Design and validation of inverse optimisation software for the attitude control of microsatellites

Nadjim Horri, P. Palmer, M. Roberts

    Research output: Contribution to journalArticlepeer-review

    6 Citations (Scopus)


    The capabilities of microsatellite attitude control hardware have considerably evolved
    during the last two decades. However, three axis attitude control software is still
    predominantly based on the conservative use of standard flight proven PD type
    controllers, which are known to be limited in terms of rapidity for a prescribed level
    of energy consumption. Microsatellites are therefore typically not as agile as they could
    be. This conservatism is due to the complexity of implementing global numerical
    optimisation techniques to satellite attitude control. In this paper, we consider the
    model of a low earth orbiting microsatellite with a four wheel configuration, where the
    speed of one of the wheels is kept constant to provide a momentum bias and guarantee
    gyroscopic stiffness to disturbances. A geometric optimal control approach is presented,
    which circumvents the tedious tasks of numerically solving online the nonlinear
    optimisation problem. The approach is based on the design of suboptimal phase space
    trajectories. The phase space trajectory of a standard linear controller, typically a PD
    law with gyro-compensation, is used as a benchmark. The proposed inverse optimal
    control technique is then used to enforce higher convergence rate constraints than the
    benchmark law, without increasing the total energy consumption. The convergence rate
    of a Lyapunov function under the effect of the optimal controller outperforms the
    convergence rate of the same function under PD control and keeps increasing until a
    design settling time limit is reached. Guidelines are given for the tuning of the
    controller. The optimal attitude control algorithms are validated on a microsatellite
    software simulator in collaboration with the space company Surrey Satellite Technology
    Limited (SSTL). The software simulator incorporates a precise model of the effects of
    estimation errors, noise, external disturbances, sampling and actuator dynamics. The
    software is similar to the flight software of typical Surrey microsatellites. The proposed
    techniques are characterised by low implementation complexity because the difficulty
    is confined to the theoretical design stage. Settling time is significantly enhanced for the
    same level of energy consumed as the PD type law, which was used as a benchmark
    without loss of generality.
    Original languageEnglish
    Pages (from-to)997-1006
    Number of pages10
    JournalActa Astronautica
    Issue number11-12
    Publication statusPublished - 3 Aug 2011

    ASJC Scopus subject areas

    • Aerospace Engineering
    • Control and Systems Engineering


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