Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2023
Tezin Dili: İngilizce
Öğrenci: BURAK YAĞLIOĞLU
Danışman: Ozan Tekinalp
Özet:
To fill the gap between the formation flying and swarm missions, cluster flying is introduced with relatively loose geometry constraints and control accuracy requirements as well as considering more spacecraft compared to formation flying which typically accommodates two spacecraft (a leader and a follower). The problem of long-term relative orbit design for and maintenance of spacecraft clusters with realistic operational considerations such as safety, station keeping and inter-spacecraft distance constraints is addressed. Two different methodologies of cluster flying design are developed in terms of station keeping and safety objectives. In the first methodology, relative orbit configurations are found minimizing deviations from reference mean orbit which would maximize the station-keeping objective. In second one, relative configurations are found from a reference initial condition by minimizing probability of collision, hence maximizing the safety objective, between the spacecraft in the cluster which are propagated numerically through a high precision orbit propagator. For the design optimization, a derivative free algorithm is proposed. Effectiveness of the methodologies is demonstrated through simulations. Using this design framework, several configurations can be found by exploring the limits of the clusters in terms of spacecraft number, distance bounds and probabilities of collision for long time intervals and various mission requirements. To accommodate different types of missions, the problem of radio frequency geolocation cluster design is also addressed. For maintenance of the clusters, reconfiguration algorithms are developed to minimize total maneuvering effort while maximizing station-keeping and ensuring safety objectives. In the first algorithm, sequential cluster configurations are found by minimizing deviations from a reference mean orbit for long time intervals and, then, spacecraft are associated into new configurations using auction algorithm which minimizes total maneuvering effort for whole cluster. For reconfiguration, optimal impulsive transfer, model predictive control and nonlinear optimal control methodologies with linear time invariant and time variant dynamic models are implemented and compared. Finally, another reconfiguration algorithm is proposed by considering relative orbital element differences as design variables and its effectiveness is shown in terms of significantly improved maneuvering requirements for whole cluster. With the developed cluster flying framework, it becomes possible to assess what type of clusters are operationally possible or not for a given set of parameters regarding constraints, availabilities, capabilities, physical characteristics, navigation uncertainties and mission requirements. Therefore, the proposed framework is a powerful design and operational analysis tool for maximizing the feasibility and mission return of cluster missions. In this manner, different types of clusters with specific mission requirements can be designed and evaluated with reasonable or small computational demand for long term uninterrupted service and safety in all phases of distributed space missions.