Graduation Year

2019

Document Type

Thesis

Degree

M.S.E.E.

Degree Name

MS in Electrical Engineering (M.S.E.E.)

Degree Granting Department

Electrical Engineering

Major Professor

Robert Bishop, Ph.D.

Committee Member

Chung Seop Jeong, Ph.D.

Committee Member

Wilfrido Moreno, Ph.D.

Keywords

fuzzy control, Kalman filter, MATLAB, MIMO control, Simulink, Topology

Abstract

This thesis investigates the concept of controlling a CubeSat constellation in low-Earth orbit. Low-Earth orbits are considered because the torque used for satellite control is supplied with magnetorquers, and the closer the satellite is to Earth’s magnetic field the more control gain can be supplied. Also, this is the expected orbit altitude of future CubeSat constellations to enable communications.

Controlling a CubeSat relies on attitude determination. This means being able to estimate its attitude relative to a given reference frame. To determine the attitude, we propose to use a star tracker and a Kalman filter. A star tracker scans the stars in the satellite’s view, correlates the object to a database, to return an attitude measurement. The measurement is then processed using the Kalman filter. The attitude estimate is then used as the reference input for the controller.

Once the attitude of the satellites is determined, a controller can be implemented; assuming the system is controllable and observable. These parameters are verified by adding enough actuators and sensors, respectively.

The novelty of this thesis is constructing a controller that will take three satellites and their attitude estimates and arrange them broadside to a target. For simplicity, the arrangement will be a linear formation, and the target and satellite constellation will all be near-field communication. The goal is to place the satellite constellation in an attitude for an intersatellite link to be established. This is a proposed solution to better budget power and computational constraints associated with CubeSats. In addition to adjusting the topology of the system, a communication method must be considered for the data to be distributed across the system requiring an antenna design to implement the communication method. Both issues are discussed in the thesis; however, the focus is the controller design for attitude control. The control approach is a multi-input multi-output (MIMO) sliding fuzzy controller. The focus of the analysis is attitude control for communication while maintaining the constellation in a linear formation. The results shown this controller to be a valid proof of concept.

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