Object Attitude Research Articles

Attitude Estimation Method of High-Spinning Body Through Onboard Sensor Fusion Under Uniaxial Gyroscope Saturation Environment

This article deals with a 3-D attitude estimation problem of a dynamic object that involves a uniaxial, high-speed rotational motion. As a high spinning dynamics typically causes an angular rate saturation in most gyros, it is also challenging to determine the object's attitude of the principal rotation axis and correspondingly the attitude of other orthogonal axes. To solve this problem, this article proposes two techniques to accomplish the attitude estimation under uniaxial gyro saturation condition. First, this article develops a new integrated filter scheme based on a reduced state model and attitude kinematics. The proposed estimation algorithm takes advantage of the magnetic measurement and gyro's partial rates to obtain a posteriori attitude estimate in the orthogonal axes and further develops to derive the principal axis attitude deterministically. Despite decent estimation performance, a measurement degeneracy may be caused in the reduced state model theoretically. To suppress the degeneracy effect, this study also exploits an augmented attitude estimation method, which adopts a post-processing computational rate in the principal axis through a time-frequency analysis on magnetic measurements. Finally, the proposed technique's performance was demonstrated through both simulation and experiment with the high spinning rate of 10846 and 2880°/s, respectively, where the error level was measured at the sub-degree in the orthogonal axes and slightly higher in the principal axis.

Observability and sensitivity analysis of lightcurve measurement models for use in space situational awareness

ABSTRACTThis paper deals with the observability and sensitivity analysis of the lightcurve measurement for use in the estimation of instantaneous pose (orientation) and shape geometry. Since several reflectance models exist that are typically used in obtaining a synthetic lightcurve measurement, they are compared to assess the observability or/and ‘sensitivity’ to determine the ‘best model’ for use. These measurement models are nonlinear with implicit and non-trivial dependency on the states; a numerical Jacobian as well as an unscented Kalman filter derived observation matrix are synthesized for each choice of the measurement model and compared. As the linearization is about an attitude (orientation) trajectory, distinct cases are considered to elaborate the results. For the cases evaluated here, it is shown that the attitude and shape/size can indeed be estimated from the lightcurve, but this is also dependent upon the initial conditions (subsequent attitude trajectory). Linear observability analysis of a discretized system is also performed with respect to the attitude states and shape/size parameters using the singular value decomposition of the observability matrix synthesized for a batch of measurements. The results are summarized for various initial conditions of the resident space object's attitude and angular velocity states.

Hamiltonian Structure and Stability Analysis for a Partially Filled Container

AbstractHamiltonian system is a special case of dynamical system. Mostly it is used for potential shaping of mechanical systems stabilization. In our present work, we are using Hamiltonian dynamics to study and control the fuel slosh inside spacecraft tank. Sloshing is the phenomenon which is related with the movement of fluid inside a container in micro and macro scale as well. Sloshing of fluid occurs whenever the frequency of container movement matches with the natural frequency of fluid inside the container. Such type of synchronization may cause the structural damage or could be a reason of moving object's attitude disturbance. In spacecraft technology, the equivalent mechanical model for sloshing is common to use for the representation of fuel slosh. This mechanical model may contain a model of pendulum or a mass attached with a spring. In this article, we are using mass-spring mechanical model coupled with rigid body to derive the equations for Hamiltonian system. Casimir functions are used for proposed model. Conditions for the stability and instability of moving mass are derived using Lyapunov function along with Casimir functions. Simulation work is presented to strengthen the derived results and to distribute the stable and unstable regions graphically.