Analysis of docking manoeuvres for 12U Cubesat with a collaborative mothercraft

The use of CubeSats as drones for inspecting the collaborative mothercraft is one of the most interesting in-orbit service missions for this kind of small spacecraft. The most challenging operation in this context is the retrieval of the CubeSat by the mothercraft after the inspection phase especially because any violation of safety constraints must be avoided. A well-established docking strategy in nominal and off-nominal conditions is fundamental already during the preliminary design phases. The present paper shows drivers and requirements that identify a set of design parameters on the state boundaries of the CubeSat, its main features, and the uncertainties due to the space environment and the system uncertainties. After the choices of the guidance, navigation, and control strategies and architectures, simulation sessions lead to an assessment of the robust performance in nominal conditions. Then, the off-nominal conditions are deduced and new simulation sessions confirm the capability of the system to react against discrepancies between actual state and desired state and system failures. The proposed solution is applied to a 12U CubeSat mission that will be released and, in case, retrieved by a mothercraft for observation purposes. The paper highlights the solution's effectiveness in nominal conditions, and when an error occurs in the approach velocity and failures affect the propulsion system, as an example of the entire analysis.