Project ATLAS Final Thesis Report; Modeling the Diffusion of Additive Manufacturing into the Aerospace Industry

Technical Project Abstract
Hybrid rocket motor technology offers a multitude of benefits over the current industry standards for rocket propulsion, namely solid-propellant and liquid-propellant rocket engines. By using a solid fuel grain and liquid oxidizer with minimal plumbing, hybrid rocket motors combine the safety of liquid rocket engines with the simplicity of solid rocket motors. The downside of hybrid rocket motors is their performance characteristics are not consistent throughout the duration of their firing time, making their combustion processes difficult to model and predict. Additionally, existing hybrid motor technology is only useful at small scales.
Aerospace Capstone Team 3 at the University of Virginia seeks to advance hybrid motor technology through Project ATLAS. Our objective is to design and construct a laboratory-scale hybrid rocket motor from scratch. This motor will serve as a testbed for several potential performance-enhancing components, which if verified to increase efficiency, consistency, and predictability could be used in future rocket motors ranging in scale.
The design phase of the project was conducted using readily available software tools such as SOLIDWORKS, NASA CEA, and Ansys, while the manufacturing phase of the project was conducted in the Mechanical and Aerospace Engineering Building as well as Lacy Hall. All additively manufactured components were 3D resin printed in the Makerspace. During these phases the team was divided into sub-teams which focused on different systems within the rocket motor. These sub-teams included: the oxidizer, combustion, data acquisition, structures, and pyrotechnics/ignition team.
The ATLAS test plan consists of a static pressure test, a non-reactive system test, and iteratively repeated hot-fire tests with data acquisition. First a hydrostatic test is conducted where the motor is mounted on the test stand and brought to operational pressure using water. Retaining structural integrity at 2000 psi permits the performance of a cold gas flow test. For this test, the functionality of our plumbing, control, and DAQ systems are verified by filling our oxidizer tank with a non-reactive gas and carrying out the ignition sequence without installing the pyrotechnic ignitor. This demonstrates the viability of our entire system under all but operational thermal loads. Following the preliminary tests, hot-fire tests are performed with pairs of injectors and fuel grains. The resulting test data is analyzed, model correlation is performed, and the data is compared to our ideal engine performance model.

STS Project Abstract
In my Science, Technology, and Society (STS) research paper I characterize the diffusion of additive manufacturing into the aerospace industry using the probit model under the technology diffusion framework developed from Everett M. Rogers’ Diffusion of Innovation theory. My analysis involves reviewing different models which support the S-Curve trend of adoption rates as a technology diffuses into a population and completing literature reviews on different classes of aerospace adopters to determine what firm characteristics influenced adoption.
Additive manufacturing began in 1980 for rapidly developing small polymer prototypes and was first adopted by aerospace firms for manufacturing scaled wing models used in wind tunnel testing. By the early 2000’s additive manufacturing processes were able to produce metal alloy parts with complex geometries at a much lower cost than traditional manufacturing methods resulting in a rapid increase in adoption rates by aerospace firms who incorporate highly specialized components into their high performance vehicles. This series of low adoption periods followed by high adoption and subsequent fall off of adoption as all potential adopters become actual adopters, results in an S-Curve of adoption rates over time.
My analysis begins by exploring the epidemic, probit, density dependence, and information cascade models. I determine the probit model’s ability to account for firm characteristics allow it to best model the diffusion of additive manufacturing across the aerospace industry. I then applied the probit model to Rogers’ five categories of adopters: the innovators, early adopters, early majority, late majority, and the laggards. During my analysis of aerospace firms within these categories of adoption I investigate varying firm characteristics and goals to determine the reasons for adoption.
I argue that the only model capable of determining these reasons for adoption is the probit model due to the caveats of other models and the probit model’s ability to account for the trade-off between controllability and flexibility. Ultimately the results of a probit model analysis are used to make predictions about how similar technologies will diffuse through similar populations so economists, competitors, and politicians can maintain control and competitive advantages.

Relationship Between the Technical and STS Projects
My Technical Project seeks to design and build a laboratory-scale hybrid rocket motor to serve as a testbed for several potential performance-enhancing components capable of increasing efficiency, consistency, and predictability in future rocket motors ranging in scale. Rocket engines are typically designed so the fuel grain and oxidizer systems supply an ideal ratio of oxidizer to fuel, or O/F ratio. The combustion process is most efficient at this optimal, or stoichiometric, O/F ratio. The nature of the propellant mixing process in hybrid motors causes the O/F ratio to vary across the combustion chamber, leading to sub-optimal performance where the ratio deviates from the ideal value. In many hybrid motor designs up to this point, these performance deficits were deemed too difficult to mitigate and the losses were built into the performance margins of the design–resulting in a waste of propellants and structural mass. Our ATLAS Project objectives are designed to reduce this waste of propellant and structural mass by additively manufacturing oxidizer injectors and fuel grains with complex geometries to maintain the ideal O/F ratio across the combustion chamber. Generally, hybrid rocket engine components are manufactured using traditional manufacturing methods such as die-casting and injection molding. These methods are not cost efficient for developing injectors and fuel grains with complex geometries. As a result, all of our injector and fuel grain pairs are additively manufactured. The oxidizer injectors are 3D resin printed using a high temperature resin, while the fuel grains are 3D printed in PLA using fused deposition modeling. This use of additive manufacturing for aerospace systems is the link between my Technical and STS Projects. My Technical Project focuses on applying additive manufacturing to hybrid rocket engines and my STS Project focuses on the adoption of additive manufacturing for aerospace systems. Student design teams such as mine fall into the laggards category of Everett M. Rogers’ five categories of adopters, which I analyze in my STS Project.

School of Engineering and Applied Science

Bachelor of Science in Aerospace Engineering

Technical Advisors: Dr. Chloe Dedic and Dr. Daniel Quinn

STS Advisor: Dr. Joshua Earle

Technical Team Members: Gavin Miller, Harshit Dhayal, Ved Thakare, Mannix Green, Aiden Winfield, Sean Dunn, Dominic Profaci, Thomas DeCanio, Joshua Bird, Harrison Bobbitt, Taka Suzuki, Darsh Devkar, Jack Spinnanger, Isaac Tisinger, Silas Agnew, Zach Hinz, Alexander Gorodchanin, Adis Gorenca, James Dalzell