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CEAS EuroGNC 2022

Robust line-of-sight pointing control on-board a stratospheric balloon-borne platform
Ervan Kassarian ISAE-Supaero, 31400, Toulouse, France.
Francesco Sanfedino ISAE-Supaero, 31400, Toulouse, France.
Daniel Alazard ISAE-Supaero, 31400, Toulouse, France.
Johan Montel CNES, 31400, Toulouse, France.
Charles-Antoine Chevrier CNES, 31400, Toulouse, France.
Abstract:
This paper addresses the lack of a general methodology for the controller synthesis of an optical instrument on-board a stratospheric balloon-borne platform, such as a telescope or siderostat, to meet pointing requirements that are becoming more and more stringent in the context of astronomy missions. Most often in the literature, a simple control structure is chosen, and the control gains are tuned empirically based on ground testings. However, due to the large dimensions of the balloon and the flight chain, experimental set-ups only involve the pointing system and the platform, whereas flight experience shows that the pointing performance is essentially limited by the rejection of the natural pendulum-like oscillations of the fully deployed system. This observation justifies the need for a model that predicts such flight conditions that cannot be replicated in laboratory, and for an adequate methodology addressing the line-of-sight controller design. In particular, it is necessary to ensure robust stability and performance to the parametric uncertainties inherent to balloon-borne systems, such as complex balloon's properties or release of ballast throughout the flight, especially since experimental validation is limited. In this paper, a dynamical model of the complete system is proposed, based on a multibody approach and accounting for parametric uncertainties with Linear Fractional Transformations. The comparison with flight data shows that the frequency content of the platform's motion is accurately predicted. Then, the robust control of the line-of-sight is tackled as a H∞ problem that allows to reach the performance objectives in terms of disturbance rejection, control bandwidth and actuators limitations.
Keywords: Robust H∞ control; Line-of-sight pointing control; LFT modeling; Stratospheric balloons; multibody dynamics
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Ervan Kassarian, Francesco Sanfedino, Daniel Alazard, Johan Montel, Charles-Antoine Chevrier: Robust line-of-sight pointing control on-board a stratospheric balloon-borne platform. Proceedings of the 2022 CEAS EuroGNC conference. Berlin, Germany. May 2022. CEAS-GNC-2022-066.
BibTeX entry:

@Incollection{CEAS-GNC-2022-066,
    authors = {Kassarian, Ervan and Sanfedino, Francesco and Alazard, Daniel and Montel, Johan and Chevrier, Charles-Antoine},
    title = {Robust line-of-sight pointing control on-board a stratospheric balloon-borne platform},
    booktitle = {Proceedings of the 2022 {CEAS EuroGNC} conference},
    address = {Berlin, Germany},
    month = may,
    year = {2022},
    note = {CEAS-GNC-2022-066}
}