Available at: http://digitalcommons.calpoly.edu/theses/1501
Date of Award
MS in Aerospace Engineering
Currently, the CubeSat spacecraft is predominantly used for missions at Low- Earth Orbit (LEO). There are various limitations to expanding past that range, one of the major ones being the lack of sufficient radiation shielding on the Poly-Picosatellite Orbital Deployer (P-POD). The P-POD attaches to a launch vehicle transporting a primary spacecraft and takes the CubeSats out into their orbit. As the demand for interplanetary exploration grows, there is an equal increase in interest in sending CubeSats further out past their current regime. In a collaboration with NASA’s Jet Propulsion Laboratory (JPL), students from the Cal Poly CubeSat program worked on a preliminary design of an interplanetary CubeSat deployer, the Poly-Picosatellite Deep Space Deployer (PDSD). Radiation concerns were mitigated in a very basic manner, by simply increasing the thickness of the deployer wall panels. While this provided a preliminary idea for improved radiation shielding, full analysis was not conducted to determine what changes to the current P-POD are necessary to make it sufficiently radiation hardened for interplanetary travel.
This thesis develops a tool that can be used to further analyze the radiation environment concerns that come up with interplanetary travel. This tool is the connection between any geometry modeled in CAD software and the radiation tool OLTARIS (On- Page iv Line Tool for the Assessment of Radiation In Space). It reads in the CAD file and converts it into MATLAB, at which point it can then perform ray-tracing analysis to get a thickness distribution at any user-defined target points. This thickness distribution file is uploaded to OLTARIS for radiation analysis of the user geometry.
To demonstrate the effectiveness of the tool, the radiation environment that a CubeSat sees inside of the current P-POD is characterized to create a radiation map that CubeSat developers can use to better design their satellites. Cases were run to determine the radiation in a low altitude orbit compared to a high altitude orbit, as well as a Europa mission. For the LEO trajectory, doses were seen at levels of 102 mGy, while the GEO trajectory showed results at one order of magnitude lower. Electronics inside the P-POD can survive these doses with the current design, confirming that Earth orbits are safe for CubeSats. The Europa- Jovian Tour mission showed results on a higher scale of 107 mGy, which is too high for electronics in the P-POD. Additional cases at double the original thickness and 100 times the original thickness resulted in dose levels at orders of about 107 and 104 mGy respectively. This gives a scale to work off for a “worst case” scenario and provides a path forward to modifying the shielding on deployers for interplanetary missions. Further analysis is required since increasing the existing P-POD thickness by 100 times is unfeasible from both size and mass perspectives. Ultimately, the end result is that the current P-POD standard does not work too far outside of Earth orbits. Radiation-based changes in the design, materials, and overall shielding of the P- POD need to be made before CubeSats can feasibly perform interplanetary missions.