A Four-Steps Analysis for Safe Trajectories Assessment of a RVD Mission of Small Satellites

This paper presents a four-step analytical framework designed to ensure the safety of rendezvous and docking missions involving small satellites, which are often constrained by limited thrust and computational resources. The methodology begins with the definition of a nominal trajectory, establishing a "performance tube" that incorporates navigation and propulsion uncertainties, verified through Monte-Carlo simulations to assess Absolute Performance Error (APE) and Keep-Out Zone (KOZ) compliance. The second step focuses on identifying passive safety by simulating uncontrolled motion during critical phases to detect potential collision risks. For non-passively safe scenarios, the third step defines Collision Avoidance Manoeuvres (CAM) optimized for Delta-V efficiency, ensuring the chaser maintains a safe distance while remaining positioned for subsequent docking attempts. Finally, single-failure conditions in navigation and propulsion are modelled to evaluate system robustness under off-nominal states. The framework is applied to two case studies: a 12U CubeSat docking with a larger spacecraft and a 12U-to-12U CubeSat mission. Results demonstrate the method's effectiveness in providing a comprehensive safety assessment and supporting the definition of robust guidance strategies for proximity operations.