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Overview

The Highly-Optimized Data Gathering Explorer, or HODGE, was the Tufts Rocketry Team’s entry into the 2025 International Rocket Engineering Competition. The design was largely similar to the previous years. However, this year, the team emphasized optimization, user accessibility, and versatility.

I began the design cycle as the lead of the metalworking subteam within the mechanical team. As the metalworking lead, I was the primary point of contact for the design, analysis, and fabrication of all metal components, including bulkheads, aluminum fin sets, the payload mount, and the thrust plate. In the spring, I ascended to the position of Mechanical Co-Lead. In this role, I oversaw the finalization of designs of all rocket parts and led the fabrication of the rocket, contributing to numerous testing and validation campaigns along the way.

2025 IREC Project Technical Report.docx.pdf

Design

The design of the HODGE had many similarities with its predecessor. The 6-inch-diameter airframe, made of G12 filament-wound fiberglass, consisted of a booster section, an avionics bay, and a nosecone. The significant differences included the introduction of removable aluminum fins, accessibility features, and an overall reduction in weight, accompanied by an increase in efficiency.

The objective of the International Rocket Engineering Competition is to get as close to 10,000 ft as possible. The Tufts Rocketry Team developed a novel approach to achieve this goal. First, the team ran simulations using software called OpenRocket. Using this software, we can refine our design and choose a motor that can get us as close to 10,000 ft as possible. However, when we build the rocket, the mass of individual components varies from what we expect. To Account for this discrepancy, we made removable fins that we could swap out on the fly to quickly adjust our geometry.

Removable Fins

While the primary purpose of the removable fins was to alter our apogee on the fly, they had a secondary purpose, which was to absorb the force of an impact in the event that our recovery system failed. They were situated behind our permanent fins and were designed with intentional stress concentrations to take the load off the airframe or permanent fins. They worked by a similar principle to crumple zones in cars. If the removable fins were to deform, we could swap them out and refly. The fin mounts, however, could not deform because they secured the fins, allowing them to be interchangeable. As a result, we chose to use Aluminum 2024 due to its superior yield strength.

To create the fins, the outlines were cut out using a waterjet. The fins required slots to fit into the mounts, which were cut using a manual mill.

Component Optimization

One of our major goals with HODGE was to make the rocket much more efficient. CARM was built like a tank. It was designed in a way such that even if it plummeted out of the sky, it would survive (this happened during one of the test flights). This added strength came at the cost of weight and cost. As a result, we attempted to slim down the rocket wherever possible, emphasizing a 1.5 factor of safety on almost every component.

One of the most significant places to save weight was with the many bulkheads placed around the rocket. Bulkheads partition the airframe and serve as hardpoints for mounting recovery systems, such as parachutes, and other components, including rail buttons. They must be strong enough to take the load from the parachutes and be able to pressurize during deployment. To optimize these components, we iterated through designs and load analyses with finite element analysis software. Any sections that were not critical to the structural integrity were removed. The result of one of the bulkhead optimizations is shown on the right.

The thrustplate also had a complete redesign. Based on calculations with epoxy shear, the walls were shortened from 3 inches to 1/4 of an inch. The bottom lip that interfaces with the body tube and transfers all of the force was also shortened greatly and was validated with FEA.

These optimizations and emphasis on 1.5 factors of safety were continuously iterated upon and used in every corner of the rocket. Overall, these optimizations contributed to a 31% mass decrease over CARM.

Material Testing

To validate many of our component optimizations, we conducted an extensive materials testing campaign. The campaign consisted of two primary tests. First, we conducted lap shear testing to determine the strength of aluminum-to-fiberglass epoxy connections. Second, we attempted to calculate the shear modulus of fiberglass with fiberglass layups. This is the material we planned to use for our fins, and we wanted to determine how thin we could make them. The primary failure mechanism for the fins is flutter. Fin flutter occurs due to aeroelastic forces from the air acting on the fin. Our analysis was based on NACA TN 4197. This paper provides an estimate for flutter velocity based on geometry and material properties. The primary issue for our analysis was that our fins were made of fiberglass, an anisotropic material. This means that the material properties are not widely agreed upon and vary significantly within the material. As a result, we attempted to measure the shear modulus and determine how the addition of layups changed the strength. This analysis enabled us to reduce our core thickness by 50% while maintaining a 1.5 factor of safety for fin flutter.

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