  The paper considers autonomous rendezvous maneuver and proximity operations
of two spacecraft in presence of obstacles. A strategy that combines guidance
and control algorithms is analyzed. The proposed closed-loop system is able to
guarantee a safe path in a real environment, as well as robustness with respect
to external disturbances and dynamic obstacles. The guidance strategy exploits
a suitably designed Artificial Potential Field (APF), while the controller
relies on Sliding Mode Control (SMC), for both position and attitude tracking
of the spacecraft. As for the position control, two different first order SMC
methods are considered, namely the component-wise and the simplex-based control
techniques. The proposed integrated guidance and control strategy is validated
by extensive simulations performed with a six degree-of-freedom (DOF) orbital
simulator and appears suitable for real-time control with minimal on-board
computational effort. Fuel consumption and control effort are evaluated,
including different update frequencies of the closed-loop software.
