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ISBN 9783843914499

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978-3-8439-1449-9, Reihe Raumfahrt

Jan Thomas Harder
Optimal Quality of Service for Space Communication Architectures with Focus on Real-Time Teleoperated Spacecraft

189 Seiten, Dissertation Technische Universität München (2013), Softcover, A5

Zusammenfassung / Abstract

This thesis evaluates communication architectures of space missions with respect to their suitability for a given application. With new applications, like real-time teleoperated spacecraft for orbital maintenance tasks, gaining attention, the communication systems of such missions are facing new requirements. Parameters not relevant for existing missions need to be included in the design process of future spacecraft. With strict real-time requirements for such possible teleoperation missions, the communication architectures need to be evaluated with a coherent parameter set that includes all relevant aspects. To achieve this goal, a model is proposed that allows the comparison of different communication architectures with respect to their Quality of Service (QoS). In the first step existing QoS parameters sets are researched and extended as space communication systems face different technological challenges not reflected in these definitions. Besides the link performance measured in time delay, jitter, bandwidth and error ratio the aspect of link availability is included in the extended QoS definition. Long-duration disconnections due to orbital dynamics thus become part of the QoS. In the second step the determined QoS parameters need to be related to the user requirements for specific missions. To define this relation, utility functions are used that relate a physical parameter to a utility value between zero (= no utility) and one (= max. utility). A mathematical relation is proposed that defines the drop in utility from ideal communication conditions. The used function is based on literature values and experimental data acquired with a simulation environment for orbital proximity teleoperation. The mathematical relation includes a scaling factor that yields the thresholds of a 50% utility drop with respect to ideal communication conditions. With the relevant QoS parameters defined and the utility functions determined, communication architectures can be compared in the third step of this thesis. Different architectures were modeled with varying selections of space based data relay nodes, bandwidth, frequency, and ground based data relay nodes, with each architecture yielding specific QoS values. In a final step the determined link performance and availability values were traded against first order cost estimations, to include financial constraints. This four-step approach was applied in three different case studies to demonstrate the model’s usability.