Abstract
As the requirement for pointing accuracy of applications spacecraft such as land observation satellite becomes higher, the attitude control is subject to more and more demanding accuracy requirement. This results in the necessity of managing internal disturbance attributed to mechanical moving parts such as rotating mirror, solar array driving mechanism, and so on. Flywheels used for attitude control actuator can be a major cause of the internal disturbance. In this paper, the disturbance torques and forces induced by a flywheel is investigated precisely based on the rotor dynamics and the contact dynamics of the supporting bearings. The wheel rotor model includes static and dynamic mass unbalance as in the common practice. The bearing model with six (6) balls reflects the actual hardware currently manufactured, which uses an angular contact bearing with relatively small preload pressure to reduce the friction torque. The most challenging part of the modeling is the contact dynamics of the bearing unit consisting of inner lace-balls-retainer-outer lace configuration. At the contact point, the normal force is a nonworking constraint force while tangential and axial forces are normally working forces given as a function of velocity components at the contact. Taking this situation into account, a flywheel model is established as a multibody system with seven (7) degrees of freedom. Based upon this modeling, spinning rigid body dynamics is evaluated as well as the precise estimation of the disturbance torques and forces, and compared with the experimental results obtained from the low friction test-bed.
