DOI: https://doi.org/10.15368/theses.2019.52
Available at: https://digitalcommons.calpoly.edu/theses/2034
Date of Award
6-2019
Degree Name
MS in Aerospace Engineering
Department/Program
Aerospace Engineering
Advisor
Amelia Greig
Abstract
As the viability and capability of CubeSats increases, a demand for propulsion systems is becoming apparent. The limitations put forth in the ``CubeSat Design Specifications" and the additional difficulties of low available Size, Weight and Power (SWaP) for propulsion systems aboard CubeSats have left a technological gap that many are trying to fill. One class of propulsion, micro-propulsion systems, fills this gap nicely as they generally have low size and weight with a reasonable amount of power draw. Many can function for reasonable lifetime scales utilizing pressure vessels under one atmosphere and less then 100 watt-hours of stored chemical energy as stipulated by the CubeSat standards. Micro-thruster systems can provide station keeping to extend mission life, a method to de-orbit, or possibly even bulk position change capabilities to CubeSats, thus increasing their ever growing usage potential. Many promising micro-propulsion systems have low Technology Readiness Level (TRL) and have limited-to-no space flight heritage, making their selection for a CubeSat mission more risky. A rapid, low cost, development and demonstration platform for advanced micro-propulsion systems is needed to increase TRL of promising technologies and provide them with space flight heritage, thus making them low risk options for future mission planners.
CubeSats themselves represent an interesting test bed platform for emerging propulsion technologies as they are relatively inexpensive and less risk adverse than traditional space systems. This endeavor strives to analyze the efficacy of using CubeSats as a micro-propulsion demonstration platform to be built by students of the California Polytechnic State University's PolySat Team. This thesis will baseline the use of Pocket Rocket, an electrothermal plasma micro-thruster, originally developed by the Australian National University. The thruster has seen continued development with the PolySat team, and the PolySat version's performance and form factor is used in the following analyses. However, the platform proposed herein would not be inherently limited to this specific micro-propulsion technology.
The following analyses shows that a sun pointing control law utilizing additional deployable panels is necessary for the power budget to close. The necessary area is equal to a 2 x 3U surface of panels, which will be comprised of one 1 x 3U face and two 1/2 x 3 U deployable panels. It is also apparent that the thermal environment requires intervention to be survivable. More details will be provided in the design of an extremely SWaP efficient passive thermal management system. It also highlights the viability of the of utilizing two thrusters to impose a tumble that is easily measured. It highlights the additional complexity involved by an increasingly unbalanced craft, and the need to know the inertia tensor of the craft to accurately predict the flight functionality of the thruster. Two 1 milliNewton thrusters firing for a period of 20 seconds results in a tumble across the intended axis of about .18 hZ. This is easily measurable and also recoverable based on the selected reaction wheel bundle.