured and from it the momentum enhancement β = 3.4 − 1.0 + 0.1 was measured. Due to possible lateral expansion of debris material, this value is a lower bound on the momentum enhancement that would be imparted to an extended target.

As part of DARPA's Symbiotic Design for Cyber Physical Systems program, software tools were developed for a UAV and air taxi eVTOL design challenge. These included the development of a corpus of parts, an assembly technique, and then a 6-degree-of-freedom flight dynamics model with an autopilot based on trim states and a linear quadratic regulator to fly the assembled air vehicle. This paper describes the flight dynamics model and autopilot and controls in some detail. It also presents examples of parts, designs and performance.

Automated design processes, especially using Machine Learning/AI techniques, require proposed systems to be evaluated across all relevant attributes, requirements, and concerns. Traditionally, teams create models in a set of engineering tools for design evaluation data. We describe a Design Oracle, where automated designers can submit a system as a graph of components and request a full range of evaluations, composing analysis workflows containing multiple engineering tools across multiple physical domains, fidelity, and scenarios. Manually created system models are not required. The system works across cloud architectures, supporting the use of parallel computation.The system leverages technology developed under the DARPA Adaptive Vehicle Make/META program, which created a uniform, multi-domain design and component representation, and tools for composition to engineering tool models across multiple tool types, domains, and fidelity levels [1]. The Design Oracle has been used within the DARPA Symbiotic Design for Cyber-Physical Systems, across two classes of target designs, Unmanned Air Vehicles and Unmanned Underwater Vehicles.

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