A Singularity-free Steering Law of Roof Array of Control Moment Gyros for Agile Spacecraft Maneuver

In this paper, a singularity-free steering law for single gimbal control moment gyros (CMGs) is addressed for agile spacecraft. The geometrical array considered particularly in this work is a roof array due to the simplicity of singularity envelope. A feasible angular momentum chart which can provide a singularity-free bound is employed. The chart allows a guaranteed maximum torque output and angular momentum at any time without concerning the geometrical singularity of the array. Furthermore, a new deterministic allocation algorithm, called half-leading steering logic, of gimbal angular rates, is also suggested instead of the well-known pseudo-inverse technique to meet control torque commands required and to keep away from the singularity. It is noted that a momentum vector recovery to the initial direction is also an important task for the CMG array to overcome the singularity and for the reliable operation of CMGs. An optimization technique is addressed to restore the gimbal vectors back to their original angular position after the attitude reorientation mission. The techniques proposed are demonstrated using illustrative numerical simulations.

     

Thermal Stability Characteristics and Limit Cycle Oscillation of Smart Skin Structures

Smart skin structures are analyzed for thermal stability behaviors and limit cycle oscillations in supersonic range of airflows. The skin is made up of multi-layered sandwich panel using carbon/epoxy, glass/epoxy, and dielectric polymer layers. And the model is based on the first-order shear deformation plate theory, and von Karman strain-displacement relationships are used to consider the moderate geometrical nonlinearity of the structure. In order to study the effects of the airflow, first-order piston theory is adopted to represent the pressures. Also, Newmark time integration method is applied to obtain the numerical results in this work. To check the validity of present outcomes, results are compared with previous data. Specifically, the stability boundaries are obtained for various ranges of temperatures and aerodynamic pressures. Then, the regions for buckling, post-buckling, dynamic instability, and limit cycle oscillation of the structures are clearly discussed. For more analysis, the smart skin is investigated for the different sizes and shapes of dielectric portion within enclosure layer in detail.     

Angular Rate and Alignment Estimation for Gyroless Spacecraft by Only Star Trackers

International Journal of Control, Automation and Systems - An extended Kalman filtering technique is addressed for gyroless spacecraft to estimate the angular rate and attitude vectors of...