Tufts SEDS Rocketry Team
Tufts SEDS Rocketry Team
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HODGE - International Rocketry Engineering Competition 2025
HODGE - International Rocketry Engineering Competition 2025
During the 2024-2025 year, I served as the Mechanical Engineering Lead for our competition rocket, HODGE, the Highly-Optimized Data-Gathering Explorer. The primary focus of our project was to improve upon our work from the previous year, streamlining and optimizing all aspects of design and the fabrication process. The scope for the subteam includes design, testing, manufacturing, and analysis of all airframe and internal mechanical components. We used Computer-Aided Design (CAD), and Finite Element Analysis (FEA) software to model and simulate rocket components, allowing us to calculate expected failure criteria and simulate critical loads. Having learned a lot about high-strength composites with CARM last year, I aimed to push the boundaries of our design by heavily optimizing our fins for aerodynamic stability and precise factor of safety. Using carbon fiber cores due to their stiffness and weight, I reduced our fin thickness from 1/8” to 1/16”, lowering the vehicle’s weight and drag therefore increasing performance. To ensure that these changes were viable without risk of fin flutter, I leaned into characterizing our tip-to-tip layups and conducted testing and simulation to support design decisions. Additionally, I led the architecture design for HODGE's layout, including payload assembly and load path, avionics bay layout and accessibility hatches, and various bulkheads throughout the system.
Optimization of thrust plate in SolidWorks FEA
In order to analyze fin flutter, I developed a robust flutter velocity calculator based on NACA Technical Paper 4197. This took into account Dennis Martin's Flutter Velocity Equation, as well as corrections for specific fin geometry and separating shear modulus of an anisotropic material into its individual Young's Moduli in the lengthwise and crosswise directions, which could each be tested with our Instron Tensile Test Machine.
Dennis Martin's NACA Fin Flutter Velocity Equation
Professor John Bennett's correction for DN ≠ 39.3
Lekhnitskii's (1981) Anisotropic Shear Modulus
Extra care was given this year to characterize fin flutter through a detailed analysis involving calculations of flutter velocity across various thicknesses and layup configurations of composite materials. This was supported in large part by Instron testing which was conducted to determine the factor of safety associated with different thicknesses and layup configurations of composite materials. Samples were cut in both lengthwise and crosswise orientations to evaluate material strength through the shear modulus, a key parameter in the fin flutter equation from NACA. Tensile testing was done to the ASTM-D3039 standard. To estimate the shear modulus, we used the following relationship derived by Lekhnitskii where Ex and Ey are the Young’s moduli in the x and y directions, and vxy is Poisson’s ratio. The results of material testing were used to determine the minimum fin core thickness and number of layups to maintain the 1.5 factor of safety while reducing weight.
Another major feature of HODGE’s aft airframe is a second set of removable fins, placed behind the larger fixed fins. There are two significant reasons for this design decision. First and foremost, these fins will be designed to "break the fall" in the case of a hard landing, allowing the booster section to quickly and easily be reused after a wider range of landing scenarios. Second, these aft fins can be swapped with alternate fins of different geometries, allowing us to modify our projected altitude or stability in real time. This lets us adapt to any changes during launch day conditions, such as non-ideal wind gusts or mitigate any last-minute simulation discrepancies.
One initial concern for the second set of fins was the boundary layer behavior. As air travels along the first set of fins, a boundary layer begins to grow. In the gap between the first and second set of fins, there is a flow separation, essentially creating a vacuum. It was uncertain whether this induced stress would pose troublesome for the fins, and if so by how much. To address this, I ran a COMSOL Multiphysics CFD study to identify three criteria - drag forces due to variable fin geometry, stresses on the material, and velocity profile for each design. The geometry used in this study is a simplified section of the rocket airframe containing just the fins. Three versions of the booster section geometry were created: one with the standard fins, one with shorter fins designed to raise the apogee, and one with taller fins designed to lower the maximum altitude reached. After each simulation was completed, the max stress in the fins was identified as well as the drag forces over the fin surface using a surface integral condition. For the drag force, the viscous and pressure-driven forces were also compared. Results revealed that pressure-driven drag played more of a factor than viscous drag which varied significantly with fin design, and all stresses remained safely below material limits. Therefore, this low pressure effect was thankfully of little concern.
A summary of my sub-team's simulation and analysis work, and its greater part in the design of the HODGE launch vehicle can be found in the HODGE Preliminary Design Review, seen below.
HODGE Preliminary Design Review.pptxCompetition Flight
Competition Flight
Since I was away during the 2025 spring semester interning at Blue Origin, the majority of my contributions as mechanical lead were in the simulation and analysis supporting optimizations across the launch vehicle. My internship ended before the 2025 IREC, and I was able to attend the competition with the rest of my team. Due to several rainy weekends, the team was unable to conduct any test flights during the spring semester, meaning the competition flight would also be HODGE's maiden flight. We all held our breath during the countdown and watched as HODGE soared beautifully to an apogee of 10,203 ft, just 2% from our target apogee. Despite this strong technical showing, an administrative penalty (late report submission...) reduced what would have been 11th overall (out of 143) to 53rd place. This penalty hurt, and we made it our goal to place top 10 next year.
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