Attitude control of tethered satellites.

摘要

This dissertation presents methods of attitude control of tethered satellites. The main effort is focused on the case of a tethered space observatory that requires high pointing accuracy.; A tethered satellite is connected to a parent spacecraft by a long tether. The gravity gradient caused tension in the tether passively provides satellite attitude stability about two axes. However, active attitude control is necessary for high accuracy pointing and new control methods are required since conventional methods are not efficient due to the tether tension.; With a movable tether attachment point on a tethered satellite, active control torques can be produced about two axes by varying the offset of tether tension vector from the satellite's center of mass. For the third axis, parallel to the tension vector, the control torque can be provided by momentum devices. No mass ejection is needed.; Tether dynamics especially damping properties have significant effects on the satellite's pointing accuracy, which are studied with a flexible continuum model. Dynamic equations are solved analytically with approximations. Various damping mechanisms are analyzed including viscous, structural and linear friction damping. Ground test results are extrapolated to predict space behavior of tethers of much different sizes. Methods are developed to enhance damping.; Numerical simulations of Kinetic Isolation Tether Experiment (KITE), an orbital flight experiment being designed to demonstrate the new attitude control methods, show the pointing accuracy of one arcsecond.