Goddard Space Flight Center
June 7 – August 13, 2021
Goals of your project/s:
This summer, I worked on the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) mission. EXCLAIM will utilize a cryogenic far-infrared balloon-borne telescope to study star formation over time. This can be achieved using a new technique called intensity mapping, where EXCLAIM will survey carbon monoxide and carbon ion emission to create a three-dimensional map of the universe. One interesting fact about the telescope is that it sits in a dewar filled with liquid helium that cools the telescope’s instruments to 1.7 Kelvin (-456.61 °F). The EXCLAIM telescope contains three mirrors that direct incoming light into the telescope’s receiver, where the light is received by six sub-millimeter spectrometers. The first main goal of my project was to complete the design of new components for the photomixer testing assembly used to characterize the telescope’s spectrometers by determining their spectral response. This meant ensuring everything could be correctly fastened and assembled together and that all parts could be machined. I would need to create engineering drawings of the parts so we could send part information to machine shops for quotes on how much they would cost to manufacture. The second goal of my project was to design a new mount to connect the bottom trapezoidal ring of the telescope frame to the hexagonal ring the receiver is suspended from. This new mount had to be lightweight, cost-effective, fit within the dewar the telescope goes in, not interfere with the telescope’s optical path, and meet structural requirements set by the NASA Balloon Program Office and the Columbia Scientific Balloon Facility, which regulate NASA balloon launches.
Describe what you did during the internship:
During my internship, I spent my first five weeks working on the photomixer assembly in SolidWorks, a computer modeling program. I ensured that each part had the correct hole and thread sizes and added fasteners to the assembly, making sure to account for the differential contraction of the materials under cryogenic temperatures. I changed some parts to have threaded inserts instead of being threaded themselves because many of the parts were going to be made from copper, a soft metal. Since the parts would be assembled/disassembled multiple times, we did not want to risk damaging the threads on the parts. I corrected the alignment of the parts, removed any interferences on the model, and assigned all parts the proper material. The optical path of the photomixer required two additional absorbing filters at a 2° offset angle from the other filters, so I designed a new filter housing assembly for the extra filters to give them that angle. I created engineering drawings of all of the new components. Engineering drawings communicate part dimensions, materials, tolerances, and other information so machine shops know how to construct the parts. I sent the drawings and part models to several shops for quotes so we could choose the cheapest manufacturing option. Finally, I created and presented slides on the photomixer mechanical design to other NASA scientists and engineers at a Critical Design Review (CDR). The CDR served as a final check-off to catch any issues and demonstrate design maturity. After the CDR, it was decided that the photomixer would be tested with another kind of spectrometer, so I worked on creating an adapter plate that would allow us to mount the smaller test spectrometer to the larger bracket for the telescope’s larger spectrometers.
As for the receiver mount, I developed a new design to connect the bottom telescope ring to the receiver hexagon. The design is composed of T-shaped blocks on the trapezoidal telescope ring that are connected to square-shaped blocks on the hexagon via L-braces. These components are made of 304 Stainless Steel and connect the center of each side of the hexagon to the telescope frame for maximum support. They are the same material as both the hexagon and telescope ring so that they all similarly contract in cold temperatures. To examine the structural integrity of the design, I ran a Finite Element Analysis (FEA), which is a computer simulation that predicts how a design would react to real-world forces. I ran different load cases where the design was subjected to a 1G vertical force, 8G vertical force, and a 4G vertical force to all sides. I chose these specific cases because they were required to be tested by the Columbia Scientific Balloon Facility. The results of the analysis showed the stress values on different regions of the model, and I had to ensure that the stress on the model did not exceed the strength of the material.
Did you achieve your goals? What were the results and conclusions?
Yes, I did achieve my goals. By the end of my internship, the design of the photomixer components had been completed, and we had selected a machine shop for manufacturing and received the final cost. The photomixer CDR was a success, which meant we could proceed with the fabrication and assembly of the components. After minor adjustments, my receiver mount design passed the FEA simulation with a required positive Margin of Safety, which is essentially a ratio of structure strength to the load requirements. As a result, I concluded that the design was structurally sound.
Describe positive lessons learned from this experience:
I learned so much as a member of the EXCLAIM team! For example, I had to present my progress to the entire EXCLAIM group at our weekly meetings, which helped build my confidence, speaking, and presentation skills. During the internship, I was able to attend presentations from scientists, astronauts, and engineers across the agency to learn about their projects. I was also able to network with lots of other NASA interns at various events, and this experience taught me just how crucial it is to network. Since both my project mentors were astrophysicists, I got to learn a lot more about the advanced science behind the mission, which went beyond what I learned in my introductory physics classes at ISU. Before my internship, I had never conducted an FEA simulation before, so I developed the skills to set up, run, and analyze the results of the simulation. Seeing how the entire EXCLAIM project was run and organized taught me about project management for large engineering projects.
Describe negative lessons learned from this experience:
My summer internship was virtual, which presented some challenges with my two younger sisters also being home this summer. It was sad knowing that I was unable to visit Goddard and tour the lab to see all of the equipment. The biggest challenge I struggled with was feeling like I did not measure up to expectations since this was my first internship. However, I had to remind myself that this internship was meant to be a learning experience. I did not have to know everything right away. I just had to maintain a growth mindset and know when I should ask for help and when I should work to solve an issue on my own. I was able to learn much this way and accomplish the goals of the project!