Safe Deployment Strategies for Two CubeSats in Rendezvous, Inspection and Docking Missions

The ability to perform rendezvous, close inspection and docking operations between small-satellites represents a critical technological challenge for in-orbit assembly and close-proximity operations between multiple space segments. Although most small-sat launches are carried out in rideshare or piggyback mode, and are therefore subject to the constraints imposed by the main customer, some launchers allow preferences to be expressed regarding release conditions, i.e. the direction and timing of the release. In a launch of multiple satellites involved in close proximity, a planned release strategy can greatly facilitate the operations regarding phasing and homing in orbit. This work investigates the deployment strategy of two 12U CubeSats involved in a RendezVous and Docking (RVD) mission through a sensitivity analysis on a case study. The simulation takes into account various conditions: the impact of random tumbling motion and solar panels deployment for drag computation, different release directions, ballistic differences between the satellites, and different release times. On one hand, the analysis focuses on the safety of the release, ensuring that the distance and relative drift between the satellites do not lead to a risk of collision. On the other hand, a driver for this category of missions is to reduce the distance accumulated during the commissioning period, i.e. when the propulsion system cannot operate, in order to avoid phasing manoeuvres of excessive durations or too expensive in terms of $\Delta v$. The analysis is conducted through a parametric in-house developed Matlab tool, built around a validated high-fidelity propagator, which post-processes the resulting relative state. The simulation data is then masked, verifying the safety requirements and providing a graphical overview of the relative position between the two satellites, any collision events and the final range values after the designated commissioning period. The analysis ranks the release parameters by the separation they produce at the end of commissioning, and shows how the release direction and the magnitude of the separation impulse lead to significant differences in the relative motion, greatly impacting the $\Delta v$ required for phasing manoeuvres, while the release sequence and delay govern the minimum distance reached by the pair. The analysis results show how to tailor deployment strategies to mission requirements and how to exploit release parameters to improve timing and cost of operations, reducing mission expenses for ground personnel and saving propellant for other RVD phases.