College of Engineering
Mechanical Engineering Department
BS in Mechanical Engineering
This document serves as the final design review (FDR) report for the 2018 Cal Poly CubeSat Ultraviolet Imager senior project, sponsored by UC Berkeley Space Sciences Laboratories (SSL). SSL wants to monitor the ionosphere above Earth to gain a better understanding of its properties and particle interactions. Far Ultraviolet (FUV) imaging is a good way to obtain high quality images of the ionosphere and the Earth's auroras, and advancement in optic technologies have made cube satellites (CubeSats) an ideal vessel for a FUV imager, as they are relatively low-cost, lightweight, and can be repeatedly deployed. These CubeSat FUV imagers could be utilized to image the entirety of Earth's auroras simultaneously from different vantage points and could even be deployed further away from Earth to study the exosphere. Cal Poly has been tasked with designing, building, testing, and validating the front optics assembly of this FUV CubeSat imager. The front optics assembly design includes the lenses, baffle, aperture, and camera detector interface, all of which affect parameters such as light refraction, image focus, and field of view. Imaging ground support equipment (GSE) will be designed and built, upon which the camera's ability to obtain an image within specifications will be tested. One critical requirement of the project is the need to develop the mounting system for the optics assembly that enables high precision and fixed alignment, both before and after thermal and vibration testing. The design validation tests will be conducted with a functional visible camera to confirm the mounting configuration satisfies the requirements defined by SSL. These experimental results will be verified against theoretical results obtained by software analytical tools, such as FEA or MATLAB. During the second quarter of the project, cantilever beams were tested with different composite material stack-ups with damping materials applied between layers. Analysis was utilized to determine the optimum damping stack-ups that can be applied to the surface between the optics 9 datum and the structure of the CubeSat. Detailed design was then applied to the CubeSat structure and optics to ensure that specifications will be met upon design verification post-manufacturing and assembly. Designs were also generated for a 1-U P-POD structure that will resemble boundary conditions experienced during launch conditions. Finally, ground support equipment (GSE) was designed to achieve a variety of specified optical tests. Lists of stock parts and components that need to be procured have been generated, as well as initial cost estimates of total stock and component pricing and CNC manufacturing costs. Fabrication may commence once the budget and design are reviewed and approved by UCB during the manufacturing readiness review. Components will ideally be manufactured later in spring quarter into the summer and will be ready for assembly beginning in September. During the third quarter of the project, the Cal Poly team received anodized parts for the CubeSat, machined parts for the P-POD, lenses, and a variety of tools, parts, and optical measurement components from UCB. The optics inside the instrument were assembled by bonding the lenses to the Keeper and Lens Mount. The optics subassembly was then assembled with the rest of the instrument’s structure, utilizing strips of Viton rubber as the medium in-between for damping. The GSE was constructed, and the optical alignment of the instrument on the GSE with the laser, GSE components, and the CCD was iterated until the instrument was in focus and output quality images. Preliminary image tests for Boresight Alignment, Spot Size, Field of View (FOV) and Stray Light Rejection were performed, and these results met the specifications as outlined by UCB. The first two of these tests were then performed between environmental tests, as the instrument was placed in a Thermal Vacuum Chamber for thermal loading, and was tested with a series of vibration tests on the shake table in all three axes. Finally, all four tests were conducted after environmental testing, and all specifications were met, except one. Stray light rejection fell just outside acceptable ranges due to a thin ring of missing anodize on the iris. The stray light rejection of the instrument should meet the design requirements if the iris is properly anodized per the manufacturing drawing.