Model Development and Attitude Control for pico-satellite UWE-4

Abstract: UWE-4 is the fourth pico-satellite satellite in UWE series. After the successful
launch and operation of UWE-3 in 2013, the mission of UWE-4 is to demonstrate
electric propulsion technology for formation flying missions at the pico-satellite level
of miniaturization. The challenge in this project is to demonstrate precise orbit and
attitude control given the extremely limited resources available to the satellite. Four
vacuum arc thrusters and one PPU constitute the electric propulsion system.
In this master thesis project, attitude control of a cubesat is studied and a simu-
lation platform for attitude and orbit control is developed. More than one control
philosophies are developed, compared and implemented to fly on-board UWE-4. Dif-
ficulties with using SGP-4 orbit propagator with low thrust action has motivated the
development of a low fidelity orbit propagator which should be improved further.
Insufficient actuation in one axis has motivated the development of a quaternion
based dynamic target attitude solution to achieve precise 2D attitude control while
also having stabilization in the third axis. Due to the advantages of non-linear con-
trol, a sliding mode controller is evaluated against conventional linear PD controller
with the conclusion that a non-linear controller has some advantages over a linear
controller for this particular problem of attitude control where constant large angle
maneuvers are desired for changing the orientation of the satellite. Two operation
modes for the thrusters named as the one quadrant and the two quadrant method
are formulated and simulated in different scenarios. It is found out that the two
quadrant method results in a quicker response for the change in orientation of the
satellite.