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Asteroid Body

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Yue Wang – One of the best experts on this subject based on the ideXlab platform.

  • Body fixed orbit attitude hovering control over an Asteroid using non canonical hamiltonian structure
    Acta Astronautica, 2015
    Co-Authors: Yue Wang

    Abstract:

    Abstract The orbit-attitude hovering means that both the position and attitude of the spacecraft are kept to be stationary in the Asteroid Body-fixed frame. The orbit-attitude hovering is discussed in the framework of the gravitationally coupled orbit-attitude dynamics, also called the full dynamics, in which the spacecraft is modeled as a rigid Body to take into account the gravitational orbit-attitude coupling naturally. A feedback hovering control law is proposed by using the non-canonical Hamiltonian structure of the problem, which is consisted of two potential shapings and one energy dissipation. The first potential shaping is to create an artificial equilibrium at the desired hovering position-attitude. Then, the second potential shaping modifies the potential further so that the artificial equilibrium is a minimum of the modified Hamiltonian on the invariant manifold. Finally, the energy dissipation leads the motion to converge asymptotically to the minimum of the modified Hamiltonian, i.e., the artificial equilibrium for hovering. The feasibility of the hovering control law is verified through numerical simulations. The proposed hovering control law has a simple form and can be implemented by the spacecraft autonomously with little computation. This feature can be attributed to the utilization of the Hamiltonian structure and natural dynamical behaviors of the system in the control law design.

  • Body fixed orbit attitude hovering at equilibria near an Asteroid using non canonical hamiltonian structure
    arXiv: Earth and Planetary Astrophysics, 2014
    Co-Authors: Yue Wang

    Abstract:

    Orbit-attitude hovering of a spacecraft at the natural relative equilibria in the Body-fixed frame of a uniformly rotating Asteroid is discussed in the framework of the full spacecraft dynamics, in which the spacecraft is modeled as a rigid Body with the gravitational orbit-attitude coupling. In this hovering model, both the position and attitude of the spacecraft are kept to be stationary in the Asteroid Body-fixed frame. A Hamiltonian structure-based feedback control law is proposed to stabilize the relative equilibria of the full dynamics to achieve the orbit-attitude hovering. The control law is consisted of two parts: potential shaping and energy dissipation. The potential shaping is to make the relative equilibrium a minimum of the modified Hamiltonian on the invariant manifold by modifying the potential artificially. With the energy-Casimir method, it is shown that the unstable relative equilibrium can always be stabilized in the Lyapunov sense by the potential shaping with sufficiently large feedback gains. Then the energy dissipation leads the motion to converge asymptotically to the minimum of the modified Hamiltonian on the invariant manifold, i.e., the relative equilibrium. The feasibility of the proposed stabilization control law is validated through numerical simulations in the case of a spacecraft orbiting around a small Asteroid. The main advantage of the proposed hovering control law is that it is very simple and is easy to implement autonomously by the spacecraft with little computation. This advantage is attributed to the utilization of dynamical behaviors of the system in the control design.

Fanghua Jiang – One of the best experts on this subject based on the ideXlab platform.

  • Asteroid Body-fixed hovering using nonideal solar sails
    Research in Astronomy and Astrophysics, 2015
    Co-Authors: Xiangyuan Zeng, Fanghua Jiang

    Abstract:

    The problem of Body-fixed hovering over an Asteroid using a compact form of nonideal solar sails with a controllable area is investigated. Nonlinear dynamic equations describing the hovering problem are constructed for a spherically symmetric Asteroid. Numerical solutions of the feasible region for Body-fixed hovering are obtained. Different sail models, including the cases of ideal, optical, parametric and solar photon thrust, on the feasible region is studied through numerical simulations. The influence of the Asteroid spinning rate and the sail area-to-mass ratio on the feasible region is discussed. The required orientations for the sail and their corresponding variable lightness numbers are given for different hovering radii to identify the feasible region of the Body-fixed hovering. An attractive scenario for a mission is introduced to take advantage of solar sail hovering.

  • Asteroid Body fixed hovering using nonideal solar sails
    arXiv: Solar and Stellar Astrophysics, 2014
    Co-Authors: Xiangyuan Zeng, Fanghua Jiang

    Abstract:

    Asteroid Body-fixed hovering problem using nonideal solar sail models in a compact form with controllable sail area is investigated in this paper. The nonlinear dynamic equations for the hovering problem are constructed for a spherically symmetric Asteroid. The feasible region for the Body-fixed hovering is solved from the above equations by using a shooting method. The effect of the sail models, including the ideal, optical, parametric and solar photon thrust, on the feasible region is studied through numerical simulations. The influence of the Asteroid spinning rate and the sail area-to-mass ratio on the feasible region is discussed in a parametric way. The required sail orientations and their corresponding variable lightness numbers are given for different hovering radii to identify the feasibility of the Body-fixed hovering. An attractive mission scenario is introduced to enhance the advantage of the solar sail hovering mission.

Roberto Furfaro – One of the best experts on this subject based on the ideXlab platform.

  • Six degree-of-freedom Body-fixed hovering over unmapped Asteroids via LIDAR altimetry and reinforcement meta-learning
    Acta Astronautica, 2020
    Co-Authors: Brian Gaudet, Richard Linares, Roberto Furfaro

    Abstract:

    Abstract We optimize a six degrees of freedom hovering policy using reinforcement meta-learning. The policy maps flash LIDAR measurements directly to on/off spacecraft Body-frame thrust commands, allowing hovering at a fixed position and attitude in the Asteroid Body-fixed reference frame. Importantly, the policy does not require position and velocity estimates, and can operate in environments with unknown dynamics, and without an Asteroid shape model or navigation aids. Indeed, during optimization the agent is confronted with a new randomly generated Asteroid for each episode, insuring that it does not learn an Asteroid‘s shape, texture, or environmental dynamics. This allows the deployed policy to generalize well to novel Asteroid characteristics, which we demonstrate in our experiments. Moreover, our experiments show that the optimized policy adapts to actuator failure and sensor noise. Although the policy is optimized using randomly generated synthetic Asteroids, it is tested on two shape models from actual Asteroids: Bennu and Itokawa. We find that the policy generalizes well to these shape models. The hovering controller has the potential to simplify mission planning by allowing Asteroid Body-fixed hovering immediately upon the spacecraft’s arrival to an Asteroid. This in turn simplifies shape model generation and allows resource mapping via remote sensing immediately upon arrival at the target Asteroid.

  • Six Degree-of-Freedom Hovering using LIDAR Altimetry via Reinforcement Meta-Learning.
    , 2019
    Co-Authors: Brian Gaudet, Richard Linares, Roberto Furfaro

    Abstract:

    We optimize a six degrees of freedom hovering policy using reinforcement meta-learning. The policy maps flash LIDAR measurements directly to on/off spacecraft Body-frame thrust commands, allowing hovering at a fixed position and attitude in the Asteroid Body-fixed reference frame. Importantly, the policy does not require position and velocity estimates, and can operate in environments with unknown dynamics, and without an Asteroid shape model or navigation aids. Indeed, during optimization the agent is confronted with a new randomly generated Asteroid for each episode, insuring that it does not learn an Asteroid‘s shape, texture, or environmental dynamics. This allows the deployed policy to generalize well to novel Asteroid characteristics, which we demonstrate in our experiments. The hovering controller has the potential to simplify mission planning by allowing Asteroid Body-fixed hovering immediately upon the spacecraft’s arrival to an Asteroid. This in turn simplifies shape model generation and allows resource mapping via remote sensing immediately upon arrival at the target Asteroid.