PROJECT SCOPE

BiPROP is a student-designed and manufactured liquid bi-propellant rocket that is tasked with the challenge of reaching an exact altitude of 5,000 feet. The rocket will compete in the Friends of Amateur Rocketry (FAR) Competition in the Mojave Desert. To ensure all elements of the rocket vehicle are accounted for, the team was split into six subsystems: Chamber/Injector/Nozzle, Fluid Systems, Structures, Avionics/Recovery, Ground Systems, and Safety.  

The main objective of BiPROP is to launch and safely recover a liquid bipropellant rocket and carry a payload of at least 1 kg that transmits and records live video of the flight. From this project objective, a design of the rocket vehicle was made, which includes an overall 4-inch diameter and approximately a height of 8 feet. A thrust of 500 pounds was determined to reach the needed altitude and will be achieved using Nitrous Oxide and Isopropyl Alcohol as oxidizer and fuel respectively. A two-stage recovery system will be utilized per competition rules, as well as an altimeter/GPS to determine the altitude. 

After the analysis was performed to ensure the rocket design was optimal for the set requirements, the creation of models and manufacturing began. The team utilized Fusion 360 as the main modeling software, due to its ability to allow for collaboration between multiple members on one part of the rocket. As for the analysis, the majority was done by hand using knowledge gained through the team's experience in the classroom over the last four years. Though some parts were bought commercially off the shelf, most of the rocket was manufactured in the university’s machine shop and design center. 

To ensure the design met the main requirement of the project, which was to launch a rocket to 5,000 feet, several tests were carried out. For the fluid systems, many of the valves were manufactured in-house. So, pipe loss tests were carried out to ensure the valves not only worked but did not decrease the mass flow of the propellants significantly. Per competition rules a hydrostatic test of the propellant tank had to be carried out, this was done with help from two other Senior Capstone projects, META Controls, and Test Stand. The main test that needed to occur was the static test fire, however before that was completed a cold flow test was needed to ensure the co-axial shear injector design is operating properly. Both tests were performed on the same day and utilized the help of the teams mentioned before. 

TISARANNI'S ROLE

Structures/Avionics/Recovery Subsystem Lead

Ashley Tisaranni was the structures/avionics/recovery subsystems lead for the project, tasked with the duty of ensuring the structural integrity of the rocket, aerodynamic efficiency, an operational avionics payload bay, and a safe recovery.  The following requirements were set by Tisaranni and her sub team, driven by the overall systems requirements:

FUEL TANK

DESIGN

The largest and most demanding task for the structures subsystem was design, analysis, and testing of the propellant tank. Based on driving systems requirement, competition rules, accessibility, and safety, the propulsion of choice was Nitrous Oxide (N2O) as the oxidizer and 99% Isopropyl alcohol as the propellant.

The tank is essentially 2 aluminum tubes with bulkheads bolted to each end and silicone O-rings for sealing. The 2 aluminum tubes are concentric with the inner tank full of the fuel and the oxidizer is pumped into the outer tank through a valve. Once the outer tank is pressurized by the oxidizer, a piston on the top of the inner tank is pushed down, forcing the fuel through a valve into the injector. The liquidized Nitrous that will separate at the bottom of the tank is simultaneously forced into the injector. A quick CONOPS can be seen below for clarity:

This design was fairly simple and within our (very small) budget. With more resources, welding or outsourcing may have been the chosen idea for the pressurized vessel. With this design, the bulkheads took up the majority of the design and manufacturing effort.

ANALYSIS

To prove the design of our bulkheads, failure analysis was conducted on any and all suspected failure or yielding points. Most calculations were conducted via simply supported assumptions, Roark’s stress & strain formulas, and simple hand calculations. Below are some examples:

TESTING SETUP

To certify the tank for the FAR competition, the tank must be pressurized to a 1.3 factor of safety and held it for 3 minutes, 3 times in a row. This was conducted via a hydrostatic test and nitrogen as clients to another Florida Tech senior design team that is working on a rocket test stand. They provided the big yellow thrust structure that you see in the images below, along with the nitrogen and LabVIEW to control the valves and read the gauges.

HYDROSTATIC TEST #1

At the first hydrostatic test, there was minor failure before the tank even reached the 1.3 FS proof pressure of 1425 psi. The O-Ring slipped out of a hole that was left un-bolted because the threads were accidentally stripped during manufacturing. This was a minor kink that was not expected to cause the issue it did. There was minor deflection of the upper bulkhead as well, but we thought it was tied to the imperfect threads and bolt angles.

To ensure more perfect manufacturing, a drill guide was 3D printed for the next attempts. The O-ring groove was also moved further from the bolts to ensure that incase it slipped a bit, it wouldn’t get this close to the bolts.

HYDROSTATIC TEST #2

At the second hydrostatic test the tank successfully pressurized to proof and held for 3 minutes, the first time. However, during the second pressurization the upper bulkhead had completely ripped off of the tank, leaving both the tank walls and bulkheads damaged. Some of the bolts had torn through the tank walls and others had lost their heads. The damage can be seen below.

As apparent in the action shots of the bulkhead flying away, there was clearly a missed calculation or consideration somewhere.

Following this incident, the team returned to the design center to analyze the failure modes and videos to figure out exactly what happened, why it happened, and an action plan to fix it.

This was devastating in the moment, but it gave the team the opportunity to dive into the engineering to figure out why it happened and how to fix it. This was a lesson learned the hard way emphasizing the importance of a productive review process for everything, because nobody is perfect, not even engineers.

RE-DESIGN

Turns out a fastener failure calculation had a factor of safety of barely 1 tied to it. This was calculated in anticipation of the firing required pressure... rather than the 1.3x proof pressure. In response to this, Tisaranni built a spreadsheet with all of the possible design changes the team could make, and how it would effect the factor of safety directly. Time and cost had to be considered very heavily since with time and money running out. 

The team wanted stronger material and more bolts. In preliminary re-design, it was quickly apparent that adding more bolts would interfere with one of our valve ports, so the the factor of safety was pulled out to propose a new solution to the team.

After tweaking the models and triple checking the calculations, the team decided to thicken the tank walls around the bolted areas and use less but stronger and bigger screws. This will bring the problematic safety factor from ~1 to ~1.8.

CONTINUATION OF PROJECT

Unfortunately, the 2022-2023 team ran out of time to compete in the 2023 June FAR competition. However, the 2023-2024 team is planning to swoop right in and pick up where the previous team left off. With a strong and reliable tank ready to go, they will be able to hit the ground running with static fire and recovery testing.

Senior Design Showcase

On May 21st, 2021 Northrop Grumman sponsors the Northrop Grumman Engineering & Science Student Design Showcase at Florida Tech, an annual event during which student teams present their work and field questions from their peers, faculty members, industry professionals and local leaders. For graduating seniors, the event represents years of coursework and hands-on learning experiences put to the test through project-based learning. As the central element of students’ final capstone course, Senior Design provides an engaging context for learning, an opportunity to integrate complex material and the inspiration to discover new ways of thinking and doing.

The BiPROP team was awarded the "Northrop Grumman Best In Show for Engineering" against hundreds of other Florida Tech Capstone projects presented at the annual Northrop Grumman Senior Design Showcase on May 21st, 2022.