I was introduced to 3D printing through an internship a few years back. A part I had designed required form and fit assembly testing; we 3D printed a replica using Stereolithography (SL). My fascination with 3D printing began there while watching the SL part grow in the machine, and stayed with me throughout college. For my senior design project this year, I knew 3D printing would be crucial for construction of my team’s high powered rocket. Our previous experience with high power rocketry had revealed multiple problem areas, and we were confident 3D printing offered the advantages to solve those problems. Using Fused Deposition Modeling (FDM) coupled with a higher performance aerospace quality material, we built booster fins, the aft body structure and tailcone for our high power rocket.
As a college engineering/ design team with a small budget, we worried about the cost of 3D printing the components we needed. We were encouraged by our advisors from Raytheon to work with additive manufacturing company Stratasys Direct Manufacturing. Stratasys Direct Manufacturing showed us that the costs associated with the components we wanted to 3D print were far less than we originally expected. Our Stratasys Direct Manufacturing partnership enabled us to create something never before done in this field, and helped our project win the best overall design award at the University of Arizona design showcase.
As is the case with all design projects, time was critical. The parts we designed and had 3D printed by Stratasys Direct Manufacturing saved us countless hours in construction. The fin structure alone, which was created via Fused Deposition Modeling (FDM) with high temperature ULTEM 9085 material, would have taken seven individual pieces and three days to assemble had we constructed it manually. Due to the cavities inside and the very thin fins in our design, 3D printing was the only way to create the structure as one piece. We wrapped all 3D printed components in carbon fiber for extra strength, slid the pieces into the aft end of the rocket and were ready to go a day after receiving the pieces, just in time to launch on our targeted date.
The sustainer aft body system is comprised of a motor mount, tailcone and 3 fins with NACA 0003 airfoil cross sections. The motor mount and number of fins are a necessity to the design whereas the tailcone is a supplementary feature. Having these components exist as a single piece is not common; they are usually separate and assembled individually. It would have been impossible to manufacture this system as a single piece without additive manufacturing; we would not have been able to produce the rocket fins with airfoil cross sections.
The design we produced via 3D printing reduced drag and increased efficiency by 85% compared to a rounded flat plate. The reduced thickness in the fins incorporated intricate curvature, features very difficult to ensure in a physical product as deformed regions would jeopardize function. In addition, constructing the fins with the motor mount guaranteed equal radial spacing of 120° between fins which is essential for stable flight trajectory. Consolidation of the motor mount and fins immensely improved structural stability and mitigated fin flutter – a dynamic instability between aerodynamic and structural properties often leading to destruction. The mounting structures extended beneath the motor mount to a concentric tube, further increasing the structural integrity. The tailcone, the rearmost component of the design, served to reduce base drag by 40%. Construction techniques considered – which included CNC lathe, male and female mold composite layups or purchased parts – were not capable of completing this component as a single piece. The design which was realized with 3D printing reduced drag and assisted altitude targeting, achieving the goal of our project.
The 3D printed fin structure was placed in the aft of the sustainer stage, which is the top stage of the two stage rocket. The motor in the sustainer is ignited inflight and exhausts directly into the blast plate installed in the top of the bottom stage. The conical structure in the top of the previous picture is exposed to all of the exhaust from the ignition of the motor in a confined space. Exhaust temperatures of the motors used can reach more than 1500°F and is deflected directly towards the cone. The FDM piece made using ULTEM material behaved phenomenally and was only blackened with no detrimental loss of structural integrity.
To ensure our rocket and rocket flight computers had a safe return it was critical the rocket’s parachutes deploy at certain points during flight/ descent. On one of our first launches, it became apparent accessing the flight computers within the rocket to fix parachute deployment problems was incredibly difficult. The electronics were mounted to a sled deep within the rocket, which meant we had to disassemble the rocket to access the computers. I had previous experience creating circuit cards due to my internship, and suggested we 3D print circuit mounts for the project. We came up with the idea of mounting the electronics to a slide which we could easily pull in and out of the side of the rocket, allowing for short repair times if the electronics were malfunctioning. Once the rocket was properly positioned in the launch tower, we simply slide the 3D printed board into the rocket where it snapped in place; an exposed activation switch arms the controls.
The 3D printed tailcone for the booster stage also incorporated a 3D printed electronics sled for the sustainer stage. These two components are traditionally built using aluminum and plywood respectively. The use of 3D printing allowed us to custom tailor the components to our specifications and requirements.
From the time gained by 3D printing complex assemblies as single pieces, to the ease of use created by novel electronic mounting methods, our innovative ideas came to reality because of 3D printing.
About the Author
Matthew Dusard completed his undergraduate degree from the University of Arizona in May. Dusard’s senior project involved advanced construction of high power rocketry. He turned to 3D printing to achieve challenging design and construction goals to improve upon current structures and create an award-winning rocket.