This work concerns defense guidance problems for 3-player target–defender–attacker engagement scenarios, in which the defender is launched to capture the incoming attacker in advance of the target being hit; a line-of-sight (LOS) triangle-based prescribed-time guidance is derived as an interception strategy for the defender. Integrating both the attacker–target and defender–attacker perspectives into the relative engagement model, the 3-player nonlinear engagement model is deduced considering the second-order lag dynamics of the actuator. Next, to reduce the defender and attacker overload ratio, the LOS triangle-guidance concept is presented to keep the defender on the LOS frame between the attacker and the target, in which the lateral overloads of the defender and attacker cancel each other out. In addition, in order to achieve perfect capture of the attacker in advance, the prescribed-time control can preallocate convergence time such that the defender can be guided and kept at the LOS frame between the attacker and the target in the preset time. What is even more unique is that the proposed guidance law design ignores the maneuvering of the attacker; i.e., the overload of the attacker is unknown, which is treated as a disturbance and estimated by the improved adaptive law. Numerical simulations are executed to validate performance and superiority, which has potential application value.

The combination of increased amount of “space junk”, lack of precise tracking information and control of items orbiting Earth, and debris from past collisions posed important threats to human space missions. In this study, a strategy enabling “multispacecraft to multidebris” debris removal task is proposed. By analyzing the current distribution of space debris, 282 large debris and rocket bodies are selected as target database. The traditional-density-based spatial clustering of applications with noise algorithm is innovatively modified by defining the speed increment as threshold parameter for dividing target debris into different clusters. Then, the Hungarian-algorithm-based target allocation strategy is used to assign multispacecraft to different debris clusters for the removal mission. Simulations verify the effectiveness of the proposed “multispacecraft to multidebris” strategy that is able to remove as much as 83.33% of the total 282 target debris.

Periodic orbits are crucial in facilitating the understanding of the dynamical behavior of elongated asteroids. As a specific type of periodic orbit, resonant orbits can enrich the orbit design method of deep-space exploration missions. Herein, a dipole segment model for investigating the orbital dynamics of elongated asteroids is briefly introduced. A new numerical algorithm named the modified path searching method for identifying spin–orbit resonant orbits is proposed. Using the modified path searching and pseudo-arclength continuation methods, four spin--orbit resonant families for asteroid 2063 Bacchus are obtained. The distribution of eigenvalues and stability curves for the four resonant families are presented. In particular, some critical points corresponding to period-doubling and tangent bifurcations appear in the stability curves.

Stability for the non-autonomous bicircular four-body model is analytically investigated in this study. The governing equation is derived from Newton’s law of gravity. When the distance between the infinitesimal mass and the third primary is expanded as Taylor expansions, the governing equation can be regarded as two parts: the unperturbed conservative system and the small periodically parametric excitations. The unperturbed system’s natural frequency and parametric frequency are analyzed for the possibility of principal parametric resonances. The method of multiple scales is applied directly to the governing equation. The stability conditions are obtained analytically for the principal parametric resonance. Numerical method demonstrates the efficiency of the analytical results.