Spacecraft Close-Proximity Operations

Dear Colleagues,

Robust trajectory optimization, uncertainty modeling, non-cooperative targets:

In recent years, uncertainties and robust trajectory optimization have gradually become core research topics in close-proximity spacecraft operations. In particular, missions involving non-cooperative space targets are characterized by incomplete information and complex constraints, where safety remains the primary objective. Uncertainties mainly arise from dynamic model errors, inertia parameter identification errors, external disturbances such as aerodynamic effects, non-spherical gravity perturbations, solar radiation pressure, and actuator errors, as well as relative navigation and attitude estimation errors. These uncertainties significantly degrade the safety and success rate of close-proximity operations and, if not properly accounted for during trajectory optimization, may lead to collision risks or even mission failure. Robust trajectory optimization for spacecraft close-proximity operations under uncertainty refers to the design of trajectories that guarantee safety, feasibility and robustness in the presence of multiple sources of uncertainty during rendezvous, formation flying and inspection missions. Such approaches are typically grounded in deterministic optimal control theory and incorporate uncertainty modeling and constraints to quantify and mitigate risks at the trajectory design stage. Representative methods include min–max formulations, tube-based model predictive control strategies and stochastic, chance-constrained, and distributionally robust optimization. In practical engineering applications, robust trajectory planning often involves the treatment of complex multiple constraints in order to satisfy convexity and deterministic representations.

small-body exploration:

Small-body exploration serves as the foundation and prerequisite of planetary defense missions. Its strong similarities to spacecraft close-proximity operations in terms of modeling approaches, methodological frameworks and problem focus mean that it can be regarded as a generalized form of close-proximity operation. Compared with conventional earth-orbit missions, small-body exploration missions face significantly stronger uncertainties, including in mass, density and inertia distribution, irregular gravitational field modeling errors, rotational state uncertainty and relative navigation and attitude estimation errors, as well as external disturbances such as solar radiation pressure and ejecta. The pervasive presence of uncertainty imposes stringent requirements on the robustness of trajectory planning. Moreover, under deep-space and long-distance mission conditions, significant communication delays necessitate a high degree of autonomy in trajectory planning and execution.

spacecraft swarm covert maneuver:

With the increasing complexity of the space environment, the covert spacecraft swarm maneuvering has become an emerging and urgent research frontier. Covert-maneuver trajectory planning for spacecraft swarms refers to the design of maneuver trajectories in close-proximity multi-spacecraft cooperative missions where formation keeping, mission coordination and safety constraints are satisfied while the exposure probability of high-value spacecraft under space situational awareness surveillance is minimized, thereby achieving swarm-level covert objectives. This research topic typically involves cooperative trajectory planning for multiple spacecraft, modeling of no-fly zones and observation constraints, and the realization of coordinated covert maneuvers within multi-agent cooperative control frameworks using centralized or distributed planning strategies.

stealth attitude planning:

Stealth attitude maneuver planning for spacecraft refers to the design of active attitude maneuver strategies during close-proximity cooperative missions, with the objective of reducing the detectability, identifiability and trackability of a spacecraft by space situational awareness systems while satisfying pointing accuracy, attitude stability and actuator constraints. The stealth characteristics of a spacecraft are strongly coupled with its relative attitude with respect to observers and are commonly characterized using radar scattering properties, infrared radiation signatures, visible-light reflection characteristics and line-of-sight geometry. Stealth attitude maneuver planning is typically formulated as a multi-objective optimization problem, in which observability metrics are incorporated as cost functions or constraints and balanced against conventional performance indices such as fuel consumption and maneuver time, while simultaneously satisfying nonlinear attitude dynamics, actuator saturation, angular rate limits and forbidden pointing region constraints.

space manipulators:

With the increasing complexity of on-orbit servicing, life extension and space debris removal missions, free-floating base space manipulators, high-degree-of-freedom redundancy and multi-arm cooperation have become central research frontiers in space robotics. The strong dynamic and kinematic coupling between space manipulators and free-floating bases makes conventional planning and control methods inefficient for modeling and solving problems in high-dimensional configuration spaces. Manifold optimization approaches embed the high-degree-of-freedom configurations of space manipulators into manifold structures and directly solve optimal trajectories and control strategies on constrained manifolds using Riemannian optimization theory, thereby significantly reducing planning complexity. In dual-arm cooperative motion planning under free-floating base conditions, it is necessary not only to minimize base disturbances but also to coordinate the highly coupled motions of the two arms while simultaneously addressing collision avoidance and singularity avoidance issues.

Prof. Dr. Shunli Li
Guest Editor

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• robust trajectory optimization
• uncertainty modeling
• non-cooperative targets
• spacecraft swarm covert maneuvers
• stealth attitude planning
• space manipulators
• small-body exploration