Date of Award

Spring 1-1-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Aerospace Engineering Sciences

First Advisor

Hanspeter Schaub

Second Advisor

Jeffrey Luftig

Third Advisor

Penina Axelrad

Abstract

This thesis studies passive visual relative control for satellites. The three main problems studied are how to keep the camera pointing at the center of the target, how to move the satellite so the camera can look at the target from a perpendicular orientation or maintain a fixed orientation, and how to maintain a nominal distance from the target. Visual target tracking within the image uses a statistical pressure snake algorithm, which tracks the outer contour of a target and allows geometric moments to be calculated. The attitude control is based off of tracking the center of the visual target, which is the first moment. The attitude control can treat the inertial target angular velocities as disturbances in the control for slow, smooth reference motions and still be stable. The skewness coefficient g3, which is a non-dimensional form of the third moment, can be used as a measure of perpendicularity when certain information is known about the target. A 640x480 pixel resolution camera is used to obtain better skewness and perpendicularity information than the human eye. A distance control does not need to assume the absolute distance, but can maintain a nominal distance by using the image inertia, or second moment information.

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