Protection assessment method for advanced Whipple shield based on hazardous fragments

With the increasing threat posed by space debris to the safe operation of on-orbit spacecraft, the Whipple shield, as a critical means of defending spacecraft against hypervelocity impacts, has evolved from conventional single-layer configurations to advanced architectures employing high-performance materials such as fiber-reinforced composites. Advanced shields such as carbon fiber–reinforced composite laminates involve additional energy dissipation through failure modes including fiber fracture, delamination, and melting, resulting in shielding mechanisms that differ significantly from those of traditional Whipple shields. However, the currently predominant ballistic limit equations lack accuracy and generalizability for different advanced configurations, making them unsuitable for direct comparison of shielding performance. Hypervelocity impact experiments are costly and cannot be performed for every configuration, while existing numerical studies have mostly focused on the macroscopic morphology of debris clouds, with insufficient quantitative analysis of the hazardous fragments within them. Therefore, how to establish a method capable of quantitatively evaluating and comparing the shielding performance of different advanced Whipple shields has become a critical technical issue urgently to be addressed in the field of spacecraft space debris protection.

In a recent study published in Space: Science & Technology, researchers from the Institute of Fluid Physics, China Academy of Engineering Physics, proposed a quantitative evaluation method for the shielding performance of advanced Whipple shields based on hazardous fragments. Taking carbon fiber–reinforced composite laminates as a case study, the research employs a finite element–smoothed particle hydrodynamics (FE-SPH) adaptive method combined with mesoscale modeling techniques to simulate the debris cloud formation process resulting from hypervelocity impact of aluminum spheres on the laminates. Through numerical experiments, empirical formulas for the crater diameter and depth induced by fiber fragment impacts on aluminum plates are established, and quantitative criteria for identifying hazardous fragments among carbon fiber fragments and aluminum fragments are defined in conjunction with rear plate parameters. Based on these criteria, hazardous fragments within the debris cloud are screened, mapped into velocity space, and analyzed in terms of quantity, size, distribution range, and angular distribution characteristics of energy density, thereby enabling quantitative assessment of shielding performance. The results indicate that the number and size of projectile fragments in the debris cloud are substantially greater than those of target plate fragments, making them the primary contributors to the damaging potential of the debris cloud. Under low-velocity and small-size projectile conditions, the peak angular energy density of the carbon fiber–reinforced composite laminate is significantly lower than that of an aluminum plate of equal areal density, demonstrating superior shielding effectiveness against low-velocity, small-size space debris. However, under high-velocity and large-size conditions, the difference between the two is not significant. This evaluation framework can be extended to other advanced Whipple shields by replacing the corresponding mesoscale models and material parameters, providing a versatile quantitative analytical tool for the design selection and performance comparison of spacecraft space debris shields.

First, this paper focuses on the quantitative evaluation of shielding performance of advanced Whipple shields against hypervelocity impacts of space debris. Traditional Whipple shields protect spacecraft by causing the projectile to fragment upon impact with the outer bumper, forming a debris cloud that disperses energy and momentum, thereby reducing the risk of rear-wall penetration. With the application of high-performance materials such as fiber-reinforced composites, advanced shields involve additional energy dissipation through failure modes including fiber fracture, delamination, and melting, resulting in shielding mechanisms that differ significantly from those of conventional metallic shields. However, existing ballistic limit equations lack general applicability to different advanced configurations, making it difficult to support performance comparisons among different shield designs. To address this, the study proposes a quantitative evaluation method based on hazardous fragment analysis. Taking a carbon fiber–reinforced composite laminate as a case study, the research employs a finite element–smoothed particle hydrodynamics (FE-SPH) adaptive method combined with mesoscale modeling techniques to simulate the debris cloud formation process resulting from hypervelocity impact of aluminum spheres on the composite laminate and an aluminum plate of equal areal density. Fig. 1 presents the debris cloud morphologies at 5 μs for the carbon fiber–reinforced composite laminate and the aluminum plate with equal areal density, from which significant differences in fragment quantity, size, and spatial distribution between the two materials can be clearly observed.

Second, the study establishes hazardous fragment criteria and systematically analyzes the characteristics of hazardous fragments in the debris cloud of the carbon fiber–reinforced composite laminate. Since the debris cloud contains both aluminum fragments and carbon fiber fragments, and the two materials exhibit different damaging capacities toward the rear plate, separate criteria must be established for each. Through numerical experiments simulating hypervelocity impacts of spherical fiber projectiles on semi-infinite aluminum plates, the study derives empirical formulas for crater diameter and depth, and subsequently establishes quantitative criteria for identifying hazardous fragments and critical hazardous fragments among aluminum and carbon fiber fragments based on rear plate parameters. Hazardous fragments are defined as those capable of producing visible craters with a diameter exceeding 0.5 mm on the rear plate, while critical hazardous fragments are defined as those capable of completely penetrating the rear plate. Based on these criteria, hazardous fragments within the debris cloud are screened. Fig. 2 presents the distributions of the numbers of hazardous fragments and critical hazardous fragments under different operating conditions: with increasing impact velocity and areal density ratio, the number of hazardous fragments gradually increases, whereas the number of critical hazardous fragments exhibits a trend of first increasing and then decreasing, nearly vanishing when the areal density ratio reaches 0.5 or above. Fig. 3 maps the hazardous fragments into two-dimensional velocity space for analysis. It is found that the velocity angles of target plate fragments in the debris cloud of the carbon fiber–reinforced composite laminate are significantly larger than those of projectile fragments but with lower velocities, and their energy contribution accounts for less than 1% of the total hazardous fragment energy, thus being negligible. Consequently, projectile fragments are the primary contributors to the damaging potential of the debris cloud.

Finally, the study quantitatively evaluates the shielding performance of the composite laminate by comparing the differences between the carbon fiber–reinforced composite laminate and an aluminum plate of equal areal density in terms of hazardous fragment distribution range and angular distribution of energy density. Fig. 4 presents the maximum velocity angles of the two shield configurations under different operating conditions. When the areal density ratio is less than 0.4, the dispersion effect of the aluminum plate is superior to that of the composite laminate; however, when the areal density ratio reaches 0.4 or above, the shielding performance of the composite laminate exceeds that of the aluminum plate, indicating that the laminate is more suitable for defending against small-size debris. Fig. 5 presents the angular distributions of energy density of hazardous fragments, with each curve representing a different operating condition. As impact velocity and areal density ratio increase, the peak energy density significantly decreases and the peak position gradually shifts away from the center, indicating that the concentration of hazardous fragments in the debris cloud diminishes and the distribution range expands. Under low-velocity (4–5 km/s) and small-size (areal density ratio ≤ 0.3) conditions, the peak energy density of the carbon fiber–reinforced composite laminate is significantly lower than that of the aluminum plate of equal areal density; under high-velocity (6–7 km/s) and large-size conditions, the difference between the two is not pronounced. The study ultimately proposes a general evaluation framework, as illustrated in the flowchart of Fig. 6, comprising four steps: high-fidelity numerical simulation, hazardous fragment analysis, comparison with an aluminum plate of equal areal density, and comprehensive shielding performance evaluation. By replacing the corresponding mesoscale models and material parameters, this framework can be extended to the shielding performance evaluation of other advanced Whipple shields.