## 6 Conclusions  
The aim of this work was to elaborate and demonstrate how Close-Proximity Operations can be successfully achieved, in particular for the case study of the ClearSpace-1 mission. It was demonstrated that, as follows:  
* The guidelines of [11] are well posed and can be adopted in general, providing methods for design, development, and validation in other missions from the perspective of GNC, Mission Analysis, and the Concept of Operations;
* The approach zones are well defined, being mutually exclusive, and with clear entry criteria;
* The corridors were defined, and the corresponding contingency actions (Abort and Cancel) were shown to be effective in achieving active and passive safety;
* The GNC subsystems were defined to achieve the goal of safely operating around a non-cooperative target: \(\odot\) The Navigation operated in the presence of external interferences (Earth behind the target and illumination conditions), providing for a continuous estimate of the relative state. Furthermore, the nature of the estimate was enhanced as the proximity was reduced, going from angle-only in Client Phasing, to 6 DOF at Close Rendezvous;
* The control was robust to perturbations and other effects found in the CPO phases, attaining the desired performance levels;
* Guidance strategies based on ROEs were designed to allow for inspection. Also, the close-proximity profiles were compliant with aspects such as the control authority and the capability to assess the decision points criteria for the go/no go. * The combination of a dedicated fast simulator with a high-fidelity simulator proved effective for the validation of active safety (CAM). The fast simulator enabled extensive testing of the initial states to identify worst-case configurations that were reproduced and investigated in detail in the high-fidelity simulator. There is a known balance between applicable requirements and the cost of compliant solutions. Conservative requirements can impose unnecessary costs or even the unfeasibility of a commercial service, whereas a relaxation of the requirements can yield undesired consequences. The guidelines verified and validated were formulated for general ADR and IOS application and were shown to be correctly defined and achievable for the CS-1 mission, setting the ground for other commercial solutions to follow. The guidelines derived are agnostic to target dimensions, being scalable to bodies of different sizes. The dimensions of the ROE ellipses and of the Approach and Abort  
Figure 23: Cancel simulation with a stop at FKP (**a**) and with a failed stop-hop (**b**). corridors should be scaled to consider the larger/smaller regions for the involved targets. In particular, smaller targets may allow for an abort corridor with a closer proximity to the PNR, and a PNR closer to the target. Regarding ground intervention, the solutions were designed to be independent of ground services, with on-board guidance, navigation, control and FDIR algorithms that are autonomous, and an interface with the ground only in monitoring and at go/no go at the decision points. Autonomy is a key characteristic for ADR and IOS missions, in particular for constellations or large-scale debris removal. The approach adopted in CS-1 is driven towards full autonomy, and it is expected that ground control will be relieved as in-flight experience demonstrates the reliability of the derived solutions. Future work may address generalization to rendezvous in other scenarios, such as small asteroids and small bodies, which have similarities (forced approach for capture and a combination of simulators for validation) as well as challenges (very limited ground communication and hence a high GNC autonomy). Conceptualization, J.V. and S.G.; methodology, J.V., S.G., T.A., C.B. and A.C.; software, J.V., S.G., T.A. and C.B. ; validation, J.V., S.G., T.A. and C.B. ; writing--original draft preparation, S.G.; writing--review and editing, J.V. and C.B. ; project administration, A.C. and A.F.