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  1. Nonlinear angles-only orbit estimation for autonomous distributed space systems

    Sullivan, Joshua Anthony
    [Stanford, California] : [Stanford University], 2020

    There is a growing interest in future space mission concepts which involve the interaction of multiple satellites, including on-orbit servicing and debris mitigation, space situational awareness, and swarm-based sensing. These so-called distributed space systems place strict requirements on spaceborne relative navigation accuracy and robustness, autonomy in early phases of the mission, scalability to multiple agents, and resource efficiency in order to meet mission specifications. This research rises to these demands by focusing on a mid- to far-range estimation method called angles-only navigation, wherein observer satellites use bearing angles obtained from onboard monocular camera imagery of target space objects to infer the target orbital trajectories. In this context, vision-based estimation is chosen because it provides a passive and high-dynamic-range navigation technology that uses simple, flight-proven, and miniaturization-friendly hardware. However, since a target appears as only a cluster of pixels in the images, estimating its orbital motion with respect to the observer is fundamentally constrained due to a lack of range information and generally results in poor (or even divergent) navigation performance. To overcome this limitation, a novel angles-only navigation architecture is developed which leverages a deep insight into the relative motion dynamics and advanced filtering techniques to capture key nonlinearities in the dynamics and measurement modeling that lead to range disambiguation. Whereas current approaches require repetition of complex maneuver profiles to gain new vantage points on the target for range rectification, the new methods posed here are completely maneuver-free. To address further deficiencies in the current state of the art, the proposed framework generalizes the applicability of angles-only navigation to new domains beyond low Earth orbit, to situations where no prior state knowledge is available for estimator initialization, and to new scenarios involving multiple observers and/or targets. The functionality and performance of the proposed navigation architecture are verified using rigorous software-based and hardware-in-the-loop simulation. Finally, the algorithms developed in this work have led to the systematic design of the Starling Formation-flying Optical eXperiment (StarFOX), which will test angles-only navigation for future deep-space swarms while flying on board NASA's Starling1 technology demonstration formation in 2021

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