Impact ejecting is a critical part of the impact process and plays a pivotal role in engineering applications and scientific analyses in deep space exploration. Its importance extends to space missions such as asteroid surface anchoring for mission stability, impact sampling for scientific analysis of extraterrestrial materials, kinetic impact deflection for planetary defense strategies, and the detailed analysis of ejecta deposition patterns on planetary surfaces to understand surface evolution and regolith dynamics. With small asteroids whose surfaces are commonly covered with regolith, granular targets are employed in laboratory settings to simulate the impact ejecting process. This paper presents a review of the research progress concerning the behavior of impact ejecting on granular targets. The formation process of impact ejecting and methods for describing ejecta curtains are evaluated. An analysis of the dimensional similarity laws governing impact ejecta, along with their applicability and limitations, is conducted. Additionally, the influence of factors, such as target material parameters, impact conditions, target surface morphology, and impactor shape and structure, on impact ejecting behavior is summarized. Finally, existing research challenges are objectively identified, and potential directions for further scientific research about the behavior of impact ejecta on granular targets are proposed.

As an essential tool for realistic description of the current or future debris environment, the Space Debris Environment Engineering Model (SDEEM) has been developed to provide support for risk assessment of spacecraft. In contrast with SDEEM2015, SDEEM2019, the latest version, extends the orbital range from the Low Earth Orbit (LEO) to Geosynchronous Orbit (GEO) for the years 1958–2050. In this paper, improved modeling algorithms used by SDEEM2019 in propagating simulation, spatial density distribution, and spacecraft flux evaluation are presented. The debris fluxes of SDEEM2019 are compared with those of three typical models, i.e., SDEEM2015, Orbital Debris Engineering Model 3.1 (ORDEM 3.1), and Meteoroid and Space Debris Terrestrial Environment Reference (MASTER-8), in terms of two assessment modes. Three orbital cases, including the Geostationary Transfer Orbit (GTO), Sun-Synchronous Orbit (SSO) and International Space Station (ISS) orbit, are selected for the spacecraft assessment mode, and the LEO region is selected for the spatial density assessment mode. The analysis indicates that compared with previous algorithms, the variable step-size orbital propagating algorithm based on semi-major axis control is more precise, the spatial density algorithm based on the second zonal harmonic of the non-spherical Earth gravity (J₂) is more applicable, and the result of the position-centered spacecraft flux algorithm is more convergent. The comparison shows that SDEEM2019 and MASTER-8 have consistent trends due to similar modeling processes, while the differences between SDEEM2019 and ORDEM 3.1 are mainly caused by different modeling approaches for uncatalogued debris.

Hypervelocity impacts of Micrometeoroid and Orbital Debris (M/OD) may lead to catastrophic failure of long-term flight manned spacecraft in orbit. Risk assessment for manned spacecraft in M/OD environment is of great significance for the safety of human space missions. For typical catastrophic failure modes of manned spacecraft such as gas-leakage-induced astronaut hypoxia, sealed cabin fracture, and spacecraft breakup, catastrophic failure assessment method using critical perforation diameters and critical crack lengths of sealed cabins and critical fragment size of spacecraft breakup as failure criteria are proposed. In addition, corresponding modules of catastrophic failure assessment were developed and integrated with Meteoroid and Orbital Debris Assessment and Optimization System Tools, providing an effective assessment tool for researching on the safety of manned spacecraft. On the basis of which, catastrophic failure evaluation of sealed cabin for a specific ultralarge manned spacecraft in the M/OD environment was conducted, providing references for on-orbit mission safety evaluation.