Advanced Control Strategy Enables Effective Surrounding of Noncooperative Targets by Spacecraft Formations

Advanced Control Strategy Enables Effective Surrounding of Noncooperative Targets by Spacecraft Formations
by Simon Mansfield
Sydney, Australia (SPX) Aug 30, 2024

Researchers at the Beijing Institute of Technology have developed a sophisticated control strategy for spacecraft formations, enabling them to surround noncooperative targets effectively within a finite time. This development could play a key role in future space missions where precise formation flying and target interaction are crucial.

The research team introduced a comprehensive model of spacecraft relative orbit dynamics, laying the groundwork for a control algorithm that allows a spacecraft formation to enclose a target within the convex hull formed by the member spacecraft. The concept is illustrated through detailed simulations that demonstrate the dynamics of the process.

Central to the strategy is the communication between spacecraft, articulated through graph theory. The system is defined by the Laplacian matrix (L), which describes the interconnections between the spacecraft, and the communication matrix (B), which links the reference spacecraft to the others in the formation. For the mission to succeed, it is assumed that at least one spacecraft in the formation has access to the target's orbital information.

The study models the dynamics in a local-vertical local-horizon coordinate system, taking into account the similarities between the target and the formation members. The desired positions of each spacecraft relative to the target are established, and the researchers define the spacecraft formation relative orbit error. Using these parameters, they derive an error dynamics model, emphasizing that only neighboring spacecraft with established communication links can exchange information.

An innovative observer and controller were then designed to estimate unknown dynamics and ensure the formation successfully surrounds the target. A novel finite-time extended state observer (FTESO) was developed to rapidly estimate disturbances impacting the formation, given that the target is noncooperative and does not share information. The FTESO was shown to outperform traditional linear extended state observers (LESO) in simulations, offering quicker convergence and smaller observation errors.

The effectiveness of this control strategy was demonstrated through numerical simulations involving four spacecraft attempting to surround a noncooperative target. The simulations revealed that the spacecraft, initially not forming an enclosure, successfully moved to desired positions, forming a tetrahedron around the target. The FTESO method proved superior in minimizing errors and achieving faster convergence compared to LESO.

This research opens avenues for future studies that will address additional constraints in practical applications, such as maneuver limitations and collision avoidance among spacecraft.

For more detailed information, refer to the publication: 'Noncooperative Target Finite-Time Surrounding Control of Spacecraft Formation' (http://dx.doi.org/10.34133/space.0156).